mercury/compiler/mode_errors.m

%---------------------------------------------------------------------------%
% vim: ft=mercury ts=4 sw=4 et
%---------------------------------------------------------------------------%
% Copyright (C) 1994-2012 The University of Melbourne.
% Copyright (C) 2014-2026 The Mercury team.
% This file may only be copied under the terms of the GNU General
% Public License - see the file COPYING in the Mercury distribution.
%---------------------------------------------------------------------------%
%
% File: mode_errors.m.
% Main author: fjh.
%
% This module contains all the error-reporting routines for the mode-checker.
%
%---------------------------------------------------------------------------%

:- module check_hlds.mode_errors.
:- interface.

:- import_module check_hlds.mode_info.
:- import_module hlds.
:- import_module hlds.hlds_goal.
:- import_module hlds.hlds_pred.
:- import_module hlds.instmap.
:- import_module hlds.pred_name.
:- import_module mdbcomp.
:- import_module mdbcomp.prim_data.
:- import_module parse_tree.
:- import_module parse_tree.error_spec.
:- import_module parse_tree.parse_tree_out_info.
:- import_module parse_tree.prog_data.
:- import_module parse_tree.set_of_var.

:- import_module assoc_list.
:- import_module bool.
:- import_module list.
:- import_module maybe.
:- import_module one_or_more.
:- import_module set.

%---------------------------------------------------------------------------%

% Our representation of mode errors needs to work for *two* use cases.
%
% The first use case is the obvious one: reporting mode errors to users.
% For this, both the structured representation below and a representation
% consisting of just an error_spec would do.
%
% The second use case is the handling of subgoals that require as input
% the values of some variables that have not been produced yet by subgoals
% to their left in a conjunction. Such subgoals must be rescheduled
% to a later program point, one that occurs *after* all those variables
% have been produced. For this, an error_spec would NOT do, both because
% it does not specify the set of variables to wait for (which the
% mode_error_info does contain), and because the creation of a useful
% error_spec may take far too much time. While most real-life modules
% tend to average only a small handful of mode errors per compilation,
% they have *far* more subgoals that get rescheduled. This requires
% a mode error representation that pays the cost of constructing
% readable diagnostics only when the user will see those diagnostics.
%
% Mode analysis is almost the only semantic analysis pass of the Mercury
% compiler to which this consideration applies. (Type analysis in the presence
% of type inference is another, but type inference is rare in practice.)
% All other semantic analysis passes, when they discover a situation that
% calls for an error or a warning, immediately construct an error_spec
% to report it.
%

:- type mode_error_info
    --->    mode_error_info(
                % The variables which caused the error (we will attempt
                % to reschedule the goal if one of these variables becomes
                % more instantiated).
                set_of_progvar,

                % The nature of the error.
                mode_error,

                % Where the error occurred.
                prog_context,
                mode_context
            ).

%---------------------%

:- type mode_error
    % Mode errors in var/var unifications.

    --->    mode_error_unify_var_var(prog_var, prog_var, mer_inst, mer_inst)
            % Attempt to unify two variables whose initial insts *cannot*
            % be unified.
            % XXX But see also the comment on the code that constructs these
            % kinds of errors.

    ;       mode_error_unify_var_poly(prog_var, mer_inst)
            % A variable in a polymorphic unification with unknown type
            % has inst other than `ground' or `any'.

    % Mode errors in var/functor unifications.

    ;       mode_error_unify_var_functor(prog_var, cons_id, list(prog_var),
                mer_inst, list(mer_inst))
            % Attempt to unify a var with a structured term, where their
            % initial insts *cannot* be unified.
            % XXX But see also the comment in modecheck_unify_functor.

    % Mode errors in var/lambda unifications.

    ;       mode_error_unify_var_lambda(prog_var, mer_inst, mer_inst)
            % Attempt to unify a var with a lambda expression, where their
            % initial insts *cannot* be unified.

    ;       mode_error_unify_var_multimode_pf(prog_var,
                pred_id_var_multimode_error)
            % Attempt to construct a closure using a multi-moded predicate or
            % function.

    ;       mode_error_non_ground_non_local_lambda_var(prog_var, mer_inst)
            % Attempt to pass a live non-ground var as a non-local variable
            % to a lambda goal.

    % Mode errors in any kind of unification.

    ;       mode_error_higher_order_unify(prog_var, mode_error_unify_rhs,
                mer_type, pred_or_func)
            % An attempt to unify two higher-order terms. The first term
            % is a variable, the second term may be anything that can occur
            % on a right hand side of a unification.

    % Mode errors in plain first order calls.

    ;       mode_error_var_is_not_sufficiently_instantiated(prog_var,
                mer_inst, mer_inst, maybe(pred_id_var_multimode_error))
            % An argument in a call to a predicate or function with one mode
            % is not sufficiently instantiated.
            % The first inst is the var's actual inst, the second is its
            % expected inst.
            % XXX The "with one mode" part may be a lie.
            % XXX Document the last arg.

    ;       mode_error_clobbered_var_is_live(prog_var)
            % A call will clobber this variable, but it is still live.

    ;       mode_error_callee_pred_has_no_mode_decl(pred_id)
            % A call to a predicate for which there are no mode declarations
            % (and mode inference is not enabled). Note that there are no
            % *functions* without mode declarations: if the user does not
            % provide one, the compiler will.

    ;       mode_error_no_matching_mode(match_what, instmap, list(prog_var),
                mode_mismatch, list(mode_mismatch))
            % A call with one or more insufficiently instantiated variables.
            % The call may be to a declared or inferred predicate or function,
            % or to a higher order variable. Or it may be a call-like goal,
            % such as an event or a cast. The first argument specifies which
            % it is.
            %
            % The third argument gives the argument vars of the call.
            % Looking them up in the instmap gives their insts at the time
            % of the call.
            %
            % For calls the predicates or functions with more than one mode,
            % the fourth argument gives the list of the required initial insts
            % of the argument vars in the first mode, and the fifth argument
            % does the same for the later modes.
            %
            % For other kinds of calls, the fourth argument gives the list
            % of the required initial insts, and the fifth argument will be
            % the empty list.
            %
            % All the lists of insts must have exactly one inst for
            % each var in the list of vars.

    % Mode errors in higher order calls.

    ;       mode_error_bad_higher_order_inst(prog_var, mer_inst,
                pred_or_func, user_arity, higher_order_mismatch_info)
            % The variable has the given inst, which does not match
            % the expected higher order inst with the given pred_or_func
            % and the given arity. The last argument specifies the
            % nature of the mismatch.

    % Mode errors in conjunctions.

    ;       mode_error_unschedulable_conjuncts(one_or_more(delayed_goal),
                schedule_culprit)
            % A conjunction contains one or more unscheduleable goals;
            % schedule_culprit gives the reason why they couldn't be scheduled.

    ;       mode_error_merge_par_conj(one_or_more(merge_error))
            % Different arms of a parallel conj result in mutually exclusive
            % bindings, which means that the process of unifying the instmaps
            % from the end of each conjunct has failed.

    % Mode errors in disjunctions (of various kinds).

    ;       mode_error_merge_disj(merge_context, one_or_more(merge_error))
            % Different arms of a disjunction result in different insts
            % for some non-local variables.

    % Mode errors in coerce expressions.

    ;       mode_error_coerce_error(list(coerce_error))
            % Mode error in coerce expression.

    % Mode errors in trace goals expressions.

    ;       mode_error_nonground_trace_goal(prog_var, list(prog_var))
            % The nonlocal variables of the trace goal are not ground.

    % Mode errors that can happen in more than one kind of goal.

    ;       mode_error_bind_locked_var(var_lock_reason, prog_var,
                mer_inst, mer_inst)
            % Attempt to bind a non-local variable inside a negated context,
            % or attempt to re-bind a variable in a parallel conjunct.
            % The two insts are the insts of the variable before and after
            % *something*, but the code that creates this error is not clear
            % on what that "something" is :-( Presumably, the identity of that
            % "something" may depend on the reason for the lock.

    % Mode errors in procedure as a whole.

    ;       mode_error_unexpected_final_inst(int, prog_var, mer_inst, mer_inst,
                final_inst_error)
            % The head variable in the given argument position did not have
            % the expected final inst on exit from the proc.
            % The first inst gives its actual final inst,
            % the second inst gives its expected final inst.
            % The last argument specifies the nature of the discrepancy
            % between these two insts.

    % Mode errors caused by limitations of the current mode analyzer.

    ;       mode_error_in_callee(list(prog_var), list(mer_inst),
                pred_id, proc_id, list(mode_error_info))
            % Call to a predicate with initial argument insts for which mode
            % inference gave a mode error in the callee.
            % XXX I (zs) see nothing in either the code that generates
            % this kind of error, or in the message we generate for it,
            % that restricts it to occur only in the presence of mode
            % inference.

    ;       mode_error_cannot_create_implied_mode(cannot_create_reason,
                prog_var, mer_inst, mer_inst)
            % A call to a predicate with an overly instantiated variable
            % would use an implied mode of the predicate, but we can't
            % introduce a simple unification after calling the predicate
            % for the reason given by the first argument.
            % The first inst is the current inst of the variable, while
            % the second is the expected initial inst in the original,
            % non-implied mode.

    % Purity errors.

    ;       purity_error_should_be_in_promise_purity_scope(
                negated_context_desc, prog_var)
            % The condition of an if-then-else or the body of a negation
            % contains a nonlocal variable with inst `any', but is not
            % inside a promise_purity scope.

    ;       purity_error_lambda_should_be_any(one_or_more(prog_var)).
            % A ground lambda term contains the given nonlocal variables
            % that have inst `any', but is not marked impure.

:- type higher_order_mismatch_info
    --->    ho_mismatch_not_higher_order_type
    ;       ho_mismatch_no_higher_order_inst_info
    ;       ho_mismatch_pred_vs_func(pred_or_func)
            % actual PorF (expected is in enclosing term)
    ;       ho_mismatch_on_arity(user_arity).
            % actual arity (expected is in enclosing term)

:- type match_what
    --->    match_plain_call(pred_id)
    ;       match_higher_order_call(generic_call)
    ;       match_unify
    ;       match_cast
    ;       match_event.

:- type exact_or_not
    --->    eon_not_exact
    ;       eon_exact.

:- type mode_mismatch
    --->    mode_mismatch(
                exact_or_not,
                % We check whether the current insts of the actual arguments
                % of a call match the required initial insts of the formal
                % arguments of the callee by invoking either
                % modecheck_vars_are_live_no_exact_match (the usual case) or
                % modecheck_vars_are_live_exact_match.
                % This argument records which, with the intention being
                % that we can specialize find_satisfied_initial_insts_in_proc
                % to repeat the test that led to the error *exactly*.
                % XXX We do not yet do this, so this field is unused.

                list(mer_inst),
                % The required initial insts of the formal arguments.

                set(inst_var)
                % If this set is not empty, then the actual arguments of the
                % call *do* match the required initial insts of the formal
                % arguments, but the match binds the given set of inst_vars.
                % This is not allowed, because it would make the caller unable
                % to do its job if one or more of the given inst vars
                % has a value that is incompatible with the one that this
                % call binds it to.
            ).

%---------------------%

:- type pred_id_var_multimode_error
    --->    pred_id_var_multimode_error(pred_id, var_multimode_error).

:- type var_multimode_error
    --->    no_matching_mode(
                % The modes of these arguments match no mode of the callee.
                list(prog_var)
            )
    ;       more_than_one_matching_mode(
                % The modes of these arguments match more than one mode
                % of the callee ...
                list(prog_var),
                % ... specifically, these modes.
                proc_id, proc_id, list(proc_id)
            )
    ;       some_ho_args_non_ground(
                % These higher order arguments of the call are not ground.
                list(prog_var)
            ).

%---------------------%

:- type mode_error_unify_rhs
    --->    error_at_var(prog_var)
    ;       error_at_functor(cons_id, list(prog_var))
    ;       error_at_lambda(list(prog_var), list(from_to_insts)).

%---------------------%

:- type delayed_goal
    --->    delayed_goal(
                set_of_progvar,     % The vars the goal is waiting on.
                mode_error_info,    % The reason the goal can't be scheduled.
                hlds_goal           % The goal itself.
            ).

:- type schedule_culprit
    --->    goal_itself_was_impure
    ;       goals_followed_by_impure_goal(hlds_goal)
    ;       conj_floundered.        % We have reached the end of a conjunction
                                    % and there were still delayed goals.

%---------------------%

:- type merge_error
    --->    merge_error(prog_var, assoc_list(prog_context, mer_inst)).
            % The given variable had incompatible insts in different branches.
            % The second arg effectively maps the context of each branch
            % with inst of the variable in that branch.

:- type merge_context
    --->    merge_disj
    ;       merge_if_then_else
    ;       merge_stm_atomic.

%---------------------%

:- type coerce_error
    --->    coerce_error(
                % Path to subterm where the mode error was detected.
                list(coerce_error_term_path_step),
                % Type of the subterm.
                mer_type,
                % Target type of the conversion.
                mer_type,
                coerce_error_reason
            ).

:- type coerce_error_term_path_step
    --->    coerce_error_term_path_step(cons_id, int).

:- type coerce_error_reason
    --->    input_inst_not_ground(mer_inst)
    ;       cons_id_errors(mer_inst,
                bound_functor_cons_id_error, list(bound_functor_cons_id_error))
    ;       has_inst_expect_upcast(mer_inst).

:- type bound_functor_cons_id_error
    --->    bad_cons_id_input(cons_id)
            % The cons_id does not exist in the input type.
    ;       bad_cons_id_input_inst_arity(cons_id, arity, arity)
            % The cons_id exists in the input type, but the inst specifies
            % the wrong arity for it.
            % XXX This should not happen, since such errors *should* be
            % detected when pushing types into insts, but we prepare for it
            % happening anyway, just in case that process lets through
            % something it shouldn't have let through.
            % The cons_id, its arity in the inst of X, and the expected arity.
    ;       bad_cons_id_result(cons_id).
            % The cons_id does not exist in the result type.

%---------------------%

:- type final_inst_error
    --->    too_instantiated
    ;       not_instantiated_enough
    ;       wrongly_instantiated.
            % A catchall for anything that does not fit into
            % the above two categories.

%---------------------%

:- type cannot_create_reason
    --->    cannot_init_any
    ;       cannot_deep_copy_partial_term.

%---------------------%

:- type negated_context_desc
    --->    if_then_else
    ;       negation.

%---------------------------------------------------------------------------%

:- type mode_warning_info
    --->    mode_warning_info(
                mode_warning,       % The nature of the error.
                prog_context,       % Where the error occurred.
                mode_context        % Where the error occurred.
            ).

:- type mode_warning
    --->    cannot_succeed_var_var(prog_var, prog_var, mer_inst, mer_inst)
    ;       cannot_succeed_var_functor(prog_var, mer_inst, cons_id)
    ;       cannot_succeed_ground_occur_check(prog_var, cons_id).

%---------------------------------------------------------------------------%

    % Generate a message for the given mode error in the context
    % described by the mode_info.
    %
:- func mode_error_info_to_spec(mode_info, mode_error_info) = error_spec.

    % Generate a message for the given mode warning in the context
    % described by the mode_info.
    %
:- func mode_warning_info_to_spec(mode_info, mode_warning_info) = error_spec.

    % What it says on the tin.
    %
:- func should_report_mode_warning_for_pred_origin(pred_origin) = bool.

%---------------------------------------------------------------------------%

    % XXX This utility predicate does not really fit in this module,
    % being completely independent of the rest of the module,
    % but it doesn't fit any better in any other modules either :-(,
    % and it cannot be moved to its caller's module, because it is
    % called from more than one other module.
    %
:- func mode_decl_to_string(output_lang, proc_id, pred_info) = string.

%---------------------------------------------------------------------------%
%---------------------------------------------------------------------------%

:- implementation.

