[Bug c++/96560] New: Substitution triggers compile-time error when it shouldn't

[Bug c++/96560] New: Substitution triggers compile-time error when it shouldn't

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96560

            Bug ID: 96560
           Summary: Substitution triggers compile-time error when it
                    shouldn't
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mpolacek at gcc dot gnu.org
  Target Milestone: ---

This triggers the static_assert while it shouldn't, because DR 1227 says "The
substitution proceeds in lexical order and stops when a condition that causes
deduction to fail is encountered."  Compiles with clang++/EDG.

template<bool, typename = void>
struct enable_if { };

template<typename T>
struct enable_if<true, T> {
  using type = T;
};

template<class T>
struct hard_error {
  static_assert(sizeof(T) == 0);
  static inline constexpr bool value = true;
};

template<class T>
struct always_false {
  static inline constexpr bool value = false;
};

template<class T>
int foo (int, typename enable_if<always_false<T>::value, int>::type = 0,
              typename enable_if<hard_error<T>::value, int>::type = 0 )
{
  return 0;
}

template<class T>
char const *foo (long)
{
  return "";
}

int
main ()
{
  char const *sz = foo<int>(0);
}

[Bug c++/96560] Substitution triggers compile-time error when it shouldn't

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96560

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2021-04-28
                 CC|                            |ppalka at gcc dot gnu.org
     Ever confirmed|0                           |1
           Assignee|unassigned at gcc dot gnu.org      |ppalka at gcc dot gnu.org
             Status|UNCONFIRMED                 |ASSIGNED

[Bug c++/96560] Substitution triggers compile-time error when it shouldn't

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96560

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Patch: https://gcc.gnu.org/pipermail/gcc-patches/2021-April/569184.html

[Bug c++/96560] Substitution triggers compile-time error when it shouldn't

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96560

--- 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:b0d73a66ae3962fa83309527d85613d72a6aa43d

commit r12-1398-gb0d73a66ae3962fa83309527d85613d72a6aa43d
Author: Patrick Palka <ppalka@redhat.com>
Date:   Fri Jun 11 16:00:52 2021 -0400

    c++: Substitute into function parms in lexical order [PR96560]

    This makes tsubst_arg_types substitute into a function's parameter types
    in left-to-right instead of right-to-left order, in accordance with DR
1227.

            DR 1227
            PR c++/96560

    gcc/cp/ChangeLog:

            * pt.c (tsubst_arg_types): Rearrange so that we substitute into
            TYPE_ARG_TYPES in forward order while short circuiting
            appropriately.  Adjust formatting.

    gcc/testsuite/ChangeLog:

            * g++.dg/template/sfinae-dr1227.C: New test.

[Bug c++/96560] Substitution triggers compile-time error when it shouldn't

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96560

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED
   Target Milestone|---                         |12.0

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