[llvm-dev] Widescale clang-tidy (or similar) based cleanup

[David Blaikie via llvm-dev]

On Fri, Apr 7, 2017 at 3:14 PM Adrian Prantl <aprantl at apple.com> wrote:

>
> > On Apr 7, 2017, at 3:05 PM, David Blaikie via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> >
> > There have been some efforts recently to use clang-tidy or similar
> automated refactoring to make project-wide cleanups/improvements to the
> LLVM codebase that appear to me to be a bit out of character with the sort
> of changes & philosophies that have been applied in the past.
> >
> > I think there are a few issues at hand which I'll try to summarize:
> >
> > * Churn/blame-convenience:
> > Previously, large scale changes (classically whitespace cleanup, with
> things like clang-format) have been rejected or discouraged due to the risk
> of making it harder to find the original source of a semantic change.
> > I'm not too wedded to this issue myself, but it did seem to be the
> status-quo previously so I'm curious to better understand if/how people see
> this applying or not, to more semantic changes.
>
> Personally I think that this is a shortcoming of one's tooling if this is
> a problem. Many git-blame viewers allow you to roll back to the previous
> revision at the current line at one keypress.
>
> >
> > * Efficiency:
> > Sending individual or even batched reviews for automated changes like
> this seems inefficient. I'd rather see, for example, an email to llvm-dev
> to discuss whether a particular change makes sense to make across the
> project (ie: does the LLVM project want to cleanup all instances of classic
> for to range-based-for when clang-tidy can do so?) and then not send the
> individual changes for review, but commit them directly where possible. (if
> the person doing this automated cleanup doesn't have permission, yeah, send
> it out and reference the original discussion thread).
>
> I think it makes sense to send out a phabricator review per kind of
> clang-tidy change, i.e., one patch that performs the same kind of change
> all over the project. Having only one kind of transformation per review
> will make it really easy to skim over the patch and detect situations where
> clang-tidy changes the code for the worse.
>

Reckon it's worth elevating these reviews to llvm-dev rather than only
llvm-commits? (in effect what I'd expect to see is a "hey, thinking about
applying this pattern-based* cleanup - here are some examples of what it
does, the corner cases, cases it doesn't handle, etc (and, as an aside, the
attached patch shows the changes created by applying this tool to all of
LLVM (or LLVM+Clang, etc))")

Anyone have opinions on whether llvm-dev would be a sufficient medium to
approve automated cleanup of other subprojects? (Clang? compiler-rt? lld?
lldb?). Or would it be necessary to have a discussion aobut each
subproject? (roughly I feel like LLVM+Clang are close enough together that
a single approval would suffice there at least - but maybe Clang devs**
have other ideas... )

*thanks, Reid, for that choice of terminology

** Pure Clang devs notably not included in this email thread...


>
> -- adrian
> >
> > Some points of comparison: sometimes there's similar cleanup done in a
> non-automated fashion as Mehdi pointed out in one of the threads I brought
> this up (see this thread:
> http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20170403/443547.html
> ). Usually some amount of cleanup has been acceptable if the code was
> generally being churned anyway (eg: clang-formatting a file so it's
> consistent, before doing major surgery to it anyway, so the surgical
> changes don't create formatting inconsistencies), or as a result of a new
> API change (add a range-based accessor then fix up existing call sites to
> use range-based-for). I'd also not be surprised by a whitespace cleanup
> shortly after new code was committed - and have done this myself "oops,
> forgot to format my commit, here's a new commit that does the formatting".
> That seems different to me from these wider-scale cleanups.
> >
> > I think I'm personally mostly in favor of this sort of stuff (though I
> think I would like some community buy-in to sign off project-wide on each
> clang-tidy rule/pattern/etc that's going to be applied) but it does seem
> new/different from the way some things have been done in the past so I'm
> curious how other people think about the differences/similarities/guiding
> principles.
> >
> > - David
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
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