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Malte UblandClaude Opus 5.5
541b05ddea
A cast to a generic type alias spelled over the enclosing function's own type parameters (`return x as Catalog<G, P>`) stays symbolic in the checker inside the body, so a mapped type with key remapping, a template key filter or a conditional member refused with SC2001 in every instance. The checker interns alias instantiations, so the body's `Catalog<G, P>` is the same type the signature declares. Binding unification now records, per call-keyed instance, each declared generic alias reference together with the alias the call's resolved signature instantiates. When the symbolic form does not map, mapType maps that concrete instantiation instead. A body forwarding its own alias to another generic resolves through the enclosing instance. Types that already mapped are unaffected. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>