[go_router] Fix SelectionArea dead zones after ShellRoute navigation

[davidmigloz]

Description

When a SelectionArea wraps a ShellRoute's child (a common pattern for enabling text selection across an app), offstage pages kept their Text widgets registered with the SelectableRegion. These invisible selectables intercepted drag-to-select events, creating "dead zones" on the currently visible page where selection silently failed.

Fix

ShellRoute: Adds _OffstageSelectionDisabler — a lightweight widget inserted around each route's content that detects non-current routes via ModalRoute.of(context) and wraps them with SelectionContainer.disabled to unregister their selectables.

StatefulShellRoute: Wraps inactive branches with SelectionContainer.disabled in _IndexedStackedRouteBranchContainer._buildRouteBranchContainer. Navigator state is preserved via GlobalObjectKey reparenting.

Reproduction

• Live demo (dart2wasm): https://davidmigloz.github.io/flutter_selection_bug/
• Reproduction repo: https://github.com/davidmigloz/flutter_selection_bug

Fixes flutter/flutter#182573

Tests

Added 12 new widget tests in builder_test.dart covering:

• ShellRoute: builder, pageBuilder, back navigation, deep linking, 3+ level nesting, CustomTransitionPage, pop navigation
• StatefulShellRoute: branch selection toggle, navigator state preservation, composition with route-level disabling

[gemini-code-assist]

Code Review

The pull request successfully addresses the issue of text selection "dead zones" by disabling selection for offstage routes. However, the current implementation of conditionally wrapping widgets with SelectionContainer.disabled or _OffstageSelectionDisabler will cause the entire subtree (including Navigators and their pages) to be unmounted and remounted whenever a route's visibility changes. This leads to a complete loss of state (e.g., scroll positions, text field contents) for those routes. I have suggested an alternative approach that toggles the registrar property of a persistent SelectionContainer to maintain the widget tree structure and preserve state.

[Renzo-Olivares]

Hi @davidmigloz, thank you for your contribution as well as your patience on review! I think the fix for this issue should probably live in the framework that way we can fix the root issue. What do you think about submitting a change to https://github.com/flutter/flutter ? Generally any route we are making offstage/not the current route we should wrap with a SelectionContainer.disabled similar to how you've done in this pull request. Happy to help review and help with any questions. If that's not something you want to do then I'm also happy to take over as well.

[davidmigloz]

Thanks for the feedback @Renzo-Olivares !

I initially took the go_router path because it was the quickest way for me to unblock the affected app, but I agree this should be fixed structurally in the framework.

Would this be the right direction?

• Apply the fix at the route framework layer (ModalRoute scope in routes.dart)
• Ensure non-current route subtrees do not register with the active SelectionArea (so they cannot receive selection events or contribute stale selectable geometry)
• Re-enable normal selection registration when the route becomes current again
• Preserve subtree state across these transitions
• After the framework fix lands, re-evaluate this go_router PR and keep only any residual package-specific guard if still needed (e.g., inactive StatefulShellRoute branch containers)

If this direction looks correct to you, I’ll proceed with it.

[Renzo-Olivares]

@davidmigloz That sounds like a great plan! Thank you for writing such a detailed outline.

Some related issues to look out for : flutter/flutter#119772 and flutter/flutter#151536. These have similar root causes where the selectables will try to register themselves despite not being in the current route, though in those specific issues because the initial route is a nested route and we have not laid out the route route, when attempting to access the transform of selectables in the root route we get a crash. We could get a similar crash in your reproduction if we set the initial route to a nested route.