GHA to prompt reviewers to think about dependency changes when backporting (#37800)

.github/workflows/backported-dependency-change.yml

@@ -0,0 +1,137 @@
+---
+name: Backported Dependency Changes
+
+on:
+  # The pull_request_target trigger event allows PRs raised from forks to have write permissions and access secrets.
+  # We uses it in this workflow to enable writing comments to the PR.
+  pull_request_target:
+    types:
+      - opened
+      - synchronize
+      - labeled
+      - unlabeled
+  pull_request:
+    types:
+      - opened
+      - synchronize
+      - labeled
+      - unlabeled
+
+# This workflow runs for not-yet-reviewed external contributions.
+# Following a pull_request_target trigger the workflow would have write permissions,
+# so we intentionally restrict the permissions to only include write access on pull-requests.
+permissions:
+    contents: read
+    pull-requests: write
+
+jobs:
+  deps-change-comment:
+    runs-on: ubuntu-latest
+    steps:
+      - name: "Identify if go.mod files have changed"
+        uses: dorny/paths-filter@de90cc6fb38fc0963ad72b210f1f284cd68cea36 # v3.0.2
+        id: changedfiles
+        with:
+            filters: |
+                root-go-mod:
+                    - 'go.mod'
+                nested-go-mod:
+                    - '**/*/go.mod'
+            list-files: json
+
+      # This step will create or delete an existing comment; responds to changes in the PR.
+      - name: "Comment on PR if necessary"
+        uses: actions/github-script@ed597411d8f924073f98dfc5c65a23a2325f34cd # v8.0.0
+        with:
+            script: |
+              // SETUP - values needed for function definitions below.
+              const commentStart = "## Backported dependency change";
+              
+              const { number: issue_number } = context.issue;
+              const { owner, repo } = context.repo;
+              
+              // List all comments
+              const allComments = (await github.rest.issues.listComments({
+                  issue_number,
+                  owner,
+                  repo,
+              })).data;
+              const existingComment = allComments.find(c => c.body.startsWith(commentStart));
+              const comment_id = existingComment?.id;
+
+              async function createOrUpdateComment(commentDetails) {
+                const body = commentStart + "\n\n" + commentDetails;
+                let resp
+                if (existingComment) {
+                    resp = await github.rest.issues.updateComment({
+                        owner,
+                        repo,
+                        comment_id,
+                        body,
+                    });
+                } else {
+                    resp = await github.rest.issues.createComment({
+                        owner,
+                        repo,
+                        issue_number,
+                        body,
+                    });
+                }
+                if (resp.status != 200){
+                  console.error("creating/updating comment failed, here's the response:", resp )
+                  core.setFailed("creating/updating comment failed with status code " + resp.status)
+                }
+              }
+
+              async function deleteCommentIfExists() {
+                if (existingComment) {
+                  const resp = await github.rest.issues.deleteComment({
+                      owner,
+                      repo,
+                      comment_id,
+                  });
+                  if (resp.status >= 300 ){
+                    // Allow all status codes in 2XX range; deleting a non-existing comment is 204
+                    console.error("deleting comment failed, here's the response:", resp )
+                    core.setFailed("deleting comment failed with status code " + resp.status)
+                  }
+                }
+              }
+
+              async function getPrLabels() {
+                const labelsResp = await github.rest.issues.listLabelsOnIssue({
+                          owner,
+                          repo,
+                          issue_number,
+                      });
+                if (labelsResp.status != 200){
+                  console.error("getting the PR's labels failed, here's the response:", resp )
+                  core.setFailed("getting the PR's labels failed with status code " + resp.status)
+                }
+                return labelsResp
+              }
+
+              // INSPECT PR & UPDATE COMMENT
+
+              const labels = await getPrLabels()
+              const filteredLabels = labels.data.filter( label => {
+                return label.name.includes("backport")
+              })
+              const hasBackportLabel = filteredLabels.length > 0
+              const changedRootGoMod = ${{steps.changedfiles.outputs.root-go-mod}};
+              const changedNestedGoMod = ${{steps.changedfiles.outputs.nested-go-mod}};
+              const changesPresent = changedRootGoMod || changedNestedGoMod
+              if (!changesPresent){
+                console.log("This PR isn't attempting to change dependencies. No comment needed.")
+                await deleteCommentIfExists()
+              } else if (!hasBackportLabel) {
+                console.log(`This PR contains changes to dependency-related files but doesn't have a backport label. No comment needed.` + 
+                  `\nChanged root go.mod? = ${changedRootGoMod}`+ 
+                  `\nChanged a nested go.mod? = ${changedNestedGoMod}`)
+                await deleteCommentIfExists()
+              } else {
+                console.log("This PR contains changes to dependency-related files and is labelled for backport. Making sure comment is present.")
+                const comment = "This PR makes changes to dependencies in go.mod file(s) and is labelled for backport.\n\n" +
+                                "Notice to the maintainer: Before merging the backport of this PR please follow our security scanning processes."
+                await createOrUpdateComment(comment)
+              }