[cfe-dev] How to use clang-tidy for smaller projects

[Robert Underwood via cfe-dev]

All,

tl;dr is there a way to use clang-tidy for small projects without 
requiring users to rebuild most of clang/llvm provided versions match?

Let me begin by offering my gratitude to the Clang/LLVM community for 
the excellent C/C++ tools you all develop and we all benefit from.

I'm a grad student who works on a number of small libraries that use 
C/C++, and occasionally me or my colleagues change the APIs for those 
libraries, and would like to provide tools to update to the new APIs to 
our users.  As I understand there are two main options:

1. Write a new custom clang-tool to do the migrations

2. Reuse clang-tidy and write a new tidy-module or add our check to an 
existing module.

The former has some disadvantages: it means that users now need to run 
our tool and clang-tidy to get all of the fixes they need. Additionally 
what we are doing with the migrations are essentially what clang-tidy 
was designed to do.

The latter addresses these challenges, but presents a few more. Now 
users have to compile and install a custom version of clang-tidy in 
order to use our checks, and for various reasons the user probably will 
compile and install a fair bit of the clang/llvm ecosystem just to try 
our migration modules. LLVM/clang/clang-tools-extra are not small 
projects and take a while to compile and occupy substantial disk space 
once compiled for a task like this.

I considered trying to write a module external to the LLVM/Clang source 
tree and just link to the appropriate libraries in as I have done with 
clang-tools in the past, but clang-tidy uses several implementation 
specific headers that are not available outside the clang-tools-extra 
source code repository (i.e. ClangTidy.h).  I recognize that this is not 
the [recommended method for developing clang-tidy modules][1] so it 
doesn't surprise me that this does not work.

However, I think there is a use case here.  Not every project is backed 
by Google, Intel, Apple, Sony, or another large company with an 
extensive distributed build environment where rebuilding a large amount 
of clang/llvm is more feasible.  Not every clang-tidy module needs to be 
up-streamed to clang-tidy especially those for small libraries like mine.

I admit it is quite possible I am missing something, but I think there 
should be a way to make this easier for small projects to use.  I've 
read the provided documentation several times, and I've not found it.

I would appreciate your time and consideration as you consider this 
request.

Respectfully,

Robert Underwood


[1]: https://clang.llvm.org/extra/clang-tidy/Contributing.html

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