Add a ready-to-merge check (#910)

Github allows setting a list of required status before merging into a
protected branch (in our case, `master`). However, it requires the
checks to have a fixed name (no pattern matching allowed). As some of
our checks are dynamically generated using a testing matrix, the names
may change. It is not convenient to set them as required status.

This PR adds another check. It passes if all other checks pass (except
ignored checks). We can use this new check as the required status for
merging. Once we set up a proper required check, we can enable merge
queue.

This PR also adds a `merge_group` trigger for pre code review checks.

Author: qinsoon

.github/workflows/merge-check.yml

@@ -0,0 +1,26 @@
+name: Merge Check
+on:
+  merge_group:
+    branches:
+      - master
+
+jobs:
+  ready-to-merge:
+    runs-on: ubuntu-latest
+    steps:
+      - name: 'Wait for status checks'
+        id: waitforstatuschecks
+        timeout-minutes: 120
+        uses: "WyriHaximus/[email protected]"
+        with:
+          # Ignore some actions (based on what merge_group triggers):
+          # - this action
+          # - pre code review checks for stable Rust (we allow them to fail)
+          ignoreActions: "ready-to-merge,pre-code-review-checks/x86_64-unknown-linux-gnu/stable,pre-code-review-checks/i686-unknown-linux-gnu/stable,pre-code-review-checks/x86_64-apple-darwin/stable"
+          # This action uses API. We have a quota of 1000 per day.
+          # We normally run tests within 1 hours (excluding binding tests).
+          # If we check every 10 mins, we use roughly 6 API calls per trigger.
+          # We can handle ~160 triggers.
+          checkInterval: 600
+        env:
+          GITHUB_TOKEN: "${{ secrets.GITHUB_TOKEN }}"

.github/workflows/pre-review-ci.yml

@@ -4,6 +4,9 @@ on:
   pull_request:
     branches:
       - master
+  merge_group:
+    branches:
+      - master
 
 concurrency:
   # Cancels pending runs when a PR gets updated.
@@ -36,7 +39,7 @@ jobs:
           - { os: macos-12, triple: x86_64-apple-darwin }
         rust: ${{ fromJson(needs.setup-test-matrix.outputs.rust )}}
 
-    name: ${{ matrix.target.triple }} / ${{ matrix.rust }}
+    name: pre-code-review-checks/${{ matrix.target.triple }}/${{ matrix.rust }}
     runs-on: ${{ matrix.target.os }}
 
     steps: