Follow up #82: look up associations as Rails does, name constants through Object, and match packwerk on :: names and class_eval

[dduugg]

Summary

Follow-ups to #82, found while reviewing it, and the gaps they turned up.

With --experimental-parser, an association is looked up as Rails looks it up.

• Rails looks up the class of has_many :tacos from the name of the model that declares it (ActiveRecord's compute_type): in Outer::Foo, as Outer::Foo::Taco, Outer::Taco, then Taco, taking only a class of that very name. pks gave the reference the namespaces it's written in, so in class Outer::Foo it skipped Outer::Taco and found Taco, and in module Outer; class ::Foo it found Outer::Taco, which Rails never tries.
• When the class has the model's own last name, as belongs_to :company in Payroll::Company, Rails tries ::Company first, then the model's name (_klass in reflection.rb), and so does pks.
• In a module, as a concern's included block, Rails looks up the class from the name of each model that includes the module. pks records the include and prepend calls in each class and module, and looks up the class from each class that includes the module, directly or through other modules. Where none does, the module's name stands in.
• In a controller, inherited_resources looks up belongs_to :taco from the controller's namespaces, and a class_name: from the top level, and so does pks.

With --experimental-parser, a constant written through Object is named as Ruby names it. class Object::Bar inside module CoreExt defines ::Bar, and so does class Bar inside a top-level class Object. pks named them ::CoreExt::Object::Bar and ::Object::Bar, and now names them ::Bar, unless the app has a CoreExt::Object, even an empty one, in which case it's ::CoreExt::Object::Bar, as in Ruby. A reference written ::Object::Bar now resolves to ::Bar, and inside module CoreExt the resolver tries ::CoreExt::Object::Bar for Object::Bar before ::Bar. A class Object inside a namespace is still the namespace's own.

With --experimental-parser, the constants of Kernel and BasicObject are found from anywhere, after the top level's own, as in Ruby: class BasicObject::Foo is found as Foo.

Without --experimental-parser, pks matches packwerk around a name written from the top level, and in class_eval and Class.new blocks. Checked against packwerk 3.3.1 and constant_resolver 0.3.0, run directly in Ruby:

• module Outer; class ::Burrito: both name the class ::Outer::::Burrito. constant_resolver takes the parent of Outer::::Burrito, Outer::, with Ruby's String#split, which drops the empty name at the end, so Outer:: has no parent and it finds nothing (constant_resolver.rb:163). Rust's split keeps it, so pks went on to Outer and reported the class against Outer's pack. In module Aa; module Bb; class ::Cee, the same split takes packwerk from Aa::Bb:: to Aa, where pks stopped at Aa::Bb. The Zeitwerk resolver now drops the empty names at the end too.
• class ::Taco (or ::Taco = 1) at the top level of a file, then Taco.make: packwerk's own definitions for the file have ::::Taco, so the later Taco, looked for as ::Taco, isn't local, and packwerk reports it. pks also looked for :: plus the name, found ::::Taco, and dropped it. The packwerk parser now looks for the name alone. The same goes for a Taco written inside class ::Taco, for constants defined in that class (::::Taco::Shell), and for the ::::Taco pks takes from class ::Taco::Shell; each is now a reference, as in packwerk.
• packwerk names the reference a class makes to itself from every class, module, Foo.class_eval do block and Foo = Class.new do around it (parent_module_name), so module Aa; Bb.class_eval do; class ::Cee is ::Aa::Bb::::Cee, a reference to Aa. pks left out Bb, which the split change above turned into a regression: it found no reference there. The packwerk parser now keeps the same names for this, including packwerk's quirks (blocks taking _1 or it add nothing; it names no class in a block passed with &. or to super).

The CHANGELOG has an entry for each. Each can move or drop a violation, so a package_todo.yml entry can go stale until pks update.

How the experimental changes work

The experimental parser now leaves an association in a class or module, and the include/prepend calls, in new ProcessedFile fields (cached, empty ones left out of the cache file), and process_files in experimental.rs turns them into references once every file is read and the resolver is built. A file that defines a constant through Object inside a namespace is flagged, and when the app has some namespace's own Object, those files are read again knowing which. check-contents reads its file from stdin, so stdin's contents are now kept after the first read.

Test plan

• cargo test (398 passed), cargo fmt --check, and cargo clippy --all-targets --all-features -- -Dwarnings.
• New tests, each failing with its own fix reverted:
  • resolve_a_name_from_the_top_level_in_a_namespace (Zeitwerk resolver), test_list_references_to_a_class_defined_from_the_top_level_in_a_namespace, test_list_references_after_a_class_defined_from_the_top_level and test_list_references_after_a_constant_assigned_from_the_top_level: the ::Burrito, ::Cee, class ::Taco and ::Taco = 1 cases, from the file to the references listed.
  • class_defined_in_class_eval, classes_defined_in_blocks_and_assignments (36 cases, each checked against packwerk) and test_list_references_to_a_class_defined_in_class_eval_or_class_new.
  • test_list_references_from_associations_by_the_models_name, ..._in_namespaced_models, ..._in_concerns (two includers, a concern included through another, an unused one, ERB) and ..._named_for_their_model (_klass with and without ::Taco, inherited_resources with and without class_name:, a model whose name ends in Controller).
  • definitions_in_object, resolve_through_object, test_list_references_to_constants_defined_through_object and ..._through_a_namespaces_object (a namespace's own Object in another file, and an empty one), and test_check_contents_of_a_file_read_twice_with_experimental_parser.
  • test_list_references_to_constants_of_objects_ancestors, and unit tests for objects_in_namespaces and models_including.
• Mutation check: each fix, each defined_name call site, the while in nest_constant_name, and each branch of the association lookup and the class_eval naming, reverted alone, fails at least one of these tests.
• On copies of simple_app, packwerk 3.3.1 and this build give the same references for 66 files of class ::Foo, ::Foo = 1, class_eval and Class.new cases, except one older difference listed below. The build from main differed on 57 lines.
• With ActiveRecord 8.1.4: compute_type and _klass as above, including Kitchen::Taco::Taco with no ::Taco; a concern in Plain and in Billing::Invoice, and one included through another concern, give Taco, Billing::Taco and Billing::Taco. inherited_resources 2.1.0, run under Ruby 3.4.11, looks up belongs_to as described.
• Ruby 4.0.5 names class Object::Bar in module CoreExt Bar, class Object; class Qux; end; Y = 1 Qux and ::Y, class Object::Charge in a module Payments with its own Object Payments::Object::Charge, and finds BasicObject::Foo and Kernel::FOO from any module, after the top level's own.

Not covered

• An include not written as include/prepend in a class or module body (Model.include(M), send(:include, M), Foo.class_eval { include M }, ActiveSupport.on_load), and an association in a Foo.class_eval block: pks doesn't see the model, and the module's name, or none, stands in.
• Ruby also looks a constant up in a class's superclasses; pks doesn't know them.
• A reference written Object::Bar where the namespace's own Object has no Bar: Ruby raises a NameError, and pks goes on to ::Bar, as it does for any name written with a namespace.
• class A::B inside module M, where A is top-level, is ::A::B in Ruby; pks names it ::M::A::B. Telling them apart needs the namespaces Zeitwerk makes from directories, which pks doesn't read in this mode. The Object case above is the one it can tell.
• Without --experimental-parser, packwerk counts the scope Kk of Kk::Ll = 1 as a reference, and reads self::Foo as ::Foo; pks doesn't, as before this PR.