Fix the reminder about hidden messages itself being hidden.

compiler/mercury_compile_main.m:
    When we generate more messages for the user than we show, either
    because of --limited-error-context options or because the user has
    not asked for the verbose part of messages, we used to print a reminder
    about this fact in only one case:

    - at the end of the compilation, and
    - only if the exit status wasn't zero.

    Both of these condition was wrong.

    - If we were compiling modules a, b, c, d ... z, we could get a message
      about more messages being available being printed after the compilation
      of a module (z) for which we generated *no* messages at all, just because
      some message earlier in the list got such messages.

    - If the compilation generated no errors but only warnings, then
      we never printed reminders about any verbose parts of those warnings
      being held back.

    Fix both of these issues by

    - separating the code doing the reminder into its own predicate,
      and invoking it at the end of the processing of each module
      (leaving a call at its old location where it is invoked
      after we have processed all modules), and

    - not making the invocation conditional on exit status.

tests/warnings/ambiguous_overloading.exp:
tests/warnings/arg_order_rearrangment.exp:
tests/warnings/bug477.exp:
tests/warnings/infinite_recursion.exp:
tests/warnings/simple_code.exp:
tests/warnings/singleton_test.exp:
tests/warnings/singleton_test.exp2:
tests/warnings/singleton_test.exp3:
tests/warnings/singleton_test.exp4:
    Update these to expect the "For more information, recompile with `-E'"
    message, now that we don't hide it.

tests/warnings/singleton_test.m:
    Document what the four .exp files are for.

compiler/mercury_compile_main.m

@@ -781,40 +781,9 @@ do_op_mode_args(Globals, OpModeArgs, FileNamesFromStdin, DetectedGradeFlags,
             true
         )
     else
-        % If we suppressed the printing of some errors, then tell the user
-        % about this fact, because the absence of any errors being printed
-        % during a failing compilation would otherwise be likely to be
-        % baffling.
-        globals.io_get_some_errors_were_context_limited(Limited, !IO),
-        (
-            Limited = no
-        ;
-            Limited = yes,
-            io.write_string("Some error messages were suppressed " ++
-                "by `--limit-error-contexts' options.\n", !IO),
-            io.write_string("You can see the suppressed messages " ++
-                "if you recompile without these options.\n", !IO)
-        ),
-
-        % If we found some errors, but the user didn't enable the `-E'
-        % (`--verbose-errors') option, give them a hint about it.
-        % Of course, we should only output the hint when we have further
-        % information to give the user.
-        globals.lookup_bool_option(Globals, verbose_errors, VerboseErrors),
-        globals.io_get_extra_error_info(ExtraErrorInfo, !IO),
-        (
-            VerboseErrors = no,
-            (
-                ExtraErrorInfo = yes,
-                io.write_string("For more information, " ++
-                    "recompile with `-E'.\n", !IO)
-            ;
-                ExtraErrorInfo = no
-            )
-        ;
-            VerboseErrors = yes
-        )
+        true
     ),
+    maybe_print_delayed_error_messages(Globals, !IO),
     globals.lookup_bool_option(Globals, statistics, Statistics),
     (
         Statistics = yes,
@@ -823,6 +792,45 @@ do_op_mode_args(Globals, OpModeArgs, FileNamesFromStdin, DetectedGradeFlags,
         Statistics = no
     ).
 
+:- pred maybe_print_delayed_error_messages(globals::in, io::di, io::uo) is det.
+
+maybe_print_delayed_error_messages(Globals, !IO) :-
+    % Pick up the values of these flags, and then reset them
+    % for the next module.
+    globals.io_get_some_errors_were_context_limited(Limited, !IO),
+    globals.io_set_some_errors_were_context_limited(no, !IO),
+    globals.io_get_extra_error_info(ExtraErrorInfo, !IO),
+    globals.io_set_extra_error_info(no, !IO),
+
+    % If we suppressed the printing of some errors, then tell the user
+    % about this fact, because the absence of any errors being printed
+    % during a failing compilation would otherwise be likely to be baffling.
+    (
+        Limited = no
+    ;
+        Limited = yes,
+        io.write_string("Some error messages were suppressed " ++
+            "by `--limit-error-contexts' options.\n", !IO),
+        io.write_string("You can see the suppressed messages " ++
+            "if you recompile without these options.\n", !IO)
+    ),
+
+    % If we found some errors, but the user didn't enable the `-E'
+    % (`--verbose-errors') option, give them a hint about it.
+    (
+        ExtraErrorInfo = no
+    ;
+        ExtraErrorInfo = yes,
+        globals.lookup_bool_option(Globals, verbose_errors, VerboseErrors),
+        (
+            VerboseErrors = no,
+            io.write_string("For more information, recompile with `-E'.\n",
+                !IO)
+        ;
+            VerboseErrors = yes
+        )
+    ).
+
 :- type compile == pred(globals, bool, io, io).
 :- inst compile == (pred(in, out, di, uo) is det).
 
