tools: abort CQ session when landing several commits

Most PRs are meant to be squashed in one commit when landing. If the
collaborator hasn't been using `fixup!` commits, the CQ lands the PR
as several commits. This change makes the CQ abort by default
when attempting to land several commits, unless there's another
label added to the PR to force squashing or landing as several commits.

Fixes: #40436
Refs: nodejs/node-core-utils#572

PR-URL: #40577
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

doc/guides/commit-queue.md

@@ -25,7 +25,7 @@ From a high-level, the Commit Queue works as follow:
    2. Check if the last Jenkins CI is finished running (if it is not, skip this
       PR)
    3. Remove the `commit-queue` label
-   4. Run `git node land <pr>`
+   4. Run `git node land <pr> --oneCommitMax`
    5. If it fails:
       1. Abort `git node land` session
       2. Add `commit-queue-failed` label to the PR
@@ -37,6 +37,12 @@ From a high-level, the Commit Queue works as follow:
       3. Close the PR
       4. Go to next PR in the queue
 
+To make the Commit Queue squash all the commits of a pull request into the
+first one, add the `commit-queue-squash` label.
+To make the Commit Queue land a pull request containing several commits, add the
+`commit-queue-rebase` label. When using this option, make sure
+that all commits are self-contained, meaning every commit should pass all tests.
+
 ## Current limitations
 
 The Commit Queue feature is still in early stages, and as such it might not

tools/actions/commit-queue.sh

@@ -70,7 +70,15 @@ for pr in "$@"; do
   # Delete the commit queue label
   gitHubCurl "$(labelsUrl "$pr")"/"$COMMIT_QUEUE_LABEL" DELETE
 
-  git node land --autorebase --yes "$pr" >output 2>&1 || echo "Failed to land #${pr}"
+  if gitHubCurl "$(labelsUrl "$pr")" GET | jq -e 'map(.name) | index("commit-queue-squash")'; then
+    MULTIPLE_COMMIT_POLICY="--fixupAll"
+  elif gitHubCurl "$(labelsUrl "$pr")" GET | jq -e 'map(.name) | index("commit-queue-rebase")'; then
+    MULTIPLE_COMMIT_POLICY=""
+  else
+    MULTIPLE_COMMIT_POLICY="--oneCommitMax"
+  fi
+
+  git node land --autorebase --yes $MULTIPLE_COMMIT_POLICY "$pr" >output 2>&1 || echo "Failed to land #${pr}"
   # cat here otherwise we'll be supressing the output of git node land
   cat output