Remove some now unnecessary casts

Flow analysis has improved and issue #40041 is resolved. These
`FutureOr<T>` conditionals are promoting to `Future<T>` or `T` and no
longer need an explicit cast.

[email protected]

Change-Id: I925db6d7f52aad54c88434ff02e1d0ae4e72278b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/331206
Reviewed-by: Lasse Nielsen <[email protected]>
Commit-Queue: Ömer Ağacan <[email protected]>
Reviewed-by: Stephen Adams <[email protected]>
Reviewed-by: Sigmund Cherem <[email protected]>
Auto-Submit: Nate Bosch <[email protected]>
Reviewed-by: Martin Kustermann <[email protected]>
Reviewed-by: Ömer Ağacan <[email protected]>

Author: natebosch

sdk/lib/_internal/js_runtime/lib/async_patch.dart

@@ -195,11 +195,7 @@ class _AsyncAwaitCompleter<T> implements Completer<T> {
       assert(!_future._isComplete);
       _future._chainFuture(value);
     } else {
-      // TODO(40014): Remove cast when type promotion works.
-      // This would normally be `as T` but we use `as dynamic` to make the
-      // unneeded check be implicit to match dart2js unsound optimizations in
-      // the user code.
-      _future._completeWithValue(value as dynamic);
+      _future._completeWithValue(value);
     }
   }
 

sdk/lib/async/future.dart

@@ -303,12 +303,7 @@ abstract interface class Future<T> {
   factory Future.sync(FutureOr<T> computation()) {
     try {
       var result = computation();
-      if (result is Future<T>) {
-        return result;
-      } else {
-        // TODO(40014): Remove cast when type promotion works.
-        return new _Future<T>.value(result as dynamic);
-      }
+      return result is Future<T> ? result : _Future<T>.value(result);
     } catch (error, stackTrace) {
       var future = new _Future<T>();
       AsyncError? replacement = Zone.current.errorCallback(error, stackTrace);
@@ -713,8 +708,7 @@ abstract interface class Future<T> {
           result.then(nextIteration, onError: doneSignal._completeError);
           return;
         }
-        // TODO(40014): Remove cast when type promotion works.
-        keepGoing = result as bool;
+        keepGoing = result;
       }
       doneSignal._complete(null);
     });

sdk/lib/async/future_impl.dart

@@ -630,11 +630,7 @@ class _Future<T> implements Future<T> {
       }
     } else {
       _FutureListener? listeners = _removeListeners();
-      // TODO(40014): Remove cast when type promotion works.
-      // This would normally be `as T` but we use `as dynamic` to make the
-      // unneeded check be implicit to match dart2js unsound optimizations in
-      // the user code.
-      _setValue(value as dynamic); // Value promoted to T.
+      _setValue(value);
       _propagateToListeners(this, listeners);
     }
   }
@@ -673,11 +669,7 @@ class _Future<T> implements Future<T> {
       _chainFuture(value);
       return;
     }
-    // TODO(40014): Remove cast when type promotion works.
-    // This would normally be `as T` but we use `as dynamic` to make the
-    // unneeded check be implicit to match dart2js unsound optimizations in the
-    // user code.
-    _asyncCompleteWithValue(value as dynamic); // Value promoted to T.
+    _asyncCompleteWithValue(value);
   }
 
   /// Internal helper function used by the implementation of `async` functions.

sdk/lib/async/stream.dart

@@ -810,8 +810,7 @@ abstract mixin class Stream<T> {
           subscription.pause();
           newValue.then(add, onError: addError).whenComplete(resume);
         } else {
-          // TODO(40014): Remove cast when type promotion works.
-          controller.add(newValue as dynamic);
+          controller.add(newValue);
         }
       });
       controller.onCancel = subscription.cancel;