* [Bug c++/94057] [9/10 Regression] -std=gnu++20 causes failure naming nested templated class since r9-4536
[not found] <bug-94057-4@http.gcc.gnu.org/bugzilla/>
@ 2020-03-12 11:58 ` jakub at gcc dot gnu.org
2020-03-12 17:27 ` mpolacek at gcc dot gnu.org
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From: jakub at gcc dot gnu.org @ 2020-03-12 11:58 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94057
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|9.3 |9.4
--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 9.3.0 has been released, adjusting target milestone.
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2020-03-12 11:58 ` [Bug c++/94057] [9/10 Regression] -std=gnu++20 causes failure naming nested templated class since r9-4536 jakub at gcc dot gnu.org
@ 2020-03-12 17:27 ` mpolacek at gcc dot gnu.org
2020-03-12 17:43 ` mpolacek at gcc dot gnu.org
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From: mpolacek at gcc dot gnu.org @ 2020-03-12 17:27 UTC (permalink / raw)
To: gcc-bugs
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--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Not relate to parameter packs. Also happens with normal member functions:
template <typename T> class A {
template <typename U> class B {
B(A<T>::B<U>&);
void fn(A<T>::B<U> &);
};
};
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2020-03-12 11:58 ` [Bug c++/94057] [9/10 Regression] -std=gnu++20 causes failure naming nested templated class since r9-4536 jakub at gcc dot gnu.org
2020-03-12 17:27 ` mpolacek at gcc dot gnu.org
@ 2020-03-12 17:43 ` mpolacek at gcc dot gnu.org
2020-03-12 23:16 ` mpolacek at gcc dot gnu.org
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From: mpolacek at gcc dot gnu.org @ 2020-03-12 17:43 UTC (permalink / raw)
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--- Comment #4 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
The root cause isn't the C++20 feature it seems. The following version with
explicit 'typename' is rejected, but compiles fine with clang/icc:
template <typename T> class A {
template <typename U> class B {
B(typename A<T>::B<U>&);
void fn(typename A<T>::B<U> &);
};
};
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--- Comment #5 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
(We accept it when the template keyword is added: "typename A<T>::template
B<U>".)
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From: cvs-commit at gcc dot gnu.org @ 2020-03-26 22:47 UTC (permalink / raw)
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--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Marek Polacek <mpolacek@gcc.gnu.org>:
https://gcc.gnu.org/g:517f5356bb0ca717f51e937be880e38a828edbf7
commit r10-7403-g517f5356bb0ca717f51e937be880e38a828edbf7
Author: Marek Polacek <polacek@redhat.com>
Date: Wed Mar 18 19:28:14 2020 -0400
c++: DR1710, template keyword in a typename-specifier [PR94057]
Consider
template <typename T> class A {
template <typename U> class B {
void fn(typename A<T>::B<U>);
};
};
which is rejected with
error: 'typename A<T>::B' names 'template<class T> template<class U> class
A<T>::B', which is not a type
whereas clang/icc/msvc accept it.
"typename A<T>::B<U>" is a typename-specifier. Sadly, our comments
don't mention it anywhere, because the typename-specifier wasn't in C++11;
it was only added to the language in N1376. Instead, we handle it as
an elaborated-type-specifier (not a problem thus far). So we get to
cp_parser_nested_name_specifier_opt which has a loop that breaks if we
don't see a < or ::, but that means we can -- tentatively -- parse even
B<U> which is not a nested-name-specifier (it doesn't end with a ::).
I think this should compile because [temp.names]/4 says: "In a qualified-id
used as the name in a typename-specifier, elaborated-type-specifier,
using-declaration, or class-or-decltype, an optional keyword template
appearing at the top level is ignored.", added in DR 1710. Also see
DR 1812.
This issue on its own is not a significant problem or a regression.
However, in C++20, the typename here becomes optional, and so this test
is rejected in C++20, but accepted in C++17:
template <typename T> class A {
template <typename U> class B {
void fn(A<T>::B<U>);
};
};
Here we morph A<T>::B<U> into a typename-specifier, but that happens
in cp_parser_simple_type_specifier and we never handle it as above.
To fake the template keyword I'm afraid we need to use
cp_parser_template_id
with template_keyword_p=true as in the patch below. The tricky thing
is to avoid breaking concepts.
To handle DR 1710, I made cp_parser_nested_name_specifier_opt assume that
when we're naming a type, the template keyword is present, too. That
revealed a bug: DR 1710 also says that the template keyword can be followed
by an alias template, but we weren't prepared to handle that.
alias-decl?.C
exercise this.
gcc/cp:
DR 1710
PR c++/94057 - template keyword in a typename-specifier.
* parser.c (check_template_keyword_in_nested_name_spec): New.
(cp_parser_nested_name_specifier_opt): Implement DR1710, optional
'template'. Call check_template_keyword_in_nested_name_spec.
(cp_parser_simple_type_specifier): Assume that a <
following a qualified-id in a typename-specifier begins
a template argument list.
gcc/testsuite:
DR 1710
PR c++/94057 - template keyword in a typename-specifier.
* g++.dg/cpp1y/alias-decl1.C: New test.
* g++.dg/cpp1y/alias-decl2.C: New test.
* g++.dg/cpp1y/alias-decl3.C: New test.
* g++.dg/parse/missing-template1.C: Update dg-error.
* g++.dg/parse/template3.C: Likewise.
* g++.dg/template/error4.C: Likewise.
* g++.dg/template/meminit2.C: Likewise.
* g++.dg/template/dependent-name5.C: Likewise.
* g++.dg/template/dependent-name7.C: New test.
* g++.dg/template/dependent-name8.C: New test.
* g++.dg/template/dependent-name9.C: New test.
* g++.dg/template/dependent-name10.C: New test.
* g++.dg/template/dependent-name11.C: New test.
* g++.dg/template/dependent-name12.C: New test.
* g++.dg/template/dependent-name13.C: New test.
* g++.dg/template/dr1794.C: New test.
* g++.dg/template/dr314.C: New test.
* g++.dg/template/dr1710.C: New test.
* g++.dg/template/dr1710-2.C: New test.
* g++.old-deja/g++.pt/crash38.C: Update dg-error.
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2020-11-10 17:38 ` [Bug c++/94057] [9 " redi at gcc dot gnu.org
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From: mpolacek at gcc dot gnu.org @ 2020-03-26 22:50 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94057
Marek Polacek <mpolacek at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |FIXED
Status|ASSIGNED |RESOLVED
--- Comment #7 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Fixed. I don't think I want to backport this one. To make it work with G++ 9,
add the template keyword.
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From: redi at gcc dot gnu.org @ 2020-11-10 17:38 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94057
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |redi at gcc dot gnu.org
--- Comment #8 from Jonathan Wakely <redi at gcc dot gnu.org> ---
*** Bug 65943 has been marked as a duplicate of this bug. ***
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2020-11-10 17:38 ` [Bug c++/94057] [9 " redi at gcc dot gnu.org
@ 2021-08-23 0:13 ` pinskia at gcc dot gnu.org
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From: pinskia at gcc dot gnu.org @ 2021-08-23 0:13 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94057
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|9.4 |10.0
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From: redi at gcc dot gnu.org @ 2021-08-23 10:34 UTC (permalink / raw)
To: gcc-bugs
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Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |smw at gcc dot gnu.org
--- Comment #9 from Jonathan Wakely <redi at gcc dot gnu.org> ---
*** Bug 84186 has been marked as a duplicate of this bug. ***
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