Fix NoMethodError when RBS file contains class/module alias decl

[rhiroe]

Summary

Fix NoMethodError: undefined method 'define' for nil raised in Service#update_rbs_file whenever the workspace contains an RBS file with a class alias or module alias declaration (e.g. module YAML = Psych, class HashWithIndifferentAccess = ActiveSupport::HashWithIndifferentAccess).

Background

AST.create_rbs_decl has an intentionally empty when RBS::AST::Declarations::AliasDecl branch (class/module aliases are not yet implemented and are silently skipped).
However the empty when body returns nil, and the calling site AST.parse_rbs calls raw_decls.map { ... } without .compact, so the nil ends up in the resulting array and later crashes at decls.each {|decl| decl.define(@genv) }.

The two other callers of create_rbs_decl / create_rbs_member already use .compact after the map (see Genv#load_core_rbs in core/env.rb and SigModuleBaseNode#initialize in core/ast/sig_decl.rb). This PR aligns parse_rbs with the same pattern.

Reproduction

Put a single line in sig/foo.rbs:

module YAML = Psych

Start the LSP server: it crashes during workspace initialization with

NoMethodError: undefined method 'define' for nil
  decls.each {|decl| decl.define(@genv) }

Fix

Add .compact to the map in AST.parse_rbs. Class/module aliases remain unimplemented (skipped) — proper alias resolution is out of scope for this PR.

Test plan

• Added scenario/rbs/class-module-alias.rb regression test
• bundle exec rake test passes (415 tests, 0 failures)
• Verified locally: real-world RBS with module YAML = Psych no longer crashes the LSP server

[mame]

@rhiroe Thanks! I think the real issue is that AST.create_rbs_decl returns nil. Once #444 is merged, it won't return nil anymore, so this change might no longer be needed. What do you think?

[rhiroe]

@mame Yes, you're right — I think it will become unnecessary.
The reason I opened this PR was that I wanted to at least get rid of the error even in case #444 doesn't get merged smoothly.

I'll leave it up to you whether to merge or close this PR, but since .compact is already used at:

typeprof/lib/typeprof/core/env.rb

Lines 265 to 267 in 1aedffb

	decls = raw_decls.map do |raw_decl|
	AST.create_rbs_decl(raw_decl, lenv)
	end.compact

I think it would also be fine to either remove that one as well for consistency, or merge this PR to align with the existing similar code.

[mame]

I have merged #444, so closing this. Thanks!

.compact is already used at:

That's sloppy ;-P