feat: deprecation warnings on legacy namespace (shim layer for 2.0.0.alpha1) - #218
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…alpha1) v2 step 6 (ADR-004): the old-namespace constants stop forwarding silently. Each mapped pair from namespace_forwarding_test.rb now resolves lazily via a const_missing hook (snap_diff/legacy_shims.rb) that emits a deprecation warning -- exactly once per constant per process via the pre-existing SnapDiff::Deprecation machinery -- while still returning the exact same object as the SnapDiff:: replacement. - 22 of the 27 mapped constants moved from eager aliases to lazy const_missing forwarders (Capybara::Screenshot, Capybara::Screenshot::Diff, CapybaraScreenshotDiff, CapybaraScreenshotDiff::Reporters, plus BaseDriver hooked on SnapDiff::Drivers itself since the Drivers alias is same-object). - Documented eager-and-silent exceptions: Os and DSL (advertised entry-point constants probed with const_defined? by support_load_probe_test, which never triggers const_missing), VERSION (resolved by the gemspec at build time), and Drivers::ChunkyPNGDriver / Drivers::VipsDriver (real constants on the shared SnapDiff::Drivers module; the old path still warns once for ::Drivers itself). - Silencing: existing API only -- SnapDiff.silence_deprecations accessor and SNAP_DIFF_SILENCE_DEPRECATIONS=1 env var. - The gem's own code now references SnapDiff names exclusively (config_legacy, umbrella error classes, screenshot_matcher, dsl, integrations, reporters); subprocess probes assert each entry point loads and runs a comparison with zero deprecation output, plus an unsilenced control probe asserting a touched old constant does warn. - Test suite: unqualified old-name references qualified as SnapDiff::...; driver tests renested under SnapDiff::Drivers (reopening the old Drivers path would define a fresh module and shadow the lazy forwarder); test_helper silences deprecations suite-wide, with the behavior pinned by the new unit/legacy_namespace_deprecation_test.rb. Claude-Session: https://claude.ai/code/session_014BQJX6eWzBj2UTm5zQsjEs
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Reviewer's GuideImplements a const_missing-based legacy namespace shim layer that emits once-per-constant deprecation warnings while preserving object identity, and rewires internal code and tests to use canonical SnapDiff:: APIs without producing warnings, leaving a few entry-point constants eagerly defined and silent by design. Sequence diagram for lazy legacy constant resolutionsequenceDiagram
participant Caller
participant LegacyNamespace
participant Deprecation
participant SnapDiff
Caller->>LegacyNamespace: resolve legacy constant
LegacyNamespace->>LegacyNamespace: const_missing(name)
LegacyNamespace->>Deprecation: warn(legacy_name, new_name, category: :constant)
Deprecation-->>LegacyNamespace: warn once or suppress
LegacyNamespace->>SnapDiff: Object.const_get(new_name)
SnapDiff-->>Caller: return canonical object
Flow diagram for legacy constant lookup outcomesflowchart TD
Lookup[Legacy constant lookup] --> Mapped{Mapped constant?}
Mapped -->|Yes| Warn[Deprecation.warn]
Warn --> Resolve[Resolve SnapDiff replacement]
Resolve --> Identity[Return same object identity]
Mapped -->|No| NameError[super raises NameError]
Lookup -->|Eager exception| Eager[Resolve silently via existing constant]
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📝 WalkthroughWalkthroughThe change replaces eager legacy constant aliases with lazy deprecation shims. Internal runtime references and tests now use the canonical ChangesNamespace migration
Estimated code review effort: 4 (Complex) | ~45 minutes Merge Risk: 🔵 Low · up to The deprecation behavior is mergeable, but the unsilenced warning tests should isolate and restore the SNAP_DIFF_SILENCE_DEPRECATIONS environment variable so inherited settings cannot suppress expected warnings or cause inconsistent test results. Sequence Diagram(s)sequenceDiagram
participant LegacyCaller
participant LegacyShims
participant SnapDiff
LegacyCaller->>LegacyShims: request legacy constant
LegacyShims->>LegacyCaller: emit deprecation warning once
LegacyShims->>SnapDiff: resolve mapped constant
SnapDiff-->>LegacyCaller: return canonical object
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Inline comments:
In `@test/unit/legacy_namespace_deprecation_test.rb`:
- Around line 35-44: Update the setup and teardown methods in the legacy
namespace deprecation tests to save, remove, and restore the
SNAP_DIFF_SILENCE_DEPRECATIONS environment variable, while preserving the
existing silence_deprecations and deprecation reset handling so warning
assertions run unsilenced.
