[Bug c++/99213] New: Incorrect pretty printing of local class type when type's context contains a class template specialization

[Bug c++/99213] New: Incorrect pretty printing of local class type when type's context contains a class template specialization

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99213

            Bug ID: 99213
           Summary: Incorrect pretty printing of local class type when
                    type's context contains a class template
                    specialization
           Product: gcc
           Version: 10.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ppalka at gcc dot gnu.org
  Target Milestone: ---

Consider:

template <class T>
struct A {
  template <class U>
  static auto f() {
    struct S{};
    return S{};
  }
};

using type = void;
using type = decltype(A<int>::f<char>()); // A<int>::f<char>()::S


For this testcase, GCC 10/11 outputs:

<source>:11:7: error: conflicting declaration 'using type = struct
A<T>::f<char>::S'
   11 | using type = decltype(A<int>::f<char>());
      |       ^~~~

Note that the nested class type 'S' gets pretty printed as 'A<T>::f<char>::S',
i.e. the argument for the template parameter T is missing in the
nested-name-specifier.

GCC 9 outputs:

<source>:11:7: error: conflicting declaration 'using type = struct A<T>::f()
[with U = char; T = int]::S'
   11 | using type = decltype(A<int>::f<char>());
      |       ^~~~

Which isn't perfect either, but importantly all template arguments are shown in
the type.

[Bug c++/99213] Incorrect pretty printing of local class type when type's context contains a class template specialization

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99213

--- Comment #1 from Patrick Palka <ppalka at gcc dot gnu.org> ---
"Started" with r10-7705.

Fixing this is necessary for comprehensible diagnostics when using range
adaptor objects from <ranges>, since their partial application and composition
operators work by returning local lambdas.

[Bug c++/99213] Suboptimal pretty printing of local class type when type's context contains a class template specialization

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99213

--- 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:7fb9a1e929db520fd741e60d84ec1a58581a8299

commit r11-7406-g7fb9a1e929db520fd741e60d84ec1a58581a8299
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Feb 25 16:44:34 2021 -0500

    c++: Fix pretty printing the context of local class [PR99213]

    My r10-7705 patch for PR94521 made us set TFF_NO_FUNCTION_ARGUMENTS when
    pretty printing the function scope of a local class type in order to
    eliminate infinite recursion with a function signature that contains
    decltype([]{}).  But due to the way dump_function_decl works, this
    change regressed our pretty printing of local class types whose context
    contains a class template specialization, as in the testcase below, in
    which we wrongly pretty print the two local types as 'A<T>::f<char>::S1'
    and 'B<T>::f<int>::S2'.

    This patch makes dump_scope pass TFF_NO_TEMPLATE_BINDINGS instead of
    TFF_NO_FUNCTION_ARGUMENTS when pretty printing a function scope.  It
    appears this is the strictly better flag to use: it avoids the infinite
    recursion issue, it restores pretty printing of the function parameter
    list, and it stops dump_function_decl from trying to print a function
    template specialization in its own weird way.

    Summary of pretty printing differences for the below testcase:

      r10-7704:   A<T>::f() [with U = char; T = int]::S1
                  B<T>::f() [with T = int]::S2

      r10-7705:   A<T>::f<char>::S1
                  B<T>::f<int>::S2

      this patch: A<int>::f<char>()::S1
                  B<int>::f()::S2

    gcc/cp/ChangeLog:

            PR c++/99213
            PR c++/94521
            * error.c (dump_scope): Pass TFF_NO_TEMPLATE_BINDINGS instead of
            TFF_NO_FUNCTION_ARGUMENTS when dumping a function scope.

    gcc/testsuite/ChangeLog:

            PR c++/99213
            PR c++/94521
            * g++.dg/diagnostic/local1.C: New test.

[Bug c++/99213] Suboptimal pretty printing of local class type when type's context contains a class template specialization

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99213

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
   Target Milestone|---                         |11.0
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #3 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 11.