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Expose LinuxWindowRegistrar on _window_linux.dart in order to better support out of tree LinuxWindowingOwners by mattkae · Pull Request #188917 · flutter/flutter · GitHub
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Expose LinuxWindowRegistrar on _window_linux.dart in order to better support out of tree LinuxWindowingOwners - #188917

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robert-ancell merged 3 commits into
flutter:masterfrom
canonical:third-party-linux-windowing
Jul 8, 2026
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Expose LinuxWindowRegistrar on _window_linux.dart in order to better support out of tree LinuxWindowingOwners#188917
robert-ancell merged 3 commits into
flutter:masterfrom
canonical:third-party-linux-windowing

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@mattkae

@mattkae mattkae commented Jul 2, 2026 •
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Problem

While authoring https://github.com/mattkae/layer_shell.dart, I realized that the Linux Windowing platform had a few major problems when it came to extending it for out-of-tree windowing owners:

  1. 3rd party windows could not register in the _windows or _views maps, which meant that they could never be parents. This is invalid, as other windows (e.g. layer shell windows) may indeed want to be valid parents and open popups. For example, a top panel may want to open a sound control dropdown.
  2. I wanted to extend RegularWindowLinux, but that was unfortunately not possible because the regular windows realize themselves by the time the constructor returns. Gtk layer shell windows require that the window become layer shell before it is realized. We could have added an odd flag to the regular window, but that felt like duct-tape over a larger issue whereby an external author could NOT do anything sufficiently complex with the current API.

What's new?

  • Created a GtkWindowRegistrar that can be used to register and unregister 3rd party windows

Associated PR: mattkae/layer_shell.dart#1

Pre-launch Checklist

  • I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
  • I read the [AI contribution guidelines] and understand my responsibilities, or I am not using AI tools.
  • I read the [Tree Hygiene] wiki page, which explains my responsibilities.
  • I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement].
  • I signed the [CLA].
  • I listed at least one issue that this PR fixes in the description above.
  • I updated/added relevant documentation (doc comments with ///).
  • I added new tests to check the change I am making, or this PR is [test-exempt].
  • I followed the [breaking change policy] and added [Data Driven Fixes] where supported.
  • All existing and new tests are passing.

@mattkae mattkae mentioned this pull request Jul 2, 2026
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@github-actions github-actions Bot added the framework flutter/packages/flutter repository. See also f: labels. label Jul 2, 2026
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mattkae marked this pull request as ready for review July 2, 2026 15:08
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flutter-dashboard Bot commented Jul 2, 2026

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It looks like this pull request may not have tests. Please make sure to add tests or get an explicit test exemption before merging.

If you are not sure if you need tests, consider this rule of thumb: the purpose of a test is to make sure someone doesn't accidentally revert the fix. Ask yourself, is there anything in your PR that you feel it is important we not accidentally revert back to how it was before your fix?

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing. If you believe this PR qualifies for a test exemption, contact "@test-exemption-reviewer" in the #hackers channel in Discord (don't just cc them here, they won't see it!). The test exemption team is a small volunteer group, so all reviewers should feel empowered to ask for tests, without delegating that responsibility entirely to the test exemption group.

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Code Review

This pull request refactors the Linux windowing implementation by introducing a GtkWindowRegistrar to track native GTK windows and Flutter views, and exposes previously private classes and enums as @internal public types. The review feedback suggests marking GtkWindowRegistrar as final, adding assertions to prevent duplicate registrations, throwing specific StateErrors instead of generic Exceptions when lookups fail, and removing obsolete // ignore: unused_field comments from the newly exposed enums.

Comment thread packages/flutter/lib/src/widgets/_window_linux.dart Resolved
Comment thread packages/flutter/lib/src/widgets/_window_linux.dart Resolved
Comment thread packages/flutter/lib/src/widgets/_window_linux.dart Resolved
Comment thread packages/flutter/lib/src/widgets/_window_linux.dart Resolved
Comment thread packages/flutter/lib/src/widgets/_window_linux.dart Resolved
Comment thread packages/flutter/lib/src/widgets/_window_linux.dart Resolved
Comment thread packages/flutter/lib/src/widgets/_window_linux.dart Resolved
Comment thread packages/flutter/lib/src/widgets/_window_linux.dart Resolved
@mattkae mattkae added the CICD Run CI/CD label Jul 2, 2026
@robert-ancell

robert-ancell commented Jul 2, 2026 •
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Two things immediately come to mind:

  • Should this be LinuxWindow, not GtkWindow to match the existing public naming style.
  • Should Gtk/LinuxWindow contain _GtkWindow and not expose this detail to the user. We're adding a lot of API and potential footguns. I think the user should just provide the GtkWindow* pointer and it is up to them to control everything in native code or via their own FFI APIs.

