Modernize the Cherry-Picker script (pantsbuild#19230)

Modernizes our Cherry-Pick script by making it much more "talkative".
Mainly:
- Will comment on success with PR links (and remove label)
- Will comment on cherry-pick failure with helpful instructions
- Adds new "auto-cherry-pick-failed" label

Additionally, the code leverages `actions/github-script` and calls into
an in-repo file so we can test it (which found several bugs, yay).
Lastly, the cherry-pick script is gone, since the comment instructs on
how to reproduce (a new `make_pr.sh` was created though to handle the PR
creation aspect

---------

Co-authored-by: Tobias Nilsson <[email protected]>
Co-authored-by: Huon Wilson <[email protected]>

.github/workflows/BUILD

@@ -1,4 +1,16 @@
 # Copyright 2023 Pants project contributors (see CONTRIBUTORS.md).
 # Licensed under the Apache License, Version 2.0 (see LICENSE).
 
-files(sources=["*.yaml"])
+files(
+    sources=["*.yaml"],
+    overrides={
+        "auto-cherry-picker.yaml": {
+            "dependencies": [
+                "//build-support/cherry_pick/package.json:support_files",
+                "//build-support/cherry_pick/package-lock.json:support_files",
+                "//build-support/cherry_pick/helper.js:support_files",
+                "//build-support/cherry_pick/make_pr.sh:support_files",
+            ]
+        }
+    },
+)

.github/workflows/auto-cherry-picker.yaml

@@ -14,23 +14,88 @@ on:
         required: true
 
 jobs:
-  picker:
+  prerequisites:
+    name: Gather Prerequisites
     if: (github.event.pull_request.merged == true && contains(github.event.pull_request.labels.*.name, 'needs-cherrypick') ) || github.event_name == 'workflow_dispatch'
     runs-on: ubuntu-latest
+    outputs:
+      pr_num: ${{ steps.get-prereqs.outputs.pr_num }}
+      merge_commit: ${{ steps.get-prereqs.outputs.merge_commit }}
+      matrix: ${{ steps.get-prereqs.outputs.matrix }}
     steps:
+      - uses: actions/setup-node@v3
+        with:
+          node-version: 16
       - name: Check out code
         uses: actions/checkout@v3
+      - run: npm install ./build-support/cherry_pick
+      - id: get-prereqs
+        name: Get Cherry-Pick prerequisites
+        # NB: See https://github.com/actions/github-script/pull/397
+        uses: thejcannon/github-script@7ed0cc648959192a3868f0de9862110d7922b7cc
         with:
-          # Always checkout the latest commit of main, for latest changes to the script
-          ref: "main"
-          # NB: we're usually cherrypicking the HEAD of main, and we need its parent commit to diff
-          # for the cherry-pick, so we can save an extra round-trip by just getting that parent now
-          fetch-depth: 2
+          github-token: ${{ secrets.WORKER_PANTS_CHERRY_PICK_PAT }}
+          allow-empty-token: true
+          script: |
+            const Helper = require('./build-support/cherry_pick/helper.js');
+            const helper = new Helper({octokit: github, context, core});
+            const prereqs = await helper.get_prereqs();
+
+            if (prereqs !== null) {
+              core.setOutput("pr_num", prereqs.pr_num);
+              core.setOutput("merge_commit", prereqs.merge_commit);
+              core.setOutput("matrix", prereqs.milestones.map(
+                milestone => {return {
+                  milestone,
+                  branch_name: `cherry-pick-${prereqs.pr_num}-to-${milestone}`,
+                }}
+              ));
+            }
 
