clang accepts new dll attributes on explicit instantiation of already instantiated templates

[zmodem]

Bugzilla Link	20758
Version	unspecified
OS	Windows NT
CC	@DougGregor

Extended Description

Consider:

template <typename T> void f() {}
void foo() { f<int>(); }
template void __declspec(dllimport) f<int>();

or

template <typename T> struct S { void f() {} };
void bar(S<int> s) { s.f(); }
template struct __declspec(dllexport) S<int>; 

Clang accepts the code, but the attribute doesn't have any effect since it's applied too late.

I think this would be hard for us to handle, so we should warn and drop the attribute.

[Quuxplusone]

mentioned in issue llvm/llvm-bugzilla-archive#38302

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Hans Wennborg (zmodem)

| | | | --- | --- | | Bugzilla Link | [20758](https://llvm.org/bz20758) | | Version | unspecified | | OS | Windows NT | | CC | @DougGregor |

Extended Description

Consider:

template <typename T> void f() {}
void foo() { f<int>(); }
template void __declspec(dllimport) f<int>();

or

template <typename T> struct S { void f() {} };
void bar(S<int> s) { s.f(); }
template struct __declspec(dllexport) S<int>; 

Clang accepts the code, but the attribute doesn't have any effect since it's applied too late.

I think this would be hard for us to handle, so we should warn and drop the attribute.