@mattkae mattkae changed the title Expose Gtk objects on _window_linux.dart in order to better support out of tree LinuxWindowingOwners Expose GtkWindowRegistrar on _window_linux.dart in order to better support out of tree LinuxWindowingOwners Jul 6, 2026
@mattkae
mattkae force-pushed the third-party-linux-windowing branch from 7cb600e to a3d1155 Compare July 6, 2026 15:02
@mattkae

mattkae commented Jul 6, 2026

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Two things immediately come to mind:

* Should this be `LinuxWindow`, not `GtkWindow` to match the existing public naming style.

* Should `Gtk/LinuxWindow` contain `_GtkWindow` and not expose this detail to the user. We're adding a lot of API and potential footguns. I think the user should just provide the `GtkWindow*` pointer and it is up to them to control everything in native code or via their own FFI APIs.

I removed a lot of the publicizing here in favor of just exposing GtkWindowRegistrar. Out of tree windowing owners can just implement the FFI bits themselves

@mattkae mattkae changed the title Expose GtkWindowRegistrar on _window_linux.dart in order to better support out of tree LinuxWindowingOwners Expose LinuxWindowRegistrar on _window_linux.dart in order to better support out of tree LinuxWindowingOwners Jul 8, 2026
robert-ancell
robert-ancell approved these changes Jul 8, 2026
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👍

@robert-ancell
robert-ancell added this pull request to the merge queue Jul 8, 2026
Merged via the queue into flutter:master with commit 5616240 Jul 8, 2026
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@robert-ancell
robert-ancell deleted the third-party-linux-windowing branch July 8, 2026 21:56
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auto-submit Bot pushed a commit to flutter/packages that referenced this pull request Jul 10, 2026
@engine-flutter-autoroll
Manual roll Flutter from 91939cc4db78 to dc2a8703e12b (50 revisions) (#…
7a9fb61 
…12169)

Manual roll Flutter from 91939cc4db78 to dc2a8703e12b (50 revisions)

