C: don't suggest names that came from earlier failures (PR c/83056)

PR c/83056 reports an issue affecting trunk and gcc-7 in which
the C frontend's implementation of lookup_name_fuzzy uses undeclared
identifiers as suggestions when encountering subsequent undeclared
identifiers.

The fix is to filter out the names bound to error_mark_node
in lookup_name_fuzzy.

The C++ frontend is unaffected, as it already does this.

gcc/c/ChangeLog:
	PR c/83056
	* c-decl.c (lookup_name_fuzzy): Don't suggest names that came from
	earlier failed lookups.

gcc/testsuite/ChangeLog:
	PR c/83056
	* gcc.dg/spellcheck-pr83056.c: New test case.

From-SVN: r255038

gcc/c/ChangeLog

+2017-11-21  David Malcolm  <dmalcolm@redhat.com>
+
+	PR c/83056
+	* c-decl.c (lookup_name_fuzzy): Don't suggest names that came from
+	earlier failed lookups.
+
 2017-11-21  Marc Glisse  <marc.glisse@inria.fr>
 
 	* c-fold.c (c_fully_fold_internal): Handle POINTER_DIFF_EXPR.

gcc/c/c-decl.c

@@ -4035,6 +4035,8 @@ lookup_name_fuzzy (tree name, enum lookup_name_fuzzy_kind kind, location_t loc)
       {
 	if (!binding->id || binding->invisible)
 	  continue;
+	if (binding->decl == error_mark_node)
+	  continue;
 	/* Don't use bindings from implicitly declared functions,
 	   as they were likely misspellings themselves.  */
 	if (TREE_CODE (binding->decl) == FUNCTION_DECL)

gcc/testsuite/ChangeLog

+2017-11-21  David Malcolm  <dmalcolm@redhat.com>
+
+	PR c/83056
+	* gcc.dg/spellcheck-pr83056.c: New test case.
+
 2017-11-21  Martin Sebor  <msebor@redhat.com>
 
 	PR tree-optimization/82945

gcc/testsuite/gcc.dg/spellcheck-pr83056.c

+enum { TYPE_A };
+
+/* Verify that the incorrect "TYPE_B" etc don't get re-used for
+   suggestions for the later incorrect values.  */
+
+void pr83056(void)
+{
+  int b = TYPE_B; /* { dg-error "did you mean 'TYPE_A'" } */
+  int c = TYPE_C; /* { dg-error "did you mean 'TYPE_A'" } */
+  int d = TYPE_D; /* { dg-error "did you mean 'TYPE_A'" } */
+}