[cfe-dev] RFC: Pumping Clang-Tidy warnings through the Static Analyzer's BugReporter.

[Aaron Ballman via cfe-dev]

On Wed, Aug 14, 2019 at 3:24 AM Dmitri Gribenko via cfe-dev
<cfe-dev at lists.llvm.org> wrote:
>
> Hi Artem,
>
> On Wed, Aug 14, 2019 at 5:00 AM Artem Dergachev <noqnoqneo at gmail.com> wrote:
> >
> > As i've been vaguely hinting on EuroLLVM, i plan to invest some time in
> > decreasing the gap between Clang-Tidy users and Static Analyzer users
> > and make sure it's always possible for our users to take the best of
> > both worlds. In particular, i'd like to make Clang-Tidy easily
> > integratable into all UIs that already integrate the Static Analyzer.
>
> I like the idea of integrating the two tools more closely. From the
> user's point of view, I think, ClangTidy and Clang Static Analyzer are
> doing more or less the same thing, but somehow have completely
> different workflows and integrations.

Strong +1 from me!

> > Ideally i'd love to do the same to Clang-Tidy that Clang-Tidy does to
> > us: make the Static Analyzer load it as a library and expose Clang-Tidy
> > checks as its own, maybe in a separate package. This is harder to do
> > though, because Clang-Tidy lives in a separate repo and also it's a hard
> > sell to build it into the Clang binary. I'm open to suggestions here: we
> > can keep such integration under an off-by-default CMake flag (which
> > requires enabling compilation of clang-tools-extra) or we may even use
> > it as a run-time plugin (i mean, clang plugins are super wonky, but this
> > time it's actually fairly easy to avoid version conflicts, as they all
> > get compiled from the same sources simultaneously).
>
> I would like to suggest something different: move Clang Static
> Analyzer to clang-tools-extra. Build it either as a separate binary or
> compile it into the clang-tidy binary. Then let `clang -analyze`
> delegate to that binary for backwards compatibility.

I am not keen on this approach. A stand-alone tool is harder for users
to integrate into their workflows compared to the compiler itself,
which is already (generally) a part of their existing workflow. It's
far easier for a user to add a flag like -tidy to an existing clang
execution than it is to insert clang-tidy into a complex build system.
Personally, I would much rather see libClangTidy integrated into Clang
and exposed via a driver flag, similar to how the static analyzer
already works.

> Clang Static Analyzer is being developed in the clang repository for
> historical reasons -- we didn't have clang-tools-extra at the time the
> project was started. The "non-core" nature of Clang Static Analyzer is
> also validated by the fact that it is an optional part of Clang -- we
> have a CMake flag `CLANG_ENABLE_STATIC_ANALYZER`.

FWIW, I've never liked the fact that clang-tidy is a stand-alone tool
and have always considered that a deficiency that has hindered
adoption. For instance, running clang-tidy required separate effort to
get it up on godbolt, whereas --analyze has worked there since the
first time I tried it.

> Long-term, my preference would be to have all static analysis tooling
> (Clang Static Analyzer, ClangTidy, any prospective dataflow-based
> analysis) to have a consistent UI -- including invocation, integration
> with build systems, configuration strategy etc. While the
> implementation of these tools is very different, I think the audience
> is largely the same.

I think this is a good goal.

~Aaron

> > But regardless of how far do i end up going with such integration, first
> > thing first: i'll anyway need to teach Clang-Tidy how to route its
> > diagnostics through our diagnostic engine. This is also the only thing
> > that's absolutely necessary; the rest can always be hacked up on the UI
> > side.
> >
> > It's a great question why didn't we extend Clang's DiagnosticEngine to
> > begin with, but instead made our own facility. I don't know the answer
> > to that; this happened way before i even learned what an AST is :) We
> > generally needed a much more sophisticated diagnostic engine because our
> > reports are much more complicated. While we could try to unify these
> > diagnostic engines completely, i don't think it's worth it.
> >
> > So i think it's more feasible to make Clang-Tidy's diag() method return
> > a proxy object that mimics the DiagnosticBuilder interface but may also
> > pump the diagnostics to an instance of the Static Analyzer's
> > BugReporter. I hope this would avoid API breakages for clang-tidy checks.
>
> I'm very concerned about introducing lookalike APIs that don't behave
> exactly the same way as original ones. In LLVM, we are generally not
> concerned with backwards compatibility for C++ APIs. Instead, we
> should be looking to keep our code maintainable in the long run.
>
> With that in mind, my suggestion is to refactor ClangTidy to use
> BugReporter instead of DiagnosticBuilder.
>
> Dmitri
>
> --
> main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
> (j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr at gmail.com>*/
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