https://bugs.llvm.org/show_bug.cgi?id=38431
Bug ID: 38431
Summary: "too many template arguments for class template"
disallows sensible empty-parameter-pack instantiation
Product: clang
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: C++
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected]
If I compile this:
template <typename> struct X {};
template <typename... Ts> void f ( X<int, Ts...> ) {}
template <typename... Ts> struct A { X<int, Ts...> x; };
int main() {
f<> ( X<int>{} );
A<> a{ X<int>{} };
}
...(with no additional command line flags) I get:
a.cpp:2:38: error: too many template arguments for class template 'X'
template <typename... Ts> void f ( X<int, Ts...> ) {}
^ ~~~~~~
a.cpp:1:28: note: template is declared here
template <typename> struct X {};
~~~~~~~~~~~~~~~~~~~ ^
a.cpp:3:38: error: too many template arguments for class template 'X'
template <typename... Ts> struct A { X<int, Ts...> x; };
^ ~~~~~~
a.cpp:1:28: note: template is declared here
template <typename> struct X {};
~~~~~~~~~~~~~~~~~~~ ^
a.cpp:6:5: error: no matching function for call to 'f'
f<> ( X<int>{} );
^~~
3 errors generated.
...but I'm guessing (and GCC 8.2 and GCC trunk apparently agree) that this code
is valid because f() and A can be reasonably instantiated with an empty
parameter pack, as illustrated in main(). I think the error should only come at
the point of any instantiation that actually instantiates X with too many
template arguments.
Godbolt indicates that this happens on 6.0.0 and trunk (338661).
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