[Sema]: don't warn about optional Void async-lets either

Author: jamieQ

lib/Sema/TypeCheckPattern.cpp

@@ -1232,12 +1232,9 @@ Pattern *TypeChecker::coercePatternToType(
     } else if (diagTy->isEqual(Context.TheEmptyTupleType)) {
       // Async-let bindings are commonly used to run a Void-returning
       // synchronous function in an async context. As a policy choice, don't
-      // diagnose a Void result on these bindings as potentially unexpected.
-      if (!isOptional && var->isAsyncLet()) {
-        shouldRequireType = false;
-      } else {
-        shouldRequireType = true;
-      }
+      // diagnose an inferred Void type (or optional thereof) on such bindings
+      // as potentially unexpected.
+      shouldRequireType = var->isAsyncLet() ? false : true;
     } else if (auto MTT = diagTy->getAs<AnyMetatypeType>()) {
       if (MTT->getInstanceType()->isAnyObject())
         shouldRequireType = true;

test/decl/var/async_let.swift

@@ -63,11 +63,16 @@ func testVoidResultTypeDiagnostics() async {
   async let void6 = asyncVoid()
   await void6
 
-  // expected-warning @+2 {{constant 'maybeVoid' inferred to have type '()?', which may be unexpected}}
-  // expected-note @+1 {{add an explicit type annotation to silence this warning}}
   async let maybeVoid = { Bool.random() ? () : nil }()
   await maybeVoid
 
+  do {
+    final class C: Sendable { func doit() {} }
+    let c: C? = nil
+    async let maybeVoid2 = c?.doit()
+    let _: ()? = await maybeVoid2
+  }
+
   // expected-warning @+2 {{constant 'boxOVoid' inferred to have type '[()]', which may be unexpected}}
   // expected-note @+1 {{add an explicit type annotation to silence this warning}}
   async let boxOVoid = { [(), (), ()] }()