c-family: offer suggestions for missing command-line options [PR82892]

Some builtin macros are only defined when certain command-line options
are provided.  Update the error messages for them so that we suggest
the pertinent option ('-fopenacc' for '_OPENACC', and '-fopenmp' for
'_OPENMP')

gcc/c-family/ChangeLog:
	PR c/82892
	* c-common.h (get_option_for_builtin_define): New decl.
	* c-cppbuiltin.cc (get_option_for_builtin_define): New.
	* known-headers.cc: Include "opts.h".
	(suggest_missing_option::suggest_missing_option): New.
	(suggest_missing_option::~suggest_missing_option): New.
	* known-headers.h (class suggest_missing_option): New.

gcc/c/ChangeLog:
	PR c/82892
	* c-decl.cc (lookup_name_fuzzy): Provide hints for missing
	command-line options.

gcc/cp/ChangeLog:
	PR c/82892
	* name-lookup.cc (suggest_alternatives_for_1): Provide hints for
	missing command-line options.

gcc/testsuite/ChangeLog:
	PR c/82892
	* c-c++-common/spellcheck-missing-option.c: New test.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/gcc/c/c-decl.cc b/gcc/c/c-decl.cc
index b9c688e..1c11c21 100644
--- a/gcc/c/c-decl.cc
+++ b/gcc/c/c-decl.cc
@@ -4547,6 +4547,17 @@ lookup_name_fuzzy (tree name, enum lookup_name_fuzzy_kind kind, location_t loc)
 						  IDENTIFIER_POINTER (name),
 						  header_hint));
 
+  /* Next, look for exact matches for builtin defines that would have been
+     defined if the user had passed a command-line option (e.g. -fopenmp
+     for "_OPENMP").  */
+  diagnostic_option_id option_id
+    = get_option_for_builtin_define (IDENTIFIER_POINTER (name));
+  if (option_id.m_idx > 0)
+    return name_hint (nullptr,
+		      new suggest_missing_option (loc,
+						  IDENTIFIER_POINTER (name),
+						  option_id));
+
   /* Only suggest names reserved for the implementation if NAME begins
      with an underscore.  */
   bool consider_implementation_names = (IDENTIFIER_POINTER (name)[0] == '_');