[Bug c++/108242] New: '__FUNCTION__' was not declared when used inside a lambda declared inside a template function

[Bug c++/108242] New: '__FUNCTION__' was not declared when used inside a lambda declared inside a template function

[n.eugene536 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108242

            Bug ID: 108242
           Summary: '__FUNCTION__' was not declared when used inside a
                    lambda declared inside a template function
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: n.eugene536 at gmail dot com
  Target Milestone: ---

Target: x86_64-linux-gnu
Broken since gcc 12.1; works fine with gcc <= 11.3

g++ a.cpp -std=c++14

template<class F>
void my_fun()
{
    auto fun = [&](auto res) {
        static constexpr char const* fun_name = __FUNCTION__;
        struct
        {
            constexpr const char* operator()() const { return fun_name; };
        } t;
        t();
    };

    fun(12);
}


int main() {
    my_fun<int>();
}


output: Compilation error
source>:8:63: error: '__FUNCTION__' was not declared in this scope
    8 |             constexpr const char* operator()() const { return fun_name;
};


expected: successful compilation

Works perfectly fine with clang

[Bug c++/108242] '__FUNCTION__' was not declared when used inside a generic (templated) lambda declared inside a template function

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108242

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|'__FUNCTION__' was not      |'__FUNCTION__' was not
                   |declared when used inside a |declared when used inside a
                   |templated lambda declared   |generic (templated) lambda
                   |inside a template function  |declared inside a template
                   |                            |function
      Known to fail|                            |11.3.0

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Reduced slightly more:
template<int F>
void my_fun()
{
    [&](auto) {
        static constexpr char const* fun_name = __func__;
        struct t
        {
            t() { fun_name; };
        } t1;
    }(12);
}

int main() {
    my_fun<1>();
}

[Bug c++/108242] [10/11/12/13 Regression] '__FUNCTION__' was not declared when used inside a generic (templated) lambda declared inside a template function

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108242

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |needs-bisection
   Target Milestone|---                         |10.5
      Known to work|                            |7.1.0
   Last reconfirmed|                            |2022-12-28
            Summary|'__FUNCTION__' was not      |[10/11/12/13 Regression]
                   |declared when used inside a |'__FUNCTION__' was not
                   |generic (templated) lambda  |declared when used inside a
                   |declared inside a template  |generic (templated) lambda
                   |function                    |declared inside a template
                   |                            |function
      Known to fail|                            |8.1.0
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note the original testcase works in GCC 8 to GCC 11 while my testcase in
comment #1 fails with those versions. 
Would be interesting to see what patch broke the original testcase and my
testcase.

[Bug c++/108242] [10/11/12/13 Regression] '__FUNCTION__' was not declared when used inside a generic (templated) lambda declared inside a template function

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108242

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=84925,
                   |                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=82029

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
related to PR 84925 and PR 82029 . The first one was caused by the second one
and the second one was caused by r8-2720-gf44a8dd56f5bfb which I suspect might
have introduced this bug ...

[Bug c++/108242] [10/11/12/13 Regression] '__FUNCTION__' was not declared when used inside a generic (templated) lambda declared inside a template function

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108242

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|needs-bisection             |
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
The original testcase started to be rejected with
r12-4425-g1595fe44e11a969d8ae462212886fb0a87b46226
The second one indeed starting with
r8-2720-gf44a8dd56f5bfbd0596c39693e268ef880c06221

[Bug c++/108242] [10/11/12/13 Regression] '__FUNCTION__' was not declared when used inside a generic (templated) lambda declared inside a template function

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108242

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2

[Bug c++/108242] [10/11/12/13 Regression] '__FUNCTION__' was not declared when used inside a generic (templated) lambda declared inside a template function