:- import_module check_hlds.inst_match.
:- import_module check_hlds.modecheck_util.
:- import_module hlds.error_msg_inst.
:- import_module hlds.hlds_error_util.
:- import_module hlds.hlds_markers.
:- import_module hlds.hlds_module.
:- import_module hlds.hlds_out.
:- import_module hlds.hlds_out.hlds_out_goal.
:- import_module hlds.hlds_out.hlds_out_util.
:- import_module hlds.hlds_proc_util.
:- import_module hlds.inst_test.
:- import_module hlds.mode_util.
:- import_module libs.
:- import_module libs.globals.
:- import_module libs.maybe_util.
:- import_module libs.op_mode.
:- import_module libs.options.
:- import_module mdbcomp.sym_name.
:- import_module parse_tree.error_util.
:- import_module parse_tree.parse_tree_out_cons_id.
:- import_module parse_tree.parse_tree_out_pred_decl.
:- import_module parse_tree.parse_tree_out_sym_name.
:- import_module parse_tree.parse_tree_out_term.
:- import_module parse_tree.parse_tree_out_type.
:- import_module parse_tree.prog_mode.
:- import_module parse_tree.prog_util.
:- import_module parse_tree.var_db.
:- import_module parse_tree.var_table.

:- import_module int.
:- import_module map.
:- import_module pair.
:- import_module require.
:- import_module string.
:- import_module string.builder.
:- import_module term.
:- import_module varset.

%---------------------------------------------------------------------------%
%---------------------------------------------------------------------------%
%
% The structure of the implementation section is as follows.
%
% - The code that switches on the kinds of mode errors, and invokes
%   each one's handler. The switch arms are in the same order as the
%   errors' function symbols in the mode_error type above.
%
% - The code specific to each kind of mode error handler. These follow
%   the same order.
%
% - The utility predicates needed by two or more of these error handlers.
%
% - The code that switches on the kinds of mode warnings, and invokes
%   each one's handler. The switch arms are in the same order as the
%   warnings' function symbols in the mode_warning type above.
%
% - The code specific to each kind of mode error handler. These follow
%   the same order.
%
% - The utility predicates needed by some warning handlers, and maybe
%   by some error handlers.
%
% - The code of should_report_mode_warning_for_pred_origin.
%
% - The code of mode_decl_to_string.
%
%---------------------------------------------------------------------------%
%---------------------------------------------------------------------------%

mode_error_info_to_spec(ModeInfo0, ModeErrorInfo) = Spec :-
    some [!ModeInfo] (
        !:ModeInfo = ModeInfo0,
        ModeErrorInfo = mode_error_info(_, ModeError, Context, ModeContext),
        mode_info_set_context(Context, !ModeInfo),
        mode_info_set_mode_context(ModeContext, !ModeInfo),
        Spec = mode_error_to_spec(!.ModeInfo, ModeError)
    ).

:- func mode_error_to_spec(mode_info, mode_error) = error_spec.

mode_error_to_spec(ModeInfo, ModeError) = Spec :-
    (
        ModeError = mode_error_unify_var_var(VarA, VarB, InstA, InstB),
        Spec = mode_error_unify_var_var_to_spec(ModeInfo, VarA, VarB,
            InstA, InstB)
    ;
        ModeError = mode_error_unify_var_poly(Var, Inst),
        Spec = mode_error_unify_var_poly_to_spec(ModeInfo, Var, Inst)
    ;
        ModeError = mode_error_unify_var_functor(Var, Name, Args, Inst,
            ArgInsts),
        Spec = mode_error_unify_var_functor_to_spec(ModeInfo, Var, Name,
            Args, Inst, ArgInsts)
    ;
        ModeError = mode_error_unify_var_lambda(VarA, InstA, InstB),
        Spec = mode_error_unify_var_lambda_to_spec(ModeInfo, VarA,
            InstA, InstB)
    ;
        ModeError = mode_error_unify_var_multimode_pf(Var,
            PredMultiModeError),
        Spec = mode_error_unify_var_multimode_pf_to_spec(ModeInfo, Var,
            PredMultiModeError)
    ;
        ModeError = mode_error_non_ground_non_local_lambda_var(Var, Inst),
        Spec = mode_error_non_ground_non_local_lambda_var_to_spec(ModeInfo,
            Var, Inst)
    ;
        ModeError = mode_error_higher_order_unify(Var, RHS, Type, PredOrFunc),
        Spec = mode_error_higher_order_unify_to_spec(ModeInfo, Var, RHS, Type,
            PredOrFunc)
    ;
        ModeError = mode_error_var_is_not_sufficiently_instantiated(Var,
            ActualInst, ExpectedInst, MaybeMultiMode),
        Spec = mode_error_var_is_not_sufficiently_instantiated_to_spec(
            ModeInfo, Var, ActualInst, ExpectedInst, MaybeMultiMode)
    ;
        ModeError = mode_error_clobbered_var_is_live(Var),
        Spec = mode_error_clobbered_var_is_live_to_spec(ModeInfo, Var)
    ;
        ModeError = mode_error_callee_pred_has_no_mode_decl(PredId),
        Spec = mode_error_callee_pred_has_no_mode_decl_to_spec(ModeInfo,
            PredId)
    ;
        ModeError = mode_error_no_matching_mode(MatchWhat, InstMap, ArgVars,
            ModeMismatch, ModeMismatches),
        Spec = mode_error_no_matching_mode_to_spec(ModeInfo, MatchWhat,
            InstMap, ArgVars, ModeMismatch, ModeMismatches)
    ;
        ModeError = mode_error_bad_higher_order_inst(Var, Inst,
            ExpectedPredOrFunc, ExpectedUserArity, Mismatch),
        Spec = mode_error_bad_higher_order_inst_to_spec(ModeInfo, Var, Inst,
            ExpectedPredOrFunc, ExpectedUserArity, Mismatch)
    ;
        ModeError = mode_error_unschedulable_conjuncts(OoMErrors, Culprit),
        Spec = mode_error_unschedulable_conjuncts_to_spec(ModeInfo, OoMErrors,
            Culprit)
    ;
        ModeError = mode_error_merge_par_conj(MergeErrors),
        Spec = mode_error_merge_par_conj_to_spec(ModeInfo, MergeErrors)
    ;
        ModeError = mode_error_merge_disj(MergeContext, MergeErrors),
        Spec = mode_error_merge_disj_to_spec(ModeInfo, MergeContext,
            MergeErrors)
    ;
        ModeError = mode_error_coerce_error(CoerceErrors),
        Spec = mode_error_coerce_error_to_spec(ModeInfo, CoerceErrors)
    ;
        ModeError = mode_error_nonground_trace_goal(HeadNGVar, TailNGVars),
        Spec = mode_error_nonground_trace_goal_to_spec(ModeInfo,
            HeadNGVar, TailNGVars)
    ;
        ModeError = mode_error_bind_locked_var(Reason, Var, InstA, InstB),
        Spec = mode_error_bind_locked_var_to_spec(ModeInfo, Reason, Var,
            InstA, InstB)
    ;
        ModeError = mode_error_unexpected_final_inst(ArgNum, Var,
            ActualInst, ExpectedInst, Reason),
        Spec = mode_error_unexpected_final_inst_to_spec(ModeInfo, ArgNum, Var,
            ActualInst, ExpectedInst, Reason)
    ;
        ModeError = mode_error_in_callee(Vars, Insts,
            CalleePredId, CalleeProcId, CalleeErrors),
        Spec = mode_error_in_callee_to_spec(ModeInfo, Vars, Insts,
            CalleePredId, CalleeProcId, CalleeErrors)
    ;
        ModeError = mode_error_cannot_create_implied_mode(Reason,
            Var, ActualInst, NonImpliedInitialInst),
        Spec = mode_error_cannot_create_implied_mode_to_spec(ModeInfo, Reason,
            Var, ActualInst, NonImpliedInitialInst)
    ;
        ModeError = purity_error_should_be_in_promise_purity_scope(NegCtxt,
            Var),
        Spec = purity_error_should_be_in_promise_purity_scope_to_spec(NegCtxt,
            ModeInfo, Var)
    ;
        ModeError = purity_error_lambda_should_be_any(Vars),
        Spec = purity_error_lambda_should_be_any_to_spec(ModeInfo, Vars)
    ).

%---------------------------------------------------------------------------%

:- func mode_error_unify_var_var_to_spec(mode_info, prog_var,
    prog_var, mer_inst, mer_inst) = error_spec.

mode_error_unify_var_var_to_spec(ModeInfo, X, Y, InstX, InstY) = Spec :-
    Preamble = mode_info_context_preamble(ModeInfo),
    mode_info_get_context(ModeInfo, Context),
    mode_info_get_var_table(ModeInfo, VarTable),
    Pieces = [words("mode error in unification of"),
        quote(mercury_var_to_name_only(VarTable, X)), words("and"),
        quote(mercury_var_to_name_only(VarTable, Y)), suffix("."), nl,
        words("Variable")] ++
        color_as_subject([quote(mercury_var_to_name_only(VarTable, X))]) ++
        has_instantiatedness(ModeInfo, yes(color_inconsistent), InstX, ",") ++
        [words("variable")] ++
        color_as_subject([quote(mercury_var_to_name_only(VarTable, Y))]) ++
        has_instantiatedness(ModeInfo, yes(color_inconsistent), InstY, "."),
    Spec = spec($pred, severity_error,
        phase_mode_check(report_in_any_mode), Context, Preamble ++ Pieces).

%---------------------------------------------------------------------------%

:- func mode_error_unify_var_poly_to_spec(mode_info, prog_var, mer_inst)
    = error_spec.

mode_error_unify_var_poly_to_spec(ModeInfo, Var, VarInst) = Spec :-
    Preamble = mode_info_context_preamble(ModeInfo),
    mode_info_get_context(ModeInfo, Context),
    mode_info_get_var_table(ModeInfo, VarTable),
    ExpectedInstPieces =
        color_as_correct([quote("ground")]) ++ [words("or")] ++
        color_as_correct([quote("any"), suffix(".")]),
    MainPieces = [words("in polymorphically-typed unification:"), nl,
        words("mode error: variable")] ++
        color_as_subject([quote(mercury_var_to_name_only(VarTable, Var))]) ++
        has_instantiatedness(ModeInfo, yes(color_incorrect), VarInst, ",") ++
        [words("expected instantiatedness was")] ++
        ExpectedInstPieces ++ [nl],
    VerbosePieces = [words("When unifying two variables whose type"),
        words("will not be known until runtime, the variables must both"),
        words("be ground (or have inst"), quote("any"), suffix(")."),
        words("Unifications of polymorphically-typed variables with"),
        words("partially instantiated modes are not allowed.")],
    Spec = error_spec($pred, severity_error,
        phase_mode_check(report_in_any_mode),
        [simple_msg(Context,
            [always(Preamble ++ MainPieces),
            verbose_only(verbose_once, VerbosePieces)])]).

%---------------------------------------------------------------------------%

:- func mode_error_unify_var_functor_to_spec(mode_info, prog_var,
    cons_id, list(prog_var), mer_inst, list(mer_inst)) = error_spec.

mode_error_unify_var_functor_to_spec(ModeInfo, X, ConsId, ArgVars,
        InstX, ArgInsts) = Spec :-
    Preamble = mode_info_context_preamble(ModeInfo),
    mode_info_get_context(ModeInfo, Context),
    mode_info_get_var_table(ModeInfo, VarTable),
    mode_info_get_module_info(ModeInfo, ModuleInfo),
    FunctorConsIdStr = functor_cons_id_to_string(ModuleInfo,
        vns_var_table(VarTable), print_name_only, ConsId, ArgVars),
    ConsIdStr = mercury_cons_id_to_string(output_mercury,
        does_not_need_brackets, ConsId),
    % inst_name_to_pieces and inst_name_to_inline_pieces look for this
    % specific fake module qualifier, and allow the lookup of a user_inst
    % with this qualifier to fail. They will then treat ConsIdStr as we
    % want it to be treated: as a wrapper around ArgInsts.
    FakeTermInstModuleName = unqualified("FAKE_CONS_ID"),
    FakeTermInstSymName = qualified(FakeTermInstModuleName, ConsIdStr),
    FakeTermInst = defined_inst(user_inst(FakeTermInstSymName, ArgInsts)),
    InstColor = yes(color_inconsistent),
    Pieces = [words("mode error in unification of"),
        quote(mercury_var_to_name_only(VarTable, X)),
        words("and"), words_quote(FunctorConsIdStr), suffix("."), nl,
        words("Variable")] ++
        color_as_subject([quote(mercury_var_to_name_only(VarTable, X))]) ++
        has_instantiatedness(ModeInfo, InstColor, InstX, ",") ++
        [words("term")] ++
        color_as_subject([words_quote(FunctorConsIdStr)]) ++
        has_instantiatedness(ModeInfo, InstColor, FakeTermInst, "."),
    Spec = spec($pred, severity_error,
        phase_mode_check(report_in_any_mode), Context, Preamble ++ Pieces).

%---------------------------------------------------------------------------%

:- func mode_error_unify_var_lambda_to_spec(mode_info, prog_var,
    mer_inst, mer_inst) = error_spec.

mode_error_unify_var_lambda_to_spec(ModeInfo, X, InstX, InstY) = Spec :-
    Preamble = mode_info_context_preamble(ModeInfo),
    mode_info_get_context(ModeInfo, Context),
    mode_info_get_var_table(ModeInfo, VarTable),
    InstColor = yes(color_inconsistent),
    Pieces = [words("mode error in unification of"),
        quote(mercury_var_to_name_only(VarTable, X)),
        words("and lambda expression."), nl,
        words("Variable")] ++
        color_as_subject([quote(mercury_var_to_name_only(VarTable, X))]) ++
        has_instantiatedness(ModeInfo, InstColor, InstX, ",") ++
        color_as_subject([words("lambda expression")]) ++
        has_instantiatedness(ModeInfo, InstColor, InstY, "."),
    Spec = spec($pred, severity_error,
        phase_mode_check(report_in_any_mode), Context, Preamble ++ Pieces).

%---------------------------------------------------------------------------%

:- func mode_error_unify_var_multimode_pf_to_spec(mode_info, prog_var,
    pred_id_var_multimode_error) = error_spec.

mode_error_unify_var_multimode_pf_to_spec(ModeInfo, X, PredMultiModeError)
        = Spec :-
    PredMultiModeError = pred_id_var_multimode_error(PredId, MultiModeError),
    Preamble = mode_info_context_preamble(ModeInfo),
    mode_info_get_context(ModeInfo, Context),
    mode_info_get_var_table(ModeInfo, VarTable),
    mode_info_get_module_info(ModeInfo, ModuleInfo),
    module_info_pred_info(ModuleInfo, PredId, PredInfo),
    PredOrFunc = pred_info_is_pred_or_func(PredInfo),
    PredModule = pred_info_module(PredInfo),
    PredName = pred_info_name(PredInfo),
    pred_info_get_orig_arity(PredInfo, PredFormArity),
    SymName = qualified(PredModule, PredName),
    PFSNA = pf_sym_name_arity(PredOrFunc, SymName, PredFormArity),
    % XXX What should we color as incorrect or as possible cause here?
    % The variable X? PFSNA, the name of the predicate or function?
    % Both? Neither? Something else?
    StartPieces = [words("mode error in unification of"),
        quote(mercury_var_to_name_only(VarTable, X)),
        words("and higher-order term based on multi-moded"),
        qual_pf_sym_name_pred_form_arity(PFSNA), suffix("."), nl],
    (
        MultiModeError = some_ho_args_non_ground(NonGroundArgVars),
        VarOrVars = choose_number(NonGroundArgVars, "variable", "variables"),
        NonGroundArgVarPieces = named_and_unnamed_vars_to_pieces(VarTable,
            color_subject, NonGroundArgVars),
        DetailPieces = [words("The higher order argument"),
            words(VarOrVars)] ++ NonGroundArgVarPieces ++
            color_as_correct([words("should be ground,")]) ++
            [words("but")] ++
            color_as_incorrect([words("are not.")]) ++
            [nl]
    ;
        (
            MultiModeError = no_matching_mode(ArgVars),
            MatchPieces = [words(choose_number(ArgVars, "does", "do")),
                words("not match any")],
            EndPieces = [suffix(".")]
        ;
            MultiModeError = more_than_one_matching_mode(ArgVars,
                ProcA, ProcB, ProcCs),
            MatchPieces = [words(choose_number(ArgVars, "matches", "match")),
                words("more than one")],
            ProcIdToPiece =
                ( func(ProcId) = nth_fixed(ModeNum) :-
                    % ProcIds start at zero, mode numbers start at 1.
                    ModeNum = proc_id_to_int(ProcId) + 1
                ),
            ModeNumberPieces =
                list.map(ProcIdToPiece, [ProcA, ProcB | ProcCs]),
            EndPieces = [suffix(","), words("specifically the")] ++
                piece_list_to_pieces("and", ModeNumberPieces) ++ [suffix(".")]
        ),
        ModeOrModes = choose_number(ArgVars, "mode", "modes"),
        VarOrVars = choose_number(ArgVars, "variable", "variables"),
        ArgVarPieces = named_and_unnamed_vars_to_pieces(VarTable,
            color_subject, ArgVars),
        DetailPieces = [words("The"), words(ModeOrModes),
            words("of the argument"), words(VarOrVars)] ++ ArgVarPieces ++
            color_as_incorrect(MatchPieces) ++ [words("of the called"),
            p_or_f(PredOrFunc), suffix("'s"), words("modes")] ++
            EndPieces ++ [nl]
    ),
    Spec = spec($pred, severity_error, phase_mode_check(report_in_any_mode),
        Context, Preamble ++ StartPieces ++ DetailPieces).

