[m-rev.] diff: disable very verbose messages form library grade detection by default

[Julien Fischer]

Disable very verbose messages from library grade detection by default.

compiler/mercury_compile.m;
 	Make very verbose messages from library grade detection depend
 	upon a compile-time trace flag.  Currently, such messages will
 	appear before the usage message if the compiler is invoked
 	without any arguments and that looks confusing.

Julien.

diff --git a/compiler/mercury_compile.m b/compiler/mercury_compile.m
index 8e702d7..82626d3 100644
--- a/compiler/mercury_compile.m
+++ b/compiler/mercury_compile.m
@@ -2064,6 +2064,9 @@ maybe_output_prof_call_graph(Verbose, Stats, !HLDS, !IO) :-
  % Library grade detection.
  %

+% Enable the compile-time trace flag "debug-detect-libgrades" to enable
+% debugging messages for library grade detection in the very verbose output.
+
  :- pred detect_libgrades(globals::in, maybe(list(string))::in,
      list(string)::out, io::di, io::uo) is det.

@@ -2072,7 +2075,9 @@ detect_libgrades(Globals, MaybeConfigMerStdLibDir, GradeOpts, !IO) :-
      (
          Detect = yes,
          globals.lookup_bool_option(Globals, verbose, Verbose),
-        maybe_write_string(Verbose, "% Detecting library grades ...\n", !IO),
+        trace [io(!TIO), compile_time(flag("debug-detect-libgrades"))] (
+            maybe_write_string(Verbose, "% Detecting library grades ...\n", !TIO)
+        ),
          globals.lookup_bool_option(Globals, very_verbose, VeryVerbose),
          % NOTE: a standard library directory specified on the command line
          % overrides one set using the MERCURY_STDLIB_DIR variable.
@@ -2093,7 +2098,9 @@ detect_libgrades(Globals, MaybeConfigMerStdLibDir, GradeOpts, !IO) :-
          else
              GradeOpts = []
          ),
-        maybe_write_string(Verbose, "% done.\n", !IO)
+        trace [io(!TIO), compile_time(flag("debug-detect-libgrades"))] (
+            maybe_write_string(Verbose, "% done.\n", !TIO)
+        )
      ;
          Detect = no,
          GradeOpts = []
@@ -2166,12 +2173,14 @@ do_detect_libgrade(VeryVerbose, DirName, FileName, FileType, Continue,
      io::di, io::uo) is det.

  maybe_report_detected_libgrade(VeryVerbose, GradeStr, !IO) :-
-    (
-        VeryVerbose = yes,
-        io.format("%% Detected library grade: %s\n", [s(GradeStr)], !IO)
-    ;
-        VeryVerbose = no
-    ). 
+    trace [io(!TIO), compile_time(flag("debug-detect-libgrades"))] (
+        (
+            VeryVerbose = yes,
+            io.format("%% Detected library grade: %s\n", [s(GradeStr)], !TIO)
+        ;
+            VeryVerbose = no
+        )
+    ).

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