Manual roll requested by bensonluk@google.com

flutter/flutter@91939cc...dc2a870

2026-07-09 chris@bracken.jp [ios,macos] Update swiftc.py flags to match swiftc (flutter/flutter#189174)
2026-07-09 jesswon@google.com [AGP 9] Update Warn Version to AGP 9+ (flutter/flutter#189109)
2026-07-09 154381524+flutteractionsbot@users.noreply.github.com Sync CHANGELOG.md from stable (flutter/flutter#189203)
2026-07-09 mdebbar@google.com [web] Roll Chrome to 145 (framework) (flutter/flutter#182861)
2026-07-09 engine-flutter-autoroll@skia.org Roll Packages from 52d84d6 to 20928d5 (6 revisions) (flutter/flutter#189194)
2026-07-09 zhongliu88889@gmail.com [web] Avoid absolute positioning for base CanvasKit canvas (flutter/flutter#188337)
2026-07-09 engine-flutter-autoroll@skia.org Roll Dart SDK from cdb7217e65aa to a11fb7ed40a5 (6 revisions) (flutter/flutter#189195)
2026-07-09 matt.kosarek@canonical.com Fix dereference of nullptr in the moved-to-rect signal in the Linux embedder (flutter/flutter#189152)
2026-07-09 katelovett@google.com Fix data for design packages (flutter/flutter#189140)
2026-07-09 engine-flutter-autoroll@skia.org Roll Skia from 7b42d1251d54 to ab3a7b98c94d (2 revisions) (flutter/flutter#189181)
2026-07-09 engine-flutter-autoroll@skia.org Roll Skia from 05d9d214e0b7 to 7b42d1251d54 (2 revisions) (flutter/flutter#189175)
2026-07-09 engine-flutter-autoroll@skia.org Roll Skia from 542c8bdd7f4f to 05d9d214e0b7 (4 revisions) (flutter/flutter#189169)
2026-07-09 97480502+b-luk@users.noreply.github.com UberSDF rect handling for thin (line-like) rectangles (flutter/flutter#188821)
2026-07-09 engine-flutter-autoroll@skia.org Roll Skia from dd572c07f63c to 542c8bdd7f4f (4 revisions) (flutter/flutter#189160)
2026-07-09 markzipan@google.com [flutter_tools] Fix hot restart for WASM web builds (flutter/flutter#187898)
2026-07-08 robert.ancell@canonical.com Split FlViewRenderer into OpenGL and software backends (flutter/flutter#188824)
2026-07-08 awolff@google.com Promote android_hardware_smoke_tests out of bringup in CI (flutter/flutter#189081)
2026-07-08 engine-flutter-autoroll@skia.org Roll Skia from 8df24be66531 to dd572c07f63c (4 revisions) (flutter/flutter#189150)
2026-07-08 matt.kosarek@canonical.com Expose LinuxWindowRegistrar on _window_linux.dart in order to better support out of tree LinuxWindowingOwners (flutter/flutter#188917)
2026-07-08 137456488+flutter-pub-roller-bot@users.noreply.github.com Roll pub packages (flutter/flutter#189149)
2026-07-08 codefu@google.com fix(ci): harden some workflows (flutter/flutter#189087)
2026-07-08 engine-flutter-autoroll@skia.org Roll Skia from 51a62da33da0 to 8df24be66531 (1 revision) (flutter/flutter#189139)
2026-07-08 iinozemtsev@google.com Roll Dart SDK to Dart 3.13 beta3 (flutter/flutter#189122)
2026-07-08 digvijaysinghiam@gmail.com [flutter_tools] Don't crash on non-UTF-8 plugin pubspec.yaml (flutter/flutter#188976)
2026-07-08 bkonyi@google.com [flutter_tools] Watch transitive #include headers for FragmentProgram hot reload (flutter/flutter#187945)
2026-07-08 engine-flutter-autoroll@skia.org Roll Skia from 040d9f55de00 to 51a62da33da0 (1 revision) (flutter/flutter#189135)
2026-07-08 engine-flutter-autoroll@skia.org Roll Packages from 92525f5 to 52d84d6 (7 revisions) (flutter/flutter#189134)
2026-07-08 bkonyi@google.com [flutter_tools] Forcefully kill hung subprocesses 5 seconds after timeout (flutter/flutter#187178)
2026-07-08 malo.allee@gmail.com Expose the app's build name and number as compile-time constants (flutter/flutter#187935)
2026-07-08 engine-flutter-autoroll@skia.org Roll Skia from 1ff92f879815 to 040d9f55de00 (1 revision) (flutter/flutter#189131)
2026-07-08 engine-flutter-autoroll@skia.org Roll Skia from 6137414bef5c to 1ff92f879815 (6 revisions) (flutter/flutter#189126)
2026-07-08 brackenavaron@gmail.com [test cross imports] More test/rendering + flutter_test/test fixes (flutter/flutter#188954)
2026-07-08 112751483+shivanshu877@users.noreply.github.com engine: explain why each candidate build was skipped in Flutter web loader (flutter/flutter#186254)
2026-07-08 chris@bracken.jp vscode: add missing unicode.h (flutter/flutter#189102)
2026-07-08 engine-flutter-autoroll@skia.org Roll Fuchsia Linux SDK from 7RjQJBW3m-3Jl-7jr... to QcRFUtvCw2EobfJ8s... (flutter/flutter#189104)
2026-07-08 engine-flutter-autoroll@skia.org Roll Skia from 075fbe4778d9 to 6137414bef5c (10 revisions) (flutter/flutter#189106)
2026-07-08 112751483+shivanshu877@users.noreply.github.com engine: warn on WASM load failure when not crossOriginIsolated (flutter/flutter#186252)
2026-07-08 engine-flutter-autoroll@skia.org Roll Dart SDK from c9bccc09e733 to db2155f56bf3 (2 revisions) (flutter/flutter#189105)
2026-07-08 bkonyi@google.com [flutter_tools] Prevent interactive device selection in machine mode (flutter/flutter#188267)
2026-07-08 bkonyi@google.com [flutter_tools] Fix wireless ADB device discovery when serial contains spaces (flutter/flutter#187943)
2026-07-07 zhongliu88889@gmail.com [web] Fix grouped autofill on iOS Chrome (flutter/flutter#187459)
2026-07-07 rmolivares@renzo-olivares.dev Fix TextSelectionOverlay crash when layout is degenerate (flutter/flutter#188672)
2026-07-07 87962825+kyungilcho@users.noreply.github.com [flutter_tools] Provision Android NDK in the main Gradle invocation (flutter/flutter#186337)
2026-07-07 awolff@google.com Android_hardware_smoke_test: Migrate to AGP 9 (flutter/flutter#189082)
...
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@robert-ancell robert-ancell robert-ancell approved these changes
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