Say "ambiguous use of 'foo'" instead of "'foo(bar:)'".

...unless the argument labels are the same for every possible
overload.

Only affects diagnostics.

(cherry picked from commit a14e329)

Author: jrose-apple

lib/Sema/CSDiag.cpp

@@ -312,12 +312,26 @@ static unsigned countDistinctOverloads(ArrayRef<OverloadChoice> choices) {
 
 /// \brief Determine the name of the overload in a set of overload choices.
 static DeclName getOverloadChoiceName(ArrayRef<OverloadChoice> choices) {
+  DeclName name;
   for (auto choice : choices) {
-    if (choice.isDecl())
-      return choice.getDecl()->getFullName();
+    if (!choice.isDecl())
+      continue;
+
+    DeclName nextName = choice.getDecl()->getFullName();
+    if (!name) {
+      name = nextName;
+      continue;
+    }
+
+    if (name != nextName) {
+      // Assume all choices have the same base name and only differ in
+      // argument labels. This may not be a great assumption, but we don't
+      // really have a way to recover for diagnostics otherwise.
+      return name.getBaseName();
+    }
   }
 
-  return DeclName();
+  return name;
 }
 
 static bool diagnoseAmbiguity(ConstraintSystem &cs,

test/expr/unary/selector/selector.swift

@@ -15,6 +15,9 @@ class C1 {
   @objc class func method3(_ a: A, b: B) { } // expected-note{{found this candidate}}
   @objc class func method3(a: A, b: B) { } // expected-note{{found this candidate}}
 
+  @objc(ambiguous1:b:) class func ambiguous(a: A, b: A) { } // expected-note{{found this candidate}}
+  @objc(ambiguous2:b:) class func ambiguous(a: A, b: B) { } // expected-note{{found this candidate}}
+
   @objc func getC1() -> AnyObject { return self }
 
   @objc func testUnqualifiedSelector(_ a: A, b: B) {
@@ -83,7 +86,8 @@ func testSelector(_ c1: C1, p1: P1, obj: AnyObject) {
 }
 
 func testAmbiguity() {
-  _ = #selector(C1.method3) // expected-error{{ambiguous use of 'method3(_:b:)'}}
+  _ = #selector(C1.method3) // expected-error{{ambiguous use of 'method3'}}
+  _ = #selector(C1.ambiguous) // expected-error{{ambiguous use of 'ambiguous(a:b:)'}}
 }
 
 func testUnusedSelector() {