The improvements take two forms.
The first is that when the mode checker tries to schedule a unification
of the form X = curried_pred(A1, ... An), but fails, perhaps because
curried_pred has more than one declared mode matching the current insts
of the Ai, we record this fact in the mode_info. Then, if later we find
that X is insufficiently instantiated, we print the message we originally
generated for the X = curried_pred(A1, ... An) unification (but which we
threw away when the scheduling attempt failed) as a possible explanation
of this insufficient instantiation.
The second is that when scheduling X = curried_pred(A1, ... An) but fails,
we record more information about the reason, to print it later in the hope that
it may help the user diagnose the problem.
compiler/mode_errors.m:
Change the representation of the errors resulting for not being able
to schedule rhs_lambda unifications of the form X = curried_pred(Ai).
Merge the previous two separate errors into one, and add a parameter
that that distinguishes the three (not two) possible different causes
of the error. Print better diagnostics for all three, based on a common
template.
Change the representation of the errors that say a variable is not
sufficiently instantiated, to make it possible (but of course not
compulsory) to record what error of the X = curried_pred(Ai) kind
may be responsible for it. Include the error message for this cause
in the error message about the insufficiently instantiated variable.
compiler/mode_info.m:
Add a field to the mode_info that allows a failed attempt to schedule
X = curried_pred(Ai) to record the error it generates as a possible
cause of the later insufficient instantiation of X.
compiler/modecheck_unify.m:
Gather the extra information now needed by the representation of mode
errors for failed attempts to schedule X = curried_pred(Ai).
Record the errors for such attempts in the new mode_info field.
compiler/modecheck_util.m:
When generating "variable is not sufficiently instantiated" errors,
see if the new mode_info field say that the insufficiently instantiated
variable was, in a previous conjunct, involved in a failed
X = curried_pred(Ai) unification, and if yes, record this fact
as a possible cause of the error.
compiler/modecheck_goal.m:
Reset the new field at the start of every branched control structure,
to prevent us from using information about X = curried_pred(Ai)
unifications in one branch in other, parallel branches.
Avoid allocating a context at every goal.
library/term.m:
Add a utility predicate to enable that avoidance.
NEWS:
Mention the new utility predicate.
Fix some no-longer-valid entries.
compiler/modecheck_call.m:
Make some code need less stack space.
Fix some comments.
compiler/modecheck_conj.m:
Clarify some code.
tests/invalid/uint_bitwise_xor_mode.{m,err_exp}:
A new test case for both improvements. It is a version of
tests/hard_coded/uint_bitwise.m cut down to contain just the bug
that previously we generate only a misleading error message for.
tests/invalid/Mmakefile:
Enable the new test.
tests/invalid/multimode_addr_problems.err_exp:
Update this expected output to account for the second improvement.
