[neilvcarvalho]

Fourth step of the sequence of refactors toward a compiled, non-cloning core. Stacked on #1851 (step 3), #1848 (step 2) and #1847 (step 1); merge those first.

What changed

Each factory used to define an anonymous Evaluator subclass per snapshot, inheriting from the parent's, with one method per attribute and a singleton method per override, so that Ruby method lookup performed attribute inheritance.

• CompiledFactory now carries an ordered Hash of attributes instead of an evaluator class. Factory#attributes_over merges the parent's Hash, the factory's own definition and the requested traits. A later definition wins but keeps the first definition's position, which reproduces the assignment order of the class chain, and a name declared transient anywhere stays transient, which the suite pins in spec/acceptance/transient_attributes_spec.rb ("redefining a transient attribute without the transient block"). Attribute#as_transient produces the copy used for that case, alongside the transient reader that Refactor remaining internal ignored state to transient terminology #1834 renamed from ignored.
• Evaluator is a single BasicObject over that Hash. method_missing looks up the memo, then the attributes, then the instance, then SyntaxRunner. It is a BasicObject so attribute names such as hash, display, method, format and system are not shadowed by Object; inside the class, constants are written as ::FactoryBot::... and ::Kernel.raise. respond_to?, send, public_send, nil? and inspect are defined explicitly since callbacks receive the evaluator.
• A hash-mode flag replaces NullObject: under attributes_for there is no instance, and a method the build class defines answers nil, exactly what the null object did.
• The memo is a copy of the overrides instead of the same Hash. Before, an attribute evaluated by a before callback leaked into __override_names__ and into the alias logic.
• The initialize_with helpers new and attributes still shadow attributes of the same name only while constructing, now as plain methods that fall through to method_missing otherwise.
• AttributeAssigner takes the attribute Hash instead of reading evaluator.class.attribute_list.

Deleted

• lib/factory_bot/evaluator_class_definer.rb, lib/factory_bot/null_object.rb, their requires and their specs.
• Evaluator.define_attribute, Evaluator.attribute_list, the attribute_lists and attribute_blocks class attributes, the Construction prepend module, the per-override singleton methods, and AttributeAssigner#build_hash and #hash_instance_methods_to_respond_to.

Acceptance edit

One acceptance example changes, as the plan notes: spec/acceptance/callbacks_spec.rb read the strategy through context.instance_values["build_strategy"], which a BasicObject does not have. It now reads context.instance_eval { @build_strategy }. Nothing else in the acceptance suite or the features changed.

Behavior

Beyond the suite, I compared this branch with main on attribute names that collide with Object methods under build and attributes_for, blocks referencing build class methods under both strategies, an unknown method under attributes_for, send, respond_to? and nil? on the evaluator inside a callback, and the initialize_with edge cases from step 2. All match. One visible difference, which is the aliasing fix above: a factory declaring both user and user_id whose before(:build) callback reads evaluator.user now assigns user_id; on main the read made user look like an override and user_id was skipped.

Verification

All on Ruby 4.0.1.

• bundle exec standardrb: no offenses.
• bundle exec rake all_specs (default Gemfile): 324 unit examples, 445 acceptance examples, 4 Cucumber scenarios, all passing.
• BUNDLE_GEMFILE=gemfiles/7.0.gemfile bundle exec rake all_specs: same counts, all passing.
• BUNDLE_GEMFILE=gemfiles/main.gemfile bundle exec rake all_specs: same counts, all passing.