-      - name: Cherry-Pick
+  cherry_picker:
+    name: Cherry-Pick
+    needs: prerequisites
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        include: ${{ fromJSON(needs.prerequisites.outputs.matrix) }}
+    steps:
+      - name: Check out code
+        uses: actions/checkout@v3
+      - name: Prepare cherry-pick branch
+        if: ${{ !env.ACT }}
         run: |
           git config --local user.email "[email protected]"
           git config --local user.name "Worker Pants (Pantsbuild GitHub Automation Bot)"
-          bash -x build-support/bin/cherry_pick.sh ${{ github.event.pull_request.number || inputs.PR_number }} origin
+
+          git fetch --depth=2 origin "${{ needs.prerequisites.outputs.merge_commit }}"
+          # NB: If this fetch fails, we assume that means the milestone branch hasn't been created yet
+          git fetch --depth 1 origin "${{ matrix.milestone }}" || exit 0
+          git checkout -b "${{ matrix.branch_name }}" FETCH_HEAD
+          git cherry-pick "${{ needs.prerequisites.outputs.merge_commit }}"
+          git push -u origin "${{ matrix.branch_name }}"
+      - name: Create Cherry-Pick Branch
         env:
           GH_TOKEN: ${{ secrets.WORKER_PANTS_CHERRY_PICK_PAT }}
+        run: |
+          bash build-support/cherry_pick/make_pr.sh "${{ needs.prerequisites.outputs.pr_num }}" "${{ matrix.milestone }}"
+
+  post_pick:
+    name: Post-Pick Actions
+    needs: [cherry_picker, prerequisites]
+    runs-on: ubuntu-latest
+    if: always()
+    steps:
+      - name: Check out code
+        uses: actions/checkout@v3
+      - run: npm install ./build-support/cherry_pick
+      - name: Run Script
+        # NB: See https://github.com/actions/github-script/pull/397
+        uses: thejcannon/github-script@7ed0cc648959192a3868f0de9862110d7922b7cc
+        with:
+          github-token: ${{ secrets.WORKER_PANTS_CHERRY_PICK_PAT }}
+          allow-empty-token: true
+          script: |
+            const Helper = require('./build-support/cherry_pick/helper.js');
+            const helper = new Helper({octokit: github, context, core});
+            await helper.cherry_pick_finished("${{ needs.prerequisites.outputs.merge_commit }}", ${{ needs.prerequisites.outputs.matrix }});

.github/workflows/tests/BUILD

@@ -5,13 +5,8 @@
 # These aren't meant to be comprehensive, as they can be quite expensive to run. However, they are
 # still useful as they can expose bugs before the action is run in "prod".
 
-experimental_test_shell_command(
-    name="Test workflow_dispatch dryrun",
-    command="./act workflow_dispatch --dryrun",
-    execution_dependencies=[
-        "//build-support/bin/act:act-at-root",
-        ".github/workflows:workflows",
-    ],
-    workdir="/",
+python_tests(
+    name="tests",
+    dependencies=["//build-support/bin/act:act-at-root"],
     timeout=120,
 )

.github/workflows/tests/auto_cherry_picker_smoke_test.py

@@ -0,0 +1,76 @@
+# Copyright 2023 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+import subprocess
+from textwrap import dedent
+
+import pytest
+
+
+@pytest.fixture(scope="session", autouse=True)
+def stub_make_pr():
+    with open("build-support/cherry_pick/make_pr.sh", "w") as f:
+        f.write(
+            dedent(
+                """\
+                #!/usr/bin/env bash
+                set -euo pipefail
+
+                echo "make_pr.sh $@"
+                # We exit 1 to test we still call the finish job
+                exit 1
+                """
+            )
+        )
+
+
+@pytest.fixture(scope="session", autouse=True)
+def stub_helper():
+    with open("build-support/cherry_pick/helper.js", "w") as f:
+        f.write(
+            dedent(
+                """\
+                class CherryPickHelper {
+                    constructor({ octokit, context, core }) {}
+                    async get_prereqs() {
+                        return {
+                            pr_num: 12345,
+                            merge_commit: "ABCDEF12345",
+                            milestones: ["2.16.x", "2.17.x"],
+                        };
+                    }
+
+                    async cherry_pick_finished(merge_commit_sha, matrix_info) {
+                        console.log(`cherry_picked_finished: ${merge_commit_sha} ${JSON.stringify(matrix_info)}`);
+                    }
+                };
+
+                module.exports = CherryPickHelper;
+                """
+            )
+        )
+
+
+def test_auto_cherry_pick():
+    result = subprocess.run(
+        [
+            "./act",
+            "workflow_dispatch",
+            "-W",
+            ".github/workflows/auto-cherry-picker.yaml",
+            "--input",
+            "PR_number=17295",
+            "--env",
+            "GITHUB_REPOSITORY=pantsbuild/pants",
+        ],
+        text=True,
+        capture_output=True,
+        check=False,
+    )
+    stdout = result.stdout
+    print(stdout)
+    assert "make_pr.sh 12345 2.16.x" in stdout
+    assert "make_pr.sh 12345 2.17.x" in stdout
+    assert (
+        'cherry_picked_finished: ABCDEF12345 [{"milestone":"2.16.x","branch_name":"cherry-pick-12345-to-2.16.x"},{"milestone":"2.17.x","branch_name":"cherry-pick-12345-to-2.17.x"}]'
+        in stdout
+    )

build-support/cherry_pick/BUILD

@@ -0,0 +1,11 @@
+# Copyright 2023 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+package_json(name="package.json")
+
+javascript_sources()
+javascript_tests(name="tests")
+
+shell_sources(name="shell")
+
+files(name="support_files", sources=["*"])