Automatically get Flutter version from `pubspec.yaml`

[bartekpacia]

Use case

I like to define my Flutter version like this in pubspec.yaml:

name: awesome_flutter_app
description: Some random cross-platform app.
version: 1.0.0+1
publish_to: none

environment:
  sdk: ">=3.3.2 <4.0.0"
  flutter: 3.19.4

dependencies:
  # ...

This is useful and I really like it because it's very easy to retrieve the version with yq:

$ yq '.environment.flutter' pubspec.yaml
3.19.4

It avoids ambiguity and makes sure both developers and CI use the same Flutter version when building. Right now this is how I accomplish this in my workflows:

jobs:
  main:
    # ...

    steps:
      # ...

      - name: Get Flutter version
        id: get_flutter_version
        run: |
          brew install yq
          echo "result=$(yq '.environment.flutter' pubspec.yaml)" >> $GITHUB_OUTPUT

      - name: Set up Flutter
        uses: subosito/flutter-action@v2
        with:
          channel: stable
          flutter-version: ${{ steps.get_flutter_version.outputs.result }}

Proposal

It'd be great if we could do this instead:

jobs:
  main:
    # ...

    steps:
      # ...

      - name: Set up Flutter
        uses: subosito/flutter-action@v2
        with:
          channel: stable
          flutter-version-file: pubspec.yaml # path to the pubspec.yaml file

Of course, it would only work if yq '.environment.flutter' pubspec.yaml returns a valid semver version, and not something like flutter: ">=3.19.4". People who prefer things the way they are currently would not have to do anything at all, and continue using this action without any breaking changes.

This would be shorter

Both ubuntu-* and macos-* GitHub runners come with yq already installed (just like they come with jq already installed), so this small additional dependency shouldn't be blocker.

More context

• The feature I suggest here is already available in several official GitHub Actions, such as actions/setup-go@v5 and actions/setup-ruby@v1. I think it'd be great if this awesome action also supported it :-)

• This feature was discussed in https://github.com/subosito/flutter-action/discussions/215, but in a slightly different (worse) form

[yurikoles]

And the principal difference between this issue and #211 with #215 is?

[bartekpacia]

The differences:

• This is an issue, not a discussion, thus it gets a bit more visibility. If @subosito agrees I am happy to implement this feature.
• This issue proposes to use flutter-version-file instead of trying to do so implicitly
• This issue proposes for this action to only accept simple semver versions (like "3.19.4"), and not deal with version ranges.