Simplify more code in mercury_compile_main.m.

compiler/mercury_compile_main.m:
    Simplify the code interpreting the result of calls to lookup_mmc_options.

    Eliminate the one remaining redundant computation of the
    default option table.

compiler/options_file.m:
    Expand the documentation of the predicates that read options files.

    Document that the predicates that only look things up in the data
    structures representing already-read-in options files can return
    only errors, not warnings.

    Delete a long-obsolete comment.

compiler/maybe_error.m:
    Add a utility predicate that could be useful later. (I thought it
    would be useful in this diff, but it wasn't.)

compiler/maybe_error.m

@@ -83,6 +83,9 @@
 :- pred project_ok1(maybe1(T1)::in, T1::out) is semidet.
 :- pred det_project_ok1(maybe1(T1)::in, T1::out) is det.
 
+:- pred separate_ok1_error1(list(maybe1(T1))::in,
+    list(T1)::out, list(error_spec)::out) is det.
+
 %---------------------------------------------------------------------------%
 %---------------------------------------------------------------------------%
 
@@ -139,6 +142,27 @@ det_project_ok1(Maybe1, Item) :-
         unexpected($pred, "error1")
     ).
 
+%---------------------%
+
+separate_ok1_error1(Maybes, OKs, Specs) :-
+    separate_ok1_error1_loop(Maybes, [], RevOKs, [], Specs),
+    list.reverse(RevOKs, OKs).
+
+:- pred separate_ok1_error1_loop(list(maybe1(T1))::in,
+    list(T1)::in, list(T1)::out, list(error_spec)::in, list(error_spec)::out)
+    is det.
+
+separate_ok1_error1_loop([], !RevOKs, !Specs).
+separate_ok1_error1_loop([Maybe | Maybes], !RevOKs, !Specs) :-
+    (
+        Maybe = ok1(OK),
+        !:RevOKs = [OK | !.RevOKs]
+    ;
+        Maybe = error1(CurSpecs),
+        !:Specs = CurSpecs ++ !.Specs
+    ),
+    separate_ok1_error1_loop(Maybes, !RevOKs, !Specs).
+
 %---------------------------------------------------------------------------%
 :- end_module parse_tree.maybe_error.
 %---------------------------------------------------------------------------%

compiler/mercury_compile_main.m

@@ -248,8 +248,9 @@ real_main_after_expansion(ProgressStream, ErrorStream, CmdLineArgs, !IO) :-
             unexpected($pred,
                 "extra arguments with --arg-file: " ++ string(ExtraArgs))
         ),
-        process_options_arg_file(ArgFile, DetectedGradeFlags, OptionsVariables,
-            MaybeMCFlags, OptionArgs, NonOptionArgs, OptionSpecs, !IO)
+        process_options_arg_file(DefaultOptionTable, ArgFile,
+            DetectedGradeFlags, OptionsVariables, MaybeMCFlags,
+            OptionArgs, NonOptionArgs, OptionSpecs, !IO)
     else
         process_options_std(ErrorStream, DefaultOptionTable, CmdLineArgs,
             DetectedGradeFlags, OptionsVariables, MaybeMCFlags,
@@ -311,13 +312,14 @@ real_main_after_expansion(ProgressStream, ErrorStream, CmdLineArgs, !IO) :-
         io.set_exit_status(1, !IO)
     ).
 
-:- pred process_options_arg_file(string::in,
+:- pred process_options_arg_file(option_table::in, string::in,
     list(string)::out, options_variables::out, maybe(list(string))::out,
     list(string)::out, list(string)::out, list(error_spec)::out,
     io::di, io::uo) is det.
 
-process_options_arg_file(ArgFile, DetectedGradeFlags, OptionsVariables,
-        MaybeMCFlags, OptionArgs, NonOptionArgs, Specs, !IO) :-
+process_options_arg_file(DefaultOptionTable, ArgFile, DetectedGradeFlags,
+        OptionsVariables, MaybeMCFlags, OptionArgs, NonOptionArgs,
+        Specs, !IO) :-
     io.environment.get_environment_var_map(EnvVarMap, !IO),
     % All the configuration and options file options are passed in the
     % given file, which is created by the parent `mmc --make' process.
@@ -338,11 +340,8 @@ process_options_arg_file(ArgFile, DetectedGradeFlags, OptionsVariables,
     (
         MaybeArgs1 = yes(Args1),
         % Separate the option args from the non-option args.
-        % XXX HANDLE_OPTIONS Later calls to handle_given_options
-        % will compute OptionTable0 again and again.
         % XXX HANDLE_OPTIONS Ignoring _MaybeError seems a bit careless.
-        getopt.init_option_table(option_defaults, OptionTable0),
-        getopt.record_arguments(short_option, long_option, OptionTable0,
+        getopt.record_arguments(short_option, long_option, DefaultOptionTable,
             Args1, NonOptionArgs, OptionArgs, _MaybeError, _OptionValues)
     ;
         MaybeArgs1 = no,
@@ -353,11 +352,10 @@ process_options_arg_file(ArgFile, DetectedGradeFlags, OptionsVariables,
     OptionsVariables = options_variables_init(EnvVarMap),
     MaybeMCFlags = yes([]).
 
-:- pred process_options_std(io.text_output_stream::in,
-    option_table(option)::in, list(string)::in,
-    list(string)::out, options_variables::out, maybe(list(string))::out,
-    list(string)::out, list(string)::out, list(error_spec)::out,
-    io::di, io::uo) is det.
+:- pred process_options_std(io.text_output_stream::in, option_table::in,
+    list(string)::in, list(string)::out, options_variables::out,
+    maybe(list(string))::out, list(string)::out, list(string)::out,
+    list(error_spec)::out, io::di, io::uo) is det.
 
 process_options_std(ErrorStream, DefaultOptionTable, CmdLineArgs,
         DetectedGradeFlags, OptionsVariables, MaybeMCFlags,
@@ -369,7 +367,7 @@ process_options_std(ErrorStream, DefaultOptionTable, CmdLineArgs,
     % XXX Doing every task in handle_given_options is wasteful
     % in the very likely case of their being an option file.
     % We should do just enough to find the setting of the two options
-    % whose values we look up right here.
+    % whose values we look up right here, and the few options we need below.
     handle_given_options(ErrorStream, DefaultOptionTable, CmdLineArgs,
         OptionArgs, NonOptionArgs, _Errors0, ArgsGlobals, !IO),
     globals.lookup_accumulating_option(ArgsGlobals, options_search_directories,
@@ -463,15 +461,15 @@ process_options_std_config_file(FlagsArgsGlobals, EnvVarMap, WarnUndef,
         (
             ConfigErrors = no,
             lookup_mmc_options(OptionsVariables, MaybeMCFlags1),
-            Specs0 = ConfigSpecs ++ get_any_errors1(MaybeMCFlags1),
-            Errors0 = contains_errors(FlagsArgsGlobals, Specs0),
             (
-                Errors0 = no,
-                det_project_ok1(MaybeMCFlags1, MCFlags1),
-                MaybeMCFlags = yes(MCFlags1)
+                MaybeMCFlags1 = ok1(MCFlags1),
+                MaybeMCFlags = yes(MCFlags1),
+                Specs0 = ConfigSpecs
             ;
-                Errors0 = yes,
-                MaybeMCFlags = no
+                MaybeMCFlags1 = error1(MCFlagsSpecs),
+                % All error_specs in MCFlagsSpecs are errors, not warnings.
+                MaybeMCFlags = no,
+                Specs0 = ConfigSpecs ++ MCFlagsSpecs
             ),
             % XXX Record _StdLibGrades in the final globals structure.
             maybe_detect_stdlib_grades(FlagsArgsGlobals, OptionsVariables,
@@ -497,15 +495,15 @@ process_options_std_config_file(FlagsArgsGlobals, EnvVarMap, WarnUndef,
         DetectedGradeFlags = [],
         OptionsVariables = options_variables_init(EnvVarMap),
         lookup_mmc_options(OptionsVariables, MaybeMCFlags1),
-        Specs = get_any_errors1(MaybeMCFlags1),
-        Errors = contains_errors(FlagsArgsGlobals, Specs),
         (
-            Errors = no,
-            det_project_ok1(MaybeMCFlags1, MCFlags1),
-            MaybeMCFlags = yes(MCFlags1)
+            MaybeMCFlags1 = ok1(MCFlags1),
+            MaybeMCFlags = yes(MCFlags1),
+            Specs = []
         ;
-            Errors = yes,
-            MaybeMCFlags = no
+            MaybeMCFlags1 = error1(MCFlagsSpecs),
+            % All error_specs in MCFlagsSpecs are errors, not warnings.
+            MaybeMCFlags = no,
+            Specs = MCFlagsSpecs
         )
     ).
 

