clear m2-cache prior to mill execution

Author: lostiniceland

.github/workflows/mill-plugin-tests.yaml

@@ -19,10 +19,9 @@ jobs:
         with:
           java-version: 11
           distribution: 'temurin'
-      - name: Cache maven dependencies
-        uses: actions/cache@v5
-        env:
-          cache-name: cache-maven-repository
+      - name: Restore cache (read-only)
+        # only use restore keys, no save key because we need to clear the cache before running the examples
+        uses: actions/cache/restore@v4
         with:
           path: |
             ~/.m2/repository
@@ -31,19 +30,24 @@ jobs:
             !~/.gradle/caches/*/plugin-resolution/
             !~/.m2/repository/org/openapitools/
             !~/.cache/coursier/v1/https/repo1.maven.org/maven2/org/openapitools/
-            !~/.m2/repository/com/fasterxml/
-            !~/.m2/repository/org/slf4j/
-            !~/.m2/repository/javax/validation/
           key: ${{ runner.os }}-build-${{ env.cache-name }}-${{ hashFiles('**/pom.xml') }}
-          restore-keys: |
-            ${{ runner.os }}-test-mill-plugin-${{ env.cache-name }}-
-            ${{ runner.os }}-test-mill-plugin-
+
       - name: Maven Clean Install
         env:
           GRADLE_ENTERPRISE_ACCESS_KEY: ${{ secrets.GRADLE_ENTERPRISE_ACCESS_KEY }}
         run: |
           ./mvnw clean install -DskipTests -Dmaven.javadoc.skip=true
 
+      # This is needed because of differences in how Maven and Coursier download artifacts
+      # Maven will only download the pom when the transitive dependency is not needed in the current projects compile classpath
+      # whereas Coursier expects the artifact (jar) to be present in a Maven repository.
+      - name: Clear m2 cache except openapitools (because otherwise coursier will fail to resolve artifacts where only poms are downloaded)
+        run: |
+          mv ~/.m2/repository/org/openapitools /tmp/openapitools-backup || true
+          rm -rf ~/.m2/repository/*
+          mkdir -p ~/.m2/repository/org
+          mv /tmp/openapitools-backup ~/.m2/repository/org/openapitools || true
+
       - name: Mill Example - Test Validation Command
         env:
           GRADLE_ENTERPRISE_ACCESS_KEY: ${{ secrets.GRADLE_ENTERPRISE_ACCESS_KEY }}