[CS] Don't fix an _OptionalNilComparison argument

We should only be attempting such overloads for
nil literal args.

Resolves SR-12426.

Author: hamishknight

lib/Sema/CSSimplify.cpp

@@ -3301,6 +3301,17 @@ bool ConstraintSystem::repairFailures(
     if (hasFixFor(loc, FixKind::AllowInvalidUseOfTrailingClosure))
       return true;
 
+    // Don't attempt to fix an argument being passed to a
+    // _OptionalNilComparisonType parameter. Such an overload should only take
+    // effect when a nil literal is used in valid code, and doesn't offer any
+    // useful fixes for invalid code.
+    if (auto *nominal = rhs->getAnyNominal()) {
+      if (nominal->isStdlibDecl() &&
+          nominal->getName() == getASTContext().Id_OptionalNilComparisonType) {
+        return false;
+      }
+    }
+
     if (repairByInsertingExplicitCall(lhs, rhs))
       break;
 

test/Constraints/fixes.swift

@@ -356,3 +356,10 @@ func testKeyPathSubscriptArgFixes(_ fn: @escaping () -> Int) {
   _ = \S.[nil] // expected-error {{'nil' is not compatible with expected argument type 'Int'}}
   _ = \S.[fn] // expected-error {{function produces expected type 'Int'; did you mean to call it with '()'?}} {{13-13=()}}
 }
+
+func sr12426(a: Any, _ str: String?) {
+  a == str // expected-error {{cannot convert value of type 'Any' to expected argument type 'String'}}
+  // expected-error@-1 {{value of optional type 'String?' must be unwrapped to a value of type 'String'}}
+  // expected-note@-2 {{coalesce using '??' to provide a default when the optional value contains 'nil'}}
+  // expected-note@-3 {{force-unwrap using '!' to abort execution if the optional value contains 'nil'}}
+}

test/Constraints/operator.swift

@@ -217,10 +217,11 @@ func rdar46459603() {
   var arr = ["key": e]
 
   _ = arr.values == [e]
-  // expected-error@-1 {{binary operator '==' cannot be applied to operands of type 'Dictionary<String, E>.Values' and '[E]'}}
+  // expected-error@-1 {{referencing operator function '==' on 'Equatable' requires that 'Dictionary<String, E>.Values' conform to 'Equatable'}}
+  // expected-error@-2 {{cannot convert value of type '[E]' to expected argument type 'Dictionary<String, E>.Values'}}
   _ = [arr.values] == [[e]]
-  // expected-error@-1 {{value of protocol type 'Any' cannot conform to 'Equatable'; only struct/enum/class types can conform to protocols}}
-  // expected-note@-2 {{requirement from conditional conformance of '[Any]' to 'Equatable'}}
+  // expected-error@-1 {{operator function '==' requires that 'Dictionary<String, E>.Values' conform to 'Equatable'}}
+  // expected-error@-2 {{cannot convert value of type '[E]' to expected element type 'Dictionary<String, E>.Values'}}
 }
 
 // SR-10843

test/Misc/misc_diagnostics.swift

@@ -140,7 +140,10 @@ func test17875634() {
 
 // <rdar://problem/20770032> Pattern matching ranges against tuples crashes the compiler
 func test20770032() {
-  if case let 1...10 = (1, 1) { // expected-warning{{'let' pattern has no effect; sub-pattern didn't bind any variables}} {{11-15=}} expected-error{{expression pattern of type 'ClosedRange<Int>' cannot match values of type '(Int, Int)'}}
+  if case let 1...10 = (1, 1) { // expected-warning{{'let' pattern has no effect; sub-pattern didn't bind any variables}} {{11-15=}}
+    // expected-error@-1 {{expression pattern of type 'ClosedRange<Int>' cannot match values of type '(Int, Int)'}}
+    // expected-error@-2 {{'(Int, Int)' cannot conform to 'Equatable'; only struct/enum/class types can conform to protocols}}
+    // expected-note@-3 {{required by operator function '~=' where 'T' = '(Int, Int)'}}
   }
 }