https://bugs.llvm.org/show_bug.cgi?id=41895
Bug ID: 41895
Summary: [clang-cl] __declspec(dllexport) on class declaration
implicitly instantiates templates
Product: clang
Version: 7.0
Hardware: PC
OS: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: Driver
Assignee: unassignedclangb...@nondot.org
Reporter: m...@mark-ingram.com
CC: llvm-bugs@lists.llvm.org, neeil...@live.com,
richard-l...@metafoo.co.uk
Created attachment 21952
--> https://bugs.llvm.org/attachment.cgi?id=21952&action=edit
Test file
Attempting to export a class declaration that will be partially specialised
results in an error:
template<typename T>
class __declspec(dllexport) Foo
{
public:
static const int Bar;
};
template<> const int Foo<char>::Bar = 42;
Using clang-cl:
$ clang-cl -c test.cpp
test.cpp(8,33): error: explicit specialization of 'Bar' after instantiation
template<> const int Foo<char>::Bar = 42;
^
test.cpp(5,19): note: implicit instantiation first required here
static const int Bar;
^
1 error generated.
Using cl:
> cl /c test.cpp /nologo
test.cpp
The work around that I have is to export individual class members, which
prevents the implicit template instantiation, and allows a subsequent partial
template specialisation.
Also, the diagnostic isn't quite right, because the implicit instantiation
happens when the class is exported, not when the member is defined (removing
the __declspec(dllexport) allows the code to compile with clang-cl).
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