Fix a bug I found while preparing my devmtg talk: When passing NULL to a

function that takes a const Foo&, where Foo is convertible from a large number
of pointer types, we print ALL the overloads, no matter the setting of
-fshow-overloads.

There is potential follow-on work in unifying the "print candidates, but not
too many" logic between OverloadCandidateSet::NoteCandidates and
ImplicitConversionSequence::DiagnoseAmbiguousConversion.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@167596 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 33 insertions, 2 deletions

diff --git a/lib/Sema/SemaOverload.cpp b/lib/Sema/SemaOverload.cpp
index 8e8580d701..bf2b89741a 100644
--- a/lib/Sema/SemaOverload.cpp
+++ b/lib/Sema/SemaOverload.cpp
@@ -7992,10 +7992,20 @@ void ImplicitConversionSequence::DiagnoseAmbiguousConversion(
                                  const PartialDiagnostic &PDiag) const {
   S.Diag(CaretLoc, PDiag)
     << Ambiguous.getFromType() << Ambiguous.getToType();
-  for (AmbiguousConversionSequence::const_iterator
-         I = Ambiguous.begin(), E = Ambiguous.end(); I != E; ++I) {
+  // FIXME: The note limiting machinery is borrowed from
+  // OverloadCandidateSet::NoteCandidates; there's an opportunity for
+  // refactoring here.
+  const OverloadsShown ShowOverloads = S.Diags.getShowOverloads();
+  unsigned CandsShown = 0;
+  AmbiguousConversionSequence::const_iterator I, E;
+  for (I = Ambiguous.begin(), E = Ambiguous.end(); I != E; ++I) {
+    if (CandsShown >= 4 && ShowOverloads == Ovl_Best)
+      break;
+    ++CandsShown;
     S.NoteOverloadCandidate(*I);
   }
+  if (I != E)
+    S.Diag(SourceLocation(), diag::note_ovl_too_many_candidates) << int(E - I);
 }
 
 namespace {
diff --git a/test/SemaCXX/ambiguous-conversion-show-overload.cpp b/test/SemaCXX/ambiguous-conversion-show-overload.cpp
new file mode 100644
index 0000000000..64296512ff
--- /dev/null
+++ b/test/SemaCXX/ambiguous-conversion-show-overload.cpp
@@ -0,0 +1,21 @@
+// RUN: %clang_cc1 -fsyntax-only -fshow-overloads=best -fno-caret-diagnostics %s 2>&1 | FileCheck %s
+struct S {
+  S(void*);
+  S(char*);
+  S(unsigned char*);
+  S(signed char*);
+  S(unsigned short*);
+  S(signed short*);
+  S(unsigned int*);
+  S(signed int*);
+};
+void f(const S& s);
+void g() {
+  f(0);
+}
+// CHECK: {{conversion from 'int' to 'const S' is ambiguous}}
+// CHECK-NEXT: {{candidate constructor}}
+// CHECK-NEXT: {{candidate constructor}}
+// CHECK-NEXT: {{candidate constructor}}
+// CHECK-NEXT: {{candidate constructor}}
+// CHECK-NEXT: {{remaining 4 candidates omitted; pass -fshow-overloads=all to show them}}