Gate forwarding parameter syntax behind parser option - #3087
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`(...)` forwarding parameters (#3042) are syntax-only for now: nothing defines their type checking semantics yet, and distributing signatures that use them would break older parsers and tools that silently drop the node. Introduce `rbs_parser_options_t` and `rbs_parser_new_with_options()` so the syntax must be opted into at the C API level. `rbs_parser_new()` uses the zero-initialized options, which disable every optional syntax, and the Ruby API doesn't expose the option, so `(...)` is a syntax error everywhere in the gem. The AST, types, and serialization support stays in place for when the semantics are settled. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_015bgoC4byczqmYRzNrDkVrL
Gating `(...)` behind a C-level option left the enabled path with no test coverage from Ruby, where the whole suite lives. Without it the forwarding branch of `parse_params`, its AST translation, and its serialization would be free to rot until the semantics are settled. Thread the option through the private `_parse_method_type` and `_parse_signature` entry points (and their `_to_bytes` variants), which tests already call directly. The public `RBS::Parser` API keeps passing `false`, so signatures written for the gem still can't use the syntax. This also strengthens the restriction tests: they used to pass simply because the gate rejected `(...)` outright, and now run with the option enabled, so they check the grammar restrictions they name. The WebAssembly parser has no way to enable the option, so its shim raises `NotImplementedError` rather than quietly parsing without it. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_015bgoC4byczqmYRzNrDkVrL
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#3042 added
(...)parsing, but nothing consumesTypes::Function#forwardingyet — the syntax has no type checking semantics, and Steep silently drops it. This gates it behindrbs_parser_options_t: off by default, not exposed to the public Ruby API, so(...)stays a syntax error until the semantics are settled. #3042 is unreleased, so nothing depends on it.The private
_parse_*entry points take the flag so tests still cover the enabled path. AST, serializers, and schemas are unchanged.