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📒 Files selected for processing (62)
lib/capybara/screenshot/diff/annotation_service.rblib/capybara/screenshot/diff/area_calculator.rblib/capybara/screenshot/diff/browser_helpers.rblib/capybara/screenshot/diff/config_legacy.rblib/capybara/screenshot/diff/difference.rblib/capybara/screenshot/diff/drivers.rblib/capybara/screenshot/diff/drivers/base_driver.rblib/capybara/screenshot/diff/image_compare.rblib/capybara/screenshot/diff/image_preprocessor.rblib/capybara/screenshot/diff/os.rblib/capybara/screenshot/diff/reporters/default.rblib/capybara/screenshot/diff/screenshot_matcher.rblib/capybara/screenshot/diff/screenshoter.rblib/capybara/screenshot/diff/stable_screenshoter.rblib/capybara/screenshot/diff/utils.rblib/capybara/screenshot/diff/vcs.rblib/capybara/screenshot/diff/version.rblib/capybara_screenshot_diff.rblib/capybara_screenshot_diff/attempts_reporter.rblib/capybara_screenshot_diff/dsl.rblib/capybara_screenshot_diff/error_with_filtered_backtrace.rblib/capybara_screenshot_diff/reporters/html.rblib/capybara_screenshot_diff/screenshot_assertion.rblib/capybara_screenshot_diff/screenshot_namer.rblib/capybara_screenshot_diff/snap.rblib/capybara_screenshot_diff/snap_manager.rblib/snap_diff.rblib/snap_diff/dsl.rblib/snap_diff/integrations/cucumber.rblib/snap_diff/integrations/minitest.rblib/snap_diff/integrations/rspec.rblib/snap_diff/legacy_shims.rblib/snap_diff/screenshot_matcher.rblib/snap_diff/screenshoter.rblib/snap_diff/snap_manager.rbtest/integration/browser_screenshot_test.rbtest/integration/test_methods_system_test.rbtest/support/test_doubles.rbtest/system_test_case.rbtest/test_helper.rbtest/unit/annotation_service_test.rbtest/unit/area_calculator_test.rbtest/unit/backtrace_filter_test.rbtest/unit/compare_api_test.rbtest/unit/difference_test.rbtest/unit/drivers/chunky_png_driver_test.rbtest/unit/drivers/utils_test.rbtest/unit/drivers/vips_driver_test.rbtest/unit/image_compare_test.rbtest/unit/image_preprocessor_test.rbtest/unit/legacy_namespace_deprecation_test.rbtest/unit/registry_concurrency_test.rbtest/unit/reporters/default_test.rbtest/unit/reporters/html_reporter_test.rbtest/unit/screenshot_matcher_test.rbtest/unit/screenshot_namer_test.rbtest/unit/screenshoter_test.rbtest/unit/snap_diff_deprecation_test.rbtest/unit/snap_manager_cleanup_test.rbtest/unit/snap_manager_test.rbtest/unit/stable_screenshoter_test.rbtest/unit/vcs_test.rb
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v2 step 8 (ADR-004): the test suite now exercises the canonical SnapDiff:: names everywhere except tests whose purpose IS the legacy surface. - Migrate every deprecated old-namespace constant reference in test/ to its SnapDiff:: equivalent (ImageCompare -> Comparison, Difference -> ComparisonResult, SnapManager, ScreenshotAssertion, Vcs, StableScreenshoter, Screenshoter, BrowserHelpers, Reporters::HTML, Snap, DSL, ...). - Replace the suite-wide SnapDiff.silence_deprecations = true (from #218) with the opposite guard: a Warning hook in test_helper that RAISES on any [snap_diff deprecation] warning, so accidental old-name use inside the suite fails loud at the resolution site. Legacy-surface tests opt out per test: namespace_forwarding_test silences deprecations in its own setup; legacy_namespace_deprecation_test and snap_diff_deprecation_test flag their captured warnings as expected (module flag, not thread-local, so warnings from spawned threads are covered too). - Deliberate legacy keeps, each scoped and documented in place: namespace_forwarding_test / legacy_namespace_deprecation_test / support_load_probe_test (their purpose), snap_diff_test's alias-pinning test, one static_test case pinning the CapybaraScreenshotDiff.serve forwarder, the legacy entry-point requires in the rspec fixtures, and system_test_case's 'include Capybara::Screenshot::Diff' v1 mixin path. rake test:unit 488/0/0 and rake test 521/0/6 -- unchanged run counts, zero deprecation output. Mutation-checked: reintroducing one old constant in a migrated file makes the guard raise.
