ci: run style check on GitHub and GitLab

We don't run style checks on our CI, even though we have a
'.clang-format' setup in the repository. Let's add one, the job will
validate only against the new commits added and will only run on merge
requests. Since we're introducing it for the first time, let's allow
this job to fail, so we can validate if this is useful and eventually
enforce it.

For GitHub, we allow the job to pass by adding 'continue-on-error: true'
to the workflow. This means the job would show as passed, even if the
style check failed. To know the status of the job, users have to
manually check the logs.

For GitLab, we allow the job to pass by adding 'allow_failure: true', to
the job. Unlike GitHub, here the job will show as failed with a yellow
warning symbol, but the pipeline would still show as passed.

Also for GitLab, we use the 'CI_MERGE_REQUEST_TARGET_BRANCH_SHA'
variable by default to obtain the base SHA of the merged pipeline (which
is only available for merged pipelines [1]). Otherwise we use the
'CI_MERGE_REQUEST_DIFF_BASE_SHA' variable.

[1]: https://docs.gitlab.com/ee/ci/variables/predefined_variables.html#predefined-variables-for-merge-request-pipelines

Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

.github/workflows/check-style.yml

@@ -0,0 +1,34 @@
+name: check-style
+
+# Get the repository with all commits to ensure that we can analyze
+# all of the commits contributed via the Pull Request.
+
+on:
+  pull_request:
+    types: [opened, synchronize]
+
+# Avoid unnecessary builds. Unlike the main CI jobs, these are not
+# ci-configurable (but could be).
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  check-style:
+    env:
+      CC: clang
+      jobname: ClangFormat
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+      with:
+        fetch-depth: 0
+
+    - run: ci/install-dependencies.sh
+
+    - name: git clang-format
+      continue-on-error: true
+      id: check_out
+      run: |
+        ./ci/run-style-check.sh \
+          "${{github.event.pull_request.base.sha}}"

.gitlab-ci.yml

@@ -123,6 +123,24 @@ check-whitespace:
   rules:
     - if: $CI_PIPELINE_SOURCE == 'merge_request_event'
 
+check-style:
+  image: ubuntu:latest
+  allow_failure: true
+  variables:
+    CC: clang
+    jobname: ClangFormat
+  before_script:
+    - ./ci/install-dependencies.sh
+  # Since $CI_MERGE_REQUEST_TARGET_BRANCH_SHA is only defined for merged
+  # pipelines, we fallback to $CI_MERGE_REQUEST_DIFF_BASE_SHA, which should
+  # be defined in all pipelines.
+  script:
+    - |
+      R=${CI_MERGE_REQUEST_TARGET_BRANCH_SHA-${CI_MERGE_REQUEST_DIFF_BASE_SHA:?}} || exit
+      ./ci/run-style-check.sh "$R"
+  rules:
+    - if: $CI_PIPELINE_SOURCE == 'merge_request_event'
+
 documentation:
   image: ubuntu:latest
   variables:

ci/install-dependencies.sh

@@ -87,6 +87,10 @@ macos-*)
 esac
 
 case "$jobname" in
+ClangFormat)
+	sudo apt-get -q update
+	sudo apt-get -q -y install clang-format
+	;;
 StaticAnalysis)
 	sudo apt-get -q update
 	sudo apt-get -q -y install coccinelle libcurl4-openssl-dev libssl-dev \

ci/run-style-check.sh

@@ -0,0 +1,8 @@
+#!/bin/sh
+#
+# Perform style check
+#
+
+baseCommit=$1
+
+git clang-format --style file --diff --extensions c,h "$baseCommit"