Add canonical interface checker

[thiagoa]

Pairwise comparison verifies that every adjacent pair of classes in a list agree with each other, which works well when all classes are peers with no single authoritative definition. Canonical interface comparison takes a different approach: one class is designated as the reference, and every other class is checked against it directly. This is useful when the interface already has a clear owner — an abstract base, a well-established implementation, or a purpose-built interface class — and you want to confirm that all other implementations conform to that definition. Because all comparisons share the same right-hand side, failures from multiple classes are aggregated into a single result, making it easier to see the full picture at a glance.

• Adds CanonicalInterfaceChecker, which compares every class in a list against a single canonical reference rather than in consecutive pairs. All failures are aggregated into one result, so a single assertion reports every non-conforming class at once.

• Exposes assert_canonical_interface_match(canonical, objects, **opts) in the Minitest integration and implement_canonical_interface(canonical, **opts) in the RSpec integration. All existing options (type:, methods:, strict:, name:, namespace:) are supported.

• Extracts shared checker initialization (argument validation, object resolution, name inference, checker construction) into InterfaceSetup, eliminating duplication between BulkInterfaceChecker and CanonicalInterfaceChecker.

[Copilot]

Pull request overview

Adds a new “canonical interface” comparison mode to DuckTyper, enabling N implementations to be checked directly against a single authoritative reference, with aggregated failures for easier diagnosis. This also refactors shared checker setup logic to reduce duplication between checkers.

Changes:

• Introduces DuckTyper::CanonicalInterfaceChecker (+ aggregated Result) and wires it into the main gem entrypoint.
• Adds Minitest (assert_canonical_interface_match) and RSpec (implement_canonical_interface) integrations for canonical checks.
• Extracts shared initialization logic into InterfaceSetup and factors common result-message helpers into ResultFormatting.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
test/duck_typer/canonical_interface_checker_test.rb	Adds unit tests for canonical checker behavior and messaging.
test/duck_typer/bulk_interface_checker_test.rb	Updates expected argument-validation error messages after refactor.
lib/duck_typer/rspec.rb	Adds implement_canonical_interface matcher.
lib/duck_typer/result_formatting.rb	Extracts shared failure-message helpers (interface_label, strict_note).
lib/duck_typer/objects_resolver.rb	Adds an objects/namespace resolution helper module.
lib/duck_typer/minitest.rb	Adds assert_canonical_interface_match helper.
lib/duck_typer/interface_setup.rb	Centralizes checker argument validation, object resolution, name inference, checker construction.
lib/duck_typer/interface_checker/result.rb	Reuses ResultFormatting and exposes diff_message for aggregation.
lib/duck_typer/canonical_interface_checker/result.rb	Implements aggregated failure message for canonical comparisons.
lib/duck_typer/canonical_interface_checker.rb	Implements canonical comparison loop against a reference class/module.
lib/duck_typer/bulk_interface_checker.rb	Refactors to use InterfaceSetup.
lib/duck_typer.rb	Requires canonical checker so it’s available when requiring duck_typer.
README.md	Documents canonical interface usage for Minitest and RSpec.

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[Copilot]

Pull request overview

Copilot reviewed 15 out of 15 changed files in this pull request and generated no new comments.

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