[CP-beta]Don't throw an exception if no web define variable is set by flutteractionsbot · Pull Request #182548 · flutter/flutter

flutteractionsbot · 2026-02-18T16:18:33Z

This pull request is created by automatic cherry pick workflow
Please fill in the form below, and a flutter domain expert will evaluate this cherry pick request.

Issue Link:

What is the link to the issue this cherry-pick is addressing?

#182243

Impact Description:

What is the impact (ex. visual jank on Samsung phones, app crash, cannot ship an iOS app)?
Does it impact development (ex. flutter doctor crashes when Android Studio is installed),
or the shipping of production apps (the app crashes on launch).
This information is for domain experts and release engineers to understand the consequences of saying yes or no to the cherry pick.

flutter build web is broken for apps that use the {{...}} pattern in web/index.html.

Changelog Description:

Explain this cherry pick:

In one line that is accessible to most Flutter developers.
That describes the state prior to the fix.
That includes which platforms are impacted.
See best practices for examples.

Don't throw an exception if no web define variable is set.

Workaround:

Is there a workaround for this issue?

It's possible to workaround this issue by adding --web-define=foo={{foo}}.

Risk:

What is the risk level of this cherry-pick?

Low
Medium
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Test Coverage:

Are you confident that your fix is well-tested by automated tests?

Yes
No

Validation Steps:

What are the steps to validate that this fix works?

Follow repro steps in #182243

…2273)  This PR fixes a problem introduced in flutter#175805 that caused a build to exception to be thrown if variables like `{{this}}` were defined in the web `index.html`, but were not explicitly set by `--web-define=this=VALUE`. Resolves flutter#182243 Note: As per flutter#182076, this will always show the warning if ran with `flutter build web`, whereas `flutter run -d ...` works fine, regardless of whether you've set the variable or not. That is set to be fixed in flutter#182079, and does not have to do with this PR. ## Pre-launch Checklist - [x] I read the [Contributor Guide] and followed the process outlined there for submitting PRs. - [x] I read the [Tree Hygiene] wiki page, which explains my responsibilities. - [x] I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement]. - [x] I signed the [CLA]. - [x] I listed at least one issue that this PR fixes in the description above. - [x] I updated/added relevant documentation (doc comments with `///`). - [x] I added new tests to check the change I am making, or this PR is [test-exempt]. - [x] I followed the [breaking change policy] and added [Data Driven Fixes] where supported. - [x] All existing and new tests are passing. If you need help, consider asking for advice on the #hackers-new channel on [Discord]. **Note**: The Flutter team is currently trialing the use of [Gemini Code Assist for GitHub](https://developers.google.com/gemini-code-assist/docs/review-github-code). Comments from the `gemini-code-assist` bot should not be taken as authoritative feedback from the Flutter team. If you find its comments useful you can update your code accordingly, but if you are unsure or disagree with the feedback, please feel free to wait for a Flutter team member's review for guidance on which automated comments should be addressed.  [Contributor Guide]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#overview [Tree Hygiene]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md [test-exempt]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#tests [Flutter Style Guide]: https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md [Features we expect every widget to implement]: https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md#features-we-expect-every-widget-to-implement [CLA]: https://cla.developers.google.com/ [flutter/tests]: https://github.com/flutter/tests [breaking change policy]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#handling-breaking-changes [Discord]: https://github.com/flutter/flutter/blob/main/docs/contributing/Chat.md [Data Driven Fixes]: https://github.com/flutter/flutter/blob/main/docs/contributing/Data-driven-Fixes.md --------- Co-authored-by: Navaron Bracke <[email protected]>

flutter-dashboard · 2026-02-18T16:18:36Z

This pull request was opened from and to a release candidate branch. This should only be done as part of the official Flutter release process. If you are attempting to make a regular contribution to the Flutter project, please close this PR and follow the instructions at Tree Hygiene for detailed instructions on contributing to Flutter.

Reviewers: Use caution before merging pull requests to release branches. Ensure the proper procedure has been followed.

flutteractionsbot · 2026-02-18T16:18:37Z

@mdebbar please fill out the PR description above, afterwards the release team will review this request.

gemini-code-assist

Code Review

The pull request modifies the web build process to handle missing web-define variables more gracefully. Instead of throwing a ToolExit exception, the system now logs a warning and skips the unhandled variable. This change involves passing the Logger instance to relevant functions and updating the WebTemplate class to use the logger for warnings. Additionally, test cases have been updated to reflect this new behavior.

gemini-code-assist · 2026-02-18T16:21:33Z

packages/flutter_tools/lib/src/build_system/targets/web.dart

      serviceWorkerVersion: serviceWorkerVersion,
      flutterJsFile: flutterJsFile,
      buildConfig: buildConfig,
+      logger: environment.logger,


The logger: environment.logger parameter is being added to the bootstrapTemplate.withSubstitutions call. This is a necessary change to allow the WebTemplate to log warnings instead of throwing an exception when web-define variables are missing.

gemini-code-assist · 2026-02-18T16:21:33Z

packages/flutter_tools/lib/src/build_system/targets/web.dart

          flutterJsFile: flutterJsFile,
          buildConfig: buildConfig,
          flutterBootstrapJs: bootstrapContent,
+          logger: environment.logger,


The logger: environment.logger parameter is being added to the indexHtmlTemplate.withSubstitutions call. This is a necessary change to allow the WebTemplate to log warnings instead of throwing an exception when web-define variables are missing.

gemini-code-assist · 2026-02-18T16:21:33Z

packages/flutter_tools/lib/src/isolated/web_asset_server.dart

    required this.webRenderer,
    required this.useLocalCanvasKit,
    required this.fileSystem,
+    required this.logger,


The logger parameter is being added to the WebAssetServer constructor. This allows the server to log warnings instead of throwing exceptions when web-define variables are missing.

gemini-code-assist · 2026-02-18T16:21:33Z

packages/flutter_tools/lib/src/isolated/web_asset_server.dart

      webRenderer: webRenderer,
      useLocalCanvasKit: useLocalCanvasKit,
      fileSystem: fileSystem,
+      logger: logger,


The logger: logger parameter is being added to the WebAssetServer constructor call. This is a necessary change to pass the logger instance to the WebAssetServer.

gemini-code-assist · 2026-02-18T16:21:33Z

packages/flutter_tools/lib/src/isolated/web_asset_server.dart

  final bool useLocalCanvasKit;

  final FileSystem fileSystem;
+  final Logger logger;


The logger field is being added to the WebAssetServer class. This field will store the logger instance used for logging warnings.

gemini-code-assist · 2026-02-18T16:21:35Z

packages/flutter_tools/test/general.shard/web_template_test.dart

        flutterJsFile: flutterJs,
        buildConfig: '(build config)',
        flutterBootstrapJs: '(flutter bootstrap script)',
+        logger: logger,
