[Bug c++/105518] New: [rejects valid] nested lambda using an outer type alias fails with constexpr integer in that alias

[Bug c++/105518] New: [rejects valid] nested lambda using an outer type alias fails with constexpr integer in that alias

[leventyilmaz at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105518

            Bug ID: 105518
           Summary: [rejects valid] nested lambda using an outer type
                    alias fails with constexpr integer in that alias
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: leventyilmaz at gmail dot com
  Target Milestone: ---

The following valid code is fails to compile. 

https://godbolt.org/z/v1sd9snGx

// Simple run-time to compile-time integer conversion:
template<class F>
auto toStatic(int i, F f) {
    switch(i) {
        case 0: return f( std::integral_constant<int, 0>{} );
        case 1: return f( std::integral_constant<int, 1>{} );
        case 2: return f( std::integral_constant<int, 2>{} );
        default: assert("too big");
    }
}


// example types:
struct Base {
    virtual void show() const = 0;
};
template <size_t I> struct F {
    template <size_t J> struct K : Base {
        void show() const override {
            std::cout << I << " " << J << std::endl;
        }
    };
};


// nested lambda complains "I" is not captured
// even though it is only being used at compile-time
void show(int i, int j) {
    return toStatic(i, [j](auto I) {
        using A = F<I>;
        // using A = F<decltype(I)::value>; // this works
        return toStatic(j, [](auto J)  {
            using impl = typename A::template K<J>;
            impl{}.show();
        });
    });
}


source>:32:19: error: 'I' is not captured
   32 |             using impl = typename A::template K<J>;
      |                   ^~~~

[Bug c++/105518] [rejects valid] nested lambda using an outer type alias fails with constexpr integer in that alias

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105518

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Created attachment 53819
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53819&action=edit
full testcase

[Bug c++/105518] [rejects valid] nested lambda using an outer type alias fails with constexpr integer in that alias

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105518

--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:be124477b38a71ba8ba0b24d859ae764bb44a4eb

commit r13-4729-gbe124477b38a71ba8ba0b24d859ae764bb44a4eb
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Dec 15 15:54:31 2022 -0500

    c++: local alias in typename in lambda [PR105518]

    We substitute the qualifying scope of a TYPENAME_TYPE directly using
    tsubst_aggr_type (so that we can pass entering_scope=true) instead of
    going through tsubst, which means we don't properly reuse typedefs
    during this substitution.  This ends up causing us to reject the below
    testcase because we substitute the TYPENAME_TYPE alias::type as if it
    were written without the A<t> alias, and thus we expect the non-capturing
    lambda to capture t.

    This patch fixes this by making tsubst_aggr_type delegate typedefs
    to tsubst so that get consistently reused, and then adjusting the result
    appropriately if entering_scope is true.  In passing, this refactors
    tsubst_aggr_type into two functions, one that's intended to be called
    directly and a more minimal one that's intended to be called only from
    the RECORD/UNION/ENUMERAL_TYPE cases of tsubst (and contains only the
    necessary bits for that call site).

            PR c++/105518

    gcc/cp/ChangeLog:

            * pt.cc (tsubst_aggr_type): Handle typedefs by delegating to
            tsubst and adjusting the result if entering_scope.  Split out
            the main part of the function into ...
            (tsubst_aggr_type_1) ... here.
            (tsubst): Use tsubst_aggr_type_1 instead of tsubst_aggr_type.
            Handle TYPE_PTRMEMFUNC_P RECORD_TYPEs here instead of in
            tsubst_aggr_type_1.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp0x/lambda/lambda-alias1.C: New test.

[Bug c++/105518] [rejects valid] nested lambda using an outer type alias fails with constexpr integer in that alias

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105518

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |13.0
         Resolution|---                         |FIXED
           Assignee|unassigned at gcc dot gnu.org      |ppalka at gcc dot gnu.org
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |ppalka at gcc dot gnu.org

--- Comment #3 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 13, thanks for the bug report.