[go_router] Make ImperativeRouteMatch.complete idempotent

[Khairul989]

Description

Popping an imperatively-pushed route (context.push) can complete its result Completer more than once, throwing an uncaught Bad state: Future already completed. The second completion originates inside go_router itself (GoRouterDelegate._handlePopPageWithRouteMatch → _completeRouteMatch → ImperativeRouteMatch.complete), triggered when the same route's removal is dispatched twice before the first settles — commonly a rapid double-pop, and more likely on lower-end devices where the frame window is wide.

This is a long-standing, still-open crash reported across many issues, reproducible through the current version:

• #156809 (go_router_builder, two consecutive pops)
• #123369, #146938, #157219, #163813, #160696, #180002

ImperativeRouteMatch.complete is non-idempotent in every version to date.

Fix

Make ImperativeRouteMatch.complete idempotent: return early when the completer is already completed. The awaited push result is delivered by the first completion, so the duplicate is a safe no-op rather than a crash.

void complete([dynamic value]) {
  if (completer.isCompleted) {
    return;
  }
  completer.complete(value);
}

(Alternative considered: guarding in GoRouterDelegate._completeRouteMatch. Happy to move it there if maintainers prefer.)

Tests

Added a regression test in match_test.dart asserting a second complete() call does not throw and the first value wins.

Related Issues

Fixes flutter/flutter#156809

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[gemini-code-assist]

Code Review

This pull request updates the go_router package to version 17.3.1, introducing a fix for a crash caused by completing an imperatively-pushed route's future more than once. Specifically, ImperativeRouteMatch.complete is made idempotent by checking if the underlying completer is already completed before attempting to complete it. A corresponding regression test has been added to verify this behavior. There are no review comments, and I have no feedback to provide.