[go_router] Make ImperativeRouteMatch.complete idempotent

packages/go_router/CHANGELOG.md

@@ -1,3 +1,10 @@
+## 17.3.1
+
+- Fixes a "Bad state: Future already completed" crash when an imperatively-pushed
+  route's completion is triggered more than once (for example a rapid double-pop).
+  `ImperativeRouteMatch.complete` is now idempotent. See
+  https://github.com/flutter/flutter/issues/156809.
+
 ## 17.3.0
 
 - Updates minimum supported SDK version to Flutter 3.38/Dart 3.10.

packages/go_router/lib/src/match.dart

@@ -444,6 +444,15 @@ class ImperativeRouteMatch extends RouteMatch {
   /// Called when the corresponding [Route] associated with this route match is
   /// completed.
   void complete([dynamic value]) {
+    // Completing is idempotent. The pushed route can be removed more than once
+    // — e.g. a rapid double-pop, or a pop dispatched while a prior removal is
+    // still in flight on a slow device — which would otherwise call complete()
+    // a second time and throw "Bad state: Future already completed". The
+    // awaited result is delivered by the first completion, so the duplicate is
+    // a no-op. See https://github.com/flutter/flutter/issues/156809.
+    if (completer.isCompleted) {
+      return;
+    }
     completer.complete(value);
   }
 

packages/go_router/pubspec.yaml

@@ -1,7 +1,7 @@
 name: go_router
 description: A declarative router for Flutter based on Navigation 2 supporting
   deep linking, data-driven routes and more
-version: 17.3.0
+version: 17.3.1
 repository: https://github.com/flutter/packages/tree/main/packages/go_router
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+go_router%22
 

packages/go_router/test/match_test.dart

@@ -178,6 +178,20 @@ void main() {
     final completer1 = Completer<void>();
     final completer2 = Completer<void>();
 
+    test('complete is idempotent and does not throw when called twice', () async {
+      // Regression test for https://github.com/flutter/flutter/issues/156809:
+      // the pushed route's completer could be completed more than once
+      // (e.g. a rapid double-pop), throwing "Bad state: Future already
+      // completed".
+      final completer = Completer<Object?>();
+      final match = ImperativeRouteMatch(pageKey: key1, matches: matchList1, completer: completer);
+
+      match.complete('result');
+      // A second completion must be a no-op rather than a crash.
+      expect(() => match.complete('ignored'), returnsNormally);
+      expect(await completer.future, 'result');
+    });
+
     test('can equal and has', () async {
       var match1 = ImperativeRouteMatch(pageKey: key1, matches: matchList1, completer: completer1);
       var match2 = ImperativeRouteMatch(pageKey: key1, matches: matchList1, completer: completer1);