https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104867
Bug ID: 104867
Summary: Base class matching ignores type of `auto` template
parameter
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: pdimov at gmail dot com
Target Milestone: ---
The following program
```
enum class Foo
{
A1
};
enum class Bar
{
B1
};
template <auto EnumVal> struct enum_
{
};
template<class...> struct list {};
struct enum_type_map: list<enum_<Foo::A1>, int>, list<enum_<Bar::B1>, double>
{};
template<class V> V f( list<enum_<Bar::B1>, V> const& )
{
return {};
}
int main()
{
f( enum_type_map() );
}
```
yields
```
<source>: In function 'int main()':
<source>:26:6: error: no matching function for call to 'f(enum_type_map)'
26 | f( enum_type_map() );
| ~^~~~~~~~~~~~~~~~~~~
<source>:19:21: note: candidate: 'template<class V> V f(const
list<enum_<Bar::B1>, V>&)'
19 | template<class V> V f( list<enum_<Bar::B1>, V> const& )
| ^
<source>:19:21: note: template argument deduction/substitution failed:
<source>:26:6: note: 'const list<enum_<Bar::B1>, V>' is an ambiguous base
class of 'enum_type_map'
26 | f( enum_type_map() );
| ~^~~~~~~~~~~~~~~~~~~
```
which is caused by `A1` and `B1` having the same value 0, even though their
types differ. (https://godbolt.org/z/3854zrY7x)
Clang successfully compiles the code (https://godbolt.org/z/eKEdf1zdo).
This is a distilled version of a bug report against `mp_map_find` from Mp11:
https://github.com/boostorg/mp11/issues/72
