Merge pull request #19554 from xedin/rdar-44770297

[CSBindings] Don't consider dependent member types even if they are w…

Author: xedin

lib/Sema/CSSolver.cpp

@@ -118,8 +118,11 @@ Optional<Type> ConstraintSystem::checkTypeOfBinding(TypeVariableType *typeVar,
     return None;
   }
 
-  // Don't bind to a dependent member type.
-  if (type->is<DependentMemberType>()) return None;
+  // Don't bind to a dependent member type, even if it's currently
+  // wrapped in any number of optionals, because binding producer
+  // might unwrap and try to attempt it directly later.
+  if (type->lookThroughAllOptionalTypes()->is<DependentMemberType>())
+    return None;
 
   // Okay, allow the binding (with the simplified type).
   return type;

validation-test/compiler_crashers_2_fixed/0174-rdar44770297.swift

@@ -0,0 +1,11 @@
+// RUN: not %target-swift-frontend -typecheck %s
+
+protocol P {
+  associatedtype A
+}
+
+func foo<T: P>(_: () throws -> T) -> T.A? {
+  fatalError()
+}
+
+_ = foo() { fatalError() } & nil