Allow to automatically run `flutter precache`

[bartekpacia]

I often have the following code in my workflows

- name: Set up Flutter
  uses: subosito/flutter-action@v2
  with:
    flutter-version: ${{ matrix.flutter-version }}
    channel: ${{ matrix.flutter-channel }}

- name: Preload Flutter artifacts
  run: flutter precache

I wish I could so something like:

- name: Set up Flutter
  uses: subosito/flutter-action@v2
  with:
    flutter-version: ${{ matrix.flutter-version }}
    channel: ${{ matrix.flutter-channel }}
    precache: true

Possibly it should also allow for more granular selection of artifacts to precache, e.g. flutter precache --android --ios would translate to:

- name: Set up Flutter
  uses: subosito/flutter-action@v2
  with:
    flutter-version: ${{ matrix.flutter-version }}
    channel: ${{ matrix.flutter-channel }}
    precache: ['android', 'ios']

[subosito]

I like this idea @bartekpacia, I would be happy to merge the PR.

[bartekpacia]

awesome, I'll start on it :)

[bartekpacia]

GitHub Actions doesn't support passing arrays to actions. For example, I would want to have this API:

- name: Set up Flutter
  uses: subosito/flutter-action@v2
  with:
    channel: stable
    flutter-version: '3.19.0'
    precache: [android, ios]

but it doesn't work:

Only strings, integers, or booleans can be passed, so that's how actually the API would look like:

- name: Set up Flutter
  uses: subosito/flutter-action@v2
  with:
    channel: stable
    flutter-version: '3.19.0'
    precache: '[android, ios]'

I think it's pretty ugly. So right now I'm leaning toward making precache a boolean.

- name: Set up Flutter
  uses: subosito/flutter-action@v2
  with:
    channel: stable
    flutter-version: '3.19.0'
    precache: true

Someone can contribute the more complex version later, and meanwhile they can continue with calling flutter precache manually.

[yurikoles]

What about nested booleans?

precache:
  ios: true
  android: false

[bartekpacia]

That's some solution, thanks! However it results in quite "tall" code.

[bartekpacia]

I think this would be cool:

Precache artifacts for all currently enabled platforms:

precache: true

OR

precache artifacts for specific platforms:

precache:
  ios: true
  android: false

Both syntaxes would be correct. I'm not sure if GitHub Actions supports this though (mixed type: value vs list of values).

@yurikoles what do you think?

[yurikoles]

This feature is mostly for GitHub-hosted runners only. Self-hosted runners retain their state, so precaching seems less important for them. Cheaper Linux runners are preferred due to higher billing multipliers for macOS and Windows runners. Most users require only iOS support on macOS runners. Therefore, I propose to implement one boolean, which will run flutter precache with no options on Linux, flutter precache --windows on Windows, and flutter precache --ios on macOS.

[bartekpacia]

see https://github.com/subosito/flutter-action/pull/276#issuecomment-2028826138