[C++20] [Modules] Only check decls under namespace scope in CheckRedeclarationExported

[ChuanqiXu]

Summary

Since only the decls inhabit in a namespace scope could be exported, it is not meaningful to check it in CheckRedeclarationExported, which implements [module.interface]/p6: http://eel.is/c++draft/module.interface#6.

[ChuanqiXu]

clang/lib/Sema/SemaDecl.cpp

1643–1648

This is formatted by clang-format, the original may be too long:

if (!New->getLexicalDeclContext()->getNonTransparentContext()->isFileContext() ||
    ...

[urnathan]

clang/lib/Sema/SemaDecl.cpp

1643–1648

I like continuation lines where the operator is on the start of the new line rather than the end of the old one :)

clang/lib/Sema/SemaDecl.cpp

bool Sema::CheckRedeclarationModuleOwnership(NamedDecl *New, NamedDecl *Old) {
 
   return false;
 }
 
 // [module.interface]p6:
 // A redeclaration of an entity X is implicitly exported if X was introduced by
 // an exported declaration; otherwise it shall not be exported.
 bool Sema::CheckRedeclarationExported(NamedDecl *New, NamedDecl *Old) {
+  // [module.interface]p1:
+  // An export-declaration shall inhabit a namespace scope.
+  //
+  // So it is meaningless to talk about redeclaration which is not at namespace
+  // scope.
+  if (!New->getLexicalDeclContext()
+           ->getNonTransparentContext()
+           ->isFileContext() ||
+      !Old->getLexicalDeclContext()
+           ->getNonTransparentContext()
+           ->isFileContext())
+    return false;
+
   bool IsNewExported = New->isInExportDeclContext();
   bool IsOldExported = Old->isInExportDeclContext();
 
   // It should be irrevelant if both of them are not exported.
   if (!IsNewExported && !IsOldExported)
     return false;
 
   if (IsOldExported)

clang/test/CXX/module/module.interface/p6.cpp

 
 int var;        // expected-note {{previous declaration is here}}
 export int var; // expected-error {{cannot export redeclaration 'var' here since the previous declaration is not exported}}
 
 template <typename T>
 T TemplVar; // expected-note {{previous declaration is here}}
 export template <typename T>
 T TemplVar; // expected-error {{cannot export redeclaration 'TemplVar' here since the previous declaration is not exported}}
+
+// Test the compiler wouldn't complain about the redeclaration of friend in exported class.
+namespace Friend {
+template <typename T>
+class bar;
+class gua;
+template <typename T>
+void hello();
+void hi();
+export class foo;
+bool operator<(const foo &a, const foo &b);
+export class foo {
+  template <typename T>
+  friend class bar;
+  friend class gua;
+  template <typename T>
+  friend void hello();
+  friend void hi();
+  friend bool operator<(const foo &a, const foo &b);
+};
+} // namespace Friend