@@ -1082,6 +1090,7 @@ do_process_compiler_arg(Globals0, OpModeArgs, OptionArgs, FileOrModule,
             split_into_compilation_units_perform_checks(ParseTreeSrc,
                 RawCompUnits, Specs0, Specs),
             write_error_specs_ignore(Specs, Globals, !IO),
+            maybe_print_delayed_error_messages(Globals, !IO),
             (
                 InterfaceFile = omif_int0,
                 list.foldl(
@@ -1994,7 +2003,8 @@ maybe_grab_optfiles(Globals, OpModeAugment, Verbose, MaybeTransOptDeps,
     then
         maybe_write_string(Verbose, "% Reading .opt files...\n", !IO),
         maybe_flush_output(Verbose, !IO),
-        grab_opt_files(Globals, ModuleAndImports0, ModuleAndImports1, Error1, !IO),
+        grab_opt_files(Globals, ModuleAndImports0, ModuleAndImports1, Error1,
+            !IO),
         maybe_write_string(Verbose, "% Done.\n", !IO)
     else
         ModuleAndImports1 = ModuleAndImports0,

tests/warnings/ambiguous_overloading.exp

@@ -62,3 +62,4 @@ ambiguous_overloading.m:083:   The function symbol `lookup_bool_option'/2 is
 ambiguous_overloading.m:083:   also overloaded here.
 ambiguous_overloading.m:084:   The function symbol `lookup_bool_option'/2 is
 ambiguous_overloading.m:084:   also overloaded here.
+For more information, recompile with `-E'.

tests/warnings/arg_order_rearrangment.exp

@@ -7,3 +7,4 @@ arg_order_rearrangment.m:014:   Please ensure that this argument rearrangement
 arg_order_rearrangment.m:014:   does not introduce performance problems.
 arg_order_rearrangment.m:014:   These warnings can be suppressed by
 arg_order_rearrangment.m:014:   `--no-warn-accumulator-swaps'.
+For more information, recompile with `-E'.

tests/warnings/bug477.exp

@@ -1,2 +1,3 @@
 bug477.m:036: Warning: recursive call to predicate `reconstruct_route'/3 will
 bug477.m:036:   lead to infinite recursion.
+For more information, recompile with `-E'.

tests/warnings/infinite_recursion.exp

@@ -4,3 +4,4 @@ infinite_recursion.m:034: Warning: recursive call to predicate `loop'/0 will
 infinite_recursion.m:034:   lead to infinite recursion.
 infinite_recursion.m:046: Warning: recursive call to predicate `funny_append'/3
 infinite_recursion.m:046:   will lead to infinite recursion.
+For more information, recompile with `-E'.

tests/warnings/simple_code.exp

@@ -26,3 +26,4 @@ simple_code.m:080:   warning: unification of `HeadVar__1' and 2 cannot succeed.
 simple_code.m:080:   `HeadVar__1' has instantiatedness `bound(1)'.
 simple_code.m:113: Warning: recursive call to predicate `anc'/2 will lead to
 simple_code.m:113:   infinite recursion.
+For more information, recompile with `-E'.

tests/warnings/singleton_test.exp

@@ -25,3 +25,4 @@ singleton_test.m:095:   scope.
 singleton_test.m:095: In clause for predicate `singleton_test.test_head'/6:
 singleton_test.m:095:   warning: variables `A, B' occur only once in this
 singleton_test.m:095:   scope.
+For more information, recompile with `-E'.

tests/warnings/singleton_test.exp2

@@ -26,3 +26,4 @@ singleton_test.m:095:   scope.
 singleton_test.m:095: In clause for predicate `singleton_test.test_head'/6:
 singleton_test.m:095:   warning: variables `A, B' occur only once in this
 singleton_test.m:095:   scope.
+For more information, recompile with `-E'.

tests/warnings/singleton_test.exp3

@@ -28,3 +28,4 @@ singleton_test.m:095:   scope.
 singleton_test.m:095: In clause for predicate `singleton_test.test_head'/6:
 singleton_test.m:095:   warning: variables `A, B' occur only once in this
 singleton_test.m:095:   scope.
+For more information, recompile with `-E'.

tests/warnings/singleton_test.exp4

@@ -30,3 +30,4 @@ singleton_test.m:095:   scope.
 singleton_test.m:095: In clause for predicate `singleton_test.test_head'/6:
 singleton_test.m:095:   warning: variables `A, B' occur only once in this
 singleton_test.m:095:   scope.
+For more information, recompile with `-E'.

tests/warnings/singleton_test.m

@@ -1,11 +1,11 @@
 %---------------------------------------------------------------------------%
 % vim: ts=4 sw=4 et ft=mercury
 %---------------------------------------------------------------------------%
+% The .exp files are for C, C#, Java and Erlang respectively.
 
 :- module singleton_test.
 :- interface.
-:- import_module io.
-:- import_module list.
+:- import_module io, list.
 
 :- pred my_append(list(int), list(int), list(int)).
 :- mode my_append(in, in, out) is det.