Create empty code-coverage branch and allow custom commit message (#318)

* Create empty `code-coverage` branch and allow custom commit message

Use `--orphan` instead of using the current branchs content and history.
Set the commit title in an environment variable and only amend commits
with that title to allow for custom commits.

* Add explaining comments for coverage commit overwrite

* Always amend last commit of coverage branch

Avoids people treating this branch as permanent in any way.

Author: Flamefire

.github/workflows/code-coverage.yml

@@ -1,5 +1,6 @@
 #
 # Copyright (c) 2026 Sam Darwin
+# Copyright (c) 2026 Alexander Grund
 #
 # Distributed under the Boost Software License, Version 1.0. (See accompanying
 # file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
@@ -28,6 +29,8 @@ on:
 env:
   GIT_FETCH_JOBS: 8
   NET_RETRY_COUNT: 5
+  # Commit title of the automatically created commits
+  GCOVR_COMMIT_MSG: "Update coverage data"
 
 jobs:
   build:
@@ -62,7 +65,8 @@ jobs:
                 echo "The code-coverage branch exists. Continuing."
             else
                 echo "The code-coverage branch does not exist. Creating it."
-                git checkout -b code-coverage
+                git switch --orphan code-coverage
+                git commit --allow-empty -m "$GCOVR_COMMIT_MSG"
                 git push origin code-coverage
                 git checkout $GITHUB_REF_NAME
             fi
@@ -111,5 +115,5 @@ jobs:
             cp gh_pages_dir/develop/index.html gh_pages_dir/master/index.html
             cd gh_pages_dir
             git add .
-            git commit --amend -m code-coverage
+            git commit --amend -m "$GCOVR_COMMIT_MSG"
             git push -f origin code-coverage

docs/code-coverage.md

@@ -11,6 +11,8 @@ Copy the file `.github/workflows/code-coverage.yml` from boost-ci into your Boos
 
 Run the workflow at least once, which can be done [manually](https://docs.github.com/actions/how-tos/manage-workflow-runs/manually-run-a-workflow).
 This will create a branch called "code-coverage" to store reports.
+On this branch a single commit will be created and updated (amended) with every run of the workflow to reduce the size of the repository.
+Hence it is not intended for other commits as the last one will always be changed.
 
 Next, enable GitHub Pages. Go to https://github.com/ORGANIZATION/REPO/settings/pages and enable the new branch.