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v2 step 6 — deprecation shim layer (ADR-004)
Every old-namespace constant that previously forwarded silently now emits a deprecation warning exactly once per constant per process when resolved via its old name, pointing at the
SnapDiff::replacement, while still resolving to the exact same object (identity stays pinned bytest/unit/namespace_forwarding_test.rb, untouched).Mechanism
lib/snap_diff/legacy_shims.rbinstalls aconst_missinghook per old namespace (Capybara::Screenshot,Capybara::Screenshot::Diff,CapybaraScreenshotDiff,CapybaraScreenshotDiff::Reporters, andSnapDiff::DriversforBaseDriver). The hook warns through the pre-existingSnapDiff::Deprecationmachinery (mutex-guarded seen-set → warn-once;Kernel#warn→Warning.warnchannel) and returnsObject.const_get(new_name)without defining the constant, so identity is same-object and warn-once is owned by one place. Unmapped names stillsuperto a normalNameError.Lazy vs. eager (and why)
Moved to lazy const_missing (22 of the 27 mapped pairs): BrowserHelpers, Screenshoter | Vcs, StableScreenshoter, ImagePreprocessor, AreaCalculator, AnnotationService, Utils, ScreenshotMatcher, Drivers, ImageCompare, Difference | SnapManager, Snap, ScreenshotNamer, AttemptsReporter, BacktraceFilter, ErrorWithFilteredBacktrace, ScreenshotAssertion, AssertionRegistry | Reporters::HTML | Drivers::BaseDriver.
Stayed eager and silent (documented in
legacy_shims.rband at each site):Capybara::Screenshot::Os,CapybaraScreenshotDiff::DSL(and the unmappedCapybaraScreenshotDiff::Minitest::Assertions) — advertised entry-point constants probed withObject.const_defined?bysupport_load_probe_test.rb;const_defined?never triggersconst_missing, so a lazy shim would break that contract.Capybara::Screenshot::Diff::VERSION— resolved by the gemspec atgem buildtime; a lazy shim would make every build warn.Drivers::ChunkyPNGDriver/Drivers::VipsDriver— real constants on the sharedSnapDiff::Driversmodule (theDriversalias is same-object by contract), soconst_missingcan never fire for the leaf names; the old path still warns once for...::Driversitself.Silencing
Existing
SnapDiff::DeprecationAPI only, nothing new:SnapDiff.silence_deprecations = trueorSNAP_DIFF_SILENCE_DEPRECATIONS=1("true"also accepted).Internal code is warning-free
All gem-internal references to mapped old names were switched to
SnapDiff::(config_legacy defaults/AVAILABLE_DRIVERS/compare, umbrella error superclasses,screenshot_matcher,dsl, integrations'BrowserHelpers,Reporters::Default, sessionregistry). Pinned by subprocess probes in the newtest/unit/legacy_namespace_deprecation_test.rb: each entry point (capybara_screenshot_diff,/minitest,/rspec,capybara-screenshot-diff,snap_diff) is loaded in a bare unsilenced process, runs a real comparison plus the session lifecycle, and must emit zero deprecation output — with an unsilenced control probe asserting that touching an old constant in the same setup does warn.Known edge (by design)
const_missingcannot hook lookups that bypass it:include Capybara::Screenshot::Diff+ bareVcs(ancestor lookup) or reopeningmodule ...Diff::Drivers(defines a fresh module) no longer resolve the old names. Our own suite had both — fixed by qualifying asSnapDiff::...and renesting the driver tests underSnapDiff::Drivers.test_helpersilences deprecations suite-wide (tests exercise old names on purpose); the pre-existingsnap_diff_deprecation_testnow sets the flag false in its own setup.Gate evidence
legacy_namespace_deprecation_test.rbwritten before the shim — 23 red (22 warn-once pairs + control probe), green after.rake test:unit: 483 runs, 0 failures, 0 errors (455 baseline + 28 new); zero deprecation lines in suite output.rake test(full): 516 runs, 0 failures, 0 errors, 6 skips (pre-existing env skips).standardrb: clean (142 files, no offenses).first_time = true) → all 22 warn-once tests red (Expected: 1, Actual: 2);test_silencing_suppresses_shim_warningsred;Vcsmapping removed →namespace_forwarding_testred for exactly that pair (NameError: uninitialized constant Capybara::Screenshot::Diff::Vcs).All three reverted; suites re-verified green.
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Summary by Sourcery
Introduce a deprecation shim layer that guides legacy namespace users to the canonical SnapDiff constants without breaking compatibility.
New Features:
Bug Fixes:
Enhancements:
Tests:
Summary by CodeRabbit
New Features
SnapDiffnamespace.Documentation
Tests