Pratt parser

.gitignore

@@ -1,4 +1,9 @@
 node_modules
+.DS_Store
+types/
 test/fixtures/*.actual.css
-src/parser.js
 yarn-error.log
+reports/
+.stryker-tmp/
+test/corpus/github/files/
+test/corpus/github/.harvest-state.json

README.md

@@ -120,6 +120,61 @@ div[data-size="calc(3*3)"] {
 }
 ```
 
+#### `onParseError`
+
+Callback invoked when a `calc()` body fails to parse or simplify. Matches
+[`@csstools/css-calc`][csstools-css-calc]'s shape:
+
+```js
+calc({
+  onParseError: (err, input) => {
+    throw err; // or log, route to a different channel, etc.
+  }
+})
+```
+
+When omitted, errors are reported via PostCSS `result.warn()` so the
+plugin never throws at the postcss level.
+
+### Behavior differences from the legacy parser
+
+The legacy [jison][jison]-generated parser was replaced by a hand-written
+Pratt parser whose simplifier follows [CSS Values 4][css-values-4]. Most
+inputs reduce to identical output; the differences are spec-aligned or
+canonical-form decisions:
+
+- **Strict whitespace (§10.1).** `calc(2px+3px)` is invalid CSS (binary
+  `+` / `-` require surrounding whitespace) and is preserved with a
+  warning instead of reduced.
+- **Canonical operand order.** Commutative operands serialize
+  numeric-first, matching [`@csstools/css-calc`][csstools-css-calc]:
+  `calc(var(--foo) + 10px)` → `calc(10px + var(--foo))`.
+- **Zero buckets are kept.** `calc(100px - (100px - 100%))` →
+  `calc(0px + 100%)`, not `100%` — [WPT calc-serialization-002][wpt-calc-serialization]
+  requires the zero term because it carries the length-percentage type.
+- **Constant folding.** `calc(43 + pi)` now folds to `46.14159` (§10.7.1).
+  Previously `pi` / `e` stayed symbolic.
+- **Reciprocal conversion.** `calc(var(--x) / 2)` becomes
+  `calc(var(--x) * 0.5)`. The two are mathematically equivalent;
+  previously the division shape was kept.
+- **Distributive multiplication.** `calc(0.5 * (100vw - 10px))` becomes
+  `calc(50vw - 5px)`.
+- **Unit case normalization.** `2PX` becomes `2px` (CSS units are case-
+  insensitive; lowercase is conventional).
+- **Calc unwrap (§10.6).** `calc(var(--foo))` becomes `var(--foo)` — a
+  `calc()` containing a single value is replaced by that value.
+- **Spec-style spaced operators.** `2px*var(--x)` is serialized as
+  `2px * var(--x)`. The tokenizer is unaffected; only output spacing
+  differs.
+- **Division by zero / by a unit.** `calc(500px/0)` reduces to
+  `calc(infinity * 1px)` (§10.13) instead of throwing. Use `onParseError`
+  if you want validation behavior.
+
+[css-values-4]: https://www.w3.org/TR/css-values-4/
+[csstools-css-calc]: https://www.npmjs.com/package/@csstools/css-calc
+[wpt-calc-serialization]: https://github.com/web-platform-tests/wpt/blob/master/css/css-values/calc-serialization-002.html
+[jison]: https://github.com/zaach/jison
+
 ---
 
 ## Related PostCSS plugins
@@ -149,5 +204,5 @@ npm test
 [PostCSS]: https://github.com/postcss
 [PostCSS Calc]: https://github.com/postcss/postcss-calc
 [PostCSS Custom Properties]: https://github.com/postcss/postcss-custom-properties
-[tests]: src/__tests__/index.js
+[tests]: test/index.js
 [W3C calc() implementation]: https://www.w3.org/TR/css3-values/#calc-notation

eslint.config.js

@@ -1,18 +1,63 @@
 const js = require('@eslint/js');
 const eslintConfigPrettier = require('eslint-config-prettier');
+const sonarjs = require('eslint-plugin-sonarjs');
 
 module.exports = [
   {
-    ignores: ['src/parser.js'],
+    ignores: ['node_modules/**', '.stryker-tmp/**', 'reports/**', 'types/**'],
   },
   js.configs.recommended,
+  // SonarJS — code smells, cognitive complexity, dead stores, etc.
+  {
+    files: ['src/**/*.js', 'test/**/*.mjs', 'scripts/**/*.mjs'],
+    plugins: { sonarjs },
+    rules: {
+      ...sonarjs.configs.recommended.rules,
+      // Math hot paths (simplify, tokenizer, foldConstArgs, naive oracles)
+      // have intrinsic complexity that's not extractable without diluting
+      // single-pass intent. Default 15 is too tight; 25 still flags real
+      // accidental complexity.
+      'sonarjs/cognitive-complexity': ['error', 25],
+    },
+  },
+  {
+    rules: {
+      // Underscore-prefix is the convention for "intentionally unused".
+      'no-unused-vars': [
+        'error',
+        { argsIgnorePattern: '^_', varsIgnorePattern: '^_' },
+      ],
+    },
+  },
   eslintConfigPrettier,
   {
+    files: ['src/**/*.js', 'test/**/*.js', 'eslint.config.js'],
     languageOptions: {
       sourceType: 'commonjs',
+      globals: {
+        process: 'readonly',
+        require: 'readonly',
+        module: 'readonly',
+        __dirname: 'readonly',
+        Buffer: 'readonly',
+      },
     },
     rules: {
       curly: 'error',
     },
   },
+  {
+    files: ['**/*.mjs'],
+    languageOptions: {
+      sourceType: 'module',
+      globals: {
+        console: 'readonly',
+        performance: 'readonly',
+        process: 'readonly',
+        fetch: 'readonly',
+        URL: 'readonly',
+        setTimeout: 'readonly',
+      },
+    },
+  },
 ];

package.json

@@ -22,31 +22,35 @@
     "LICENSE"
   ],
   "scripts": {
-    "prepare": "pnpm run build && tsc",
-    "build": "jison ./parser.jison -o src/parser.js",
     "lint": "eslint . && tsc",
-    "test": "node --test"
+    "test": "node --test",
+    "test:mutation": "stryker run"
   },
   "author": "Andy Jansson",
   "license": "MIT",
   "engines": {
     "node": "^22.12 || ^24.11 || >=26.0"
   },
   "devDependencies": {
+    "@csstools/css-calc": "^3.2.0",
     "@eslint/js": "^10.0.1",
+    "@rmenke/css-tokenizer-tests": "^1.2.0",
+    "@stryker-mutator/core": "^9.6.1",
+    "@stryker-mutator/typescript-checker": "^9.6.1",
     "@types/node": "^26.1.1",
     "eslint": "^10.6.0",
     "eslint-config-prettier": "^10.1.8",
-    "jison-gho": "0.6.1-216",
+    "eslint-plugin-sonarjs": "^4.0.3",
+    "fast-check": "^4.7.0",
     "postcss": "^8.5.16",
     "prettier": "^3.9.5",
     "typescript": "~6.0.3"
   },
   "dependencies": {
-    "postcss-selector-parser": "^7.1.4",
+    "@csstools/css-tokenizer": "^4.0.0",
     "postcss-value-parser": "^4.2.0"
   },
   "peerDependencies": {
     "postcss": "^8.5.16"
   }
-}
+}