DAS: remove_unused_local fix: Conditionally keep code on the right-side of an assignment

We already conditionally keep code on the right-side of a variable
declaration (the initializer); see test cases like
"test_assigned_awaitedInvocation". But we did not have the same behavior
for an assignment expression which follows a variable declaration.

Change-Id: I43415bced3b228db1b4d094c272a7f8af2d5d1fd
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/490660
Commit-Queue: Samuel Rawlins <srawlins@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>

Author: srawlins

pkg/analysis_server/lib/src/services/correction/dart/remove_unused_local_variable.dart

@@ -274,14 +274,19 @@ class RemoveUnusedLocalVariable extends ResolvedCorrectionProducer {
   }
 
   SourceRange _forAssignmentExpression(AssignmentExpression node) {
-    // TODO(pq): consider node.parent is! ExpressionStatement to handle
-    // assignments in parens, etc.
     var parent = node.parent!;
     if (parent is ArgumentList) {
       return range.startStart(node, node.operator.next!);
-    } else {
-      return utils.getLinesRange(range.node(parent));
     }
+
+    if (node.rightHandSide.unParenthesized
+        case MethodInvocation() ||
+            FunctionExpressionInvocation() ||
+            AwaitExpression()) {
+      return range.startStart(node, node.rightHandSide);
+    }
+
+    return utils.getLinesRange(range.node(parent));
   }
 
   LocalVariableElement? _localVariableElement() {

pkg/analysis_server/test/src/services/correction/fix/remove_unused_local_variable_test.dart

@@ -187,6 +187,48 @@ void f() {
 ''');
   }
 
+  Future<void> test_assigned_inAssignment_awaited() async {
+    await resolveTestCode(r'''
+void f() async {
+  int v;
+  v = await Future.value(1);
+}
+''');
+    await assertHasFix(r'''
+void f() async {
+  await Future.value(1);
+}
+''');
+  }
+
+  Future<void> test_assigned_inAssignment_functionExpressionInvocation() async {
+    await resolveTestCode(r'''
+void f() {
+  int v;
+  v = (() => 0)();
+}
+''');
+    await assertHasFix(r'''
+void f() {
+  (() => 0)();
+}
+''');
+  }
+
+  Future<void> test_assigned_inAssignment_methodInvocation() async {
+    await resolveTestCode(r'''
+void f() {
+  String v;
+  v = 1.toString();
+}
+''');
+    await assertHasFix(r'''
+void f() {
+  1.toString();
+}
+''');
+  }
+
   Future<void> test_assigned_inDeclaration() async {
     await resolveTestCode(r'''
 List<String> l = [];