Add deterministic Tailwind parity checks (#144)

* Add deterministic Tailwind parity checks

Compare RustyWind with pinned real-world TSX, Svelte, and Astro
corpora through xtask. Lock formatter inputs and corpus fingerprints so
large parser changes can be checked reproducibly.

Treat shared-order and extraction differences as failures while reporting
custom utilities separately.

* Harden Tailwind parity checks

Resolve the release binary from Cargo's artifact output so custom target
directories are honored. Classify every Tailwind token, bound child
processes, and scrub configured paths from errors.

Author: praveenperera

justfile

@@ -6,6 +6,9 @@ fmt:
 clippy:
     cargo clippy -- -D warnings
 
+compare-tailwind *args:
+    cargo xtask compare run {{args}}
+
 update:
     cargo update --workspace
 

tests/tailwind-compare/README.md

@@ -0,0 +1,49 @@
+# Tailwind comparison engine
+
+This package compares RustyWind's ordering of static quoted class attributes
+with Prettier's Tailwind CSS plugin across a pinned external corpus. It supports
+TSX, Svelte, and Astro sources. The engine reverses eligible class lists in
+memory before invoking either formatter, so already-sorted source does not
+produce false agreement.
+
+Install the exact toolchain and run the focused unit tests with:
+
+```bash
+cd tests/tailwind-compare
+npm ci
+npm test
+```
+
+The repository's `xtask` command is the intended orchestration layer. It checks
+out the corpus and supplies every input explicitly:
+
+```bash
+node compare.mjs \
+  --corpus example/project \
+  --repo /path/to/project \
+  --revision 0123456789abcdef0123456789abcdef01234567 \
+  --scope src \
+  --kind tsx \
+  --limit 30 \
+  --rustywind ../../target/release/rustywind \
+  --stylesheet tailwind.css \
+  --output /path/to/report.json
+```
+
+Candidates are ranked by descending static attribute count, then by bytewise
+UTF-8 relative path. The report fingerprint is SHA-256 over those ordered
+selected records: relative path, NUL, scrambled source, NUL. Reports contain
+only logical corpus paths, not checkout or executable paths.
+
+The process exits nonzero for invalid arguments, missing inputs, and a failed
+Tailwind classification probe. Source parse errors and RustyWind failures are
+recorded in the report for the caller to interpret alongside ordering and
+extraction findings.
+
+Only quoted `class` and `className` literals without template delimiters are in
+scope. Dynamic expressions, `class:list`, helper calls such as `cn` and `cva`,
+and project-specific Tailwind configuration are outside this comparison. A
+token is Tailwind-known when the pinned Prettier plugin moves it past two
+unknown sentinels using the supplied minimal Tailwind 4 stylesheet. Differences
+that preserve the order of known tokens are reported separately as
+`custom-only`.