Only run the pre-commit hook on changed files (#3145)

* Only run the pre-commit hook on changed files

* Let's change a haskell file

* Didn't use the PATTERN field correctly

* Move pre-commit block before building stylish-haskell

* Try to evaluate GIT_DIFF value to pass to pre-commit

* Try to evaluate GIT_DIFF value to pass to pre-commit

* Move pre-commit action back to original spot

* Introduce bad formatting in a file

* Conditionally run the pre-commit job only when there are haskell source
changes

* Restore haskell files we used for testing

* workflow fixes

* Try changing haskell source files with new workflow structure

* Revert all changes to files during testing

Co-authored-by: Pepe Iborra <pepeiborra@gmail.com>

.github/workflows/pre-commit.yml

@@ -6,11 +6,24 @@ on:
     branches: [master]
 
 jobs:
+  file-diff:
+    runs-on: ubuntu-latest
+    outputs:
+      git-diff: ${{ steps.git-diff.outputs.diff }}
+    steps:
+        - name: Checkout code
+          uses: actions/checkout@v3
+        - name: Find changed files
+          uses: technote-space/get-diff-action@v4.0.1
+          id: git-diff
+          with:
+            PATTERNS: |
+              +(src|exe|test|ghcide|plugins|hls-plugin-api|hie-compat|hls-graph|hls-test-utils)/**/*.hs
   pre-commit:
     runs-on: ubuntu-latest
+    needs: file-diff
     steps:
     - uses: actions/checkout@v3
-
     - uses: ./.github/actions/setup-build
       with:
         os: ${{ runner.os }}
@@ -40,3 +53,5 @@ jobs:
 
     - uses: actions/setup-python@v4
     - uses: pre-commit/action@v3.0.0
+      with:
+        extra_args: --files ${{ needs.file-diff.outputs.git-diff }}