[PATCH] D28467: [Sema] Add warning for unused lambda captures

[Aaron Ballman via cfe-commits]

On Jan 18, 2017 7:34 PM, "Akira Hatanaka via Phabricator" <
reviews at reviews.llvm.org> wrote:

ahatanak added a comment.

In https://reviews.llvm.org/D28467#649861, @krasin wrote:

> This change makes Clang hardly incompatible with MSVC++. Consider the
following program:
>
>   #include <stdio.h>
>
>   int main(void) {
>     const int kDelta = 10000001;
>     auto g = [kDelta](int i)
>              {
>                printf("%d\n", i % kDelta);
>              };
>     g(2);
>   }
>
>
> Clang will warn about the unused lambda capture:
>
>   $ clang++ lala.cc -o lala -std=c++14 -Wall -Werror && ./lala
>   lala.cc:5:13: error: lambda capture 'kDelta' is not required to be
captured for use in an unevaluated context [-Werror,-Wunused-lambda-capture]
>     auto g = [kDelta](int i)
>               ^
>   1 error generated.
>


Is kDelta considered to be used in an unevaluated context here? I thought
unevaluated context in c++ means the expression is used as operands of
operators such as typeid and decltype.


It is not used in an unevaluated context -- that is a bug.

~Aaron



Repository:
  rL LLVM

https://reviews.llvm.org/D28467
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