flutter_flutter/docs/tool/Engine-artifacts.md
auto-submit[bot] 4ab2102665
Reverts "Content aware hash moved to script and tracked (#166717)" (#166864)
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Reverts: flutter/flutter#166717
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Initiated by: matanlurey
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Reason for reverting: Broke tree on
[postsubmit](https://logs.chromium.org/logs/flutter/buildbucket/cr-buildbucket/8718108088961866849/+/u/test:_run_suite_safari-dart2js-canvaskit-engine/stdout)
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Original PR Author: jtmcdole
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Reviewed By: {matanlurey}
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This change reverts the following previous change:
1. Calculate the hash in only two places: `content_aware_hash.{ps1|sh}`
2. Call this from the workflow
3. Eventually call this from `update_engine_version.{ps1|sh}`

 The files of import:
* `DEPS`: tracks third party dependencies related to building the engine
* `engine`: all the code in the engine folder
* `bin/internal/content_aware_hash.ps1`: script for calculating the hash
on windows
* `bin/internal/content_aware_hash.sh`: script for calculating the hash
on mac/linux
* `.github/workflows/content-aware-hash.yml`: github action for CI/CD
hashing

Tested on windows and mac:

```shell
PS C:\src\flutter> C:\src\flutter\bin\internal\content_aware_hash.ps1
c24231e276e0719738e175e0622e040ad21a7012
```

```shell
❯ ~/src/flutter/bin/internal/content_aware_hash.sh
c24231e276e0719738e175e0622e040ad21a7012
```
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Co-authored-by: auto-submit[bot] <flutter-engprod-team@google.com>
2025-04-09 17:58:47 +00:00

2.9 KiB

How flutter fetches engine artifacts

While in the same repository, the flutter (tool), which is used to run and test the framework, needs to know how to download the engine artifacts for the current platform and target device. Engine artifacts include dart (the standalone Dart SDK), which runs flutter itself, and per-platform and build mode prebuilt engines (which include the C++ compiled engine, and the embedders for Android, iOS, and so-on).

An example of cached engine artifacts

When using a released version of Flutter, i.e. from a channel such as stable, bin/internal/engine.version is set to the git commit SHA for a merged commit in https://github.com/flutter/flutter, where the engine artifacts have already been pre-built and uploaded.

When using the master channel, or contributing to Flutter (which is typically as a fork of Flutter's master channel), the git commit SHA is computed by using git merge-base HEAD upstream/master (falling back to git merge-base HEAD origin/master to support direct forks or flutter/flutter).

For advanced use-cases, such as on CI platforms, or for custom 1-off testing using a pre-built Flutter engine (to use a locally built Flutter engine see locally built engines), the environment variable FLUTTER_PREBUILT_ENGINE_VERSION can be set, again to a git commit SHA for a merged commit in flutter/flutter:

$ FLUTTER_PREBUILT_ENGINE_VERSION=abc123 flutter --version
..
Engine • revision abc123 ..
..
stateDiagram-v2
    [*] --> CheckEnvVar
    CheckEnvVar: <code>FLUTTER_PREBUILT_ENGINE_VERSION</code> set?
    UseEnvVar: Use <code>FLUTTER_PREBUILT_ENGINE_VERSION</code>
    CheckReleaseFile: <code>bin/internal/engine.version</code> exists?
    UseReleaseFile: Use <code>bin/internal/engine.version</code>
    UseMergeBase: <code>git merge-base HEAD upstream/master</code>

    CheckEnvVar --> UseEnvVar: Yes
    CheckEnvVar --> CheckReleaseFile: No
    UseEnvVar --> [*]: Done
    CheckReleaseFile --> UseReleaseFile: Yes
    CheckReleaseFile --> UseMergeBase: No
    UseReleaseFile --> [*]: Done
    UseMergeBase --> [*]: Done

References

The script(s) that compute (and test the computation of) the engine version:

The tool uses the engine version in the following locations: