format-check: rework to test modified files only

The Github UI for required checks does not integrate with the workflows
described in the .github directory. Currently jobs that are never
started due to conditional execution are not even reported, so the UI
shows "expected" and locks up merges.

Rework the format-check workflow to first list the modified files that
need to be checked, and then run the check only on those files. This
way the test runs on every pull request, but has minimal impact unless
one or more source files are actually modified.

Requires a branched version of jidicula/clang-format-action 4.15.0 that
adds the 'check-files-from' input parameter.

Signed-off-by: Luca Burelli <l.burelli@arduino.cc>

Author: pillo79

.github/workflows/format_check.yml

@@ -4,11 +4,6 @@ on:
   push:
     branches:
       - 'main'
-    paths:
-      - '**/*.c'
-      - '**/*.cpp'
-      - '**/*.h'
-      - '**/*.hpp'
 
   pull_request:
     types:
@@ -18,43 +13,37 @@ on:
       - synchronize
     branches:
       - 'main'
-    paths:
-      - '**/*.c'
-      - '**/*.cpp'
-      - '**/*.h'
-      - '**/*.hpp'
-
-  workflow_dispatch:
-    inputs:
-      logLevel:
-        description: 'Log level'     
-        required: true
-        default: 'warning'
 
 jobs:
-  format-check:
+  verify-format:
     runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        path:
-          - check: 'cores/arduino/'
-            exclude: 'cores/arduino/api/'
-          - check: 'loader/'
-            exclude: 'loader/llext_exports\.c$'
-          - check: 'libraries/'
-            exclude: '(examples|extras|ea_malloc)'
-      fail-fast: false
-
     steps:
       - name: Checkout code
         uses: actions/checkout@v4
         with:
           submodules: false
           persist-credentials: false
-
+      - name: Get changed source files that need format check
+        id: changed-files
+        uses: tj-actions/changed-files@ed68ef82c095e0d48ec87eccea555d944a631a4c # v46.0.5
+        with:
+          files: |
+            cores/arduino/**/*.{c,cpp,h,hpp,ino}
+            loader/**/*.{c,cpp,h,hpp,ino}
+            libraries/**/*.{c,cpp,h,hpp,ino}
+          files_ignore: |
+            cores/arduino/api/**
+            loader/llext_exports.c
+            libraries/examples/**
+            libraries/extras/**
+            libraries/ea_malloc/**
+          write_output_files: true
+      - name: List changed files
+        if: steps.changed-files.outputs.any_changed == 'true'
+        run: cat .github/outputs/all_changed_files.txt
       - name: Run clang-format check
-        uses: jidicula/clang-format-action@v4.15.0
+        if: steps.changed-files.outputs.any_changed == 'true'
+        uses: pillo79/clang-format-action@05f671e71f0758aba4d3c9dbb0ee81bc5f0137c6
         with:
           clang-format-version: '19'
-          check-path: ${{ matrix.path['check'] }}
-          exclude-regex: ${{ matrix.path['exclude'] }}
+          check-files-from: .github/outputs/all_changed_files.txt