Merge pull request #24483 from xedin/rdar-50438071

[ConstraintSystem] Tighten "missing call" fix conditions by checking …

Author: xedin

lib/Sema/CSSimplify.cpp

@@ -2032,7 +2032,8 @@ bool ConstraintSystem::repairFailures(
         // If left-hand side is a function type but right-hand
         // side isn't, let's check it would be possible to fix
         // this by forming an explicit call.
-        if (!rhs->is<FunctionType>() && !rhs->isVoid() &&
+        auto convertTo = rhs->lookThroughAllOptionalTypes();
+        if (!convertTo->is<FunctionType>() && !convertTo->isVoid() &&
             fnType->getNumParams() == 0 &&
             matchTypes(fnType->getResult(), rhs, ConstraintKind::Conversion,
                        TypeMatchFlags::TMF_ApplyingFix, locator)

test/Constraints/optional.swift

@@ -345,3 +345,15 @@ func rdar47776586() {
   dict[1] += 1 // expected-error {{value of optional type 'Int?' must be unwrapped to a value of type 'Int'}}
   // expected-note@-1 {{force-unwrap using '!' to abort execution if the optional value contains 'nil'}} {{10-10=!}}
 }
+
+struct S {
+  var foo: Optional<() -> Int?> = nil
+  var bar: Optional<() -> Int?> = nil
+
+  mutating func test(_ clj: @escaping () -> Int) {
+    if let fn = foo {
+      bar = fn  // Ok
+      bar = clj // Ok
+    }
+  }
+}