https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114275
--- Comment #4 from Nathaniel Shead <nshead at gcc dot gnu.org> --- I suspect there are a number of issues tied together here. Some of the things I've discovered so far: - 'tsubst_friend_class' calls 'lookup_name', which when called from a module that doesn't export the class that was befriended fails to find it, and so it substitutes in a new instance of that type (which then later fails duplicate_decls). - Instantiating an elaborated type specifier doesn't attach it to the module the containing template was declared in. - Sometimes it seems that the container of a MK_local_friend decl is not always correctly streamed: in particular, in the comment 2 testcase the container streamed is a complete type on write, but on read is not complete (TYPE_SIZE is null) and so is not properly read on stream-in in the first place. Additionally, it looks like you can hide some of the errors by making the importer a named module, because on instantiation it only calls 'duplicate_decls' on names imported from a partition.