:- func named_and_unnamed_vars_to_pieces(var_table, color_name,
    list(prog_var)) = list(format_piece).

named_and_unnamed_vars_to_pieces(VarTable, Color, Vars) = Pieces :-
    list.filter_map(
        ( pred(V::in, N::out) is semidet :-
            lookup_var_entry(VarTable, V, E),
            E = vte(N, _, _),
            N \= ""
        ), Vars, NamedVarNames, UnnamedVars),
    (
        NamedVarNames = [],
        Pieces = []
    ;
        NamedVarNames = [_ | _],
        NamedVarNamePieces = list.map((func(N) = quote(N)), NamedVarNames),
        NamedVarPieces = piece_list_to_color_pieces(Color, "and", [],
            NamedVarNamePieces),
        (
            UnnamedVars = [],
            Pieces = NamedVarPieces
        ;
            UnnamedVars = [_ | _],
            Pieces = [words("including") | NamedVarPieces]
        )
    ).

%---------------------------------------------------------------------------%

:- func mode_error_non_ground_non_local_lambda_var_to_spec(mode_info, prog_var,
    mer_inst) = error_spec.

mode_error_non_ground_non_local_lambda_var_to_spec(ModeInfo, Var, VarInst)
        = Spec :-
    Preamble = mode_info_context_preamble(ModeInfo),
    mode_info_get_context(ModeInfo, Context),
    mode_info_get_var_table(ModeInfo, VarTable),
    Pieces = [words("mode error: variable")] ++
        color_as_subject([quote(mercury_var_to_name_only(VarTable, Var))]) ++
        has_instantiatedness(ModeInfo, yes(color_incorrect), VarInst, ",") ++
        [words("expected instantiatedness for non-local variables"),
        words("of lambda goals is")] ++
        color_as_correct([quote("ground"), suffix(".")]) ++
        [nl],
    Spec = spec($pred, severity_error,
        phase_mode_check(report_in_any_mode), Context, Preamble ++ Pieces).

%---------------------------------------------------------------------------%

:- func mode_error_higher_order_unify_to_spec(mode_info, prog_var,
    mode_error_unify_rhs, mer_type, pred_or_func) = error_spec.

mode_error_higher_order_unify_to_spec(ModeInfo, LHSVar, RHS, Type, PredOrFunc)
        = Spec :-
    Preamble = mode_info_context_preamble(ModeInfo),
    mode_info_get_context(ModeInfo, Context),
    mode_info_get_var_table(ModeInfo, VarTable),
    mode_info_get_instvarset(ModeInfo, InstVarSet),
    mode_info_get_module_info(ModeInfo, ModuleInfo),
    (
        RHS = error_at_var(Y),
        RHSStr = mercury_var_to_name_only(VarTable, Y)
    ;
        RHS = error_at_functor(ConsId, ArgVars),
        RHSStr = functor_cons_id_to_string(ModuleInfo, vns_var_table(VarTable),
            print_name_only, ConsId, ArgVars)
    ;
        RHS = error_at_lambda(ArgVars, ArgFromToInsts),
        ArgModes = list.map(from_to_insts_to_mode, ArgFromToInsts),
        assoc_list.from_corresponding_lists(ArgVars, ArgModes, ArgVarsModes),
        RHSStr = "lambda(["
            ++ var_modes_to_string(output_debug, vns_var_table(VarTable),
                InstVarSet, print_name_only, ArgVarsModes)
            ++ "] ... )"
    ),
    varset.init(TypeVarSet),
    LHSVarName = mercury_var_to_name_only(VarTable, LHSVar),
    MainPieces = [words("In unification of")] ++
        color_as_subject([quote(LHSVarName)]) ++ [words("with")] ++
        color_as_subject([quote(RHSStr), suffix(":")]) ++ [nl,
        words("mode error: you cannot unify two higher-order values."), nl,
        words("These two terms have type"),
        quote(mercury_type_to_string(TypeVarSet, print_name_only, Type)),
        suffix("."), nl],
    VerbosePieces = [words("Your code is trying to test whether two"),
        words(pred_or_func_to_full_str(PredOrFunc) ++ "s"),
        words("are equal, by unifying them."),
        words("In the general case, testing equivalence of"),
        words(pred_or_func_to_full_str(PredOrFunc) ++ "s"),
        words("is an undecidable problem,"),
        words("and so this is not allowed by the Mercury mode system."),
        words("In some cases, you can achieve the same effect by"),
        words("writing an explicit universal quantification, e.g."),
        quote("all [X] call(PredA, X) <=> call(PredB, X)"), suffix(","),
        words("instead of"), quote("PredA = PredB"), suffix("."), nl],
    Spec = error_spec($pred, severity_error,
        phase_mode_check(report_in_any_mode),
        [simple_msg(Context,
            [always(Preamble ++ MainPieces),
            verbose_only(verbose_once, VerbosePieces)])]).

%---------------------------------------------------------------------------%

:- func mode_error_var_is_not_sufficiently_instantiated_to_spec(mode_info,
    prog_var, mer_inst, mer_inst, maybe(pred_id_var_multimode_error))
    = error_spec.

mode_error_var_is_not_sufficiently_instantiated_to_spec(ModeInfo, Var,
        VarInst, ExpectedInst, MaybeMultiModeError) = Spec :-
    Preamble = mode_info_context_preamble(ModeInfo),
    mode_info_get_context(ModeInfo, Context),
    mode_info_get_var_table(ModeInfo, VarTable),
    MainPieces = [words("mode error: variable")] ++
        color_as_subject([quote(mercury_var_to_name_only(VarTable, Var))]) ++
        has_inst_expected_inst_was(ModeInfo, VarInst, ExpectedInst),
    MainMsgs = [msg(Context, Preamble ++ MainPieces)],
    Phase = phase_mode_check(report_in_any_mode),
    ( if
        inst_has_uniqueness(VarInst, mostly_unique),
        inst_has_uniqueness(ExpectedInst, unique)
    then
        UniqPieces = [words("This kind of uniqueness mismatch"),
            words("is usually caused by doing")] ++
            color_as_hint([words("input/output")]) ++
            [words("or")] ++
            color_as_hint([words("some other kind of"),
                words("destructive update")]) ++
            color_as_incorrect([words("in a context where"),
                words("it can be backtracked over,")]) ++
            [words("such as the condition of an if-then-else."), nl,
            words("Note that it is possible that the cause is code"),
            words("that is intended to be a")] ++
            color_as_correct([words("call")]) ++
            [words("to the current predicate or function, but"),
            words("has been accidentally turned into a")] ++
            color_as_incorrect([words("clause")]) ++
            [words("for it by a typo at the end of the previous line"),
            words("that replaces a comma by a period."), nl],
        UniqMsgs = [msg(Context, UniqPieces)]
    else
        UniqMsgs = []
    ),
    (
        MaybeMultiModeError = no,
        MultiModeMsgs = []
    ;
        MaybeMultiModeError = yes(PredMultiModeError),
        ConnectPieces = [words("This may have been caused by"),
            words("the following error."), nl],
        ConnectMsgs = [msg(Context, ConnectPieces)],
        SubSpec0 = mode_error_unify_var_multimode_pf_to_spec(ModeInfo, Var,
            PredMultiModeError),
        mode_info_get_module_info(ModeInfo, ModuleInfo),
        module_info_get_globals(ModuleInfo, Globals),
        extract_spec_msgs_and_maybe_add_id(Globals, SubSpec0, SubMsgs),
        MultiModeMsgs = ConnectMsgs ++ SubMsgs
    ),
    AllMsgs = MainMsgs ++ UniqMsgs ++ MultiModeMsgs,
    Spec = error_spec($pred, severity_error, Phase, AllMsgs).

:- pred inst_has_uniqueness(mer_inst::in, uniqueness::in) is semidet.

inst_has_uniqueness(Inst, SearchUniq) :-
    require_complete_switch [Inst]
    (
        ( Inst = free
        ; Inst = any(_, _)
        ; Inst = not_reached
        ; Inst = inst_var(_)
        ),
        fail
    ;
        Inst = defined_inst(_),
        % We could expand the defined inst, but the novice Mercury programmers
        % that the error message addendum this code helps to construct
        % will virtually never encounter defined insts that expand out
        % to unique or mostly_unique.
        fail
    ;
        ( Inst = ground(Uniq, _)
        ; Inst = bound(Uniq, _, _)
        ),
        Uniq = SearchUniq
    ;
        Inst = constrained_inst_vars(_, SubInst),
        inst_has_uniqueness(SubInst, SearchUniq)
    ).

%---------------------------------------------------------------------------%

:- func mode_error_clobbered_var_is_live_to_spec(mode_info, prog_var)
    = error_spec.

mode_error_clobbered_var_is_live_to_spec(ModeInfo, Var) = Spec :-
    Preamble = mode_info_context_preamble(ModeInfo),
    mode_info_get_context(ModeInfo, Context),
    mode_info_get_var_table(ModeInfo, VarTable),
    VarName = mercury_var_to_name_only(VarTable, Var),
    Pieces = [words("unique-mode error: the called procedure"),
        words("would clobber its argument, but variable")] ++
        color_as_subject([quote(VarName)]) ++
        [words("is")] ++
        color_as_incorrect([words("still live.")]) ++
        [nl],
    Spec = spec($pred, severity_error,
        phase_mode_check(report_in_any_mode), Context, Preamble ++ Pieces).

%---------------------------------------------------------------------------%

:- func mode_error_callee_pred_has_no_mode_decl_to_spec(mode_info, pred_id)
    = error_spec.

mode_error_callee_pred_has_no_mode_decl_to_spec(ModeInfo, PredId) = Spec :-
    Preamble = mode_info_context_preamble(ModeInfo),
    mode_info_get_module_info(ModeInfo, ModuleInfo),
    PredDotPieces = describe_one_pred_name(ModuleInfo, yes(color_subject),
        should_module_qualify, [suffix(".")], PredId),
    mode_info_get_context(ModeInfo, Context),
    % Functions have a default mode, so they do not need a mode declaration,
    Pieces = [words("error: there is")] ++
        color_as_incorrect([words("no mode declaration")]) ++
        [words("for")] ++ PredDotPieces ++ [nl],
    Spec = spec($pred, severity_error,
        phase_mode_check(report_in_any_mode), Context, Preamble ++ Pieces).

%---------------------------------------------------------------------------%

:- func mode_error_no_matching_mode_to_spec(mode_info, match_what, instmap,
    list(prog_var), mode_mismatch, list(mode_mismatch)) = error_spec.

mode_error_no_matching_mode_to_spec(ModeInfo, MatchWhat, InstMap, Vars,
        HeadMismatch, TailMismatches) = Spec :-
    PrefixPieces = mode_info_context_preamble(ModeInfo) ++
        [words("mode error:")],
    mode_info_get_mode_context(ModeInfo, ModeContext),
    mode_info_get_module_info(ModeInfo, ModuleInfo),
    (
        ( ModeContext = mode_context_call_arg(ModeCallId, _)
        ; ModeContext = mode_context_call(ModeCallId)
        ),
        (
            ModeCallId = mode_call_generic(GenericCall0),
            (
                GenericCall0 = higher_order(_, _, PredOrFunc, _, _)
            ;
                GenericCall0 = class_method(_, _, _, PFSymNameArity),
                PFSymNameArity = pf_sym_name_arity(PredOrFunc, _, _)
            ;
                ( GenericCall0 = event_call(_)
                ; GenericCall0 = cast(_)
                ),
                PredOrFunc = pf_predicate
            ),
            % XXX Setting NumExtra to 0 means that we do not separate out
            % any arguments added by polymorphism.m. Since most higher order
            % values are monomorphic, this should not be too much of a loss.
            % If and when it becomes one, this should be fixed.
            NumExtra = 0
        ;
            ModeCallId = mode_call_plain(PredId0),
            some [PredInfo, PFSymNameArity] (
                module_info_pred_info(ModuleInfo, PredId0, PredInfo),
                pred_info_get_pf_sym_name_arity(PredInfo, PFSymNameArity),
                PredOrFunc = pred_info_is_pred_or_func(PredInfo),
                pred_info_get_orig_arity(PredInfo, pred_form_arity(OrigArity))
            ),
            list.length(Vars, NumVars),
            NumExtra = NumVars - OrigArity
        )
    ;
        ( ModeContext = mode_context_unify(_, _)
        ; ModeContext = mode_context_not_call_or_unify
        ),
        unexpected($pred, "invalid context")
    ),
    mode_info_get_var_table(ModeInfo, VarTable),
    construct_argnum_var_type_inst_tuples(VarTable, InstMap, 1,
        Vars, ArgTuples),
    find_satisfied_initial_insts_in_procs(ModuleInfo, ArgTuples,
        [HeadMismatch | TailMismatches], 1, map.init, OkOrNotMap),
    map.foldl(is_any_extra_arg_bad(NumExtra), OkOrNotMap,
        all_extra_args_good, SomeExtraIsBad),
    map.foldl(acc_not_ok_in_any_proc_args, OkOrNotMap, [], NeverOkArgNums),
    (
        SomeExtraIsBad = all_extra_args_good,
        ArgNumMinus = NumExtra
    ;
        SomeExtraIsBad = some_extra_arg_is_bad,
        ArgNumMinus = 0
    ),
    report_all_possibly_mismatched_args(ModeInfo, OkOrNotMap, NeverOkArgNums,
        PredOrFunc, NumExtra, ArgNumMinus, ArgTuples,
        ArgNamePieceListsToPrint1, MaybeReturnValueNamePieces, BadArgPieces),
    list.det_drop(ArgNumMinus,
        ArgNamePieceListsToPrint1, ArgNamePieceListsToPrint2),
    (
        MaybeReturnValueNamePieces = no,
        ArgNamePieceListsToPrint = ArgNamePieceListsToPrint2
    ;
        MaybeReturnValueNamePieces = yes(ReturnValueNamePieces),
        ArgNamePieceListsToPrint = ArgNamePieceListsToPrint2 ++
            [ReturnValueNamePieces]
    ),
    % Use "insts" and "do not match" when we have two or more *entities*
    % (meaning arguments *and* return values), but use "arguments"
    % only if we have two actual arguments (which are *not* return values).
    InstOrInsts = choose_number(ArgNamePieceListsToPrint, "inst", "insts"),
    DoesOrDo = choose_number(ArgNamePieceListsToPrint, "does", "do"),
    ArgOrArgs = choose_number(ArgNamePieceListsToPrint2,
        "argument", "arguments"),
    ArgsNoMatchPieces = [words("the"), words(InstOrInsts),
        words("of"), words(ArgOrArgs)] ++
        pieces_list_to_pieces("and", ArgNamePieceListsToPrint) ++
        color_as_incorrect([words(DoesOrDo), words("not match")]),

