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From: "ppalka at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/110122] [13/14 Regression] using an aggregate with a member
 variable with a user defined copy constructor in a class NTTP causes capture
 and use of the `this` pointer in a generic lambda to produce the following
 error "-copy ctor- used before its definition"
Date: Mon, 05 Jun 2023 14:08:12 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 13.1.0
X-Bugzilla-Keywords: rejects-valid
X-Bugzilla-Severity: normal
X-Bugzilla-Who: ppalka at gcc dot gnu.org
X-Bugzilla-Status: ASSIGNED
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Message-ID: <bug-110122-4-ZBiK0rPll7@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-110122-4@http.gcc.gnu.org/bugzilla/>
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110122

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2023-06-05
      Known to work|                            |12.3.0
                 CC|                            |ppalka at gcc dot gnu.org
           Keywords|                            |rejects-valid
      Known to fail|                            |13.1.0, 14.0
     Ever confirmed|0                           |1
            Summary|using an aggregate with a   |[13/14 Regression] using an
                   |member variable with a user |aggregate with a member
                   |defined copy constructor in |variable with a user
                   |a class NTTP causes capture |defined copy constructor in
                   |and use of the `this`       |a class NTTP causes capture
                   |pointer in a generic lambda |and use of the `this`
                   |to produce the following    |pointer in a generic lambda
                   |error "-copy constructor-   |to produce the following
                   |used before its definition" |error "-copy ctor- used
                   |                            |before its definition"
   Target Milestone|---                         |13.2
           Assignee|unassigned at gcc dot gnu.org      |ppalka at gcc dot g=
nu.org
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=3D104577
             Status|UNCONFIRMED                 |ASSIGNED

--- Comment #1 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Confirmed, thanks very much for the detailed analysis and reproducer.  Star=
ted
with r13-1045-gcb7fd1ea85feea.

Here's another version of the testcase (with a commented out workaround) th=
at
uses a non-capturing generic lambda and a non-member function:

struct Foo {
    constexpr Foo() =3D default;
    constexpr Foo(Foo const&) {}
};

struct Bar {
    Foo _;

    // Workaround: force Bar's copy ctor to be synthesized early
    // static Bar force_synthesize_copy_ctor(Bar& b) { return b; };
};

template<Bar v>
struct Doppelganger { };

template<Bar v>
void disguise() {
    [](auto){ Doppelganger<v> d; }(0);
};

void execute() {
    disguise<Bar{}>();
}=