Resolve constants against enclosing lexical scope in class << self

[splantio]

Summary

Fixes a constant-resolution bug in class << self bodies. Constants referenced from inside a singleton class block (or from methods defined inside one) were not resolving against the enclosing lexical scope. For example:

module A
  module B
    class Sibling; end

    class Main
      class << self
        def m
          Sibling   # was left unresolved
        end
      end
    end
  end
end

Root cause

The resolution algorithm already walks lexical scopes correctly; it follows the nesting linked list on each Name. The bug was in the indexer: when the singleton class Name was created, its nesting was set to None, so the walk terminated at the singleton class frame and never reached A::B or A.

Fix

One-line change in RubyIndexer::visit_singleton_class_node: populate the singleton class Name's nesting with the current lexical scope at the point of the class << self block, matching how regular classes and modules are indexed.

Two existing tests are updated to reflect the new Name identity: <Foo> with a nesting interns to a different Name than <Foo> without one.

Tests

Added 5 tests covering:

• Sibling used inside a method in class << self
• Sibling used inside class << self nested under an outer class
• Sibling used directly in the class << self body (not inside a method)
• Non-regression: sibling still resolves from instance method / class body / top level
• Does not over-resolve unknown constants

All 528 rubydex tests pass; clippy and fmt are clean.

[vinistock]

Oh, wow I can't believe we forgot to add a test for that. Thanks for the PR! The scenarios are all great, but the fix is actually significantly simpler. The resolution algorithm already walks lexical scopes correctly, but we're mistakenly not associating the nesting with the name objects for singleton.

Here's the fix (needs some test updates too, but logic changes it's just this):

--- a/rust/rubydex/src/indexing/ruby_indexer.rs
+++ b/rust/rubydex/src/indexing/ruby_indexer.rs
@@ -1507,9 +1507,10 @@ impl Visit<'_> for RubyIndexer<'_> {
         };
 
         let string_id = self.local_graph.intern_string(singleton_class_name);
+        let nesting = self.current_lexical_scope_name_id();
         let name_id = self
             .local_graph
-            .add_name(Name::new(string_id, ParentScope::Attached(attached_target), None));
+            .add_name(Name::new(string_id, ParentScope::Attached(attached_target), nesting));

[vinistock]

The failure for lint is fixed on main, so a rebase will probably fix it. Thanks for the contribution!