The pinned sample inherits Airbnb 19.0.4, Airbnb Base 15.0.0, and the recommended configuration from JSDoc 64.3.6. Core rule functions use the ESLint 8.57.1 source baseline without installing or executing its engine. Other providers are React 7.37.5, JSX a11y 6.10.2, import 2.32.0, and Stylistic 5.10.0. Oxlint 1.82.0 runs the rules.
The imported corpus retains pass/fail decisions, diagnostic multiplicity, message text or message identifiers and substitution data, all specified primary locations, options, globals, settings, and expected fixes and suggestions. Diagnostic identifiers use this package's plugin namespaces. Terminal rendering and parser diagnostics are not part of message parity. Legacy locations with a zero end column are normalized to the same source offset on the preceding line. Invalid locations beyond an empty line are clamped to that line.
tests/fixtures/upstream.json contains distinct serialized scenarios. scripts/import-upstream.ts captures assertions from pinned source checkouts; it never executes an ESLint runner. It does not inspect lint outcomes to select passing cases. The import report records unsupported parser capabilities and upstream-disabled parser combinations. Flow, experimental Babel syntax, custom synthetic ASTs, and the obsolete TypeScript parser's AST are outside the supported parser contract. Modern JavaScript, JSX, TypeScript, and TSX remain supported.
The harness translates upstream assertion formats unsupported by Oxlint's RuleTester. Numeric suggestion expectations are checked at the report boundary; assertions containing both a suggestion description and message ID are validated for agreement before the message-ID assertion is passed to RuleTester. Auxiliary upstream rules and comment directives are retained. Nonfatal parser errors are tolerated only in the imported RuleTester corpus so rules designed to diagnose those constructs can be tested; consumer parsing remains Oxlint's responsibility.
The handwritten adapters address standalone scope metadata and comment globals, legacy context accessors and positional reports, incremental versus completed control-flow graphs, absent versus null AST fields, leading dependency comments, and ESM/CommonJS helper interoperability. Shared build chunks preserve state between cooperating rules. Behavioral tests exercise actual Oxlint CLI processes in addition to the upstream unit corpus.
Vitest coverage includes every handwritten TypeScript runtime file under packages/*/src, including files not otherwise imported. Thresholds are 95% for statements, lines, and functions and 90% for branches. Vendored source is assessed through conformance rather than included in that percentage. Repeated CLI executions used to check stability are not counted as distinct corpus scenarios.
For TypeScript files, the preset uses Oxlint's native no-unused-vars, no-shadow, no-useless-constructor, and no-empty-function implementations to understand type signatures and constructor parameter properties. It retains inherited settings, explicitly preserves the baseline's caughtErrors: none default, and uses Stylistic's TypeScript-capable indentation rule with the inherited four-space setting. These syntax-specific overrides have dedicated cases for all four TypeScript extensions; exact upstream JavaScript conformance continues to use the pinned implementations. Type-only declarations and modern TypeScript binding behavior are governed by these documented overrides rather than an ESLint TypeScript parser or a typed lint service.