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From: "eric.niebler at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/109781] New: erroneous error "lambda-expression in template
 parameter type" for tparam lambda returning a lambda
Date: Mon, 08 May 2023 21:35:10 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 14.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109781

            Bug ID: 109781
           Summary: erroneous error "lambda-expression in template
                    parameter type" for tparam lambda returning a lambda
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: eric.niebler at gmail dot com
  Target Milestone: ---

template <auto A =3D []{ return []{}; }>
struct C {};


... on trunk with `-std=3Dc++20` results in:

<source>: In lambda function:
<source>:1:31: error: lambda-expression in template parameter type
    1 | template <auto A =3D []{ return []{}; }>
      |                               ^
Compiler returned: 1


I don't know of a reason why this code should be rejected.=