[cfe-dev] [clang-tdy] RFC: Support for plugin modules.

[Dmitry Polukhin via cfe-dev]

There is an alternative solution that is already working. With Clang
tarball release you can build custom clang-tidy with additional checks
outside of LLVM sources like you do with any other Clang tool after
https://reviews.llvm.org/D73236 and https://reviews.llvm.org/D73300. Minimal
boilerplate looks like this:

#include <clang/Config/config.h>
#include <llvm/Support/Compiler.h>
#include <clang-tidy/tool/ClangTidyMain.h>

namespace clang {
namespace tidy {

// This anchor is used to force the linker to link the CustomModule.
extern volatile int CustomModuleAnchorSource;
static int LLVM_ATTRIBUTE_UNUSED CustomModuleAnchorDestination =
    CustomModuleAnchorSource;

} // tidy
} // clang

int main(int argc, const char **argv) {
   return clang::tidy::clangTidyMain(argc, argv);
}

I think it is reasonable alternative to clang-tidy plugins that works
everywhere. Anyway clang-tidy plugins are version dependent so they will
work with almost the same version of Clang only.

On Tue, Jun 23, 2020 at 2:24 PM Aaron Ballman via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> On Tue, Jun 23, 2020 at 8:42 AM Nathan James via cfe-dev
> <cfe-dev at lists.llvm.org> wrote:
> >
> > Dear List,
> >
> > I've heard a few small discussions about this topic and they seem to be
> > positive so I thought I'd query it here to see what the consensus is.
> >
> > The general idea is to add a `add-plugin` command line option to clang-
> > tidy, akin to the plugins clang supports. This will be used to load one
> > or more plugins that link additional ClangTidyModules to better enable
> > users to utilise their own custom clang-tidy checks.
> >
> > Currently the only way to do that is to download the entire llvm
> > source, create the module and link it into clang-tidy the same way all
> > the built-in modules are linked.
> >
> > Under this new proposal one could just get the required libraries. Then
> > build their module out of tree and tell clang-tidy to link at runtime
> > with `-add-plugin=<path-to-module>` command line option.
> >
> > A typical modules source code could be as simple as this for just one
> > check
> >
> > -----------------------------------------------------------------------
> >
> > #include "ClangTidy.h"
> > #include "ClangTidyCheck.h"
> > #include "ClangTidyModule.h"
> > #include "ClangTidyModuleRegistry.h"
> >
> > using namespace clang;
> > using namespace clang::tidy;
> > using namespace clang::ast_matchers;
> > using namespace llvm;
> >
> > class AwesomeFunctionCheck : public ClangTidyCheck {
> > public:
> >   using ClangTidyCheck::ClangTidyCheck;
> >
> >   void registerMatchers(MatchFinder *Finder) override {
> >     Finder->addMatcher(
> >         functionDecl(unless(matchesName("Awesome$"))).bind("Function"),
> > this);
> >   }
> >   void check(const MatchFinder::MatchResult &Result) override {
> >     const auto *Function =
> > Result.Nodes.getNodeAs<FunctionDecl>("Function");
> >     diag(Function->getLocation(), "Function '%0' is not sufficiently
> > awesome")
> >         << Function
> >         << FixItHint::CreateReplacement(
> >                Function->getLocation(),
> >                (Function->getName() + "Awesome").str());
> >   }
> > };
> >
> > class MyPluginModule : public ClangTidyModule {
> > public:
> >   void addCheckFactories(ClangTidyCheckFactories &CheckFactories)
> > override {
> >     CheckFactories.registerCheck<AwesomeFunctionCheck>(
> >         "my-plugin-awesome-function");
> >   }
> > };
> >
> > // Register the MyPluginModule using this statically initialized
> > variable.
> > static ClangTidyModuleRegistry::Add<MyPluginModule>
> >     X("my-plugin-module", "Adds my plugin checks.");
> >
> > -----------------------------------------------------------------------
> >
> > Obviously larger code bases may want multiple different checks in which
> > case it would be nicer to seperate the checks out into their own
> > implementation files (The way clang tidy is written now).
> >
> > Once a plugin is linked its checks will still need to be turned on
> > using the `Checks` option from config files or the `checks` command
> > line option.
> >
> > There will also need to be some documentation detailing how to create
> > plugins. https://clang.llvm.org/extra/clang-tidy/Contributing.html
> > already has some useful information but not everything needed for this
> purpose.
> >
> > On the point of getting the required libraries I'm not too sure how
> > everything is packaged. From what I can see the clangTidy libraries are
> > packaged but the headers aren't. That would probably need addressing as
> > well.
>
> I recently had a use case at work where we wanted to write a
> clang-tidy plugin but couldn't due to the lack of infrastructure and
> so we wound up writing a clang static analyzer plugin instead.
> Unfortunately, because LLVM-based plugin systems do not work on
> Windows, this functionality still wouldn't have helped us out for our
> needs. That said, I'm still 100% behind the proposal -- even with the
> general plugin limitations this is a feature I have often wished for
> and been surprised wasn't supported.
>
> ~Aaron
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> cfe-dev at lists.llvm.org
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