Fix validation for async let thunks

Author: calda

lib/Sema/MiscDiagnostics.cpp

@@ -1799,9 +1799,9 @@ static void diagnoseImplicitSelfUseInClosure(const Expr *E,
         // Implicit self is always allowed in autoclosure thunks generated
         // during type checking. An example of this is when storing an instance
         // method as a closure (e.g. `let closure = someInstanceMethodOnSelf`).
-        auto isThunk =
-            autoclosure->getThunkKind() != AutoClosureExpr::Kind::None;
-        if (isThunk) {
+        auto thunkKind = autoclosure->getThunkKind();
+        if (thunkKind == AutoClosureExpr::Kind::SingleCurryThunk ||
+            thunkKind == AutoClosureExpr::Kind::DoubleCurryThunk) {
           return true;
         }
 

test/expr/closure/closures.swift

@@ -1726,11 +1726,21 @@ struct TestInvalidSelfCaptureInStruct {
   }
 }
 
-struct TestAsyncLet {
+class TestAsyncLetInClass {
+  init() { }
+  func bar() -> Int { 0 }
+  func foo() async {
+    let _ = { // expected-note {{capture 'self' explicitly to enable implicit 'self' in this closure}}
+      async let x = bar() // expected-error{{call to method 'bar' in closure requires explicit use of 'self' to make capture semantics explicit}} expected-warning {{initialization of immutable value 'x' was never used; consider replacing with assignment to '_' or removing it}} expected-note{{reference 'self.' explicitly}}
+    }
+  }
+}
+
+struct TestAsyncLetInStruct {
   func bar() -> Int { 0 }
   func foo() async {
     let _ = {
-      async let _ = bar()
+      async let x = bar() // expected-warning{{initialization of immutable value 'x' was never used; consider replacing with assignment to '_' or removing it}}
     }
   }
 }