[PATCH v3 3/3] c++: note other candidates when diagnosing deletedness

[Patrick Palka <ppalka@redhat.com>]

With the previous two patches in place, we can now extend our
deletedness diagnostic to note the other considered candidates, e.g.:

  deleted16.C: In function 'int main()':
  deleted16.C:10:4: error: use of deleted function 'void f(int)'
     10 |   f(0);
        |   ~^~~
  deleted16.C:5:6: note: declared here
      5 | void f(int) = delete;
        |      ^
  deleted16.C:5:6: note: candidate: 'void f(int)' (deleted)
  deleted16.C:6:6: note: candidate: 'void f(...)'
      6 | void f(...);
        |      ^
  deleted16.C:7:6: note: candidate: 'void f(int, int)'
      7 | void f(int, int);
        |      ^
  deleted16.C:7:6: note:   candidate expects 2 arguments, 1 provided

These notes are controlled by a new command line flag -fnote-all-cands,
which also controls whether we note ignored candidates more generally.

gcc/ChangeLog:

	* doc/invoke.texi (C++ Dialect Options): Document -fnote-all-cands.

gcc/c-family/ChangeLog:

	* c.opt: Add -fnote-all-cands.

gcc/cp/ChangeLog:

	* call.cc (print_z_candidates): Only print ignored candidates
	when -fnote-all-cands is set.
	(build_over_call): When diagnosing deletedness, call
	print_z_candidates if -fnote-all-cands is set.

gcc/testsuite/ChangeLog:

	* g++.dg/overload/error6.C: Pass -fnote-all-cands.
	* g++.dg/cpp0x/deleted16.C: New test.
---
 gcc/c-family/c.opt                     |  4 ++++
 gcc/cp/call.cc                         |  8 +++++++-
 gcc/doc/invoke.texi                    |  5 +++++
 gcc/testsuite/g++.dg/cpp0x/deleted16.C | 25 +++++++++++++++++++++++++
 gcc/testsuite/g++.dg/overload/error6.C |  1 +
 5 files changed, 42 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/deleted16.C

diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
index 44b9c862c14..a76f73cc661 100644
--- a/gcc/c-family/c.opt
+++ b/gcc/c-family/c.opt
@@ -2006,6 +2006,10 @@ fnil-receivers
 ObjC ObjC++ Var(flag_nil_receivers) Init(1)
 Assume that receivers of Objective-C messages may be nil.
 
+fnote-all-cands
+C++ ObjC++ Var(flag_note_all_cands)
+Note all candidates during overload resolution failure.
+
 flocal-ivars
 ObjC ObjC++ Var(flag_local_ivars) Init(1)
 Allow access to instance variables as if they were local declarations within instance method implementations.
diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index 81cc029dddb..7ace0e65096 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -4090,6 +4090,8 @@ print_z_candidates (location_t loc, struct z_candidate *candidates,
     {
       if (only_viable_p.is_true () && candidates->viable != 1)
 	break;
+      if (ignored_candidate_p (candidates) && !flag_note_all_cands)
+	break;
       print_z_candidate (loc, N_("candidate:"), candidates);
     }
 }
@@ -9933,7 +9935,11 @@ build_over_call (struct z_candidate *cand, int flags, tsubst_flags_t complain)
   if (DECL_DELETED_FN (fn))
     {
       if (complain & tf_error)
-	mark_used (fn);
+	{
+	  mark_used (fn);
+	  if (cand->next && flag_note_all_cands)
+	    print_z_candidates (input_location, cand, /*only_viable_p=*/false);
+	}
       return error_mark_node;
     }
 
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 5a9284d635c..ac82299416c 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -3479,6 +3479,11 @@ Disable built-in declarations of functions that are not mandated by
 ANSI/ISO C@.  These include @code{ffs}, @code{alloca}, @code{_exit},
 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
 
+@opindex fnote-all-cands
+@item -fnote-all-cands
+Permit the C++ front end to note all candidates during overload resolution
+failure, including when a deleted function is selected.
+
 @opindex fnothrow-opt
 @item -fnothrow-opt
 Treat a @code{throw()} exception specification as if it were a
diff --git a/gcc/testsuite/g++.dg/cpp0x/deleted16.C b/gcc/testsuite/g++.dg/cpp0x/deleted16.C
new file mode 100644
index 00000000000..506caae76b6
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/deleted16.C
@@ -0,0 +1,25 @@
+// Verify -fnote-all-cands causes us to note other candidates when a deleted
+// function is selected by overload resolution.
+// { dg-do compile { target c++11 } }
+// { dg-additional-options "-fnote-all-cands" }
+
+void f(int) = delete; // { dg-message "declared here|candidate" }
+void f(...); // { dg-message "candidate" }
+void f(int, int); // { dg-message "candidate" }
+
+// An example where the perfect candidate optimization causes us
+// to ignore function templates.
+void g(int) = delete; // { dg-message "declared here|candidate" }
+template<class T> void g(T); // { dg-message "candidate" }
+
+// An example where we have a strictly viable candidate and
+// an incompletely considered bad candidate.
+template<class T> void h(T, T) = delete; // { dg-message "declared here|candidate" }
+void h(int*, int) = delete; // { dg-message "candidate" }
+
+int main() {
+  f(0); // { dg-error "deleted" }
+  g(0); // { dg-error "deleted" }
+  h(1, 1); // { dg-error "deleted" }
+           // { dg-error "invalid conversion" "" { target *-*-* } .-1 } when noting 2nd cand
+}
diff --git a/gcc/testsuite/g++.dg/overload/error6.C b/gcc/testsuite/g++.dg/overload/error6.C
index 86a12eaa8de..ac513824887 100644
--- a/gcc/testsuite/g++.dg/overload/error6.C
+++ b/gcc/testsuite/g++.dg/overload/error6.C
@@ -1,5 +1,6 @@
 // Verify we note even non-template candidates when diagnosing
 // overload resolution failure for a template-id.
+// { dg-additional-options "-fnote-all-cands" }
 
 template<class T> void f(T); // { dg-message "candidate" }
 void f(int); // { dg-message {candidate: 'void f\(int\)' \(ignored\)} }
-- 
2.42.0.482.g2e8e77cbac