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Don't throw an exception if no web define variable is set#182273

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EricApostal:fix/missing-web-define-variable
Feb 13, 2026
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Don't throw an exception if no web define variable is set#182273
auto-submit[bot] merged 12 commits intoflutter:masterfrom
EricApostal:fix/missing-web-define-variable

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@EricApostal
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This PR fixes a problem introduced in #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 #182243

Note: As per #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 #182079, and does not have to do with this PR.

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@github-actions github-actions bot added the tool Affects the "flutter" command-line tool. See also t: labels. label Feb 12, 2026
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This pull request changes the behavior of --web-define. Previously, if a variable was present in index.html but not provided via --web-define, the build would fail with an error. This change modifies that behavior to instead log a warning and leave the placeholder in the output file. This is achieved by plumbing a Logger instance down to the template substitution logic and replacing the throwToolExit with logger.printWarning. The associated help text and tests have been updated to reflect this new behavior.

@EricApostal
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I originally used globals.logger.printWarning, but looking at other usages it appears that the right call is to use the logger from the build system environment. Consequently, this change was a little bit larger than I expected. If this is not how this should be handled I can revert that.

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LGTM, with nits. I still need to run the tests locally, just to check if these do the right thing.

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Thanks @EricApostal for the fix!

@navaronbracke I appreciate the thorough review 🙂

LGTM

@mdebbar mdebbar added cp: beta cherry pick this pull request to beta release candidate branch cp: stable cherry pick this pull request to stable release candidate branch labels Feb 12, 2026
@mdebbar mdebbar removed cp: beta cherry pick this pull request to beta release candidate branch cp: stable cherry pick this pull request to stable release candidate branch labels Feb 12, 2026
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LGTM.

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Thank you guys very much! It means a ton how quickly you guys were able to get eyes and hands on this.

@mdebbar mdebbar added the autosubmit Merge PR when tree becomes green via auto submit App label Feb 13, 2026
@auto-submit auto-submit bot added this pull request to the merge queue Feb 13, 2026
Merged via the queue into flutter:master with commit f8a1b34 Feb 13, 2026
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@flutter-dashboard flutter-dashboard bot removed the autosubmit Merge PR when tree becomes green via auto submit App label Feb 13, 2026
@mdebbar mdebbar added cp: beta cherry pick this pull request to beta release candidate branch cp: stable cherry pick this pull request to stable release candidate branch and removed cp: beta cherry pick this pull request to beta release candidate branch cp: stable cherry pick this pull request to stable release candidate branch labels Feb 18, 2026
flutteractionsbot pushed a commit to flutteractionsbot/flutter that referenced this pull request Feb 18, 2026
…2273)

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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
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addressed.

<!-- Links -->
[Contributor Guide]:
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[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]:
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[CLA]: https://cla.developers.google.com/
[flutter/tests]: https://github.com/flutter/tests
[breaking change policy]:
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[Discord]:
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[Data Driven Fixes]:
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---------

Co-authored-by: Navaron Bracke <[email protected]>
flutteractionsbot pushed a commit to flutteractionsbot/flutter that referenced this pull request Feb 18, 2026
…2273)

<!--
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Reviewers are typically assigned within a week of filing a request.
To learn more about code review, see our documentation on Tree Hygiene:
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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.

<!-- Links -->
[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]>
@mdebbar
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mdebbar commented Feb 18, 2026

Cherry-picks have been created: #182549 (stable) and #182548 (beta)

rickhohler pushed a commit to rickhohler/flutter that referenced this pull request Feb 19, 2026
…2273)

<!--
Thanks for filing a pull request!
Reviewers are typically assigned within a week of filing a request.
To learn more about code review, see our documentation on Tree Hygiene:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md
-->

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.

<!-- Links -->
[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]>
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New --web-define feature breaks existing html templates and cannot be disabled

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