    % Note that MatchWhat *almost* duplicates the information contained in
    % ModeContext, which we process above. However, despite the call to
    % unexpected above for mode_context_unify, this predicate *can* get called
    % for errors discovered during unifications (whose processing presumably
    % did not set the mode context), and we want to generate an error message
    % that does not generate confusing wording in this eventuality.
    (
        MatchWhat = match_plain_call(PredId),
        some [PredInfo, PFSymNameArity] (
            module_info_pred_info(ModuleInfo, PredId, PredInfo),
            pred_info_get_pf_sym_name_arity(PredInfo, PFSymNameArity),
            CallIdStr = pf_sym_name_pred_form_arity_to_string(PFSymNameArity),
            pred_info_get_proc_table(PredInfo, ProcTable)
        ),
        map.count(ProcTable, NumProcs),
        ( if NumProcs = 1 then
            MatchWhatPieces =
                [words("the only mode of"),
                words(CallIdStr), suffix("."), nl]
        else if NumProcs = 2 then
            MatchWhatPieces =
                [words("either of the two modes of"),
                words(CallIdStr), suffix("."), nl]
        else
            MatchWhatPieces =
                [words("any of the"), int_name(NumProcs), words("modes"),
                words("for"), words(CallIdStr), suffix("."), nl]
        )
    ;
        MatchWhat = match_higher_order_call(GenericCall),
        VarNameSrc = vns_var_table(VarTable),
        CalleePieces = generic_callee_to_pieces(print_ho_var_name,
            VarNameSrc, GenericCall),
        MatchWhatPieces =
            [words("the mode of")] ++ CalleePieces ++ [suffix("."), nl]
    ;
        MatchWhat = match_event,
        MatchWhatPieces =
            [words("the input mode required for event arguments."), nl]
    ;
        MatchWhat = match_cast,
        MatchWhatPieces =
            [words("the input mode required for values being cast."), nl]
    ;
        MatchWhat = match_unify,
        MatchWhatPieces =
            [words("the input mode required for unifications."), nl]
    ),

    mode_info_get_instvarset(ModeInfo, InstVarSet),
    report_bound_inst_vars(InstVarSet, [HeadMismatch | TailMismatches], 1,
        BoundInstVarPieces0),
    (
        BoundInstVarPieces0 = [],
        BoundInstVarPieces = []
    ;
        BoundInstVarPieces0 = [_ | _],
        % XXX Should this addeddum be in a verbose_once message?
        BoundInstVarPieces = BoundInstVarPieces0 ++
            [words("(If a call binds an inst variable, then"),
            words("the caller loses the generality promised by"),
            words("its own mode declaration.)"), nl]
    ),

    Pieces = PrefixPieces ++ ArgsNoMatchPieces ++ MatchWhatPieces ++
        [nl_indent_delta(1)] ++ BadArgPieces ++ [nl_indent_delta(-1)] ++
        BoundInstVarPieces,
    Phase = phase_mode_check(report_in_any_mode),
    mode_info_get_context(ModeInfo, Context),
    Spec = spec($pred, severity_error, Phase, Context, Pieces).

:- type argnum_var_type_inst
    --->    argnum_var_type_inst(int, prog_var, mer_type, mer_inst).

:- pred construct_argnum_var_type_inst_tuples(var_table::in, instmap::in,
    int::in, list(prog_var)::in, list(argnum_var_type_inst)::out) is det.

construct_argnum_var_type_inst_tuples(_, _, _, [], []).
construct_argnum_var_type_inst_tuples(VarTable, InstMap, ArgNum,
        [Var | Vars], [ArgTuple | ArgTuples]) :-
    lookup_var_type(VarTable, Var, Type),
    instmap_lookup_var(InstMap, Var, Inst),
    ArgTuple = argnum_var_type_inst(ArgNum, Var, Type, Inst),
    construct_argnum_var_type_inst_tuples(VarTable, InstMap, ArgNum + 1,
        Vars, ArgTuples).

%---------------------%

    % For a given argument, collect together
    % - all the proc_ids for which the arguments inst satisfies its mode, and
    % - all the proc_ids for which the arguments inst does not satisfy it
    % as the values corresponding to oon_ok and oon_not_ok respectively.
    %
:- type arg_ok_or_not
    --->    arg_ok_or_not(
                ok_procs        :: set(int),    % proc_ids
                not_ok_procs    :: set(int)     % proc_ids
            ).

    % Map each argument (including the args added by the compiler),
    % as identified by its argument number, to the info about
    % which procedures' mode it satisfies.
    %
:- type ok_or_not_map == map(int, arg_ok_or_not).

%---------------------%

:- pred find_satisfied_initial_insts_in_procs(module_info::in,
    list(argnum_var_type_inst)::in, list(mode_mismatch)::in, int::in,
    ok_or_not_map::in, ok_or_not_map::out) is det.

find_satisfied_initial_insts_in_procs(_ModuleInfo, _ArgTuples,
        [], _ProcNum, !OkOrNotMap).
find_satisfied_initial_insts_in_procs(ModuleInfo, ArgTuples,
        [ProcMismatch | ProcMismatches], ProcNum, !OkOrNotMap) :-
    ProcMismatch = mode_mismatch(_ExactOrNot, ProcReqInitialInsts,
        _BoundInstVars),
    find_satisfied_initial_insts_in_proc(ModuleInfo, ArgTuples,
        ProcReqInitialInsts, ProcNum, !OkOrNotMap),
    find_satisfied_initial_insts_in_procs(ModuleInfo, ArgTuples,
        ProcMismatches, ProcNum + 1, !OkOrNotMap).

:- pred find_satisfied_initial_insts_in_proc(module_info::in,
    list(argnum_var_type_inst)::in, list(mer_inst)::in, int::in,
    ok_or_not_map::in, ok_or_not_map::out) is det.

find_satisfied_initial_insts_in_proc(_ModuleInfo, [], [],
        _ProcNum, !OkOrNotMap).
find_satisfied_initial_insts_in_proc(_ModuleInfo, [], [_ | _],
        _ProcNum, !OkOrNotMap) :-
    unexpected($pred, "length mismatch").
find_satisfied_initial_insts_in_proc(_ModuleInfo, [_ | _], [],
        _ProcNum, !OkOrNotMap) :-
    unexpected($pred, "length mismatch").
find_satisfied_initial_insts_in_proc(ModuleInfo,
        [ArgTuple | ArgTuples], [ProcInitialInst | ProcInitialInsts],
        ProcNum, !OkOrNotMap) :-
    ArgTuple = argnum_var_type_inst(ArgNum, _Var, VarType, VarInst),
    ( if
        inst_matches_initial_sub(VarType, VarInst, ProcInitialInst,
            ModuleInfo, _UpdatedModuleInfo, map.init, _Subst)
    then
        record_ok_proc_num(ArgNum, ProcNum, !OkOrNotMap)
    else
        record_not_ok_proc_num(ArgNum, ProcNum, !OkOrNotMap)
    ),
    find_satisfied_initial_insts_in_proc(ModuleInfo,
        ArgTuples, ProcInitialInsts, ProcNum, !OkOrNotMap).

:- pred record_ok_proc_num(int::in, int::in,
    ok_or_not_map::in, ok_or_not_map::out) is det.

record_ok_proc_num(ArgNum, ProcNum, !OkOrNotMap) :-
    ( if map.search(!.OkOrNotMap, ArgNum, ArgOkOrNot0) then
        ArgOkOrNot0 = arg_ok_or_not(OkProcs0, NotOkProcs0),
        set.insert(ProcNum, OkProcs0, OkProcs),
        ArgOkOrNot = arg_ok_or_not(OkProcs, NotOkProcs0),
        map.det_update(ArgNum, ArgOkOrNot, !OkOrNotMap)
    else
        ArgOkOrNot = arg_ok_or_not(set.make_singleton_set(ProcNum), set.init),
        map.det_insert(ArgNum, ArgOkOrNot, !OkOrNotMap)
    ).

:- pred record_not_ok_proc_num(int::in, int::in,
    ok_or_not_map::in, ok_or_not_map::out) is det.

record_not_ok_proc_num(ArgNum, ProcNum, !OkOrNotMap) :-
    ( if map.search(!.OkOrNotMap, ArgNum, ArgOkOrNot0) then
        ArgOkOrNot0 = arg_ok_or_not(OkProcs0, NotOkProcs0),
        set.insert(ProcNum, NotOkProcs0, NotOkProcs),
        ArgOkOrNot = arg_ok_or_not(OkProcs0, NotOkProcs),
        map.det_update(ArgNum, ArgOkOrNot, !OkOrNotMap)
    else
        ArgOkOrNot = arg_ok_or_not(set.init, set.make_singleton_set(ProcNum)),
        map.det_insert(ArgNum, ArgOkOrNot, !OkOrNotMap)
    ).

%---------------------%

:- type maybe_some_extra_arg_is_bad
    --->    all_extra_args_good
    ;       some_extra_arg_is_bad.

:- pred is_any_extra_arg_bad(int::in, int::in, arg_ok_or_not::in,
    maybe_some_extra_arg_is_bad::in, maybe_some_extra_arg_is_bad::out) is det.

is_any_extra_arg_bad(NumExtra, ArgNum, ArgOkOrNot, !SomeExtraIsBad) :-
    ( if set.is_non_empty(ArgOkOrNot ^ not_ok_procs) then
        ( if ArgNum =< NumExtra then
            !:SomeExtraIsBad = some_extra_arg_is_bad
        else
            true
        )
    else
        true
    ).

%---------------------%

:- pred acc_not_ok_in_any_proc_args(int::in, arg_ok_or_not::in,
    list(int)::in, list(int)::out) is det.

acc_not_ok_in_any_proc_args(ArgNum, ArgOkOrNot, !NeverOkArgNums) :-
    ArgOkOrNot = arg_ok_or_not(OkProcs, _NotOkProcs),
    ( if set.is_empty(OkProcs) then
        !:NeverOkArgNums = [ArgNum | !.NeverOkArgNums]
    else
        true
    ).

%---------------------%

:- pred report_all_possibly_mismatched_args(mode_info::in, ok_or_not_map::in,
    list(int)::in, pred_or_func::in, int::in, int::in,
    list(argnum_var_type_inst)::in,
    list(list(format_piece))::out, maybe(list(format_piece))::out,
    list(format_piece)::out) is det.

report_all_possibly_mismatched_args(_, _, _, _, _, _, [], [], no, []).
report_all_possibly_mismatched_args(ModeInfo, OkOrNotMap, NeverOkArgNums,
        PredOrFunc, NumExtra, ArgNumMinus, [ArgTuple | ArgTuples],
        ArgNamePiecesList, MaybeReturnValueNamePieces, BadArgPieces) :-
    ArgTuple = argnum_var_type_inst(ArgNum, Var, _VarType, VarInst),
    mode_info_get_var_table(ModeInfo, VarTable),
    VarNamePiece = var_in_table_to_quote_piece(VarTable, Var),
    ( if
        PredOrFunc = pf_function,
        ArgTuples = []
    then
        ReturnValueNamePieces = [words("the")] ++
            color_as_subject([words("return value"), VarNamePiece]),
        MaybeReturnValueNamePieces = yes(ReturnValueNamePieces),
        ArgNamePiecesList = [],
        TailBadArgPieces = [],
        ArgNumCommaPieces = [words("return value")]
    else
        report_all_possibly_mismatched_args(ModeInfo, OkOrNotMap,
            NeverOkArgNums, PredOrFunc, NumExtra, ArgNumMinus, ArgTuples,
            TailVarNamePiecesList, MaybeReturnValueNamePieces,
            TailBadArgPieces),
        HeadVarNamePieces = color_as_subject([VarNamePiece]),
        ArgNamePiecesList = [HeadVarNamePieces | TailVarNamePiecesList],
        ArgNumCommaPieces = [nth_fixed(ArgNum - NumExtra), words("argument,")]
    ),

    map.lookup(OkOrNotMap, ArgNum, ArgOkOrNot),
    ArgOkOrNot = arg_ok_or_not(OkProcNumSet, NotOkProcNumSet),
    set.to_sorted_list(NotOkProcNumSet, NotOkProcNums),
    ( if
        % Do not generate an error message about this argument if ...
        (
            % ... this argument is ok in all procedures, or ...
            NotOkProcNums = []
        ;
            % ... this argument is compiler-generated, and we are ignoring
            % compiler-generated arguments, or ...
            ArgNum =< ArgNumMinus
        ;
            % ... this argument is ok in *at least one* procedure, and
            % there are arguments that are not ok in *any* procedure.
            set.is_non_empty(OkProcNumSet),
            NeverOkArgNums = [_ | _]
        )
    then
        BadArgPieces = TailBadArgPieces
    else
        ( if ArgNum =< NumExtra then
            % An argument added by the polymorphism transformation cannot be
            % a function result.
            ArgNumNamePieces = [words("The inst of the compiler-generated"),
                nth_fixed(ArgNum), words("argument,")] ++
                color_as_subject([VarNamePiece]) ++ [suffix(",")]
        else
            ArgNumNamePieces = [words("The inst of the")] ++
                ArgNumCommaPieces ++
                color_as_subject([VarNamePiece]) ++ [suffix(",")]
        ),
        WhichIsPieces = [words("which is")] ++
            color_as_incorrect(report_inst(ModeInfo, quote_short_inst,
                [suffix(",")], [nl_indent_delta(1)],
                [suffix(","), nl_indent_delta(-1)], VarInst)),
        ( if set.is_non_empty(OkProcNumSet) then
            NthNotOkProcNums = list.map(nth_fixed_str, NotOkProcNums),
            DoesNotMatchWhatPieces = [words("the inst required by"),
                words("some of the modes of the callee, namely the")] ++
                fixed_list_to_pieces("and", NthNotOkProcNums) ++
                [words(choose_number(NthNotOkProcNums, "mode.", "modes."))]
        else
            list.length(NotOkProcNums, NumNotOkProcNums),
            ( if NumNotOkProcNums = 1 then
                DoesNotMatchWhatPieces = [words("the required inst.")]
            else
                DoesNotMatchWhatPieces = [words("any of the required insts.")]
            )
        ),
        mode_info_get_module_info(ModeInfo, ModuleInfo),
        % XXX Instead of reporting this hint, we should *check* here
        % whether this *is* the cause of the mismatch.
        %
        % - If the answer is yes, we should say that this IS the cause
        %   of the problem, instead of saying that it MAY BE the cause.
        %
        % - If the answer is no, we should say nothing.
        ( if inst_contains_higher_order(ModuleInfo, VarInst) then
            HOPieces = [words("(For higher order insts like this,"),
                words("the mismatch is sometimes caused by"),
                words("the arity of the predicate or function"),
                words("being different in the inst than in the type.)"), nl]
        else
            HOPieces = []
        ),
        DoesNotMatchPieces = [words("does not match")] ++
            DoesNotMatchWhatPieces ++ [nl],
        HeadBadArgPieces = [blank_line] ++ ArgNumNamePieces ++
            WhichIsPieces ++ DoesNotMatchPieces ++ HOPieces,
        BadArgPieces = HeadBadArgPieces ++ TailBadArgPieces
    ).

