C/C++: add fix-it hints for various missing symbols

The patch improves our C/C++ frontends' handling of missing
symbols, by making c_parser_require and cp_parser_require use
"better" locations for the diagnostic, and insert fix-it hints,
under certain circumstances (see the comments in the patch for
full details).

For example, for this code with a missing semicolon:

  $ cat test.c
  int missing_semicolon (void)
  {
    return 42
  }

  trunk currently emits:

  test.c:4:1: error: expected ';' before '}' token
   }
   ^

This patch adds a fix-it hint for the missing semicolon, and puts
the error at the location of the missing semicolon, printing the
followup token as a secondary location:

  test.c:3:12: error: expected ';' before '}' token
     return 42
              ^
              ;
   }
   ~

More examples can be seen in the test cases.

gcc/c-family/ChangeLog:
	* c-common.c (enum missing_token_insertion_kind): New enum.
	(get_missing_token_insertion_kind): New function.
	(maybe_suggest_missing_token_insertion): New function.
	* c-common.h (maybe_suggest_missing_token_insertion): New decl.

gcc/c/ChangeLog:
	* c-parser.c (c_parser_require): Add "type_is_unique" param and
	use it to guard calls to maybe_suggest_missing_token_insertion.
	(c_parser_parms_list_declarator): Override default value of new
	"type_is_unique" param to c_parser_require.
	(c_parser_asm_statement): Likewise.
	* c-parser.h (c_parser_require): Add "type_is_unique" param,
	defaulting to true.

gcc/cp/ChangeLog:
	* parser.c (get_required_cpp_ttype): New function.
	(cp_parser_error_1): Call it, using the result to call
	maybe_suggest_missing_token_insertion.

gcc/testsuite/ChangeLog:
	* c-c++-common/cilk-plus/AN/parser_errors.c: Update expected
	output to reflect changes to reported locations of missing
	symbols.
	* c-c++-common/cilk-plus/AN/parser_errors2.c: Likewise.
	* c-c++-common/cilk-plus/AN/parser_errors3.c: Likewise.
	* c-c++-common/cilk-plus/AN/pr61191.c: Likewise.
	* c-c++-common/gomp/pr63326.c: Likewise.
	* c-c++-common/missing-close-symbol.c: Likewise, also update for
	new fix-it hints.
	* c-c++-common/missing-symbol.c: Likewise, also add test coverage
	for missing colon in ternary operator.
	* g++.dg/cpp1y/digit-sep-neg.C: Likewise.
	* g++.dg/cpp1y/pr65202.C: Likewise.
	* g++.dg/missing-symbol-2.C: New test case.
	* g++.dg/other/do1.C: Update expected output to reflect
	changes to reported locations of missing symbols.
	* g++.dg/parse/error11.C: Likewise.
	* g++.dg/template/error11.C: Likewise.
	* gcc.dg/missing-symbol-2.c: New test case.
	* gcc.dg/missing-symbol-3.c: New test case.
	* gcc.dg/noncompile/940112-1.c: Update expected output to reflect
	changes to reported locations of missing symbols.
	* gcc.dg/noncompile/971104-1.c: Likewise.
	* obj-c++.dg/exceptions-6.mm: Likewise.
	* obj-c++.dg/pr48187.mm: Likewise.
	* objc.dg/exceptions-6.m: Likewise.

From-SVN: r253690

3 files changed, 33 insertions, 5 deletions

diff --git a/gcc/c/ChangeLog b/gcc/c/ChangeLog
index baf57c1..1f697f1 100644
--- a/gcc/c/ChangeLog
+++ b/gcc/c/ChangeLog
@@ -1,3 +1,13 @@
+2017-10-12  David Malcolm  <dmalcolm@redhat.com>
+
+	* c-parser.c (c_parser_require): Add "type_is_unique" param and
+	use it to guard calls to maybe_suggest_missing_token_insertion.
+	(c_parser_parms_list_declarator): Override default value of new
+	"type_is_unique" param to c_parser_require.
+	(c_parser_asm_statement): Likewise.
+	* c-parser.h (c_parser_require): Add "type_is_unique" param,
+	defaulting to true.
+
 2017-10-11  Nathan Sidwell  <nathan@acm.org>
 
