[cfe-dev] Question about custom Clang static analyzer checker registration in clang-tidy without using plugin

[Li Kan via cfe-dev]

Hi,

I have a question about how to register custom checkers without using a
plugin. The background is, I have been working on a checker and I was able
to come up with a solution to integrate into our code review system by
using AnalysisConsumer and load custom checkers using plugins. However, the
team of our company who works on clang-tidy integration requests me to do
that in clang-tidy, instead of a separate set of things.

The way clang-tidy is used in the code review system is to create
ClangTidyASTConsumerFactory and then create a ClangTidyASTConsumer, which
is later used to parse the codebase. Therefore the goal here is to find a
way to let the users of clang libraries, especially
ClangTidyASTConsumer{,Factory}, to let AnalysisConsumer pickup custom
checkers statically linked into the program;

Currently the checker registration is very deep in the stack, the only
places it looks for checkers are a set of builtin checkers and plugins.
There are a few directions I can think of
1) Add some arguments to AnalysisConsumer constructor and pass it down to
createCheckerManager, and add logic there to look for checkers passed in;
however, this is problematic because all the users of AnalysisConsumer,
such as ClangTidyASTConsumer, needs to expose the arguments as well;
2) Have some static variable that stores the list of checkers factories,
and expose a function that allows user to add checkers factories to it.
Later the ClangCheckerRegistry picks up the checkers in the list. This is
the ordinary way, but the existence of a static variable looks ugly and not
thread-safe.
3) Like registerBuiltinCheckers, add a weak function
registerCustomCheckers, initially empty, and client code is allowed to
override it, filled in with their custom checkers. In ClangCheckerRegistry
it invokes the function, just after it invokes the registerBuiltinCheckers.
This is the least intrusive way but the drawback is if there are multiple
places in the system that needs to add a checker, it is not very convenient.

What's the best approach, or is there other better approach? I am more than
happy to help and send out some patch to add some mechanism. I want to hear
the opinions from Clang developers and get blessed by the direction, before
I actually start on it, to avoid any arguments.
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