:- pred report_bound_inst_vars(inst_varset::in, list(mode_mismatch)::in,
    int::in, list(format_piece)::out) is det.

report_bound_inst_vars(_, [], _, []).
report_bound_inst_vars(InstVarSet, [Mismatch | Mismatches], ProcNum, Pieces) :-
    report_bound_inst_vars(InstVarSet, Mismatches, ProcNum + 1, TailPieces),
    Mismatch = mode_mismatch(_, _, BoundInstVars),
    ( if set.is_empty(BoundInstVars) then
        Pieces = TailPieces
    else
        ( if ProcNum = 1, Mismatches = [] then
            TheProcPieces = [words("The mode")]
        else
            TheProcPieces = [words("The"), nth_fixed(ProcNum), words("mode")]
        ),
        set.map(varset.lookup_name(InstVarSet),
            BoundInstVars, BoundInstVarNames),
        set.to_sorted_list(BoundInstVarNames, SortedBoundInstVarNames),
        VarOrVars = choose_number(SortedBoundInstVarNames,
            "variable", "variables"),
        InstVarNamePieces = quote_list_to_color_pieces(color_subject,
            "and", [suffix(".")], SortedBoundInstVarNames),
        HeadPieces = TheProcPieces ++ [words("does not match"),
            words("because it binds the inst"), words(VarOrVars)] ++
            InstVarNamePieces ++ [nl],
        Pieces = HeadPieces ++ TailPieces
    ).

%---------------------------------------------------------------------------%

:- func mode_error_bad_higher_order_inst_to_spec(mode_info, prog_var, mer_inst,
    pred_or_func, user_arity, higher_order_mismatch_info) = error_spec.

mode_error_bad_higher_order_inst_to_spec(ModeInfo, PredVar, PredVarInst,
        ExpectedPredOrFunc, ExpectedUserArity, Mismatch) = Spec :-
    PreamblePieces = mode_info_context_preamble(ModeInfo),
    mode_info_get_context(ModeInfo, Context),
    mode_info_get_var_table(ModeInfo, VarTable),
    PredVarName = mercury_var_to_name_only(VarTable, PredVar),
    PredVarNamePieces = color_as_subject([quote(PredVarName)]),
    ExpPFStr = pred_or_func_to_full_str(ExpectedPredOrFunc),
    ExpectedUserArity = user_arity(ExpUserArityInt),
    % Don't let the specification of the expected arity be broken up,
    % since that would make the error message harder to read.
    ExpArityPiece = fixed("arity " ++ int_name_str(ExpUserArityInt)),
    ExpPieces0 = [words(ExpPFStr), words("of"), ExpArityPiece, suffix(",")],
    ExpPieces = color_as_correct(ExpPieces0),
    (
        Mismatch = ho_mismatch_not_higher_order_type,
        ActPieces =
            [words("but the type of")] ++ PredVarNamePieces ++ [words("is")] ++
            color_as_incorrect([words("not a higher order type.")]) ++ [nl]
    ;
        Mismatch = ho_mismatch_no_higher_order_inst_info,
        ( if PredVarInst = free then
            FreeVarPieces = [words("free variable.")],
            ActPieces = [words("but")] ++ PredVarNamePieces ++
                [words("is a")] ++ color_as_incorrect(FreeVarPieces) ++ [nl]
        else
            mode_info_get_module_info(ModeInfo, ModuleInfo),
            mode_info_get_instvarset(ModeInfo, InstVarSet),
            PredVarInstPieces = error_msg_inst(ModuleInfo, InstVarSet,
                do_not_expand_named_insts, uod_user, quote_short_inst, [], [],
                [nl_indent_delta(1)], [nl_indent_delta(-1)], PredVarInst),
            ActPieces =
                [words("and the type of")] ++ PredVarNamePieces ++
                [words("does match that expectation."),
                words("However, to check the correctness of the call,"),
                words("the compiler also needs to know"),
                words("the modes of the arguments and the determinism"),
                words("of the"), words(ExpPFStr),
                words("that"), quote(PredVarName), words("represents."),
                words("The insts of higher order values"),
                words("should contain this information, but")] ++
                color_as_incorrect(PredVarInstPieces ++ [suffix(",")]) ++
                [words("which is the inst of"), quote(PredVarName),
                words("at this point,")] ++
                color_as_incorrect([words("does not.")]) ++
                [blank_line,
                words("The fix for this error is to add this information."),
                words("For example, given a higher order type such as"),
                nl_indent_delta(1),
                fixed(":- type callback_t == (pred(world, world, io, io))."),
                nl_indent_delta(-1),
                words("you would define a corresponding inst, such as"),
                nl_indent_delta(1),
                fixed(":- inst callback_i == (pred(in, out, di, uo) is det)."),
                nl_indent_delta(-1),
                words("This inst, which is usually called"),
                words("a higher order inst, specifies both"),
                words("the modes of the arguments"),
                words("and the determinism of a predicate."),
                words("Search for `higher order inst'"),
                words("in the Mercury language reference manual's"),
                words("chapter for higher order programming"),
                words("for a corresponding example for functions."), nl,
                blank_line,
                words("You can then tell the compiler that"),
                words("a value of type callback_t has inst callback_i"),
                words("by specifying"),
                words("either the mode"), quote("in(callback_i)"),
                words("(when taking a value of type callback_t as input)"),
                words("or the mode"), quote("out(callback_i)"),
                words("(when returning a value of type callback_t as output)"),
                suffix("."), nl]
        )
    ;
        Mismatch = ho_mismatch_pred_vs_func(ActualPredOrFunc),
        ActPFStr = pred_or_func_to_full_str(ActualPredOrFunc),
        ActPieces = [words("but")] ++ PredVarNamePieces ++ [words("is a")] ++
            color_as_incorrect([words(ActPFStr), words("variable.")]) ++ [nl]
    ;
        Mismatch = ho_mismatch_on_arity(ActualUserArity),
        ActualUserArity = user_arity(ActUserArityInt),
        ActArityPiece = fixed("arity " ++ int_name_str(ActUserArityInt)),
        ActPieces = [words("but")] ++ PredVarNamePieces ++ [words("has")] ++
            color_as_incorrect([ActArityPiece, suffix(".")]) ++ [nl]
    ),
    Pieces = PreamblePieces ++ [words("mode error: context requires a")]
        ++ ExpPieces ++ ActPieces,
    Phase = phase_mode_check(report_in_any_mode),
    Spec = spec($pred, severity_error, Phase, Context, Pieces).

%---------------------------------------------------------------------------%

:- func mode_error_unschedulable_conjuncts_to_spec(mode_info,
    one_or_more(delayed_goal), schedule_culprit) = error_spec.

mode_error_unschedulable_conjuncts_to_spec(ModeInfo, OoMErrors, Culprit)
        = Spec :-
    mode_info_get_context(ModeInfo, Context),
    OoMErrors = one_or_more(HeadError, TailErrors),
    (
        TailErrors = [],
        Msgs1 = mode_error_conjunct_to_msgs(Context, ModeInfo, HeadError)
    ;
        TailErrors = [_ | _],
        % If there is more than one error, we use the setting of
        % --verbose-errors to decide between reporting just one,
        % and reporting them all. Unfortunately, we can't use the
        % verbose_and_nonverbose functor of the error_msg_component type
        % to package up the two cases, because we need to package up
        % multiple messages, each with its own context.
        Errors = [HeadError | TailErrors],
        list.filter(is_error_important, Errors, ImportantErrors, OtherErrors),
        mode_info_get_module_info(ModeInfo, ModuleInfo),
        module_info_get_globals(ModuleInfo, Globals),
        globals.lookup_bool_option(Globals, verbose_errors, VerboseErrors),
        (
            VerboseErrors = no,
            % In the absence of --verbose-errors, report only one error.
            % We prefer that this be an important error.
            (
                ImportantErrors = [FirstImportantError | _],
                ConjMsgs = mode_error_conjunct_to_msgs(Context, ModeInfo,
                    FirstImportantError)
            ;
                ImportantErrors = [],
                (
                    OtherErrors = [FirstOtherError | _],
                    ConjMsgs = mode_error_conjunct_to_msgs(Context, ModeInfo,
                        FirstOtherError)
                ;
                    OtherErrors = [],
                    unexpected($pred, "no errors of any kind")
                )
            ),
            % MoreMsg is there to indicate that --verbose-errors would yield
            % more information.
            MoreMsg = simple_msg(Context, [verbose_only(verbose_always, [])]),
            Msgs1 = ConjMsgs ++ [MoreMsg]
        ;
            VerboseErrors = yes,
            Preamble = mode_info_context_preamble(ModeInfo),
            NumErrors = list.length(Errors),
            ConjPieces = [words("mode error in conjunction. The next"),
                int_name(NumErrors), words("error messages"),
                words("indicate possible causes of this error."), nl],
            Msgs1Start = [msg(Context, Preamble ++ ConjPieces)],
            Msgs1Rest0 = list.map(
                mode_error_conjunct_to_msgs(Context, ModeInfo),
                ImportantErrors ++ OtherErrors),
            Msgs1Rest = list.map(prefix_with_blank_line(Context), Msgs1Rest0),
            Msgs1 = Msgs1Start ++ list.condense(Msgs1Rest)
        )
    ),

    % If the goal(s) couldn't be scheduled because we couldn't reorder things
    % past an impure goal, then report that.
    (
        Culprit = conj_floundered,
        % We have already reported everything we can.
        Msgs2 = []
    ;
        Culprit = goal_itself_was_impure,
        Pieces = [words("The goal could not be reordered,"),
            words("because it was impure."), nl],
        Msgs2 = [msg(Context, Pieces)]
    ;
        Culprit = goals_followed_by_impure_goal(ImpureGoal),
        ImpureGoal = hlds_goal(_, ImpureGoalInfo),
        ImpureGoalContext = goal_info_get_context(ImpureGoalInfo),
        Pieces1 = [words("The goal could not be reordered,"),
            words("because it was followed by an impure goal."), nl],
        Pieces2 = [words("This is the location of the impure goal."), nl],
        Msgs2 = [msg(Context, Pieces1),
            msg(ImpureGoalContext, Pieces2)]
    ),
    Phase = phase_mode_check(report_in_any_mode),
    Spec = error_spec($pred, severity_error, Phase, Msgs1 ++ Msgs2).

:- func prefix_with_blank_line(prog_context, list(error_msg))
    = list(error_msg).

prefix_with_blank_line(Context, Msgs) = [BlankMsg | Msgs] :-
    BlankMsg = msg(Context, [blank_line]).

:- pred is_error_important(delayed_goal::in) is semidet.

is_error_important(Error) :-
    Error = delayed_goal(_, mode_error_info(_, ModeError, _, ModeContext), _),
    ( if
        % An error is important unless it is a non-explicit unification,
        % i.e. a head unification or a call argument unification.
        ModeContext = mode_context_unify(unify_context(UnifyContext, _), _),
        UnifyContext \= umc_explicit,

        % Except that errors in lambda goals are important even if the
        % unification that creates the lambda goal is an implicit one.
        ModeError \= mode_error_non_ground_non_local_lambda_var(_, _)
    then
        fail
    else
        true
    ).

:- func mode_error_conjunct_to_msgs(prog_context, mode_info, delayed_goal)
    = list(error_msg).

mode_error_conjunct_to_msgs(Context, !.ModeInfo, DelayedGoal) = Msgs :-
    mode_info_get_module_info(!.ModeInfo, ModuleInfo),
    module_info_get_globals(ModuleInfo, Globals),

    DelayedGoal = delayed_goal(Vars, Error, Goal),
    Error = mode_error_info(_, ModeError, ErrorContext, ModeContext),
    mode_info_set_context(ErrorContext, !ModeInfo),
    mode_info_set_mode_context(ModeContext, !ModeInfo),

    SubSpec0 = mode_error_to_spec(!.ModeInfo, ModeError),
    extract_spec_msgs_and_maybe_add_id(Globals, SubSpec0, SubMsgs),

    globals.lookup_bool_option(Globals, debug_modes, DebugModes),
    (
        DebugModes = no,
        Msgs = SubMsgs
    ;
        DebugModes = yes,
        set_of_var.to_sorted_list(Vars, VarList),
        mode_info_get_var_table(!.ModeInfo, VarTable),
        VarNames = mercury_vars_to_name_only(VarTable, VarList),
        Pieces1 = [words("Floundered goal, waiting on {"),
            words(VarNames), words("}:"), nl],
        Msg1 = msg(Context, Pieces1),
        % XXX Shouldn't we check debug_modes_verbose instead of very_verbose?
        globals.lookup_bool_option(Globals, very_verbose, VeryVerbose),
        (
            VeryVerbose = no,
            Msgs = [Msg1] ++ SubMsgs
        ;
            VeryVerbose = yes,

            OutInfo = init_hlds_out_info(Globals, output_debug),
            VarNameSrc = vns_var_table(VarTable),
            % XXX If we ever need this info again, we should print
            % the current pred_proc_id as well.
            varset.init(TVarSet),
            varset.init(InstVarSet),
            StringBuilder0 = string.builder.init,
            string.builder.append_string("\t\t",
                StringBuilder0, StringBuilder1),
            format_goal_nl(OutInfo, ModuleInfo, VarNameSrc,
                print_name_only, TVarSet, InstVarSet, 2u, ".\n", Goal,
                StringBuilder1, StringBuilder),
            GoalStr = string.builder.to_string(StringBuilder),
            % Note that GoalStr can be far, far longer than fits on one line,
            % but it will be formatted *with* newlines embedded within it.
            % It is generated by the same code as we use to generate HLDS
            % dumps, so it will look like that in the error message as well.
            % The nl's before and after ensure that GoalStr is on its own line
            % even if it turns out to be very short (which can happen e.g.
            % for unifications).
            Components2 = [always([nl, fixed(GoalStr), nl])],
            Msg2 = error_msg(no, treat_based_on_posn, 0u, Components2),
            Msgs = [Msg1, Msg2] ++ SubMsgs
        )
    ).

%---------------------------------------------------------------------------%

:- func mode_error_merge_par_conj_to_spec(mode_info, one_or_more(merge_error))
    = error_spec.

mode_error_merge_par_conj_to_spec(ModeInfo, MergeErrors) = Spec :-
    Preamble = mode_info_context_preamble(ModeInfo),
    mode_info_get_context(ModeInfo, Context),
    MainPieces = [words("mode error: mutually exclusive bindings"),
        words("in parallel conjunction."),
        words("(The current implementation does not permit"),
        words("parallel conjunctions to fail.)"), nl],
    MergeMsgLists = list.map(
        merge_error_to_msgs(ModeInfo, Context, is_not_disjunctive),
        one_or_more_to_list(MergeErrors)),
    list.condense(MergeMsgLists, MergeMsgs),
    Spec = error_spec($pred, severity_error,
        phase_mode_check(report_in_any_mode),
        [msg(Context, Preamble ++ MainPieces) | MergeMsgs]).

%---------------------------------------------------------------------------%

:- func mode_error_merge_disj_to_spec(mode_info, merge_context,
    one_or_more(merge_error)) = error_spec.

mode_error_merge_disj_to_spec(ModeInfo, MergeContext, MergeErrors) = Spec :-
    Preamble = mode_info_context_preamble(ModeInfo),
    MergeContextStr = merge_context_to_string(MergeContext),
    mode_info_get_context(ModeInfo, Context),
    MainPieces = [words("error:")] ++
        color_as_incorrect([words("mode mismatch")]) ++
        [words("in"), words(MergeContextStr), suffix("."), nl],
    MergeMsgLists = list.map(
        merge_error_to_msgs(ModeInfo, Context, is_disjunctive),
        one_or_more_to_list(MergeErrors)),
    list.condense(MergeMsgLists, MergeMsgs),
    Spec = error_spec($pred, severity_error,
        phase_mode_check(report_in_any_mode),
        [msg(Context, Preamble ++ MainPieces) | MergeMsgs]).

:- func merge_context_to_string(merge_context) = string.

merge_context_to_string(merge_disj) = "disjunction".
merge_context_to_string(merge_if_then_else) = "if-then-else".
merge_context_to_string(merge_stm_atomic) = "atomic".

