Retain previous language linkage of friend function declarations
With this extension, friend function declarations will retain the language
linkage specified for previous declarations instead of emitting an error
diagnostic.
The feature is known to be compatible with GCC and MSVC and permits a
language to be specified indirectly where it cannot otherwise be written
directly in class scope.
Work is ongoing to improve linkage spec diagnostics.
Fixes PR17337.
Reviewed by Richard Smith.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@193206 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index 81ade1f..80f95e6 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -2607,9 +2607,22 @@
}
if (haveIncompatibleLanguageLinkages(Old, New)) {
- Diag(New->getLocation(), diag::err_different_language_linkage) << New;
- Diag(Old->getLocation(), PrevDiag);
- return true;
+ // As a special case, retain the language linkage from previous
+ // declarations of a friend function as an extension.
+ //
+ // This liberal interpretation of C++ [class.friend]p3 matches GCC/MSVC
+ // and is useful because there's otherwise no way to specify language
+ // linkage within class scope.
+ //
+ // Check cautiously as the friend object kind isn't yet complete.
+ if (New->getFriendObjectKind() != Decl::FOK_None) {
+ Diag(New->getLocation(), diag::ext_retained_language_linkage) << New;
+ Diag(Old->getLocation(), PrevDiag);
+ } else {
+ Diag(New->getLocation(), diag::err_different_language_linkage) << New;
+ Diag(Old->getLocation(), PrevDiag);
+ return true;
+ }
}
if (OldQTypeForComparison == NewQType)