[ConstraintSystem] Adjust getFunctionArgApplyInfo to respect holes

Detect that direct callee couldn't be resolved e.g. due to an
invalid reference or a missing member and fail instead of
triggering an assert.

Resolves: rdar://problem/71525503

Author: xedin

lib/Sema/ConstraintSystem.cpp

@@ -4408,9 +4408,16 @@ Solution::getFunctionArgApplyInfo(ConstraintLocator *locator) const {
     // If we didn't resolve an overload for the callee, we should be dealing
     // with a call of an arbitrary function expr.
     auto *call = castToExpr<CallExpr>(anchor);
+    rawFnType = getType(call->getFn());
+
+    // If callee couldn't be resolved due to expression
+    // issues e.g. it's a reference to an invalid member
+    // let's just return here.
+    if (simplifyType(rawFnType)->is<UnresolvedType>())
+      return None;
+
     assert(!shouldHaveDirectCalleeOverload(call) &&
              "Should we have resolved a callee for this?");
-    rawFnType = getType(call->getFn());
   }
 
   // Try to resolve the function type by loading lvalues and looking through

test/Constraints/closures.swift

@@ -1042,3 +1042,17 @@ let explicitUnboundResult2: (Array<Bool>) -> Array<Int> = {
 let explicitUnboundResult3: (Array<Bool>) -> Array<Int> = {
   (arr: Array) -> Array in [true]
 }
+
+// rdar://problem/71525503 - Assertion failed: (!shouldHaveDirectCalleeOverload(call) && "Should we have resolved a callee for this?")
+func test_inout_with_invalid_member_ref() {
+  struct S {
+    static func createS(_ arg: inout Int) -> S { S() }
+  }
+  class C {
+    static subscript(s: (Int) -> Void) -> Bool { get { return false } }
+  }
+
+  let _: Bool = C[{ .createS(&$0) }]
+  // expected-error@-1 {{value of tuple type 'Void' has no member 'createS'}}
+  // expected-error@-2 {{cannot pass immutable value as inout argument: '$0' is immutable}}
+}