[clang] [clang][Modules] Complete the implementation of P2615: Meaningful exports (PR #194201)

[A. Jiang via cfe-commits]

================
@@ -3,9 +3,98 @@
 
 
 // RUN: %clang_cc1 -std=c++20 -verify -fsyntax-only %t/A.cpp
+// RUN: %clang_cc1 -std=c++20 -verify -fsyntax-only %t/B.cpp
 
 //--- A.cpp
 // expected-no-diagnostics
 export module A;
 export namespace N {int x = 42;}
 export using namespace N;
+
+//--- B.cpp
+export module B;
+
+export template <typename T> class s1 {};
+export template <typename T> class s1<T *> {}; // expected-error {{a specialization cannot be marked 'export'}}
+// expected-note at -1 {{as long as its primary template is exported, it will be too}}
+export template <> class s1<int> {}; // expected-error {{a specialization cannot be marked 'export'}}
+// expected-note at -1 {{as long as its primary template is exported, it will be too}}
+export template class s1<char>; // expected-error {{an explicit instantiation cannot be marked 'export'}}
+// expected-note at -1 {{as long as its primary template is exported, it will be too}}
+export extern template class s1<void>; // expected-error {{an explicit instantiation cannot be marked 'export'}}
+// expected-note at -1 {{as long as its primary template is exported, it will be too}}
+
+export template <typename T> int v1 = 0;
+export template <typename T> int v1<T *> = 0; // expected-error {{a specialization cannot be marked 'export'}}
+// expected-note at -1 {{as long as its primary template is exported, it will be too}}
+export template <> int v1<int> = 0; // expected-error {{a specialization cannot be marked 'export'}}
+// expected-note at -1 {{as long as its primary template is exported, it will be too}}
+export template int v1<char>; // expected-error {{an explicit instantiation cannot be marked 'export'}}
+// expected-note at -1 {{as long as its primary template is exported, it will be too}}
+export extern template int v1<void>; // expected-error {{an explicit instantiation cannot be marked 'export'}}
+// expected-note at -1 {{as long as its primary template is exported, it will be too}}
+
+export template <typename T> void f1() {}
+export template <> void f1<int>() {} // expected-error {{a specialization cannot be marked 'export'}}
+// expected-note at -1 {{as long as its primary template is exported, it will be too}}
+export template void f1<char>(); // expected-error {{an explicit instantiation cannot be marked 'export'}}
+// expected-note at -1 {{as long as its primary template is exported, it will be too}}
+export extern template void f1<void>(); // expected-error {{an explicit instantiation cannot be marked 'export'}}
+// expected-note at -1 {{as long as its primary template is exported, it will be too}}
+
+
+export { template <typename T> class s2 {}; }
+export { template <typename T> class s2<T *> {}; }
+export { template <> class s2<int> {}; }
+export { template class s2<char>; }
+export { extern template class s2<void>; }
+
+export { template <typename T> int v2 = 0; }
+export { template <typename T> int v2<T *> = 0; }
+export { template <> int v2<int> = 0; }
+export { template int v2<char>; }
+export { extern template int v2<void>; }
+
+export { template <typename T> void f2() {} }
+export { template <> void f2<int>() {} }
+export { template void f2<char>(); }
+export { extern template void f2<void>(); }
+
+
+extern "C++" template <typename T> class s3 {};
+extern "C++" template <typename T> class s3<T *> {}; // expected-error {{language linkage specification cannot be applied to a specialization}}
----------------
frederick-vs-ja wrote:

I'm not sure. But the standard requirements are well-defined even with such inconsistency. Perhaps we can submit a following-up CWG issue (https://github.com/cplusplus/CWG/issues) for this if you want.

https://github.com/llvm/llvm-project/pull/194201