[clang] [Clang] Implement C++26’s P2893R3 ‘Variadic friends’ (PR #101448)

[via cfe-commits]

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@@ -4437,6 +4441,31 @@ ExpectedDecl ASTNodeImporter::VisitFriendDecl(FriendDecl *D) {
   return FrD;
 }
 
+ExpectedDecl ASTNodeImporter::VisitFriendPackDecl(FriendPackDecl *D) {
+  // Import the major distinguishing characteristics of a declaration.
+  DeclContext *DC, *LexicalDC;
+  if (Error Err = ImportDeclContext(D, DC, LexicalDC))
+    return std::move(Err);
+
+  auto ToInstantiatedFromFriendOrErr =
+      Importer.Import(D->getInstantiatedFromFriendDecl());
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Sirraide wrote:

Hmm, I basically just copy-pasted stuff from the functions that handle `UsingPackDecl`s and `FriendDecl`s, and it seems that those always use `auto`, so this would probably be better left for a separate NFC patch imo, but I suppose I could change it in this function here.

https://github.com/llvm/llvm-project/pull/101448