[ci skip] Rework workflows to support optional paperclip build (#8583)

.github/workflows/build.yml

@@ -1,33 +1,87 @@
 # Here lie dragons!
 #
-# Note that there is no artifact step in this script. We do not want Paperclip
-# jars to be built for every push & PR; our CI handles pushes to branches, while
-# PRs can themselves link to Paperclip jars if it is necessary. Official such
-# PRs will take use of testing builds.
+# This action either builds the server or
+# builds a paperclip jar to be updated in the body
+# of the PR relating to this action.
 
 name: Build Paper
-on: [push, pull_request]
+on:
+  push:
+  pull_request:
+    types:
+      - opened
+      - reopened
+      - synchronize
+      - labeled
 
 jobs:
-    build:
-        # Only run on PRs if the source branch is on someone else's repo
-        if: ${{ github.event_name != 'pull_request' || github.repository != github.event.pull_request.head.repo.full_name }}
-        runs-on: ubuntu-latest
-        strategy:
-            matrix:
-                java: [17]
-            fail-fast: true
-        steps:
-            - uses: actions/checkout@v3
-            - name: JDK ${{ matrix.java }}
-              uses: actions/setup-java@v3.6.0
-              with:
-                  java-version: ${{ matrix.java }}
-                  cache: 'gradle'
-                  distribution: 'temurin'
-            - name: Patch and build
-              run: |
-                  git config --global user.email "no-reply@github.com"
-                  git config --global user.name "Github Actions"
-                  ./gradlew applyPatches --stacktrace
-                  ./gradlew build --stacktrace
+  build:
+    # Only run on PRs if the source branch is on someone else's repo and the pr is not labeled with `build-pr-jar`
+    if: github.event_name != 'pull_request' || github.repository != github.event.pull_request.head.repo.full_name
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        java: [17]
+      fail-fast: true
+    steps:
+      - uses: actions/checkout@v3
+      - name: JDK ${{ matrix.java }}
+        uses: actions/setup-java@v3.6.0
+        with:
+          java-version: ${{ matrix.java }}
+          distribution: 'temurin'
+      - name: Setup Gradle
+        uses: gradle/gradle-build-action@v2
+
+      - name: Configure Build
+        uses: actions/github-script@v6
+        id: determine
+        with:
+          script: |
+            const {owner, repo} = context.repo;
+            const event_name = "${{ github.event_name }}";
+            const event = ${{ toJSON(github.event) }};
+            const ref_type = "${{ github.ref_type }}";
+            const ref_name = "${{ github.ref_name }}";
+            const result = {
+              action: "build"
+            };
+
+            if (event_name === "push" && ref_type === "branch") {
+              const {data: pulls} = await github.rest.pulls.list({ owner, repo, head: `${owner}:${ref_name}`, state: "open" });
+              const pull = pulls.find((pr) => !!pr.labels.find((l) => l.name === "build-pr-jar"));
+              if (pull) {
+                result["pr"] = pull.number;
+                result["action"] = "paperclip";
+                core.info(`This is a push action but to a branch with an open PR with the build paperclip label (${JSON.stringify(result)})`);
+                return result;
+              }
+            } else if (event_name === "pull_request" && event.pull_request.labels.find((l) => l.name === "build-pr-jar")) {
+              result["pr"] = event.pull_request.number;
+              result["action"] = "paperclip";
+              core.info(`This is a pull request action with a build paperclip label (${JSON.stringify(result)})`);
+              return result;
+            }
+            core.info("This will not build a paperclip jar");
+            return result;
+
+      - name: Apply Patches
+        run: |
+          git config --global user.email "no-reply@github.com"
+          git config --global user.name "Github Actions"
+          ./gradlew applyPatches --stacktrace
+
+      - name: Build
+        if: fromJSON(steps.determine.outputs.result).action == 'build'
+        run: ./gradlew build --stacktrace
+
+      - name: Create Paperclip Jar
+        if: fromJSON(steps.determine.outputs.result).action == 'paperclip'
+        run: ./gradlew createReobfPaperclipJar --stacktrace
+
+      - name: Upload Paperclip Jar
+        if: fromJSON(steps.determine.outputs.result).action == 'paperclip'
+        uses: actions/upload-artifact@v3
+        with:
+          name: paper-${{ fromJSON(steps.determine.outputs.result).pr }}
+          path: build/libs/paper-paperclip-*-reobf.jar