[cfe-dev] Wish: Split Wunused-lambda-capture

[Nico Weber via cfe-dev]

This was discussed when the warning was added. I felt the same way, but
Aaron convinced me that this is short ("short") term pain:
http://lists.llvm.org/pipermail/cfe-commits/Week-of-Mon-20170116/183259.html
https://marc.info/?l=cfe-commits&m=148521057007058&w=2
https://marc.info/?l=cfe-commits&m=148546938216504&w=2

We disabled the warning for now in Chromium.

On Thu, Apr 5, 2018 at 12:50 PM, Tobias Hahn via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> I did that as well as posting my wish here, let's see...
>
> T
>
> > Am 05.04.2018 um 17:54 schrieb Keane, Erich via cfe-dev <
> cfe-dev at lists.llvm.org>:
> >
> > " Since I don't expect MSVC to be standards compliant any time soon,"
> >
> > I think you may wish to report this as a bug to the MSVC team.  They
> have been REALLY good about fixing standards compliance issues in the past
> two years or so.
> >
> > -----Original Message-----
> > From: cfe-dev [mailto:cfe-dev-bounces at lists.llvm.org] On Behalf Of
> Tobias Hahn via cfe-dev
> > Sent: Thursday, April 5, 2018 8:50 AM
> > To: cfe-dev at lists.llvm.org
> > Subject: [cfe-dev] Wish: Split Wunused-lambda-capture
> >
> > In migrating our codebase to Xcode 9.3, I came across the new warning
> -Wunused-lambda-capture. This seems like a helpful warning to enable; yet
> unfortunately I cannot due to incompatibility with MSVC.
> >
> > The problem is that it warns on the following code (
> https://godbolt.org/g/HDiqR8):
> >
> > int times2(int num) {
> >  const int two = 2;
> >  auto multiply = [two](int i) { return i * two; };
> >  return multiply(num);
> > }
> >
> > Per the standard, it is unnecessary to capture `two` because it is an
> integral constant. MSVC doesn't know about this, and throws C3493 (variable
> cannot be implicitly captured) if I remove `two` from the capture clause to
> fix clang's -Wunused-lambda-capture (https://godbolt.org/g/VNNfqT).
> >
> > Since I don't expect MSVC to be standards compliant any time soon, it
> would be great if this warning could be split into two warnings:
> >
> > -Wunused-lambda-capture would only warn on truly unused captures, but
> not captures that are merely unnecessary (but still used as in the example
> above).
> >
> > -Wunnecessary-lambda-capture would warn on redundant explicit captures
> (as in the example above).
> >
> > Thanks for considering my wish and making clang even better!
> >
> > Tobias
> >
> > Ableton AG, Schoenhauser Allee 6-7, 10119 Berlin, Germany Sitz
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> >
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>
> Ableton AG, Schoenhauser Allee 6-7, 10119 Berlin, Germany
> Sitz (Registered Office) Berlin, Amtsgericht Berlin-Charlottenburg, HRB
> 72838
> Vorstand (Management Board): Gerhard Behles, Jan Bohl
> Vorsitzender des Aufsichtsrats (Chair of the Supervisory Board): Uwe Struck
>
>
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