https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90291
--- Comment #13 from Nathan Sidwell <nathan at gcc dot gnu.org> --- I don't know where the DR information is available without a password (C++ physical meetings are public, see https://isocpp.org/std/ Here is the text of 2061: 2061. Inline namespace after simplifications Section: 9.7.1 [namespace.def] Status: CD4 Submitter: Richard Smith Date: 2014-12-18 Priority: 0 Drafting: Maurer [Adopted at the February, 2016 meeting.] After the resolution of issue 1795, 9.7.1 [namespace.def] paragraph 3 now says: In a named-namespace-definition, the identifier is the name of the namespace. If the identifier, when looked up (6.4.1 [basic.lookup.unqual]), refers to a namespace-name (but not a namespace-alias) introduced in the declarative region in which the named-namespace-definition appears, the namespace-definition extends the previously-declared namespace. Otherwise, the identifier is introduced as a namespace-name into the declarative region in which the named-namespace-definition appears. This appears to break code like the following: namespace A { inline namespace b { namespace C { template<typename T> void f(); } } } namespace A { namespace C { template<> void f<int>() { } } } because (by definition of “declarative region”) C cannot be used as an unqualified name to refer to A::b::C within A if its declarative region is A::b. Proposed resolution (September, 2015): Change 9.7.1 [namespace.def] paragraph 3 as follows: In a named-namespace-definition, the identifier is the name of the namespace. If the identifier, when looked up (6.4.1 [basic.lookup.unqual]), refers to a namespace-name (but not a namespace-alias) that was introduced in the declarative region namespace in which the named-namespace-definition appears or that was introduced in a member of the inline namespace set of that namespace, the namespace-definition extends the previously-declared namespace. Otherwise, the identifier is introduced as a namespace-name into the declarative region in which the named-namespace-definition appears. [nathan: I.e. we do unqualified lookup for the name, ignoring using directives. That naturally descends into the immediate set of inline-namespaces.]