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>

4 files changed, 57 insertions, 0 deletions

diff --git a/gcc/c-family/c-common.h b/gcc/c-family/c-common.h
index a323982..7834e0d 100644
--- a/gcc/c-family/c-common.h
+++ b/gcc/c-family/c-common.h
@@ -1260,6 +1260,7 @@ extern void c_stddef_cpp_builtins (void);
 extern void fe_file_change (const line_map_ordinary *);
 extern void c_parse_error (const char *, enum cpp_ttype, tree, unsigned char,
 			   rich_location *richloc);
+extern diagnostic_option_id get_option_for_builtin_define (const char *macro_name);
 
 /* In c-ppoutput.cc  */
 extern void init_pp_output (FILE *);
diff --git a/gcc/c-family/c-cppbuiltin.cc b/gcc/c-family/c-cppbuiltin.cc
index 8fbfef5..c354c79 100644
--- a/gcc/c-family/c-cppbuiltin.cc
+++ b/gcc/c-family/c-cppbuiltin.cc
@@ -1673,6 +1673,19 @@ c_cpp_builtins (cpp_reader *pfile)
     cpp_define (pfile, "__DECIMAL_BID_FORMAT__");
 }
 
+/* Given NAME, return the command-line option that would make it be
+   a builtin define, or 0 if unrecognized.  */
+
+diagnostic_option_id
+get_option_for_builtin_define (const char *name)
+{
+  if (!strcmp (name, "_OPENACC"))
+    return OPT_fopenacc;
+  if (!strcmp (name, "_OPENMP"))
+    return OPT_fopenmp;
+  return 0;
+}
+
 /* Pass an object-like macro.  If it doesn't lie in the user's
    namespace, defines it unconditionally.  Otherwise define a version
    with two leading underscores, and another version with two leading
diff --git a/gcc/c-family/known-headers.cc b/gcc/c-family/known-headers.cc
index 58a7259..2077cab 100644
--- a/gcc/c-family/known-headers.cc
+++ b/gcc/c-family/known-headers.cc
@@ -24,6 +24,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "c-family/name-hint.h"
 #include "c-family/known-headers.h"
 #include "gcc-rich-location.h"
+#include "opts.h"
 
 /* An enum for distinguishing between the C and C++ stdlibs.  */
 
@@ -323,3 +324,30 @@ suggest_missing_header::~suggest_missing_header ()
 	  " this is probably fixable by adding %<#include %s%>",
 	  m_name_str, m_header_hint, m_header_hint);
 }
+
+/* Implementation of class suggest_missing_option.  */
+
+/* suggest_missing_option's ctor.  */
+
+suggest_missing_option::suggest_missing_option (location_t loc,
+						const char *macro_name,
+						diagnostic_option_id option_id)
+: deferred_diagnostic (loc), m_name_str (macro_name), m_option_id (option_id)
+{
+  gcc_assert (macro_name);
+  gcc_assert (option_id.m_idx > 0);
+}
+
+/* suggest_missing_option's dtor.  */
+
+suggest_missing_option::~suggest_missing_option ()
+{
+  if (is_suppressed_p ())
+    return;
+
+  const char *option_name = cl_options[m_option_id.m_idx].opt_text;
+  inform (get_location (),
+	  "%qs is defined when using option %qs;"
+	  " this is probably fixable by adding %qs to the command-line options",
+	  m_name_str, option_name, option_name);
+}
diff --git a/gcc/c-family/known-headers.h b/gcc/c-family/known-headers.h
index 7c7ee78..a6cbbd2 100644
--- a/gcc/c-family/known-headers.h
+++ b/gcc/c-family/known-headers.h
@@ -41,4 +41,19 @@ class suggest_missing_header : public deferred_diagnostic
   const char *m_header_hint;
 };
 
+/* Subclass of deferred_diagnostic for suggesting to the user
+   that they have missed a command-line option.  */
+
+class suggest_missing_option : public deferred_diagnostic
+{
+ public:
+  suggest_missing_option (location_t loc, const char *name,
+			  diagnostic_option_id option_id);
+  ~suggest_missing_option ();
+
+ private:
+  const char *m_name_str;
+  diagnostic_option_id m_option_id;
+};
+
 #endif /* GCC_KNOWN_HEADERS_H */