 	* c-decl.c (grokdeclarator): Check HAS_DECL_ASSEMBLER_NAME_P too.
diff --git a/gcc/c/c-parser.c b/gcc/c/c-parser.c
index a622e2a..6b84324 100644
--- a/gcc/c/c-parser.c
+++ b/gcc/c/c-parser.c
@@ -1041,13 +1041,21 @@ get_matching_symbol (enum cpp_ttype type)
    If MATCHING_LOCATION is not UNKNOWN_LOCATION, then highlight it
    within any error as the location of an "opening" token matching
    the close token TYPE (e.g. the location of the '(' when TYPE is
-   CPP_CLOSE_PAREN).  */
+   CPP_CLOSE_PAREN).
+
+   If TYPE_IS_UNIQUE is true (the default) then msgid describes exactly
+   one type (e.g. "expected %<)%>") and thus it may be reasonable to
+   attempt to generate a fix-it hint for the problem.
+   Otherwise msgid describes multiple token types (e.g.
+   "expected %<;%>, %<,%> or %<)%>"), and thus we shouldn't attempt to
+   generate a fix-it hint.  */
 
 bool
 c_parser_require (c_parser *parser,
 		  enum cpp_ttype type,
 		  const char *msgid,
-		  location_t matching_location)
+		  location_t matching_location,
+		  bool type_is_unique)
 {
   if (c_parser_next_token_is (parser, type))
     {
@@ -1059,6 +1067,13 @@ c_parser_require (c_parser *parser,
       location_t next_token_loc = c_parser_peek_token (parser)->location;
       gcc_rich_location richloc (next_token_loc);
 
+      /* Potentially supply a fix-it hint, suggesting to add the
+	 missing token immediately after the *previous* token.
+	 This may move the primary location within richloc.  */
+      if (!parser->error && type_is_unique)
+	maybe_suggest_missing_token_insertion (&richloc, type,
+					       parser->last_token_location);
+
       /* If matching_location != UNKNOWN_LOCATION, highlight it.
 	 Attempt to consolidate diagnostics by printing it as a
 	 secondary range within the main diagnostic.  */
@@ -3975,7 +3990,8 @@ c_parser_parms_list_declarator (c_parser *parser, tree attrs, tree expr)
 	    return get_parm_info (false, expr);
 	}
       if (!c_parser_require (parser, CPP_COMMA,
-			     "expected %<;%>, %<,%> or %<)%>"))
+			     "expected %<;%>, %<,%> or %<)%>",
+			     UNKNOWN_LOCATION, false))
 	{
 	  c_parser_skip_until_found (parser, CPP_CLOSE_PAREN, NULL);
 	  return NULL;
@@ -6429,7 +6445,8 @@ c_parser_asm_statement (c_parser *parser)
       if (!c_parser_require (parser, CPP_COLON,
 			     is_goto
 			     ? G_("expected %<:%>")
-			     : G_("expected %<:%> or %<)%>")))
+			     : G_("expected %<:%> or %<)%>"),
+			     UNKNOWN_LOCATION, is_goto))
 	goto error_close_paren;
 
       /* Once past any colon, we're no longer a simple asm.  */
diff --git a/gcc/c/c-parser.h b/gcc/c/c-parser.h
index 01a7b72..21e4054 100644
--- a/gcc/c/c-parser.h
+++ b/gcc/c/c-parser.h
@@ -137,7 +137,8 @@ extern c_token * c_parser_peek_2nd_token (c_parser *parser);
 extern c_token * c_parser_peek_nth_token (c_parser *parser, unsigned int n);
 extern bool c_parser_require (c_parser *parser, enum cpp_ttype type,
 			      const char *msgid,
-			      location_t matching_location = UNKNOWN_LOCATION);
+			      location_t matching_location = UNKNOWN_LOCATION,
+			      bool type_is_unique=true);
 extern bool c_parser_error (c_parser *parser, const char *gmsgid);
 extern void c_parser_consume_token (c_parser *parser);
 extern void c_parser_skip_until_found (c_parser *parser, enum cpp_ttype type,