mise-cpp-clang-tools

clang-tools — format, tidy, clangd, iwyu

These are the modern C++ code quality stack. Pin them via mise or your team will get subtle format-churn diffs every time someone upgrades clang.

The tools

Tool	Purpose	Version pinning matters?
clang-format	Auto-format code to a style	🔴 Critical — each release changes formatting subtly
clang-tidy	Static analysis + linting with auto-fix	🟡 Matters — new checks appear per version
clangd	LSP server for IDE (VSCode, Neovim, etc.)	🟢 Less critical — but match clang-tidy version
include-what-you-use (iwyu)	Find unused / missing #includes	🟡 Matters — tied to clang version

Installing via mise

The whole LLVM bundle is the simplest approach:

[tools]
"aqua:llvm/llvm-project" = "18"

This gets you clang-format, clang-tidy, clangd, and lld all at the same version. Pin a specific major ("18") rather than latest — see the one-version rule below.

For iwyu specifically:

[tools]
"aqua:include-what-you-use/include-what-you-use" = "latest"  # verify the exact aqua path

(iwyu is tightly coupled to a specific LLVM version — always check compatibility.)

The one-version-per-project rule

Every dev and every CI run must use the exact same clang-format version. Otherwise you get rotating "format the world" PRs because clang-format 17 and 18 disagree on where to break a line.

The aqua:llvm/llvm-project pin in mise.toml enforces this. Commit mise.lock so even the patch version is consistent.

Same logic for clang-tidy: new versions add new checks, which means a previously-clean file starts reporting warnings. Pin the version in mise.toml so "the lint rules" are as reproducible as "the source code".

.clang-format setup

At the project root:

# .clang-format
BasedOnStyle: Google     # or LLVM, Microsoft, Mozilla, Chromium, WebKit
IndentWidth: 2
ColumnLimit: 100
DerivePointerAlignment: false
PointerAlignment: Left
IncludeBlocks: Regroup
# ... add project-specific overrides

And a mise task:

[tasks."fmt"]
description = "Format all C++ source and headers"
run = "clang-format -i $(find src include -name '*.cc' -o -name '*.h')"

[tasks."fmt:check"]
description = "Check formatting without modifying (for CI)"
run = "clang-format --dry-run --Werror $(find src include -name '*.cc' -o -name '*.h')"

Wire fmt:check into CI so PRs that aren't formatted fail the build.

.clang-tidy setup

# .clang-tidy
Checks: >
  -*,
  bugprone-*,
  cert-*,
  clang-analyzer-*,
  cppcoreguidelines-*,
  modernize-*,
  performance-*,
  portability-*,
  readability-*,
  -modernize-use-trailing-return-type,
  -readability-identifier-length
WarningsAsErrors: 'bugprone-*,cert-*,clang-analyzer-*'
HeaderFilterRegex: '^(src|include)/'

And the task:

[tasks."tidy"]
description = "Run clang-tidy over compile_commands.json"
depends = ["configure"]  # needs build/compile_commands.json
run = "clang-tidy -p build $(find src -name '*.cc')"

clang-tidy requires compile_commands.json — make sure the configure step sets CMAKE_EXPORT_COMPILE_COMMANDS=ON.

clangd for IDEs

clangd reads compile_commands.json too. For VSCode: install the llvm-vs-code-extensions.vscode-clangd extension. It auto-detects clangd from PATH — which mise puts there via shims.

Disable the Microsoft C/C++ extension's IntelliSense when using clangd; they fight each other.

Symlink build/compile_commands.json to the project root so clangd finds it immediately:

[tasks.configure]
run = [
  "cmake --preset dev",
  "ln -sf build/compile_commands.json ."
]

CI integration

A typical GitHub Actions job:

- uses: jdx/mise-action@v3
- run: mise run configure
- run: mise run fmt:check      # fail on format diff
- run: mise run tidy           # fail on clang-tidy warnings
- run: mise run build
- run: mise run test

Because everything is pinned via mise, CI uses the exact same clang-format/clang-tidy as local dev. Zero "works on my machine" drift.

iwyu (include-what-you-use)

iwyu tells you which #include directives are unused, and which missing includes you're accidentally getting through transitive includes. Run it periodically (not on every commit — it's slow and noisy).

[tasks."iwyu"]
description = "Run include-what-you-use (advisory)"
depends = ["configure"]
run = "iwyu_tool.py -p build"

Don't enforce iwyu as a hard CI gate — the warnings are frequently false positives for complex templates. Treat it as an advisory tool you run occasionally.

Anti-patterns

• clang-format in pre-commit hooks without a version pin. Different devs, different versions, chaos.
• Running clang-tidy without compile_commands.json. Half the checks silently don't fire.
• Checking in compile_commands.json. It's a build artifact. git-ignore it.
• Mixing clang-format from homebrew and clang-format from mise. shims should be first on PATH; verify with which clang-format.
• Disabling every clang-tidy check because "too noisy". Better: pick a small set (bugprone, cert, performance) and enforce them.

See also

• mise-cpp-toolchain-overview — the big picture.
• mise-cpp-cmake-ninja-ccache — CMAKE_EXPORT_COMPILE_COMMANDS is set there.
• mise-vscode-integration — getting clangd recognized by VSCode.
• clang-format: clang.llvm.org/docs/ClangFormat.html.
• clang-tidy: clang.llvm.org/extra/clang-tidy/.
• clangd: clangd.llvm.org.