Name a class written from the top level as Ruby does, with --experimental-parser

[dduugg]

Summary

With --experimental-parser, pks named a class or module written from the top level as if it nested in the namespaces around it. class ::Taco was defined as ::::Taco, class ::Burrito inside module Outer as ::Outer::::Burrito, and a constant assigned in one, as ::::Taco::FILLING. The resolver built its guesses the same way, so a reference to one of these was found only from inside another class ::Taco written the same way, and then under the :::: name. The rest were missed. So was Shell written inside class ::Taco, looked up as ::::Taco::Shell and then ::Shell, when another pack defines ::Taco::Shell as class Taco::Shell.

• nest_constant_name starts the name again from the top level at a namespace that begins with ::, as Ruby does.
• The experimental parser names its definitions with it, and the experimental resolver makes its guesses with it. Inside module Outer; class ::Foo, Bar is now looked up as ::Foo::Bar, then ::Outer::Bar, then ::Bar, the order of Ruby's Module.nesting.
• A reference that was found under a :::: name now has the plain one, as ::Taco::FILLING. A violation that a package_todo.yml records under the :::: name is reported again under the new name, and the old entry as stale, until pks update is run. The CHANGELOG says so.
• Without --experimental-parser, nothing changes. packwerk names class ::Taco ::::Taco among a file's local definitions too, and its constant_resolver looks Shell up as ::Taco::Shell against names that have no leading ::, so it misses the same references, or takes Shell for a top-level ::Shell. The packwerk parser and the Zeitwerk resolver keep that lookup, and the CHANGELOG says so.
• A class reopened this way, as class ::String inside module CoreExt, is now ::String, so with --experimental-parser, expose-monkey-patches lists it, and a reference to String from another pack is a reference to the pack that reopens it, as for a class String at the top level of a file. The CHANGELOG says this too.

The cache key includes pks's version, so a release doesn't serve the old names from the cache.

Test plan

• cargo test (378 passed, and 379 on a merge with main, which adds one), cargo fmt --check, and cargo clippy --all-targets --all-features -- -Dwarnings.
• definitions_from_the_top_level and resolve_in_a_namespace_from_the_top_level cover the parser's names and the resolver's lookup, and test_list_references_to_a_class_defined_from_the_top_level lists a reference to class ::Taco inside module Outer in another pack. All three fail when nest_constant_name joins the old way.
• definitions_from_the_top_level also has a module ::Foo and nestings like module A; class ::B; module C, and test_list_references_inside_a_class_defined_from_the_top_level looks Shell up inside module Outer; class ::Taco. They fail when visit_module_node names a module the old way, when only the resolver joins the old way, and when nest_constant_name starts again at the first :: namespace in place of the last. No test caught those before.
• On a copy of simple_app with class ::Taco and module Outer; class ::Burrito, -e list-definitions gives ::Taco, ::Taco::FILLING and ::Burrito, and -e list-references now lists ::Taco, ::Taco::FILLING, ::Burrito, and ::Taco::Shell from inside class ::Taco. The default parser's output is unchanged.
• With class ::Taco; FILLING = 1; end in packs/bar and FILLING written inside a class ::Taco in packs/foo, the binary before this change lists ::::Taco::FILLING, and this one ::Taco::FILLING. After pks -e update with the old binary, pks -e check with this one reports the two violations under the new name and the old todo entry as stale.