%---------------------------------------------------------------------------%

:- func mode_error_coerce_error_to_spec(mode_info, list(coerce_error))
    = error_spec.

mode_error_coerce_error_to_spec(ModeInfo, Errors) = Spec :-
    Error = list.det_head(Errors),
    Error = coerce_error(TermPath, FromType, ToType, Reason),
    Preamble = mode_info_context_preamble(ModeInfo),
    mode_info_get_context(ModeInfo, Context),
    varset.init(TypeVarSet),
    (
        TermPath = [],
        TermPathPieces = [],
        CoercedTermOrTerms = words("coerced term")
    ;
        TermPath = [_ | _],
        TermPathPieces =
            [words("in the coerced term:"), nl] ++
            list.condense(list.map(make_term_path_piece, TermPath)),
        CoercedTermOrTerms = words("coerced subterm")
    ),
    TheTermPieces = [words("the")] ++ color_as_subject([CoercedTermOrTerms]),
    FromTypeStr =
        mercury_type_to_string(TypeVarSet, print_name_only, FromType),
    ToTypeStr =
        mercury_type_to_string(TypeVarSet, print_name_only, ToType),
    (
        Reason = input_inst_not_ground(Inst),
        ReasonPieces =
            TheTermPieces ++ [words("has instantiatedness")] ++
            color_as_incorrect(
                report_inst(ModeInfo, quote_short_inst, [suffix(",")],
                    [nl_indent_delta(1)], [suffix(","), nl_indent_delta(-1)],
                    Inst)) ++
            [words("but it must have a")] ++
            color_as_correct([words("ground")]) ++ [words("inst."), nl]
    ;
        Reason = cons_id_errors(_Inst, HeadConsError, TailConsErrors),
        classify_bound_functor_cons_id_errors([HeadConsError | TailConsErrors],
            set.init, InputBadConsIdSet,
            set.init, InputBadInstArityConsIdSet,
            set.init, ResultBadConsIdSet),
        InputBadConsIds = set.to_sorted_list(InputBadConsIdSet),
        InputBadInstArityConsIds =
            set.to_sorted_list(InputBadInstArityConsIdSet),
        ResultBadConsIds = set.to_sorted_list(ResultBadConsIdSet),
        % We print one to three blocks of text, with one block for each
        % kind of error that is present, in this order:
        %
        % - cons_ids that do not occur in the input type;
        % - cons_ids that do occur in the input type but have the wrong
        %   arity in the input inst; and
        % - cons_ids that do not occur in the result type.
        %
        % Because of the mode error, we cannot construct a final inst
        % for the coerce goal, which means that there is no analogue
        % of the second category for the result type. (Our test cases often
        % contain an inst on an output argument that *should* describe
        % the term that result of the coerce operation, but that is not
        % the same thing as an inst that *does* describe that result.)
        %
        % We construct these blocks in reverse order, so that we can put
        % the right suffix (a period or a semicolon) at the end of the
        % previous block (if any).
        (
            ResultBadConsIds = [],
            ResultBadConsIdMsgPieces = [],
            BadAritySuffix = "."
        ;
            ResultBadConsIds = [_ | _],
            ResultWrapUnqual = (func(C) = qual_cons_id_and_maybe_arity(C)),
            ResultBadConsIdPieces =
                list.map(ResultWrapUnqual, ResultBadConsIds),
            ResultBadConsIdMsgPieces =
                [words("the following function"),
                words(choose_number(ResultBadConsIds,
                    "symbol in the input term's instantiatedness is",
                    "symbols in the input term's instantiatedness are"))] ++
                color_as_incorrect([words("not part of the result type:")]) ++
                [nl_indent_delta(1)] ++
                piece_list_to_color_line_pieces(color_incorrect,
                    [suffix(".")], ResultBadConsIdPieces) ++
                [nl_indent_delta(-1)],
            BadAritySuffix = ";"
        ),
        (
            InputBadInstArityConsIds = [],
            InputBadInstArityConsIdMsgPieces = [],
            BadInputSuffix = "."
        ;
            InputBadInstArityConsIds = [_ | _],
            InputBadInstArityConsIdPieces =
                list.map(report_bad_arity_pieces, InputBadInstArityConsIds),
            InputBadInstArityConsIdMsgPieces =
                [words("the following function"),
                words(choose_number(InputBadInstArityConsIds,
                    "symbol is used with an incorrect arity",
                    "symbols are used with incorrect arities")),
                words("in the input term's instantiatedness:"),
                nl_indent_delta(1)] ++
                pieces_list_to_color_line_pieces(color_incorrect,
                    [suffix(BadAritySuffix)], InputBadInstArityConsIdPieces) ++
                [nl_indent_delta(-1)],
            BadInputSuffix = ";"
        ),
        (
            InputBadConsIds = [],
            InputBadConsIdMsgPieces = []
        ;
            InputBadConsIds = [_ | _],
            InputWrapUnqual = (func(C) = qual_cons_id_and_maybe_arity(C)),
            InputBadConsIdPieces = list.map(InputWrapUnqual, InputBadConsIds),
            InputBadConsIdMsgPieces =
                [words("the following function"),
                words(choose_number(InputBadConsIds,
                    "symbol in the input term's instantiatedness is",
                    "symbols in the input term's instantiatedness are"))] ++
                color_as_incorrect([words("not part of the input type:")]) ++
                [nl_indent_delta(1)] ++
                piece_list_to_color_line_pieces(color_incorrect,
                    [suffix(BadInputSuffix)], InputBadConsIdPieces) ++
                [nl_indent_delta(-1)]
        ),
        ReasonPieces =
            [words("cannot convert")] ++ TheTermPieces ++
            [words("from type"), quote(FromTypeStr),
            words("to"), quote(ToTypeStr), words("because")] ++
            InputBadConsIdMsgPieces ++
            InputBadInstArityConsIdMsgPieces ++
            ResultBadConsIdMsgPieces
    ;
        Reason = has_inst_expect_upcast(Inst),
        ReasonPieces =
            [words("cannot convert")] ++ TheTermPieces ++
            [words("from type"), quote(FromTypeStr),
            words("to"), quote(ToTypeStr),
            words("because it has instantiatedness")] ++
            color_as_incorrect(
                report_inst(ModeInfo, quote_short_inst, [suffix(",")],
                    [nl_indent_delta(1)], [suffix(","), nl_indent_delta(-1)],
                    Inst)) ++
            [words("and")] ++ color_as_incorrect([quote(FromTypeStr)]) ++
            [words("is not a subtype of"), quote(ToTypeStr), suffix("."), nl]
    ),
    Pieces = [words("mode error:")] ++ TermPathPieces ++ ReasonPieces,
    Spec = spec($pred, severity_error,
        phase_mode_check(report_in_any_mode), Context, Preamble ++ Pieces).

:- func make_term_path_piece(coerce_error_term_path_step) =
    list(format_piece).

make_term_path_piece(Step) = Pieces :-
    Step = coerce_error_term_path_step(ConsId, ArgNum),
    ( if
        ConsId = du_data_ctor(du_ctor(_SymName, 1, _)),
        ArgNum = 1
    then
        ArgPieces = [words("in the argument")]
    else
        ArgPieces = [words("in the"), nth_fixed(ArgNum), words("argument")]
    ),
    Pieces = ArgPieces ++ [words("of function symbol"),
        unqual_cons_id_and_maybe_arity(ConsId), suffix(":"), nl].

:- pred classify_bound_functor_cons_id_errors(
    list(bound_functor_cons_id_error)::in,
    set(cons_id)::in, set(cons_id)::out,
    set({cons_id, arity, arity})::in, set({cons_id, arity, arity})::out,
    set(cons_id)::in, set(cons_id)::out) is det.

classify_bound_functor_cons_id_errors([],
        !InputBadConsIds, !InputBadInstArityConsIds, !ResultBadConsIds).
classify_bound_functor_cons_id_errors([Error | Errors],
        !InputBadConsIds, !InputBadInstArityConsIds, !ResultBadConsIds) :-
    (
        Error = bad_cons_id_input(ConsId),
        set.insert(ConsId, !InputBadConsIds)
    ;
        Error = bad_cons_id_input_inst_arity(ConsId, InstArity, ExpectedArity),
        set.insert({ConsId, InstArity, ExpectedArity},
            !InputBadInstArityConsIds)
    ;
        Error = bad_cons_id_result(ConsId),
        set.insert(ConsId, !ResultBadConsIds)
    ),
    classify_bound_functor_cons_id_errors(Errors,
        !InputBadConsIds, !InputBadInstArityConsIds, !ResultBadConsIds).

:- func report_bad_arity_pieces({cons_id, arity, arity}) = list(format_piece).

report_bad_arity_pieces({ConsId, InstArity, ExpectedArity}) = Pieces :-
    Pieces = [unqual_cons_id_and_maybe_arity(ConsId), prefix("(")] ++
        color_as_incorrect([int_fixed(InstArity)]) ++
        [suffix(";"), words("should be")] ++
        color_as_correct([int_fixed(ExpectedArity)]) ++
        [suffix(")")].

%---------------------------------------------------------------------------%

:- func mode_error_nonground_trace_goal_to_spec(mode_info,
    prog_var, list(prog_var)) = error_spec.

mode_error_nonground_trace_goal_to_spec(ModeInfo, HeadNGVar, TailNGVars)
        = Spec :-
    Preamble = mode_info_context_preamble(ModeInfo),
    mode_info_get_context(ModeInfo, Context),
    mode_info_get_var_table(ModeInfo, VarTable),
    NGVarNames = list.map(mercury_var_to_string(VarTable, print_name_only),
        [HeadNGVar | TailNGVars]),
    VarNameCommaPieces = quote_list_to_color_pieces(color_subject,
        "and", [suffix(",")], NGVarNames),
    (
        TailNGVars = [],
        VarOrVars = "variable",
        IsOrAre = "is"
    ;
        TailNGVars = [_ | _],
        VarOrVars = "variables",
        IsOrAre = "are"
    ),
    Pieces =
        [words("error: the"), words(VarOrVars)] ++ VarNameCommaPieces ++
        [words("whose value the trace goal"),
        words("expects to get from the surrounding code,"),
        words(IsOrAre)] ++ color_as_incorrect([words("not ground")]) ++
        [words("at entry to the trace goal."), nl],
    Spec = spec($pred, severity_error,
        phase_mode_check(report_in_any_mode), Context, Preamble ++ Pieces).

%---------------------------------------------------------------------------%

:- func mode_error_bind_locked_var_to_spec(mode_info, var_lock_reason,
    prog_var, mer_inst, mer_inst) = error_spec.

mode_error_bind_locked_var_to_spec(ModeInfo, Reason, Var, VarInst, Inst)
        = Spec :-
    Preamble = mode_info_context_preamble(ModeInfo),
    mode_info_get_context(ModeInfo, Context),
    mode_info_get_var_table(ModeInfo, VarTable),
    (
        Reason = var_lock_negation,
        ReasonStr = "attempt to bind a non-local variable inside a negation."
    ;
        Reason = var_lock_if_then_else,
        ReasonStr = "attempt to bind a non-local variable" ++
            " inside the condition of an if-then-else."
    ;
        Reason = var_lock_lambda(PredOrFunc),
        PredOrFuncS = pred_or_func_to_str(PredOrFunc),
        ReasonStr = "attempt to bind a non-local variable inside" ++
            " a " ++ PredOrFuncS ++ " lambda goal."
    ;
        Reason = var_lock_trace_goal,
        ReasonStr = "attempt to bind a non-local variable inside a trace goal."
    ;
        Reason = var_lock_atomic_goal,
        ReasonStr = "attempt to bind outer state variables inside an " ++
            "atomic goal."
    ;
        Reason = var_lock_par_conj,
        ReasonStr = "attempt to bind a non-local variable" ++
            " inside more than one parallel conjunct."
    ),
    VarName = mercury_var_to_name_only(VarTable, Var),
    MainPieces = [words("scope error:"), words(ReasonStr), nl] ++
        [words("Variable")] ++ color_as_subject([quote(VarName)]) ++
        has_inst_expected_inst_was(ModeInfo, VarInst, Inst),
    (
        Reason = var_lock_negation,
        VerbosePieces =
            [words("A negation is allowed to bind only variables"),
            words("which are")] ++
            color_as_correct([words("local to the negation,")]) ++
            [words("i.e. those which are"),
            words("implicitly existentially quantified"),
            words("inside the scope of the negation."), nl]
    ;
        Reason = var_lock_if_then_else,
        VerbosePieces =
            [words("The condition of an if-then-else is"),
            words("allowed to bind only variables which are")] ++
            color_as_correct([words("local to the condition,")]) ++
            [words("or which occur")] ++
            color_as_correct([words("only in the condition"),
                words("and the"), quote("then"), words("part.")]) ++
            [nl]
    ;
        Reason = var_lock_lambda(_),
        VerbosePieces =
            [words("A lambda goal is allowed to bind only")] ++
            color_as_correct([words("its arguments")]) ++
            [words("and")] ++
            color_as_correct([words("variables local to the"),
                words("lambda expression.")]) ++
            [nl]
    ;
        Reason = var_lock_trace_goal,
        VerbosePieces =
            [words("A trace goal is allowed to bind only")] ++
            color_as_correct([words("variables which are"),
                words("local to the trace goal.")]) ++
            [nl]
    ;
        Reason = var_lock_atomic_goal,
        VerbosePieces =
            [words("An atomic goal")] ++
            color_as_incorrect([words("may not use")]) ++
            [words("the state variables")] ++
            color_as_subject([words("belonging to the outer scope.")]) ++
            [nl]
    ;
        Reason = var_lock_par_conj,
        VerbosePieces =
            [words("A nonlocal variable of a parallel conjunction"),
            words("may not be bound in")] ++
            color_as_incorrect([words("two or more conjuncts.")]) ++
            [nl]
    ),
    Spec = error_spec($pred, severity_error,
        phase_mode_check(report_in_any_mode),
        [simple_msg(Context,
            [always(Preamble ++ MainPieces),
            verbose_only(verbose_always, VerbosePieces)])]).

%---------------------------------------------------------------------------%

:- func mode_error_unexpected_final_inst_to_spec(mode_info, int, prog_var,
    mer_inst, mer_inst, final_inst_error) = error_spec.

mode_error_unexpected_final_inst_to_spec(ModeInfo, RawArgNum, Var,
        ActualInst, ExpectedInst, Reason) = Spec :-
    Preamble = mode_info_context_preamble(ModeInfo),
    mode_info_get_context(ModeInfo, Context),
    mode_info_get_var_table(ModeInfo, VarTable),
    (
        Reason = too_instantiated,
        Problem = "became too instantiated."
    ;
        Reason = not_instantiated_enough,
        Problem = "did not get sufficiently instantiated."
    ;
        Reason = wrongly_instantiated,
        % I don't think this can happen. But just in case...
        Problem = "had the wrong instantiatedness."
    ),
    mode_info_get_module_info(ModeInfo, ModuleInfo),
    mode_info_get_pred_id(ModeInfo, PredId),
    module_info_pred_info(ModuleInfo, PredId, PredInfo),
    pred_info_get_polymorphism_added_args(PredInfo, NumPolyAddedArgs),
    ArgNum = RawArgNum - NumPolyAddedArgs,
    ( if ArgNum >= 1 then
        PredOrFunc = pred_info_is_pred_or_func(PredInfo),
        pred_form_arity(PredFormArityInt) =
            pred_info_pred_form_arity(PredInfo),
        ( if
            PredOrFunc = pf_function,
            ArgNum = PredFormArityInt
        then
            ArgNumPieces = [words("the function result")]
        else
            ArgNumPieces = [words("argument"), int_fixed(ArgNum)]
        )
    else
        % This should not happen. All code that passes around
        % compiler-generated arguments is of course also compiler generated,
        % and that code is supposed to be "correct by construction".
        % This is here in case that supposition turns out to be mistaken.
        ArgNumPieces = [words("compiler-generated argument"),
            int_fixed(RawArgNum)]
    ),
    VarName = mercury_var_to_name_only(VarTable, Var),
    Pieces = [words("mode error:")] ++ ArgNumPieces ++ [words(Problem), nl,
        words("Final instantiatedness of")] ++
        color_as_subject([quote(VarName)]) ++ [words("was")] ++
        color_as_incorrect(
            report_inst(ModeInfo, quote_short_inst, [suffix(","), nl],
                [nl_indent_delta(1)], [suffix(","), nl_indent_delta(-1)],
                ActualInst)) ++
        [words("expected final instantiatedness was")] ++
        color_as_correct(
            report_inst(ModeInfo, quote_short_inst, [suffix("."), nl],
                [nl_indent_delta(1)], [suffix("."), nl_indent_delta(-1)],
                ExpectedInst)),
    Spec = spec($pred, severity_error,
        phase_mode_check(report_in_any_mode), Context, Preamble ++ Pieces).

