[cfe-dev] Invariant layout between clang-format versions?

[Nico Weber via cfe-dev]

On Wed, Jun 21, 2017 at 4:15 AM, Daniel Jasper via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> I don't think there is a useful way of doing this. If you want developers
> to get the same layout, they have to use the same version of the tool. You
> can assume that every single version change leads to a different layout
> somewhere, or else we wouldn't be making the change. Often these changes
> affect a rare corner case of the syntax, but in a reasonably large
> codebase, they are still always triggered. Is it impractical to ship the
> same version of clang-format to all contributors? clang-format is
> reasonably small and you could just check in the version that the CI uses
> into your repository for everyone to use. That also enables you to update
> that version together with the formatting changes that it entails.
>
> However, I would also argue that a format check on CI builds is not
> useful. The polly project inside LLVM does that and it seems rather
> painful. Instead, verify that the changed version of a file adheres to what
> clang-format produces at the time the change is submitted. This is what
> Chromium and other large projects do and has proven to be effective. Then,
> even if the versions differ a bit, there won't be unnecessary churn as a
> formatting change is always bundled with an actually code change.
>

To add some more detail: We run `git diff -U0` to get a diff of the current
branch with trunk and then pipe that into clang-format-diff.py -i from the
LLVM tree, which then formats only the bits of each file that have been
modified.

In a presubmit, we do the same thing (without -i) and check
that clang-format-diff.py produces no output.


>
> On Tue, Jun 20, 2017 at 9:37 PM, Jonathan Müller via cfe-dev <
> cfe-dev at lists.llvm.org> wrote:
>
>> On 20.06.2017 21:20, Pim Schellart via cfe-dev wrote:
>>
>>> Dear Clang Developers,
>>>
>>> this may not be the right place to ask this question so please redirect
>>> me if I’m mistaken.
>>>
>>> We are using clang-format for automatic code layout within our project.
>>> A problem we are facing is that developers have different versions of
>>> clang-format installed.
>>> Even with identical style configuration this results in different
>>> output, leading to unnecessary diffs.
>>>
>>> While this can be fixed by mandating a specific clang-format version,
>>> this may not be practical.
>>> It would be helpful if one could pin a particular layout behavior in a
>>> forwards compatible way.
>>>
>>> If that is not possible, it would be nice to know when version changes
>>> result in layout changes.
>>> E.g. should we mandate version 5.0.0 or is 5.0.x or even 5.x enough?
>>>
>>> Thanks in advance.
>>>
>>> Kind regards,
>>>
>>> Pim Schellart
>>> _______________________________________________
>>> cfe-dev mailing list
>>> cfe-dev at lists.llvm.org
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>>>
>>>
>> I have the issue as well, I used to have a clang-format checker on my CI
>> builds, but this was annoying as my clang version updates more often than
>> the one on CI, leading to inconsistencies and thus failed builds.
>>
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>
>
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