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108242

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Makes me wonder why finish_fname returns the IDENTIFIER_NODE rather than the
VAR_DECL when processing_template_decl, though if I comment that out it ICEs.
When DECL_INITIAL is __FUNCTION__ etc. IDENTIFIER_NODE, it is looked up using
lookup_name, which works fine if it is the template function in which
__FUNCTION__ has been referenced (ok e.g. when processing DECL_EXPR of
fun_name).  But for some reason
we don't find that VAR_DECL as local specialization and trigger
                  /* This can happen for a variable used in a
                     late-specified return type of a local lambda, or for a
                     local static or constant.  Building a new VAR_DECL
                     should be OK in all those cases.  */
                  r = tsubst_decl (t, args, complain);
                  if (local_specializations)
                    /* Avoid infinite recursion (79640).  */
                    register_local_specialization (r, t);
                  if (decl_maybe_constant_var_p (r))
                    {
                      /* We can't call cp_finish_decl, so handle the
                         initializer by hand.  */
                      tree init = tsubst_init (DECL_INITIAL (t), r, args,
                                               complain, in_decl);
which then doesn't work, either it finds a different __FUNCTION__ than it
should, e.g. for:
bool v;

template<class F>
void my_fun()
{
    auto fun = [&](auto res) {
        static constexpr char const* fun_name = __FUNCTION__;
        struct
        {
            constexpr const char* operator()() const { return v ? __FUNCTION__
: fun_name; };
        } t;
        t();
    };
    fun(12);
}
or it doesn't find it at all.

[Bug c++/108242] [10/11/12/13 Regression] '__FUNCTION__' was not declared when used inside a generic (templated) lambda declared inside a template function

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108242

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=105809
                 CC|                            |mpolacek at gcc dot gnu.org

--- Comment #6 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
I was just looking into bug 105809 which looks like the same problem except
with __PRETTY_FUNCTION__.

[Bug c++/108242] [10/11/12/13 Regression] '__FUNCTION__' was not declared when used inside a generic (templated) lambda declared inside a template function

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108242

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Sorry, above doesn't compile, but
template<class F>
void my_fun()
{
  auto fun = [&](auto res) {
    static constexpr char const* fun_name = __PRETTY_FUNCTION__;
    struct
    {
      constexpr const char* operator()() const { constexpr char const*
fun_name2 = __PRETTY_FUNCTION__; return fun_name; };
    } t;
    t();
  };

  fun(12);
}


int main() {
  my_fun<int>();
}

ICEs and compiles fine with G++ 11.x.

[Bug c++/108242] [10/11/12/13 Regression] '__FUNCTION__' was not declared when used inside a generic (templated) lambda declared inside a template function

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108242

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |jason at gcc dot gnu.org

[Bug c++/108242] [10/11/12/13 Regression] '__FUNCTION__' was not declared when used inside a generic (templated) lambda declared inside a template function

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108242

--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Jason Merrill <jason@gcc.gnu.org>:

https://gcc.gnu.org/g:b323f52ccf966800297b0520b9e1d4b3951db525

commit r13-6722-gb323f52ccf966800297b0520b9e1d4b3951db525
Author: Jason Merrill <jason@redhat.com>
Date:   Thu Mar 16 15:11:25 2023 -0400

    c++: generic lambda, local class, __func__ [PR108242]

    Here we are trying to do name lookup in a deferred instantiation of t() and
    failing to find __func__.  tsubst_expr already tries to instantiate members
    of local classes, but was failing with the partial instantiation of generic
    lambdas.

            PR c++/108242

    gcc/cp/ChangeLog:

            * pt.cc (tsubst_expr) [TAG_DEFN]: Handle partial instantiation.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp1y/lambda-generic-func2.C: New test.

[Bug c++/108242] [10/11/12 Regression] '__FUNCTION__' was not declared when used inside a generic (templated) lambda declared inside a template function

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108242

--- Comment #9 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-12 branch has been updated by Jason Merrill
<jason@gcc.gnu.org>:

https://gcc.gnu.org/g:890d711a2477119a34cf435f6159b6253b124374

commit r12-9437-g890d711a2477119a34cf435f6159b6253b124374
Author: Jason Merrill <jason@redhat.com>
Date:   Thu Mar 16 15:11:25 2023 -0400

    c++: generic lambda, local class, __func__ [PR108242]

    Here we are trying to do name lookup in a deferred instantiation of t() and
    failing to find __func__.  tsubst_expr already tries to instantiate members
    of local classes, but was failing with the partial instantiation of generic
    lambdas.

            PR c++/108242

    gcc/cp/ChangeLog:

            * pt.cc (tsubst_expr) [TAG_DEFN]: Handle partial instantiation.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp1y/lambda-generic-func2.C: New test.

[Bug c++/108242] [11 Regression] '__FUNCTION__' was not declared when used inside a generic (templated) lambda declared inside a template function

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108242

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|10.5                        |11.5

--- Comment #10 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 10 branch is being closed.