[Bug c++/101013] New: Rejects-valid for alias template in a different namespace with a lambda in unevaluated context

[Bug c++/101013] New: Rejects-valid for alias template in a different namespace with a lambda in unevaluated context

[tartanllama at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101013

            Bug ID: 101013
           Summary: Rejects-valid for alias template in a different
                    namespace with a lambda in unevaluated context
           Product: gcc
           Version: 11.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tartanllama at gmail dot com
  Target Milestone: ---

Code:
namespace ns {
  template <class T>
  using void_t = decltype([]{}());
}

template<class T>
struct oh_no {
    using type = ns::void_t<T>;
};

Compiler output:
<source>:8:22: error: '<expression error>' in namespace 'ns' does not name a
type
    8 |     using type = ns::void_t<T>;
      |                      ^~~~~~~~~

Expected behaviour: 
Compile cleanly

Additional information:
The code compiles if oh_no and void_t are in the same namespace

GCC version and configuration options:
GCC 11.1.0
../gcc-11.1.0/configure --prefix=/opt/compiler-explorer/gcc-build/staging
--build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
--disable-bootstrap --enable-multiarch --with-abi=m64
--with-multilib-list=m32,m64,mx32 --enable-multilib --enable-clocale=gnu
--enable-languages=c,c++,fortran,ada,go,d --enable-ld=yes --enable-gold=yes
--enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-linker-build-id
--enable-lto --enable-plugins --enable-threads=posix
--with-pkgversion=Compiler-Explorer-Build

Command line: 
-std=c++20

Compiler explorer link:
https://godbolt.org/z/EYsbbjodj

[Bug c++/101013] Rejects-valid for alias template in a different namespace with a lambda in unevaluated context

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101013

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2021-06-10
             Status|UNCONFIRMED                 |NEW
           Keywords|                            |rejects-valid
                 CC|                            |mpolacek at gcc dot gnu.org

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Thanks for the report, confirmed.

[Bug c++/101013] Rejects-valid for alias template in a different namespace with a lambda in unevaluated context

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101013

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |14.0

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Fixed on the trunk for GCC 14 by the recent lambda template patches.