workflows/premerge: Cancel in progress jobs when a PR is merged (#125329)

Author: tstellar

.github/workflows/premerge.yaml

@@ -5,6 +5,15 @@ permissions:
 
 on:
  pull_request:
+ types:
+ - opened
+ - synchronize
+ - reopened
+ # When a PR is closed, we still start this workflow, but then skip
+ # all the jobs, which makes it effectively a no-op. The reason to
+ # do this is that it allows us to take advantage of concurrency groups
+ # to cancel in progress CI jobs whenever the PR is closed.
+ - closed
  paths:
  - .github/workflows/premerge.yaml
  push:
@@ -14,7 +23,9 @@ on:
 
 jobs:
  premerge-checks-linux:
- if: github.repository_owner == 'llvm'
+ if: >-
+ github.repository_owner == 'llvm' &&
+ (github.event_name != 'pull_request' || github.event.action != 'closed')
  runs-on: llvm-premerge-linux-runners
  concurrency:
  group: ${{ github.workflow }}-linux-${{ github.event.pull_request.number || github.sha }}
@@ -73,7 +84,9 @@ jobs:
  ./.ci/monolithic-linux.sh "$(echo ${linux_projects} | tr ' ' ';')" "$(echo ${linux_check_targets})" "$(echo ${linux_runtimes} | tr ' ' ';')" "$(echo ${linux_runtime_check_targets})"
 
  premerge-checks-windows:
- if: github.repository_owner == 'llvm'
+ if: >-
+ github.repository_owner == 'llvm' &&
+ (github.event_name != 'pull_request' || github.event.action != 'closed')
  runs-on: llvm-premerge-windows-runners
  concurrency:
  group: ${{ github.workflow }}-windows-${{ github.event.pull_request.number || github.sha }}
@@ -141,7 +154,8 @@ jobs:
  if: >-
  github.repository_owner == 'llvm' &&
  (startswith(github.ref_name, 'release/') ||
- startswith(github.base_ref, 'release/'))
+ startswith(github.base_ref, 'release/')) &&
+ (github.event_name != 'pull_request' || github.event.action != 'closed')
  steps:
  - name: Checkout LLVM
  uses: actions/checkout@v4