[cfe-dev] [RFC] Add include-what-you-use tool to clang-tools-extra

Tue Sep 5 00:42:24 PDT 2017

I'm not fundamentally opposed to the idea, but I'd expect it to be rather
painful - speaking from experience of having upstreamed a non-trivially
sized chunk of google-style code into clang, which was still
*significantly* smaller than iwyu.

Generally, we need patches to be:
1. LLVM style
2. incremental, with design ideas discussed / vetted in review

(1) is just a big chunk of work, but (2) can quickly lead code into a very
different direction from where it is now; that said, I do believe that it
would make the code, especially for iwyu, a lot better - but it would also
make it an incredible amount of work, knowing how much time went into
creating iwyu in the first place.

Additionally, with C++ modules, a new idea of "use" is emerging (I don't
know whether standardization is far enough for that to be reliable), and I
think we could / should and will build an "iwyu" implementation on top of
that.
That doesn't make a non-modules iwyu useless, but I'd argue that if we want
iwyu to live within clang-tools-extra, we want that to be aligned with the
semantics of "modules-use", which I believe to be somewhat different;
again, nothing is a show-stopper here, but I'd expect a significant amount
of work.

Finally, given the current rate of tooling contributions across clang-tidy
/ clang-format / tooling / refactoring, and the number of upstream
reviewers we have, I'd additionally expect the process to be rather slow;
for example, the refactoring contributions have a much higher priority
currently, and even those often take (imo) too long to be reviewed
(partially my fault :)

With all that said, I don't want to discourage you from trying, but I want
to set clear expectations - it might feel / look like a rewrite of iwyu
from scratch.

Cheers,
/Manuel

On Tue, Sep 5, 2017 at 3:20 AM Volodymyr Sapsai via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> As another include-what-you-use maintainer I support the proposal. I am
> doing so solely in my personal capacity and am not representing any third
> parties.
>
> Regards,
> Volodymyr
> On Mon, Sep 4, 2017 at 13:41 Kim Gräsman via cfe-dev <
> cfe-dev at lists.llvm.org> wrote:
>
>> Hi all,
>>
>> This is a proposal to integrate include-what-you-use [1] into
>> clang-tools-extra.
>>
>> # Background
>> The include-what-you-use tool analyzes #includes in C and C++ files and
>> recommends how to improve them. The goal is to capture symbol
>> dependencies in
>> code and produce the minimal set of #includes to satisfy these symbol
>> dependencies. For more information you can check the project site [2],
>> docs, and
>> presentation from 2010 LLVM Developers' Meeting [3].
>>
>> # Benefits
>> Migration to clang-tools-extra doesn't come without a cost, so I want to
>> list
>> some of the benefits this move yields.
>>
>> ## For Clang community
>> * Ability to reuse some of IWYU analysis for other purposes. Currently
>> IWYU is
>>   distributed as a CLI tool and has no API but it is possible to split
>> out a
>>   separate library. I think there could be some integration potential
>> with the
>>   budding refactoring tools, for example.
>> * More community input in deciding further IWYU direction to help it to
>> be more
>>   useful for various parties.
>>
>> ## For include-what-you-use users
>> * Easier distribution and use. For users already using other Clang tools
>> it
>>   should be easier to use IWYU as any other Clang tool. I also expect it
>> to make
>>   life easier for people packaging include-what-you-use for various *nix
>>   distributions.
>> * Moving the tool towards consistency with other Clang tools.
>>
>> ## For include-what-you-use project
>> * Exposure to more users.
>> * Easier release process. Instead of releasing IWYU separately, it could
>> be
>>   bundled with LLVM+Clang releases. It shouldn't incur more work for
>> LLVM+Clang
>>   releases as the main complexity comes from tracking different branches
>> and
>>   building binaries for different platforms.
>> * More resiliency as the project becomes more community-owned instead of
>>   personally-owned.
>>
>> # Potential downsides
>> When new Clang sub-projects are proposed, one of the most common concerns
>> is the
>> maintenance burden. Dumping the code and walking away to let the community
>> support the code is unacceptable. The longevity of the project
>> demonstrates
>> commitment to maintaining the project. The history on GitHub shows that
>> include-what-you-use is not a passing fancy that will be discarded and
>> forgotten
>> in a week or two.
>>
>> What is your opinion, is there value in having include-what-you-use in
>> clang-tools-extra?
>>
>> Thanks for any input,
>> - Kim
>>
>> [1] https://github.com/include-what-you-use/include-what-you-use
>> [2] https://include-what-you-use.org/
>> [3] http://llvm.org/devmtg/2010-11/
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