[Bug c++/79070] Unhelpful error message for ambiguous type in template parameter

[Bug c++/79070] Unhelpful error message for ambiguous type in template parameter

[barry.revzin at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79070

Barry Revzin <barry.revzin at gmail dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |barry.revzin at gmail dot com

--- Comment #3 from Barry Revzin <barry.revzin at gmail dot com> ---
Here are a few more cases, reduced from a larger example that took me a very
long time to understand. I'm adding as comments the compile error emitted for
each invalid use:

namespace N {
    template <typename T, typename U, typename V> struct Something { };
    template <typename> concept C = true;
    template <typename> struct X { };
}

using namespace N;
template <typename T> struct Something { };

// parse error in template argument list
static_assert(C<Something<int>>);

// template argument 1 is invalid
X<Something<int>> x;

// reference to Something is ambiguous
using T = Something<int>;

In the last case, the compiler error is super clear and it is obvious what the
error is. In the other two, not so much.

[Bug c++/79070] Unhelpful error message for ambiguous type in template parameter

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79070

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|2017-02-08 00:00:00         |2021-3-30

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
For Barry's example, Clang gives the exact same error in all three cases, which
is much more useful:


79070.C:11:17: error: reference to 'Something' is ambiguous
static_assert(C<Something<int>>);
                ^
79070.C:8:30: note: candidate found by name lookup is 'Something'
template <typename T> struct Something { };
                             ^
79070.C:2:58: note: candidate found by name lookup is 'N::Something'
    template <typename T, typename U, typename V> struct Something { };
                                                         ^
79070.C:14:3: error: reference to 'Something' is ambiguous
X<Something<int>> x;
  ^
79070.C:8:30: note: candidate found by name lookup is 'Something'
template <typename T> struct Something { };
                             ^
79070.C:2:58: note: candidate found by name lookup is 'N::Something'
    template <typename T, typename U, typename V> struct Something { };
                                                         ^
79070.C:17:11: error: reference to 'Something' is ambiguous
using T = Something<int>;
          ^
79070.C:8:30: note: candidate found by name lookup is 'Something'
template <typename T> struct Something { };
                             ^
79070.C:2:58: note: candidate found by name lookup is 'N::Something'
    template <typename T, typename U, typename V> struct Something { };
                                                         ^
3 errors generated.

[Bug c++/79070] Unhelpful error message for ambiguous type in template parameter

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79070

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

           What    |Removed                     |Added
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                 CC|                            |harry.linxd at gmail dot com

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 97922 has been marked as a duplicate of this bug. ***