https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101707
Bug ID: 101707
Summary: deduction of template argument fails via base class
Product: gcc
Version: 11.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: baber.nwz at gmail dot com
Target Milestone: ---
The following program fails to compile with GCC 11.2 but compiles with clang
(from version 12 to 3), MSVC (2015, 2017, 2019) and ICC:
template<typename T>
struct S {};
struct A : S<int> {};
struct B : S<float> {};
struct C : A, B, S<double> {};
template<typename T, template <typename> class TPL>
void f(TPL<T>& a)
{
}
void g()
{
A a;
B b;
C c;
f<int>(a); // OK
f<float>(b); // OK
f<double>(c); // ERROR
}
The compiler gives the following output:
source>: In function 'void g()':
<source>:21:14: error: no matching function for call to 'f<double>(C&)'
21 | f<double>(c);
| ~~~~~~~~~^~~
<source>:9:6: note: candidate: 'template<class T, template<class> class TPL>
void f(TPL<T>&)'
9 | void f(TPL<T>& a)
| ^
<source>:9:6: note: template argument deduction/substitution failed:
<source>:21:14: note: 'TPL<T>' is an ambiguous base class of 'C'
21 | f<double>(c);
| ~~~~~~~~~^~~
With the supplied template parameter (double), the base class is definitely not
ambiguous.
https://godbolt.org/z/EKn16o46a
