Declare pp dependency of RBS signatures and validate them in CI

[ksss]

Problem

The generated RBS files refer to PP (def pretty_print: (PP q) -> void in node.rbs and parse_result.rbs), but PP is defined in the pp standard library, not in core. So loading the signatures of the prism gem on their own fails:

$ rbs -r prism validate
.../sig/generated/prism/node.rbs:180:23...180:25: Could not find PP (RBS::NoTypeFoundError)

Users have to know to add -r pp (or a pp entry in rbs_collection.yaml) themselves.

This is not in a released version yet: 1.9.0 has pretty_print: (untyped q) -> untyped, and (PP q) came with 1fdd4c5. CI did not catch it because Steep type-checks the implementation with library "pp" (and sig/_shims), so it can always resolve PP, while nothing loaded sig/generated the way users of the gem do.

Fix

• Add sig/manifest.yaml declaring the dependency on pp. This is the file rbs reads to find dependencies of a gem's signatures on standard libraries (see rbs docs). It is listed in the gemspec so that it ships with the gem.
• Add rake typecheck:rbs and run it in the typecheck job. It runs rbs validate on sig/generated with only the libraries declared in sig/manifest.yaml, i.e. exactly what users of the gem get. Without sig/manifest.yaml it reports the 155 Could not find PP errors above, so both a missing manifest entry and a new unresolvable reference will fail CI from now on.

Steep itself is not affected: Steepfile already has library "pp".

Verified

Built a gem from this branch, installed it into an empty gem directory, and ran rbs 4.2.0 against it:

$ rbs -r prism validate     # => ok, no -r pp needed

RBS::EnvironmentLoader now resolves pp and prettyprint from the stdlib signatures of the rbs gem after prism. rake check_manifest and rake typecheck:rbs pass.

🤖 Generated with Claude Code

[kddnewton]

Thanks @ksss! Is it possible to remove it from steepfile now since we declare it in our yaml or no?

[ksss]

No, unfortunately we can’t remove the entries that duplicate manifest.yaml from the Steepfile at the moment. manifest.yaml only takes effect when prism’s signatures are loaded as a library. It isn’t used when type-checking prism itself, at least for now.