%---------------------------------------------------------------------------%

:- func mode_error_in_callee_to_spec(mode_info, list(prog_var), list(mer_inst),
    pred_id, proc_id, list(mode_error_info)) = error_spec.

mode_error_in_callee_to_spec(!.ModeInfo, Vars, Insts,
        CalleePredId, CalleeProcId, CalleeModeErrors) = Spec :-
    Preamble = mode_info_context_preamble(!.ModeInfo),
    mode_info_get_module_info(!.ModeInfo, ModuleInfo),
    mode_info_get_context(!.ModeInfo, Context),
    mode_info_get_var_table(!.ModeInfo, VarTable),
    (
        Vars = [],
        unexpected($pred, "Vars = []")
    ;
        Vars = [Var],
        VarPiece = var_in_table_to_quote_piece(VarTable, Var),
        MainPieces = [words("mode error: argument")] ++
            color_as_subject([VarPiece]) ++
            [words("has the following inst:")]
    ;
        Vars = [_, _ | _],
        VarPieces = list.map(var_in_table_to_quote_piece(VarTable), Vars),
        MainPieces = [words("mode error: arguments")] ++
            piece_list_to_color_pieces(color_subject, "and", [], VarPieces) ++
            [words("have the following insts:")]
    ),
    list.det_head_tail(Insts, HeadInst, TailInsts),
    NoMatchPieces =
        [nl_indent_delta(1)] ++
        inst_list_to_sep_lines(!.ModeInfo, HeadInst, TailInsts) ++
        [nl_indent_delta(-1),
        words("which does not match any of the valid modes for")],

    CalleePredIdPieces = describe_qual_pred_name(ModuleInfo, CalleePredId),
    VerboseCalleePieces = [words("the callee"),
        prefix("(")] ++ CalleePredIdPieces ++ [suffix(")"), nl,
        words("because of the following error."), nl],
    VerbosePieces = MainPieces ++ NoMatchPieces ++ VerboseCalleePieces,
    NonVerboseCalleePieces =
        [words("the callee, because of the following error."), nl],
    NonVerbosePieces = MainPieces ++ NoMatchPieces ++ NonVerboseCalleePieces,

    InitMsg = simple_msg(Context,
        [always(Preamble),
        verbose_and_nonverbose(VerbosePieces, NonVerbosePieces)]),
    (
        CalleeModeErrors = [FirstModeError | _],
        FirstModeError = mode_error_info(_, CalleeModeError,
            CalleeContext, CalleeModeContext),
        mode_info_set_pred_id(CalleePredId, !ModeInfo),
        mode_info_set_proc_id(CalleeProcId, !ModeInfo),
        mode_info_set_context(CalleeContext, !ModeInfo),
        mode_info_set_mode_context(CalleeModeContext, !ModeInfo),
        % Any variables in CalleeModeErrors have their names in
        % the var table of the callee, not in the var table of the procedure
        % we are modechecking now.
        module_info_proc_info(ModuleInfo, CalleePredId, CalleeProcId,
            CalleeProcInfo),
        proc_info_get_var_table(CalleeProcInfo, CalleeVarTable),
        mode_info_set_var_table(CalleeVarTable, !ModeInfo),
        CalleeModeErrorSpec0 = mode_error_to_spec(!.ModeInfo, CalleeModeError),
        module_info_get_globals(ModuleInfo, Globals),
        extract_spec_msgs_and_maybe_add_id(Globals,
            CalleeModeErrorSpec0, LaterMsgs0),
        (
            LaterMsgs0 = [],
            LaterMsgs = []
        ;
            LaterMsgs0 = [LaterHead0 | LaterTail],
            (
                LaterHead0 = msg(LaterContext, Pieces),
                LaterHead = error_msg(yes(LaterContext), always_treat_as_first,
                    0u, [always(Pieces)])
            ;
                LaterHead0 = no_ctxt_msg(Pieces),
                LaterHead = error_msg(no, always_treat_as_first,
                    0u, [always(Pieces)])
            ;
                LaterHead0 = simple_msg(LaterContext, Components),
                LaterHead = error_msg(yes(LaterContext), always_treat_as_first,
                    0u, Components)
            ;
                LaterHead0 = error_msg(MaybeLaterContext, _,
                    Indent, Components),
                LaterHead = error_msg(MaybeLaterContext, always_treat_as_first,
                    Indent, Components)
            ;
                LaterHead0 = blank_msg(MaybeLaterContext),
                LaterHead = blank_msg(MaybeLaterContext)
            ),
            LaterMsgs = start_each_msg_with_blank_line([LaterHead | LaterTail])
        ),
        Spec = error_spec($pred, severity_error,
            phase_mode_check(report_in_any_mode), [InitMsg | LaterMsgs])
    ;
        CalleeModeErrors = [],
        unexpected($pred, "no error")
    ).

%---------------------------------------------------------------------------%

:- func mode_error_cannot_create_implied_mode_to_spec(mode_info,
    cannot_create_reason, prog_var, mer_inst, mer_inst) = error_spec.

mode_error_cannot_create_implied_mode_to_spec(ModeInfo, Reason, Var, VarInst,
        NonImpliedInitialInst) = Spec :-
    % This "error" message is really a "sorry, not implemented" message.
    % We only print the message if we will actually generate code.
    mode_info_get_module_info(ModeInfo, ModuleInfo),
    module_info_get_globals(ModuleInfo, Globals),
    globals.get_op_mode(Globals, OpMode),
    mode_info_get_context(ModeInfo, Context),
    Phase = phase_mode_check(report_in_any_mode),
    ( if OpMode = opm_top_args(opma_augment(opmau_front_and_middle(_)), _) then
        Preamble = mode_info_context_preamble(ModeInfo),
        mode_info_get_var_table(ModeInfo, VarTable),
        (
            Reason = cannot_init_any,
            ReasonPieces = [words("initializing a solver variable")]
        ;
            Reason = cannot_deep_copy_partial_term,
            ReasonPieces = [words("copying a partially instantiated term")]
        ),
        VarName = mercury_var_to_name_only(VarTable, Var),
        Pieces = [words("sorry, the compiler currently"),
            words("cannot implement implied modes that require")] ++
            ReasonPieces ++ [suffix("."), nl,
            words("Variable")] ++
            color_as_subject([quote(VarName)]) ++
            has_inst_expected_inst_was(ModeInfo, VarInst,
                NonImpliedInitialInst),
        Spec = spec($pred, severity_error, Phase, Context, Preamble ++ Pieces)
    else
        Spec = error_spec($pred, severity_informational(report_noop), Phase,
            [simple_msg(Context, [])])
    ).

%---------------------------------------------------------------------------%

:- func purity_error_should_be_in_promise_purity_scope_to_spec(
    negated_context_desc, mode_info, prog_var) = error_spec.

purity_error_should_be_in_promise_purity_scope_to_spec(NegCtxtDesc,
        ModeInfo, Var) = Spec :-
    Preamble = mode_info_context_preamble(ModeInfo),
    mode_info_get_context(ModeInfo, Context),
    mode_info_get_var_table(ModeInfo, VarTable),
    VarName = mercury_var_to_name_only(VarTable, Var),
    (
        NegCtxtDesc = if_then_else,
        Pieces = [words("purity error: if-then-else should be inside"),
            words("a promise_purity scope, because non-local variable")] ++
            color_as_subject([quote(VarName)]) ++
            [words("has inst")] ++ color_as_incorrect([quote("any")]) ++
            [words("and appears in the condition."), nl]
    ;
        NegCtxtDesc = negation,
        Pieces = [words("purity error: negation should be inside"),
            words("a promise_purity scope, because non-local variable")] ++
            color_as_subject([quote(VarName)]) ++
            [words("has inst")] ++ color_as_incorrect([quote("any")]) ++
            [words("and appears in the body."), nl]
    ),
    Spec = spec($pred, severity_error,
        phase_mode_check(report_in_any_mode), Context, Preamble ++ Pieces).

%---------------------------------------------------------------------------%

:- func purity_error_lambda_should_be_any_to_spec(mode_info,
    one_or_more(prog_var)) = error_spec.

purity_error_lambda_should_be_any_to_spec(ModeInfo, OoMVars) = Spec :-
    Preamble = mode_info_context_preamble(ModeInfo),
    mode_info_get_context(ModeInfo, Context),
    mode_info_get_var_table(ModeInfo, VarTable),
    OoMVars = one_or_more(HeadVar, TailVars),
    (
        TailVars = [],
        VarsWhoseInstsContain = [words("variable"),
            words("whose inst contains")],
        HeadVarPiece = var_in_table_to_quote_piece(VarTable, HeadVar),
        VarsDotPieces = color_as_incorrect([HeadVarPiece, suffix(".")])
    ;
        TailVars = [_ | _],
        VarsWhoseInstsContain = [words("variables"),
            words("whose insts contain")],
        Vars = [HeadVar | TailVars],
        VarPieces = list.map(var_in_table_to_quote_piece(VarTable), Vars),
        VarsDotPieces = piece_list_to_color_pieces(color_incorrect, "and",
            [suffix(".")], VarPieces)
    ),
    Pieces = [words("purity error: lambda is"), quote("ground"),
        words("but contains the following non-local")] ++
        VarsWhoseInstsContain ++ [quote("any"), suffix(":")] ++
        VarsDotPieces ++ [nl],
    Always = always(Preamble ++ Pieces),
    VerboseOnly = verbose_only(verbose_once, [words("Predicate expressions"),
        words("with inst"), quote("any"), words("can be written"),
        quote("any_pred(Args) is det :- ..."), suffix("."),
        words("Function expressions with inst"), quote("any"),
        words("can be written"),
        quote("any_func(Args) = Result is det :- ..."), suffix("."), nl]),
    Spec = error_spec($pred, severity_error,
        phase_mode_check(report_in_any_mode),
        [simple_msg(Context, [Always, VerboseOnly])]).

%---------------------------------------------------------------------------%
%---------------------------------------------------------------------------%
%
% Utility predicates needed to print more than one kind of error.
%

:- type maybe_is_disjunctive
    --->    is_not_disjunctive
    ;       is_disjunctive.

:- func merge_error_to_msgs(mode_info, prog_context, maybe_is_disjunctive,
    merge_error) = list(error_msg).

merge_error_to_msgs(ModeInfo, MainContext, IsDisjunctive, MergeError) = Msgs :-
    MergeError = merge_error(Var, ContextsInsts0),
    mode_info_get_module_info(ModeInfo, ModuleInfo),
    mode_info_get_var_table(ModeInfo, VarTable),
    VarNamePiece = var_in_table_to_quote_piece(VarTable, Var),
    list.sort(ContextsInsts0, ContextsInsts),
    lookup_var_type(VarTable, Var, VarType),
    count_ground_insts(ModuleInfo, VarType, ContextsInsts,
        0, NumGroundInsts, 0, NumAllInsts),
    ( if
        IsDisjunctive = is_disjunctive,
        NumGroundInsts < NumAllInsts,
        NumGroundInsts * 2 > NumAllInsts
    then
        % More than half the insts are ground, so it is likely that they
        % were *all* intended to be ground, but not all actually *are* ground,
        % which is likely to be the bug.
        CommonPieces = [words("The variable")] ++
            color_as_subject([VarNamePiece]) ++
            [words("is")] ++ color_as_incorrect([words("ground")]) ++
            [words("in"), int_fixed(NumGroundInsts), words("out of"),
            int_fixed(NumAllInsts), words("branches."), nl],
        VerbosePieces =
            [words("It has the following instantiation states."), nl],
        ( if NumAllInsts - NumGroundInsts > 1 then
            NonVerbosePieces =
                [words("It has non-ground instantiation states"),
                words("in the following branches."), nl]
        else
            % The message for the non-ground branch will *say*
            % it is for such a branch.
            NonVerbosePieces = []
        ),
        VarMsg = simple_msg(MainContext,
            [always(CommonPieces),
            verbose_and_nonverbose(VerbosePieces, NonVerbosePieces)]),
        InstMsgs = list.map(
            report_inst_in_context(ModeInfo, report_inst_and_groundness,
                yes(color_inconsistent), VarNamePiece, VarType),
            ContextsInsts),
        Msgs = [VarMsg | InstMsgs]
    else if
        IsDisjunctive = is_disjunctive,
        0 < NumGroundInsts,
        NumGroundInsts < NumAllInsts
    then
        VarPieces = [words("The variable")] ++
            color_as_subject([VarNamePiece]) ++
            [words("is ground in some branches but not others."), nl],
        VarMsg = msg(MainContext, VarPieces),
        InstMsgs = list.map(
            report_inst_in_context(ModeInfo, report_groundness_only,
                yes(color_inconsistent), VarNamePiece, VarType),
            ContextsInsts),
        Msgs = [VarMsg | InstMsgs]
    else
        VarPieces = [words("The variable")] ++
            color_as_subject([VarNamePiece]) ++
            [words("has the following instantiation states."), nl],
        VarMsg = msg(MainContext, VarPieces),
        InstMsgs = list.map(
            report_inst_in_context(ModeInfo, report_inst_only,
                yes(color_inconsistent), VarNamePiece, VarType),
            ContextsInsts),
        Msgs = [VarMsg | InstMsgs]
    ).

%---------------------%

:- pred count_ground_insts(module_info::in, mer_type::in,
    assoc_list(prog_context, mer_inst)::in,
    int::in, int::out, int::in, int::out) is det.

count_ground_insts(_ModuleInfo, _Type, [], !NumGroundInsts, !NumAllInsts).
count_ground_insts(ModuleInfo, Type, [ContextInst | ContextsInsts],
        !NumGroundInsts, !NumAllInsts) :-
    ContextInst = _Context - Inst,
    ( if inst_is_ground(ModuleInfo, Type, Inst) then
        !:NumGroundInsts = !.NumGroundInsts + 1
    else
        true
    ),
    !:NumAllInsts = !.NumAllInsts + 1,
    count_ground_insts(ModuleInfo, Type, ContextsInsts,
        !NumGroundInsts, !NumAllInsts).

%---------------------%

:- type report_inst_how
    --->    report_inst_only
    ;       report_groundness_only
    ;       report_inst_and_groundness.

:- func report_inst_in_context(mode_info, report_inst_how, maybe(color_name),
    format_piece, mer_type, pair(prog_context, mer_inst)) = error_msg.

report_inst_in_context(ModeInfo, ReportIsGround, MaybeColor, VarNamePiece,
        Type, Context - Inst) = Msg :-
    (
        ReportIsGround = report_inst_only,
        Pieces = report_inst_in_branch(ModeInfo, MaybeColor, VarNamePiece,
            no, Inst),
        Msg = msg(Context, Pieces)
    ;
        ReportIsGround = report_groundness_only,
        mode_info_get_module_info(ModeInfo, ModuleInfo),
        ( if inst_is_ground(ModuleInfo, Type, Inst) then
            Pieces = report_inst_in_branch_simple(MaybeColor, VarNamePiece,
                "ground")
        else if Inst = free then
            Pieces = report_inst_in_branch_simple(MaybeColor, VarNamePiece,
                "free")
        else
            Pieces = report_inst_in_branch_simple(MaybeColor, VarNamePiece,
                "not ground")
        ),
        Msg = msg(Context, Pieces)
    ;
        ReportIsGround = report_inst_and_groundness,
        mode_info_get_module_info(ModeInfo, ModuleInfo),
        ( if inst_is_ground(ModuleInfo, Type, Inst) then
            Pieces = report_inst_in_branch(ModeInfo, MaybeColor, VarNamePiece,
                yes(ground), Inst),
            Msg = simple_msg(Context, [verbose_and_nonverbose(Pieces, [])])
        else
            Pieces = report_inst_in_branch(ModeInfo, MaybeColor, VarNamePiece,
                yes(nonground), Inst),
            Msg = msg(Context, Pieces)
        )
    ).

