Add cache hit outputs (#364)

* feat: impl cache hit outputs

* support flutter cache and pub cache outputs

* add cache output example to readme

* use cache step directly

* update readme

---------

Co-authored-by: anies1212 <all.for.me1212sna@gmail.com>

README.md

@@ -335,6 +335,38 @@ dynamic values:
 - `:hash:`
 - `:sha256:`
 
+### Using cache outputs
+
+> [!NOTE]
+> `PUB-CACHE-HIT` and `CACHE-HIT` directly use the `cache-hit` output from `actions/cache@v4`, which is the following:
+> - `cache-hit` - A string value to indicate an exact match was found for the key.
+>   - If there's a cache hit, this will be 'true' or 'false' to indicate if there's an exact match for `key`.
+>   - If there's a cache miss, this will be an empty string.
+
+Example usage (inspired by [actions/cache@v4](https://github.com/actions/cache/blob/c45d39173a637a28edbd526cb160189cc4e84f5a/README.md#skipping-steps-based-on-cache-hit) and [#346](https://github.com/subosito/flutter-action/pull/346)) to skip `melos bootstrap` if there was a pub cache hit:
+
+```
+steps:
+  - name: Checkout repository
+    uses: actions/checkout@v4
+
+  - name: Set up Flutter
+    uses: subosito/flutter-action@v2
+    id: flutter-action
+    with:
+      channel: stable
+      cache: true
+
+  - name: Conditionally run melos bootstrap
+    if: steps.flutter-action.outputs.PUB-CACHE-HIT != 'true'
+    run: melos bootstrap
+
+  - name: Continue with build
+    run: flutter build apk
+```
+
+## Outputs
+
 Use outputs from `flutter-action`:
 
 ```yaml
@@ -356,6 +388,8 @@ steps:
       echo ARCHITECTURE=${{ steps.flutter-action.outputs.ARCHITECTURE }}
       echo PUB-CACHE-PATH=${{ steps.flutter-action.outputs.PUB-CACHE-PATH }}
       echo PUB-CACHE-KEY=${{ steps.flutter-action.outputs.PUB-CACHE-KEY }}
+      echo CACHE-HIT=${{ steps.flutter-action.outputs.CACHE-HIT }}
+      echo PUB-CACHE-HIT=${{ steps.flutter-action.outputs.PUB-CACHE-HIT }}
 ```
 
 If you don't need to install Flutter and just want the outputs, you can use the
@@ -379,7 +413,11 @@ steps:
       echo ARCHITECTURE=${{ steps.flutter-action.outputs.ARCHITECTURE }}
       echo PUB-CACHE-PATH=${{ steps.flutter-action.outputs.PUB-CACHE-PATH }}
       echo PUB-CACHE-KEY=${{ steps.flutter-action.outputs.PUB-CACHE-KEY }}
+      echo CACHE-HIT=${{ steps.flutter-action.outputs.CACHE-HIT }}
+      echo PUB-CACHE-HIT=${{ steps.flutter-action.outputs.PUB-CACHE-HIT }}
     shell: bash
 ```
-[Alif Rachmawadi]: https://github.com/subosito
-[Bartek Pacia]: https://github.com/bartekpacia
+
+[Alif Rachmawadi](https://github.com/subosito)
+
+[Bartek Pacia](https://github.com/bartekpacia)

action.yaml

@@ -76,6 +76,12 @@ outputs:
   GIT_SOURCE:
     value: "${{ steps.flutter-action.outputs.GIT_SOURCE }}"
     description: Git source of Flutter SDK repository to clone
+  CACHE-HIT:
+    value: "${{ steps.cache-flutter.outputs.cache-hit }}"
+    description: "`true` if the flutter cache was a hit"
+  PUB-CACHE-HIT:
+    value: "${{ steps.cache-pub.outputs.cache-hit }}"
+    description: "`true` if the pub cache was a hit"
 
 runs:
   using: composite
@@ -109,6 +115,7 @@ runs:
           ${{ inputs.channel }}
 
     - name: Cache Flutter
+      id: cache-flutter
       uses: actions/cache@v4
       if: ${{ inputs.cache == 'true' }}
       with:
@@ -117,6 +124,7 @@ runs:
 
     - name: Cache pub dependencies
       uses: actions/cache@v4
+      id: cache-pub
       if: ${{ inputs.cache == 'true' }}
       with:
         path: ${{ steps.flutter-action.outputs.PUB-CACHE-PATH }}