0.3.0 - 2026-06-13

Release Notes

Since 0.2.0. Conformance holds at 100% of the attempted sass-spec suite
(13,896 / 13,896) — but that suite covers valid inputs plus the errors it
expects; this cycle hardened sasso to reject the same malformed inputs
dart-sass rejects, and cut more of the @extend and value hot paths.

Changed

• Strict input validation. Beyond matching dart-sass's output, sasso now
  errors — rather than silently accepting — on malformed input, each with
  dart-sass's exact message: an invalid hex literal (#00000, #0g),
  out-of-grammar rgb()/hsl() channel units and legacy-vs-modern argument
  shapes, a duplicate @mixin/@function parameter, a malformed number
  exponent (1e-), a non-identifier @use/@forward namespace, a misplaced
  @content/@extend, a style rule / declaration / @extend in a @function
  body, a map or empty list used as a CSS value (#{(a:1)}, -()), a
  malformed :nth-child() An+B or empty :not() selector, a stray ! in a
  selector, a leading-empty @extend target, and a malformed @charset /
  @at-root (…) query. Found by a leniency-mining sweep that diffed every
  category against dart-sass; the fixes are uncovered by the spec, so the
  ratchet is unchanged.

Performance

• Transitive @extend went from ~151× slower than dart-sass to faster
  on a deep extend chain: a match pre-filter with typed dedup, an incremental
  per-rule fold (killing the O(N²) closure re-derivation), borrowed
  scope-originals, and cached typed selector hashes — the @extend maps are
  now FxHash + typed Complex/Simple keys, guarded by a render-injectivity
  parity proof. Byte-identical output throughout.
• Reference-counted composite values — Str/List/Map are Rc-backed,
  so cloning a read-only $variable is an O(1) refcount bump instead of a deep
  copy (copy-on-write for the mutating builtins): ~7× fewer instructions and
  ~13× less peak memory when a large list/map is passed through a call chain.
• Cow-borrowed argument-name normalization (called 4–6× per function
  call) plus trimmed function-call-path allocations — ~15% fewer instructions
  on a function-heavy compile.
• Arena in-place realloc — the scoped bump arena extends its tail
  allocation in place instead of stranding a dead buffer on every Vec
  doubling, trimming peak memory on parse-heavy compiles.
• Net: pure-compile throughput ~7.4 ms on the large benchmark (was ~9–10),
  ~2.3–2.9× faster than grass and ~19–30× faster than the dart-sass JS bin.

Internal

• eval.rs split into an eval/ module directory and color.rs into a
  color/ directory (pure code moves); the typed selector model gained a
  parity-proof harness; the stringly hoist markers became typed OutNode
  variants; the @extend cartesian-order bool became a CartesianOrder enum;
  OutNode rule/at-rule constructors collapsed duplicated construction sites.
  All byte-identical, each verified base-binary-vs-refactor.

Tooling

• The WebAssembly npm package publishes via OIDC Trusted Publishing (no token).
• Benchmark harness uses portable temp-file handling (mktemp -d).

Install sasso 0.3.0

Install prebuilt binaries via shell script

curl --proto '=https' --tlsv1.2 -LsSf https://github.com/momiji-rs/sasso/releases/download/v0.3.0/sasso-installer.sh | sh

Install prebuilt binaries via powershell script

powershell -ExecutionPolicy Bypass -c "irm https://github.com/momiji-rs/sasso/releases/download/v0.3.0/sasso-installer.ps1 | iex"

Download sasso 0.3.0

File	Platform	Checksum
sasso-aarch64-apple-darwin.tar.xz	Apple Silicon macOS	checksum
sasso-x86_64-apple-darwin.tar.xz	Intel macOS	checksum
sasso-x86_64-pc-windows-msvc.zip	x64 Windows	checksum
sasso-aarch64-unknown-linux-gnu.tar.xz	ARM64 Linux	checksum
sasso-x86_64-unknown-linux-gnu.tar.xz	x64 Linux	checksum
sasso-aarch64-unknown-linux-musl.tar.xz	ARM64 MUSL Linux	checksum
sasso-x86_64-unknown-linux-musl.tar.xz	x64 MUSL Linux	checksum