Writing Clang Tools

Clang provides infrastructure to write tools that need syntactic and semantic information about a program. This document will give a short introduction of the different ways to write clang tools, and their pros and cons.

LibClang

LibClang is a stable high level C interface to clang. When in doubt LibClang is probably the interface you want to use. Consider the other interfaces only when you have a good reason not to use LibClang.

Canonical examples of when to use LibClang:

• Xcode
• Clang Python Bindings

Use LibClang when you...

• want to interface with clang from other languages than C++
• need a stable interface that takes care to be backwards compatible
• want powerful high-level abstractions, like iterating through an AST with a cursor, and don't want to learn all the nitty gritty details of Clang's AST.

Do not use LibClang when you...

• want full control over the Clang AST

Clang Plugins

Clang Plugins allow you to run additional actions on the AST as part of a compilation. Plugins are dynamic libraries that are loaded at runtime by the compiler, and they're easy to integrate into your build environment.

Canonical examples of when to use Clang Plugins:

• special lint-style warnings or errors for your project
• creating additional build artifacts from a single compile step

Use Clang Plugins when you...

• need your tool to rerun if any of the dependencies change
• want your tool to make or break a build
• need full control over the Clang AST

Do not use Clang Plugins when you...

• want to run tools outside of your build environment
• want full control on how Clang is set up, including mapping of in-memory virtual files
• need to run over a specific subset of files in your project which is not necessarily related to any changes which would trigger rebuilds

LibTooling

LibTooling is a C++ interface aimed at writing standalone tools, as well as integrating into services that run clang tools.

Canonical examples of when to use LibTooling:

• a simple syntax checker
• refactoring tools

Use LibTooling when you...

• want to run tools over a single file, or a specific subset of files, independently of the build system
• want full control over the Clang AST
• want to share code with Clang Plugins

Do not use LibTooling when you...

• want to run as part of the build triggered by dependency changes
• want a stable interface so you don't need to change your code when the AST API changes
• want high level abstractions like cursors and code completion out of the box
• do not want to write your tools in C++

Clang Tools

These are a collection of specific developer tools built on top of the LibTooling infrastructure as part of the Clang project. They are targeted at automating and improving core development activities of C/C++ developers.

Examples of tools we are building or planning as part of the Clang project:

• Syntax checking (clang-check)
• Automatic fixing of compile errors (clangc-fixit)
• Automatic code formatting
• Migration tools for new features in new language standards
• Core refactoring tools