github-action/wiki/QualityChecksCpp.md

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Reading C and C++ quality-check results

How a software engineer calls the shared C and C++ quality checks, reads a failed run and makes it pass. The workflow format-checks and statically checks the C and C++ files of a repository with clang tools at exact versions, changes no file and needs no secret. Its contract is ADR-0008 in this repository.

Calling the workflow

name: Quality C++

on:
  pull_request:
  push:
    branches: [ main ]

jobs:
  quality:
    permissions:
      contents: read
    uses: TirSystem/github-action/.gitea/workflows/quality-checks-cpp.yml@v1
    with:
      std: c++20

Input	Default	Meaning
working-directory	.	Directory, relative to the repository root, whose files are checked
std	c++20	C++ standard given to clang-tidy when there is no compile database, such as c++17 or gnu++20
compile-commands-dir	empty	Directory, relative to the repository root, with a compile_commands.json that your pipeline built before the call; when set, clang-tidy uses it and ignores std
clang-format-version	23.1.3	Exact version of the clang-format package
clang-tidy-version	22.1.8	Exact version of the clang-tidy package
tools-ref	v1	Tag or branch of TirSystem/github-action from which the script tools/quality-checks-cpp.sh is fetched

Reference the workflow at the major tag (@v1) or at an exact tag, never at main. A call at an exact tag is pinned completely only when tools-ref names the same tag. See the upgrade guide. The tool versions are exact: a newer version of a tool is a new release of this repository, not a silent change.

What the repository needs

• A .clang-format in the working directory or in a directory above it, up to the top of the repository. Without one the run fails with [configuration] and no tool runs.
• Optionally a .clang-tidy with the checks of the project (for example the C++ Core Guidelines). Without one clang-tidy runs its default checks.
• For precise static checks, a compile database: build it first (for example cmake -S . -B build -DCMAKE_EXPORT_COMPILE_COMMANDS=ON) and pass compile-commands-dir: build. The workflow does not build your project.

What is checked

Files	Tool	What it reports
tracked *.c, *.cc, *.cpp, *.cxx, *.h, *.hh, *.hpp, *.hxx	clang-format --dry-run -Werror	formatting that differs from .clang-format
the same files	clang-tidy	findings of the checks of .clang-tidy; *.c files are checked as C17, the other files as the C++ standard of std

Untracked files are not checked. A repository without these files passes with a notice. There is no cppcheck: only an old version of it is available as a package, and old tools are not run (ADR-0008).

Reading a run

1. Open the status check on the pull request, then the job quality-checks-cpp.
2. Each tool has its own log group. Every tool runs even when an earlier one failed, so one run shows all findings.
3. A tool ends with PASS <tool> or FAIL <tool>; the last line of a failed run names them: Quality checks failed: clang-format.
4. A finding is written by the tool itself as path:line:column: message. Paths are relative to working-directory.

Typical failures and fixes

Tool	What the log shows	Fix
clang-format	code should be clang-formatted [-Wclang-format-violations]	Run clang-format -i <file> with the same version and commit
clang-tidy	warning: ... [modernize-use-nullptr]	Fix the code, or switch the check off in .clang-tidy with a reason
clang-tidy	error: 'x.h' file not found	Build the compile database and set compile-commands-dir, or add the include path to it

To reproduce a run on your machine, install the same versions:

python3 -m venv .qc
.qc/bin/pip install clang-format==23.1.3 clang-tidy==22.1.8
git ls-files '*.cpp' '*.hpp' | xargs .qc/bin/clang-format --dry-run -Werror

When the workflow itself fails

Message	Cause	Fix
[configuration] std '<x>' is not a C++ standard	std is not like c++20 or gnu++20	Correct the input
[configuration] ... is not an exact version	A tool version is a range, a channel or empty	Give an exact version such as 23.1.3
[configuration] working-directory must be a relative path inside the repository.	An absolute path or ..	Use a path inside the repository
[configuration] No .clang-format found	The project has no style file	Add a .clang-format
[configuration] compile-commands-dir '<x>' has no compile_commands.json	The database was not built before the call	Build it in an earlier step of the job or in a job it depends on
The install step fails	PyPI or the runner network is unreachable	Re-run the job; see troubleshooting.md