[cfe-dev] More plans on Static Analyzer + Clang-Tidy interoperation.

Reid Kleckner via cfe-dev cfe-dev at lists.llvm.org
Tue Oct 13 11:52:22 PDT 2020

This all sounds good to me, as long as it is possible to continue to
disable all the analyzers to produce a smaller clang binary. In Chromium,
we decided it was worth doing this for a 7% size improvement:
https://crrev.com/c/1437255 We ship clang-tidy, and pay the runtime cost of
a second compilation for static analysis.

Now we are no longer in the strange situation of, "small" checks are in the
analyzer, "big" checks (using ASTMatchers? except the static analyzer uses
those now...) are in clang-tidy, everything is the same.


On Mon, Oct 12, 2020 at 2:26 PM Artem Dergachev via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> After a bit of hiatus i'm reviving this work. The previous discussion is
> at http://lists.llvm.org/pipermail/cfe-dev/2019-August/063092.html, also
> http://lists.llvm.org/pipermail/cfe-dev/2019-September/063229.html. The
> plan is not to turn the two Clang bug-finding tools into a single tool
> entirely but rather to make them more interchangeable, so that users who
> have existing integration of, say, static analyzer, could also have
> clang-tidy integration for as-free-as-possible. In particular,
> checks/checkers could be shared, which would resolve the constant
> struggle of "where to put the checker?".
> One thing i realized since the last discussion is that the more tools we
> integrate, the more redundant compilation work do we perform. If we are
> to compile the code + run static analyzer + clang-tidy separately over
> it, that's 3 rebuilds of the AST from scratch. Whatever solution we
> provide to run both tools, I'd much rather keep it at 2 (compilation +
> *all* analysis) because static analysis is already expensive in terms of
> build-time, no need to make it worse.
> One core component of this plan is to teach clang-tidy how to emit
> reports in various human-readable and machine-readable formats that the
> static analyzer already supports. At this point i'm pretty much ready to
> publish a clang::DiagnosticConsumer that'd produce all kinds of static
> analyzer-style reports. In particular, such consumer would enable
> clang-tidy to be used from inside scan-build instead of clang --analyze;
> both clang-tidy checks and static analyzer checkers would be ran from
> inside clang-tidy binary but produce html reports consumable by
> scan-build; a common index.html report would be generated for all
> checkers. I'm very much in favor of teaching scan-build how to run
> arbitrary clang tools, not just clang-tidy (i.e., "scan-build
> --tool=/path/to/my-clang-tool" or something like that) which would allow
> users who don't have CMake compilation databases to take advantage of
> clang tools more easily (and we have a few users who are interested in
> that).
> On the other hand, we've also made up our mind that for ourselves we do
> in fact want produce a clang binary with clang-tidy checkers integrated.
> Apart from free integration into a number of our CI systems, that'll
> allow us to avoid shipping and supporting the clang-tidy command line
> interface as a separate feature. That's about 7MB increase in clang
> binary size which we're fine with. I plan to make it an off-by-default
> cmake flag unless there are strong opinions to do the opposite. The
> alternative approach to move ourselves into a separate binary that's
> integrated at the Driver level would also technically work but that's
> too disruptive to commit to for us at the moment - even just the Driver
> work alone would require a lot of testing, let alone making sure that
> static analyzer works exactly as before from within the tool (it already
> works from inside clang-tidy but we don't really know if it actually
> works *the same* in all the potential cornercases).
> So, like, we want to support multiple workflows.
> Also i'll be making occasional commits to some clang-tidy checks that
> we're interested in - mostly to address a few false positives (say, some
> checkers aren't aware of some Objective-C constructs), but also
> sometimes tweak the warning text a little bit (for example,
> bugprone-assert-side-effect is an awesome check but the warning text
> "found assert() with side effect" sounds fairly un-compiler-ish - we're
> not playing hide-and-seek!). Hope i'm welcome with these changes ^.^
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