Static Analysis

Nix uses clang-tidy for static analysis of C++ code. This helps catch bugs, enforce coding standards, and maintain code quality.

Running clang-tidy locally

To run clang-tidy on the entire codebase in the development shell:

$ nix develop .#native-clangStdenv
$ configurePhase
$ meson compile -C build clang-tidy

This will analyze all C++ source files and report any warnings.

To automatically apply fixes for certain warnings:

$ meson compile -C build clang-tidy-fix

Warning

Review the changes before committing, as automatic fixes may not always be correct.

CI integration

clang-tidy runs automatically on every pull request via GitHub Actions. The CI job builds .#hydraJobs.clangTidy.x86_64-linux which:

1. Builds all components with debug mode (for faster compilation)
2. Runs clang-tidy on each component
3. Fails if any warnings are found (warnings are treated as errors)

Configuration

The clang-tidy configuration is in .clang-tidy at the repository root (symlinked from nix-meson-build-support/common/clang-tidy/.clang-tidy).

Suppressing warnings

If a warning is a false positive, you can suppress it in several ways:

1. Inline suppression (preferred for specific cases):

   // NOLINTBEGIN(bugprone-some-check)
   ... code ...
   // NOLINTEND(bugprone-some-check)

   Or for a single line:

   int x = something(); // NOLINT(bugprone-some-check)

2. Configuration file (for project-wide suppression): Add the check to the disabled list in .clang-tidy:

   Checks:
     - -bugprone-some-check  # Reason for disabling

3. Check options (for configuring check behavior):

   CheckOptions:
     bugprone-reserved-identifier.AllowedIdentifiers: '__some_identifier'

Adding new checks

To enable additional checks:

1. Edit nix-meson-build-support/common/clang-tidy/.clang-tidy
2. Add the check to the Checks list
3. Run clang-tidy locally to see the impact
4. Fix any new warnings or disable specific sub-checks if needed

Custom clang-tidy plugin

The Nix project includes infrastructure for custom clang-tidy checks in src/clang-tidy-plugin/. These checks can enforce Nix-specific coding patterns that aren't covered by standard clang-tidy checks.

To add a new custom check:

1. Add the check implementation in src/clang-tidy-plugin/
2. Register it in nix-clang-tidy-checks.cc
3. Enable it in .clang-tidy with the nix- prefix