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leaysgur 0f4af5d7df test(formatter_tests): assert fingerprint survives formatting (#26322 )

Historically, only JS formatter has had the `detect_code_removal` feature, which uses CI to check for missing nodes or comments.

While this would be useful in other languages (especially CSS), but setting up the mechanism is difficult. For now, just start with something simple that just guarantees the number of comments.

That said, even with a mechanism in place, it can't detect anything unless the cases are fully covered by fixtures, so this only tells us that the current state is problem-free.

2026-09-04 07:14:53 +00:00

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Coding agent guides for `crates/oxc_formatter_tests`

Test infrastructure shared by the formatter crates (e.g. oxc_formatter, oxc_formatter_json, oxc_formatter_css, etc).

codegen: build-script helper
- Consumers call generate_tests from build.rs via [build-dependencies] to emit one #[test] per fixture file
harness: fixture runtime
- Consumers implement FixtureFormatter in tests/fixtures/mod.rs via [dev-dependencies]
- Asserts FixtureFormatter::fingerprint is the same for input and output; consumers take it from the crate's own parse (parse_for_format), what it captures is consumer-owned
suite: Prettier test-suite provisioning
- ensure_prettier_suite() maintains the pinned suite at prettier/ (gitignored), no separate clone step anywhere
conformance (feature conformance): Prettier-conformance machinery
- Spec parsing, snapshot matching, report building
- Consumers add a tests/conformance.rs target with a ConformanceConfig + format callback and pin the report with insta;
- the crate's own Cargo.toml documents why the feature exists
- Option-set → typed-options mapping is shared per crate via tests/fixtures/options.rs (#[path]-included by both the fixture harness and the conformance target)

Prettier suite

Pinned by the prettier version in apps/oxfmt/package.json (the bundled oracle); provisioning mechanics live in src/suite.rs's rustdocs. Tarball extraction always yields LF content, so Windows needs no autocrlf care. CI only mounts prettier/ as a cache volume, there is no clone step to keep in sync.

Bumping Prettier = bump apps/oxfmt/package.json + regenerate conformance snapshots (one change set; the suite re-provisions itself on the next run)
Provisioning failure is a loud failure everywhere it runs (a silent skip would let conformance rot green; needs network + curl/tar)
- Environments that cannot provision opt out in ci.yml, not in crate code: CI's cross jobs (s390x/armv7) pass -- --skip prettier_conformance
  - Every suite-provisioning consumer names its conformance test fn prettier_conformance*, that name prefix is the contract the skip filter relies on
  - The inverse holds too: tests over COMMITTED fixtures (e.g. oxc_formatter's jsdoc fixture-pair test) deliberately avoid the prefix so cross targets still run them
Requires curl and tar on PATH (standard on macOS, Linux, and Windows 10+)

Dependency rule

This crate NEVER depends on a formatter language crate (oxc_formatter, oxc_formatter_json, ...). Consumers use it from both [build-dependencies] and [dev-dependencies]; a dependency on a language crate would make that a build-dep cycle, which cargo rejects.

insta stays consumer-side

build_fixture_snapshot returns the snapshot body without calling insta::assert_snapshot!. Each consumer invokes the macro from its own tests/fixtures/mod.rs so the recorded source: header points to the consumer crate (required by INSTA_REQUIRE_FULL_MATCH=1 in CI). Consumers therefore need their own insta dev-dep.

Verification

cargo c -p oxc_formatter_tests

Exercised through the fixture tests of its consumers (cargo test -p <formatter crate>).

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Coding agent guides for crates/oxc_formatter_tests