c++: remember candidates that we ignored

During overload resolution, we sometimes outright ignore a function in
the overload set and leave no trace of it in the candidates list, for
example when we find a perfect non-template candidate we discard all
function templates, or when the callee is a template-id we discard all
non-template functions.  We should still however make note of these
non-viable functions when diagnosing overload resolution failure, but
that's not possible if they're not present in the returned candidates
list.

To that end, this patch reworks add_candidates to add such ignored
functions to the list.  The new rr_ignored rejection reason is somewhat
of a catch-all; we could perhaps split it up into more specific rejection
reasons, but I leave that as future work.

gcc/cp/ChangeLog:

	* call.cc (enum rejection_reason_code): Add rr_ignored.
	(add_ignored_candidate): Define.
	(ignored_candidate_p): Define.
	(add_template_candidate_real): Do add_ignored_candidate
	instead of returning NULL.
	(splice_viable): Put ignored (non-viable) candidates last.
	(print_z_candidate): Handle ignored candidates.
	(build_new_function_call): Refine shortcut that calls
	cp_build_function_call_vec now that non-templates can
	appear in the candidate list for a template-id call.
	(add_candidates): Replace 'bad_fns' overload with 'bad_cands'
	candidate list.  When not considering a candidate, add it
	to the list as an ignored candidate.  Add all 'bad_cands'
	to the overload set as well.

gcc/testsuite/ChangeLog:

	* g++.dg/diagnostic/param-type-mismatch-2.C: Rename template
	function test_7 that (maybe accidentally) shares the same name
	as its non-template callee.
	* g++.dg/overload/error6.C: New test.

2 files changed, 19 insertions, 10 deletions

diff --git a/gcc/testsuite/g++.dg/diagnostic/param-type-mismatch-2.C b/gcc/testsuite/g++.dg/diagnostic/param-type-mismatch-2.C
index de7570a..50c25cd 100644
--- a/gcc/testsuite/g++.dg/diagnostic/param-type-mismatch-2.C
+++ b/gcc/testsuite/g++.dg/diagnostic/param-type-mismatch-2.C
@@ -129,22 +129,22 @@ int test_6 (int first, const char *second, float third, s6 *ptr)
 /* Template function.  */
 
 template <typename T>
-int test_7 (int one, T two, float three); // { dg-line test_7_decl }
+int callee_7 (int one, T two, float three); // { dg-line callee_7_decl }
 
 int test_7 (int first, const char *second, float third)
 {
-  return test_7 <const char **> (first, second, third); // { dg-line test_7_usage }
-  // { dg-message "cannot convert 'const char\\*' to 'const char\\*\\*'" "" { target *-*-* } test_7_usage }
+  return callee_7 <const char **> (first, second, third); // { dg-line callee_7_usage }
+  // { dg-message "cannot convert 'const char\\*' to 'const char\\*\\*'" "" { target *-*-* } callee_7_usage }
   /* { dg-begin-multiline-output "" }
-   return test_7 <const char **> (first, second, third);
-                                         ^~~~~~
-                                         |
-                                         const char*
+   return callee_7 <const char **> (first, second, third);
+                                           ^~~~~~
+                                           |
+                                           const char*
      { dg-end-multiline-output "" } */
-  // { dg-message "initializing argument 2 of 'int test_7\\(int, T, float\\) .with T = const char\\*\\*.'" "" { target *-*-* } test_7_decl }
+  // { dg-message "initializing argument 2 of 'int callee_7\\(int, T, float\\) .with T = const char\\*\\*.'" "" { target *-*-* } callee_7_decl }
   /* { dg-begin-multiline-output "" }
- int test_7 (int one, T two, float three);
-                      ~~^~~
+ int callee_7 (int one, T two, float three);
+                        ~~^~~
      { dg-end-multiline-output "" } */
 }
 
diff --git a/gcc/testsuite/g++.dg/overload/error6.C b/gcc/testsuite/g++.dg/overload/error6.C
new file mode 100644
index 0000000..86a12ea
--- /dev/null
+++ b/gcc/testsuite/g++.dg/overload/error6.C
@@ -0,0 +1,9 @@
+// Verify we note even non-template candidates when diagnosing
+// overload resolution failure for a template-id.
+
+template<class T> void f(T); // { dg-message "candidate" }
+void f(int); // { dg-message {candidate: 'void f\(int\)' \(ignored\)} }
+
+int main() {
+  f<int>(0, 0); // { dg-error "no match" }
+}