lix/clang-tidy/README.md

Clang tidy lints for Nix

This is a skeleton of a clang-tidy lints library for Nix.

Currently there is one check (which is already obsolete as it has served its goal and is there as an example), HasPrefixSuffixCheck.

Running fixes/checks

One file:

ninja -C build && clang-tidy --checks='-*,nix-*' --load=build/libnix-clang-tidy.so -p ../compile_commands.json --fix ../src/libcmd/installables.cc

Several files, in parallel:

ninja -C build && run-clang-tidy -checks='-*,nix-*' -load=build/libnix-clang-tidy.so -p .. -fix ../src | tee -a clang-tidy-result

Resources

• https://firefox-source-docs.mozilla.org/code-quality/static-analysis/writing-new/clang-query.html
• https://clang.llvm.org/docs/LibASTMatchersReference.html
• https://devblogs.microsoft.com/cppblog/exploring-clang-tooling-part-3-rewriting-code-with-clang-tidy/

Developing new checks

Put something like so in myquery.txt:

set traversal     IgnoreUnlessSpelledInSource
# ^ Ignore implicit AST nodes. May need to use AsIs depending on how you are
# working.
set bind-root     true
# ^ true unless you use any .bind("foo") commands
set print-matcher true
enable output     dump
match callExpr(callee(functionDecl(hasName("hasPrefix"))), optionally(hasArgument( 0, cxxConstructExpr(hasDeclaration(functionDecl(hasParameter(0, parmVarDecl(hasType(asString("const char *"))).bind("meow2"))))))))

Then run, e.g. clang-query --preload hasprefix.query -p compile_commands.json src/libcmd/installables.cc.

With this you can iterate a query before writing it in C++ and suffering from C++.

Tips and tricks for the C++

There is a function dump() on many things that will dump to stderr. Also llvm::errs() lets you print to stderr.

When I wrote HasPrefixSuffixCheck, I was not really able to figure out how the structured replacement system was supposed to work. In principle you can describe the replacement with a nice DSL. Look up the Stencil system in Clang for details.