[ConstraintSystem] Simplify diagnoseAmbiguityWithEphemeralPointers

Don't attempt to figure out what exactly is ambiguous, let
`diagnoseAmbiguity` take care of that. Simplify make sure
that only some of the solutions have fixes and these fixes
are all related to use of ephemeral pointers.

lib/Sema/ConstraintSystem.cpp

@@ -2891,8 +2891,6 @@ static bool diagnoseConflictingGenericArguments(ConstraintSystem &cs,
 static bool
 diagnoseAmbiguityWithEphemeralPointers(ConstraintSystem &cs,
                                        ArrayRef<Solution> solutions) {
-  llvm::MapVector<Expr *, ValueDecl *> ambiguities;
-
   bool allSolutionsHaveFixes = true;
   for (const auto &solution : solutions) {
     if (solution.Fixes.empty()) {
@@ -2900,23 +2898,10 @@ diagnoseAmbiguityWithEphemeralPointers(ConstraintSystem &cs,
       continue;
     }
 
-    for (const auto *fix : solution.Fixes) {
+    if (!llvm::all_of(solution.Fixes, [](const ConstraintFix *fix) {
-      if (fix->getKind() != FixKind::TreatEphemeralAsNonEphemeral)
+          return fix->getKind() == FixKind::TreatEphemeralAsNonEphemeral;
-        return false;
+        }))
-
+      return false;
-      // Ephemeral pointers are only possible in argument positions.
-      if (auto *anchor = simplifyLocatorToAnchor(fix->getLocator())) {
-        anchor = cast<InOutExpr>(anchor)->getSubExpr();
-
-        auto overload = solution.getOverloadChoiceIfAvailable(
-            cs.getConstraintLocator(anchor));
-
-        if (!(overload && overload->choice.isDecl()))
-          return false;
-
-        ambiguities.insert({anchor, overload->choice.getDecl()});
-      }
-    }
   }
 
   // If all solutions have fixes for ephemeral pointers, let's
@@ -2924,13 +2909,10 @@ diagnoseAmbiguityWithEphemeralPointers(ConstraintSystem &cs,
   if (allSolutionsHaveFixes)
     return false;
 
-  auto &DE = cs.getASTContext().Diags;
+  // If only some of the solutions have ephemeral pointer fixes
-  for (const auto &entry : ambiguities) {
+  // let's let `diagnoseAmbiguity` diagnose the problem either
-    DE.diagnose(entry.first->getLoc(), diag::ambiguous_decl_ref,
+  // with affected argument or related declaration e.g. function ref.
-                DeclNameRef(entry.second->getBaseName()));
+  return cs.diagnoseAmbiguity(solutions);
-  }
-
-  return true;
 }
 
 bool ConstraintSystem::diagnoseAmbiguityWithFixes(

test/Sema/diag_non_ephemeral.swift

@@ -520,3 +520,10 @@ func testArgumentLabelReferencing() {
   // expected-note@-5 {{implicit argument conversion from '[Int]' to 'UnsafePointer<Int>' produces a pointer valid only for the duration of the call to 'takesTwoPointers(ptr:ptr:)'}}
   // expected-note@-6 {{use the 'withUnsafeBufferPointer' method on Array in order to explicitly convert argument to buffer pointer valid for a defined scope}}
 }
+
+func ambiguous_fn(@_nonEphemeral _ ptr: UnsafePointer<Int>) {} // expected-note {{found this candidate}}
+func ambiguous_fn(_ ptr: UnsafeRawPointer) {} // expected-note {{found this candidate}}
+
+func test_ambiguity_with_function_instead_of_argument(_ x: inout Int) {
+  ambiguous_fn(&x) // expected-error {{ambiguous use of 'ambiguous_fn'}}
+}

test/Sema/diag_non_ephemeral_warning.swift

@@ -467,3 +467,10 @@ func testNonEphemeralInMemberwiseInits() {
   // expected-note@-1 {{implicit argument conversion from 'String' to 'UnsafePointer<Int8>' produces a pointer valid only for the duration of the call to 'const'}}
   // expected-note@-2 {{use the 'withCString' method on String in order to explicitly convert argument to pointer valid for a defined scope}}
 }
+
+func ambiguous_fn(@_nonEphemeral _ ptr: UnsafePointer<Int>) {} // expected-note {{found this candidate}}
+func ambiguous_fn(_ ptr: UnsafeRawPointer) {} // expected-note {{found this candidate}}
+
+func test_ambiguity_with_function_instead_of_argument(_ x: inout Int) {
+  ambiguous_fn(&x) // expected-error {{ambiguous use of 'ambiguous_fn'}}
+}