compiler/options_file.m

@@ -46,9 +46,10 @@
     % assignments in those files (and the other files they may include, either
     % directly or indirectly) and return it as Variables.
     %
-    % We return two lists of error specs. The second should be printed
-    % only if the option warn_undefined_options_variables is set, while
-    % the first list should be printed unconditionally.
+    % We return two lists of error specs. The first list consists of errors,
+    % which should be printed unconditionally. The second list consists
+    % of warnings, which should be printed only if the option
+    % warn_undefined_options_variables is set.
     %
 :- pred read_options_files_named_in_options_file_option(list(string)::in,
     list(string)::in, options_variables::out,
@@ -61,9 +62,10 @@
     % --options-search-directories, updating the database of make variable
     % name/value pairs. This is used to read the configuration file.
     %
-    % We return two lists of error specs. The second should be printed
-    % only if the option warn_undefined_options_variables is set, while
-    % the first list should be printed unconditionally.
+    % We return two lists of error specs. The first list consists of errors,
+    % which should be printed unconditionally. The second list consists
+    % of warnings, which should be printed only if the option
+    % warn_undefined_options_variables is set.
     %
 :- pred read_named_options_file(file_name::in,
     options_variables::in, options_variables::out,
@@ -79,9 +81,10 @@
     %
     % This is not quite the same as @file syntax as the environment is ignored.
     %
-    % We return two lists of error specs. The second should be printed
-    % only if the option warn_undefined_options_variables is set, while
-    % the first list should be printed unconditionally.
+    % We return two lists of error specs. The first list consists of errors,
+    % which should be printed unconditionally. The second list consists
+    % of warnings, which should be printed only if the option
+    % warn_undefined_options_variables is set.
     % XXX But see the comments near the only call to this predicate
     % in mercury_compile_main.m.
     %
@@ -90,6 +93,13 @@
     io::di, io::uo) is det.
 
 %---------------------------------------------------------------------------%
+%
+% If any of the following predicates return error1(Specs), Specs will
+% contain only errors, not warnings. (There is only one piece of code
+% in this module that generates an error_spec with severity_warning,
+% and the only exported operations whose call tree includes that code
+% are ones listed *above*.)
+%
 
     % Look up $(MAIN_TARGET).
     %
@@ -410,14 +420,6 @@ read_options_file_params(SearchInfo, PreStack0, IsOptionsFileOptional,
                         [s(FoundDir/FileToFind)], !TIO)
                 ),
 
-                % XXX Instead of setting and unsetting the input stream,
-                % we should simply pass FoundStream to read_options_lines.
-                % However, when I (zs) tried that, I quickly found that
-                % the call tree of read_options_lines includes many predicates
-                % for which it is not at all clear whether they *intend*
-                % to read from a current standard input that originates as
-                % FoundStream, or they just *happen* to do so.
-
                 SubSearchInfo = search_info(yes(FoundDir), Search),
                 read_options_lines(SubSearchInfo, InclStack0,
                     FoundStream, FileToFind, 1, !Variables,