:- type ground_or_nonground
    --->    ground
    ;       nonground.

:- func report_inst_in_branch(mode_info, maybe(color_name), format_piece,
    maybe(ground_or_nonground), mer_inst) = list(format_piece).

report_inst_in_branch(ModeInfo, MaybeColor, VarNamePiece,
        MaybeGroundOrNonGround, Inst) = Pieces :-
    (
        MaybeGroundOrNonGround = no,
        ( if Inst = ground(shared, none_or_default_func) then
            Pieces = report_inst_in_branch_simple(MaybeColor, VarNamePiece,
                "ground")
        else if Inst = free then
            Pieces = report_inst_in_branch_simple(MaybeColor, VarNamePiece,
                "free")
        else
            IntroPieces = [words("In this branch,"), VarNamePiece,
                words("has instantiatedness")],
            Pieces = report_inst_in_branch_detail(ModeInfo, IntroPieces,
                MaybeColor, Inst)
        )
    ;
        MaybeGroundOrNonGround = yes(ground),
        ( if Inst = ground(shared, none_or_default_func) then
            Pieces = report_inst_in_branch_simple(MaybeColor, VarNamePiece,
                "ground")
        else
            IntroPieces = [words("In this branch,"), VarNamePiece,
                words("has the ground instantiatedness")],
            Pieces = report_inst_in_branch_detail(ModeInfo, IntroPieces,
                MaybeColor, Inst)
        )
    ;
        MaybeGroundOrNonGround = yes(nonground),
        ( if Inst = free then
            Pieces = report_inst_in_branch_simple(MaybeColor, VarNamePiece,
                "free")
        else
            IntroPieces = [words("In this branch,"), VarNamePiece,
                words("has the non-ground instantiatedness")],
            Pieces = report_inst_in_branch_detail(ModeInfo, IntroPieces,
                MaybeColor, Inst)
        )
    ).

:- func report_inst_in_branch_simple(maybe(color_name), format_piece, string)
    = list(format_piece).

report_inst_in_branch_simple(MaybeColor, VarNamePiece, FreeOrGround)
        = Pieces :-
    MainPieces = [words("In this branch,"), VarNamePiece, words("is")] ++
        maybe_color_pieces(MaybeColor, [words(FreeOrGround), suffix(".")]) ++
        [nl],
    Pieces = [nl_indent_delta(1) | MainPieces] ++ [nl_indent_delta(-1)].

:- func report_inst_in_branch_detail(mode_info, list(format_piece),
    maybe(color_name), mer_inst) = list(format_piece).

report_inst_in_branch_detail(ModeInfo, IntroPieces, MaybeColor, Inst)
        = Pieces :-
    Pieces = [nl_indent_delta(1) | IntroPieces] ++ [nl_indent_delta(1)] ++
        maybe_color_pieces(MaybeColor,
            report_inst(ModeInfo, fixed_short_inst,
                [suffix("."), nl_indent_delta(-2)],
                [], [suffix("."), nl_indent_delta(-2)], Inst)).

%------------%

:- func inst_list_to_sep_lines(mode_info, mer_inst, list(mer_inst))
    = list(format_piece).

inst_list_to_sep_lines(ModeInfo, Inst1, Insts2plus) = Pieces :-
    (
        Insts2plus = [],
        Pieces = report_inst(ModeInfo, fixed_short_inst, [], [], [], Inst1)
    ;
        Insts2plus = [Inst2 | Insts3plus],
        HeadPieces = report_inst(ModeInfo, fixed_short_inst, [suffix(",")],
            [], [suffix(",")], Inst1) ++ [nl],
        TailPieces = inst_list_to_sep_lines(ModeInfo, Inst2, Insts3plus),
        Pieces = HeadPieces ++ TailPieces
    ).

%------------%

:- func has_inst_expected_inst_was(mode_info, mer_inst, mer_inst)
    = list(format_piece).

has_inst_expected_inst_was(ModeInfo, ActualInst, ExpectedInst) =
    has_instantiatedness(ModeInfo, yes(color_incorrect), ActualInst, ",") ++
    expected_inst_was(ModeInfo, ExpectedInst).

:- func has_instantiatedness(mode_info, maybe(color_name), mer_inst, string)
    = list(format_piece).

has_instantiatedness(ModeInfo, MaybeColor, Inst, Suffix) = Pieces :-
    InstPieces0 = report_inst(ModeInfo, quote_short_inst, [suffix(Suffix), nl],
        [nl_indent_delta(1)], [suffix(Suffix), nl_indent_delta(-1)], Inst),
    InstPieces = maybe_color_pieces(MaybeColor, InstPieces0),
    Pieces = [words("has instantiatedness") | InstPieces].

:- func expected_inst_was(mode_info, mer_inst) = list(format_piece).

expected_inst_was(ModeInfo, Inst) = Pieces :-
    InstPieces0 = report_inst(ModeInfo, quote_short_inst, [suffix("."), nl],
        [nl_indent_delta(1)], [suffix("."), nl_indent_delta(-1)], Inst),
    InstPieces = color_as_correct(InstPieces0),
    Pieces = [words("expected instantiatedness was") | InstPieces].

:- func report_inst(mode_info, short_inst,
    list(format_piece), list(format_piece), list(format_piece),
    mer_inst) = list(format_piece).

report_inst(ModeInfo, ShortInstQF, ShortInstSuffix,
        LongInstPrefix, LongInstSuffix, Inst0) = Pieces :-
    mode_info_get_module_info(ModeInfo, ModuleInfo),
    mode_info_get_instvarset(ModeInfo, InstVarSet),
    Pieces = error_msg_inst(ModuleInfo, InstVarSet, expand_named_insts,
        uod_user, ShortInstQF, [], ShortInstSuffix,
        LongInstPrefix, LongInstSuffix, Inst0).

%---------------------------------------------------------------------------%
%---------------------------------------------------------------------------%

mode_warning_info_to_spec(!.ModeInfo, Warning) = Spec :-
    Warning = mode_warning_info(ModeWarning, Context, ModeContext),
    mode_info_set_context(Context, !ModeInfo),
    mode_info_set_mode_context(ModeContext, !ModeInfo),
    (
        ModeWarning = cannot_succeed_var_var(VarA, VarB, InstA, InstB),
        Spec = mode_warning_cannot_succeed_var_var(!.ModeInfo, VarA, VarB,
            InstA, InstB)
    ;
        ModeWarning = cannot_succeed_var_functor(Var, Inst, ConsId),
        Spec = mode_warning_cannot_succeed_var_functor(!.ModeInfo,
            Var, Inst, ConsId)
    ;
        ModeWarning = cannot_succeed_ground_occur_check(Var, ConsId),
        Spec = mode_warning_cannot_succeed_ground_occur_check(!.ModeInfo,
            Var, ConsId)
    ).

%---------------------------------------------------------------------------%

:- func mode_warning_cannot_succeed_var_var(mode_info,
    prog_var, prog_var, mer_inst, mer_inst) = error_spec.

mode_warning_cannot_succeed_var_var(ModeInfo, X, Y, InstX, InstY) = Spec :-
    Preamble = mode_info_context_preamble(ModeInfo),
    mode_info_get_context(ModeInfo, Context),
    mode_info_get_var_table(ModeInfo, VarTable),
    NameX = mercury_var_to_name_only(VarTable, X),
    NameY = mercury_var_to_name_only(VarTable, Y),
    MaybeColor = yes(color_inconsistent),
    % XXX It would make sense to color as subject only the last reference
    % to each of NameX and NameY, but this would introduce an asymmetry
    % with respect to mode_warning_cannot_succeed_var_functor, which has
    % only NameX.
    Pieces = [words("warning: unification of")] ++
        color_as_subject([quote(NameX)]) ++ [words("and")] ++
        color_as_subject([quote(NameY)]) ++ [words("cannot succeed."), nl] ++
        color_as_subject([quote(NameX)]) ++
        has_instantiatedness(ModeInfo, MaybeColor, InstX, ",") ++
        color_as_subject([quote(NameY)]) ++
        has_instantiatedness(ModeInfo, MaybeColor, InstY, "."),
    Spec = spec($pred, severity_warning(warn_dodgy_simple_code),
        phase_mode_check(report_only_if_in_all_modes),
        Context, Preamble ++ Pieces).

%---------------------------------------------------------------------------%

:- func mode_warning_cannot_succeed_var_functor(mode_info, prog_var, mer_inst,
    cons_id) = error_spec.

mode_warning_cannot_succeed_var_functor(ModeInfo, X, InstX, ConsId) = Spec :-
    Preamble = mode_info_context_preamble(ModeInfo),
    mode_info_get_context(ModeInfo, Context),
    mode_info_get_var_table(ModeInfo, VarTable),
    NameX = mercury_var_to_name_only(VarTable, X),
    ConsIdStr = mercury_cons_id_to_string(output_mercury,
        does_not_need_brackets, ConsId),
    % XXX The term that X is being unified is ConsId *only* if ConsId
    % has arity zero; otherwise, it is a term in which ConsId is only
    % the principal functor. Can we find a wording here that
    %
    % - is not misleading on this issue, and
    % - is reasonably short and easily understandable?
    %
    % I (zs) feel that "unification of X and the term whose principal functor
    % is ConsId" would fail on that last point, even if we used that wording
    % only ConsId is not a constant.
    %
    % XXX See also the XXX in mode_warning_cannot_succeed_var_var.
    Pieces = [words("warning: unification of")] ++
        color_as_subject([quote(NameX)]) ++ [words("and")] ++
        color_as_subject([words(ConsIdStr)]) ++
        [words("cannot succeed."), nl] ++
        color_as_subject([quote(NameX)]) ++
        has_instantiatedness(ModeInfo, yes(color_incorrect), InstX, "."),
    Spec = spec($pred, severity_warning(warn_dodgy_simple_code),
        phase_mode_check(report_only_if_in_all_modes),
        Context, Preamble ++ Pieces).

%---------------------------------------------------------------------------%

:- func mode_warning_cannot_succeed_ground_occur_check(mode_info, prog_var,
    cons_id) = error_spec.

mode_warning_cannot_succeed_ground_occur_check(ModeInfo, X, ConsId) = Spec :-
    Preamble = mode_info_context_preamble(ModeInfo),
    mode_info_get_context(ModeInfo, Context),
    mode_info_get_var_table(ModeInfo, VarTable),
    NameX = mercury_var_to_name_only(VarTable, X),
    ConsIdStr = mercury_cons_id_to_string(output_mercury,
        does_not_need_brackets, ConsId),
    Pieces = [words("warning: unification of")] ++
        color_as_subject([quote(NameX)]) ++ [words("and")] ++
        color_as_subject([words(ConsIdStr)]) ++
        [words("cannot succeed, because")] ++
        color_as_incorrect([quote(NameX), words("cannot be equal"),
            words("to a term containing itself.")]) ++
        [nl],
    Spec = spec($pred, severity_warning(warn_dodgy_simple_code),
        phase_mode_check(report_in_any_mode), Context, Preamble ++ Pieces).

%---------------------------------------------------------------------------%
%---------------------------------------------------------------------------%
%
% Utility predicates needed to print both errors and warnings.
%

:- func mode_info_context_preamble(mode_info) = list(format_piece).

mode_info_context_preamble(ModeInfo) = Pieces :-
    mode_info_get_module_info(ModeInfo, ModuleInfo),
    mode_info_get_pred_id(ModeInfo, PredId),
    mode_info_get_proc_id(ModeInfo, ProcId),
    module_info_pred_proc_info(ModuleInfo, PredId, ProcId, PredInfo, ProcInfo),
    pred_info_get_origin(PredInfo, PredOrigin),
    ( if
        PredOrigin = origin_user(OriginUser),
        OriginUser = user_made_instance_method(PFMethodSymNameArity, _),
        PFMethodSymNameArity = pred_pf_name_arity(_, MethodSymName, _)
    then
        Name = unqualify_name(MethodSymName),
        ExtraMethodPieces = [words("type class method implementation for")]
    else
        Name = pred_info_name(PredInfo),
        ExtraMethodPieces = []
    ),
    PredOrFunc = pred_info_is_pred_or_func(PredInfo),
    mode_info_get_instvarset(ModeInfo, InstVarSet),
    SymName = unqualified(Name),
    pred_info_get_markers(PredInfo, PredMarkers),
    proc_info_declared_argmodes(ProcInfo, Modes0),
    strip_module_names_from_mode_list(strip_builtin_module_name,
        do_not_set_default_func, Modes0, Modes),
    MaybeDet = no,
    ModeSubDeclStr = mercury_mode_subdecl_to_string(output_debug, PredOrFunc,
        InstVarSet, SymName, Modes, MaybeDet),
    mode_info_get_mode_context(ModeInfo, ModeContext),
    ModeContextPieces =
        mode_context_to_pieces(ModeInfo, ModeContext, PredMarkers),
    Pieces = [words("In clause for")] ++ ExtraMethodPieces ++
        [words_quote(ModeSubDeclStr), suffix(":"), nl] ++
        ModeContextPieces.

    % XXX Some parts of the mode context never get set up.
    %
:- func mode_context_to_pieces(mode_info, mode_context, pred_markers)
    = list(format_piece).

mode_context_to_pieces(ModeInfo, ModeContext, Markers) = Pieces :-
    (
        ModeContext = mode_context_call_arg(ModeCallId, ArgNum),
        CallId = mode_call_id_to_call_id(ModeInfo, ModeCallId),
        CalleePieces = call_arg_id_to_pieces(print_ho_var_name, CallId,
            ArgNum, Markers),
        Pieces = [words("in")] ++ CalleePieces ++ [suffix(":"), nl]
    ;
        ModeContext = mode_context_call(ModeCallId),
        CallId = mode_call_id_to_call_id(ModeInfo, ModeCallId),
        CalleePieces = call_id_to_pieces(print_ho_var_name, CallId),
        Pieces = [words("in")] ++ CalleePieces ++ [suffix(":"), nl]
    ;
        ModeContext = mode_context_unify(UnifyContext, _Side),
        unify_context_first_to_pieces(is_not_first, _, UnifyContext,
            _LastContextWord, [], Pieces)
    ;
        ModeContext = mode_context_not_call_or_unify,
        Pieces = []
    ).

%---------------------------------------------------------------------------%
%---------------------------------------------------------------------------%

should_report_mode_warning_for_pred_origin(Origin) = Report :-
    (
        Origin = origin_user(OriginUser),
        (
            ( OriginUser = user_made_pred(_, _, _)
            ; OriginUser = user_made_lambda(_, _, _)
            ),
            Report = yes
        ;
            ( OriginUser = user_made_class_method(_, _)
            ; OriginUser = user_made_instance_method(_, _)
            ; OriginUser = user_made_assertion(_, _, _)
            ),
            Report = no
        )
    ;
        ( Origin = origin_compiler(_)
        ; Origin = origin_pred_transform(_, _, _)
        ; Origin = origin_proc_transform(_, _, _, _)
        ),
        Report = no
    ).

%---------------------------------------------------------------------------%
%---------------------------------------------------------------------------%

mode_decl_to_string(Lang, ProcId, PredInfo) = String :-
    PredOrFunc = pred_info_is_pred_or_func(PredInfo),
    Name = pred_info_name(PredInfo),
    SymName = unqualified(Name),
    pred_info_get_proc_table(PredInfo, Procs),
    map.lookup(Procs, ProcId, ProcInfo),
    proc_info_declared_argmodes(ProcInfo, Modes0),
    proc_info_get_declared_determinism(ProcInfo, MaybeDet),
    varset.init(InstVarSet),
    strip_module_names_from_mode_list(strip_builtin_module_name,
        do_not_set_default_func, Modes0, Modes),
    String = mercury_mode_subdecl_to_string(Lang, PredOrFunc,
        InstVarSet, SymName, Modes, MaybeDet).

%---------------------------------------------------------------------------%
:- end_module check_hlds.mode_errors.
%---------------------------------------------------------------------------%