perf: fast-path JSON.stringify for CachedSource cache keys

claude · claude · commit 4d32b9197b86 · 2026-04-22T17:20:39.000Z
CachedSource.map(), sourceAndMap() and streamChunks() key their map-entry cache with `JSON.stringify(options)`. That call is 60-100 ns on the common `{}` / `{columns: false}` shapes and dominates the entire method body once the cache is warm. Both MapOptions and the streamChunks Options type only contain boolean fields, so we can short-circuit the stringify for the three shapes that account for essentially all real traffic (undefined, empty object, columns-only) using interned string constants. Any other shape still falls through to JSON.stringify, so keys stay byte-identical to the on-disk BufferedMaps produced by previous CachedSource versions. Measured on the benchmark fixtures with JIT enabled (best of 5, ns/op): before after warmed.map({}) 79.1 4.3 (18x) warmed.map({columns:false})139.8 9.6 (14x) warmed.sourceAndMap({}) 89.6 9.8 (9x) warmed.map() / undefined 10.6 6.7 (1.6x) warmed.sourceAndMap() 12.4 7.7 (1.6x) Full --no-opt benchmark run shows +53% on `cached-source: map() (cached)`, +37.6% on `cached-source: sourceAndMap() (cached)`, +34.5% on `realistic-source-map-pipeline: warm sourceAndMap()`, and +17-21% on `replace-source: map()` / `sourceAndMap()`. 89813 tests still pass. https://claude.ai/code/session_01LZbaaPrnDTu6y7s4nK4cJz
diff --git a/lib/CachedSource.js b/lib/CachedSource.js
@@ -78,6 +78,34 @@ const bufferedMapToMap = (bufferedMap) => {
 /** @typedef {{ map?: null | RawSourceMap, bufferedMap?: null | BufferedMap }} BufferEntry */
 /** @typedef {Map<string, BufferEntry>} BufferedMaps */
 
+const CACHE_KEY_EMPTY = "{}";
+const CACHE_KEY_COLUMNS_FALSE = '{"columns":false}';
+const CACHE_KEY_COLUMNS_TRUE = '{"columns":true}';
+
+/**
+ * Fast-path replacement for `JSON.stringify(options)` when used as a cache
+ * key. MapOptions / streamChunks Options are both small boolean-only shapes
+ * and the overwhelmingly common shapes (`undefined`, `{}`, `{columns}`) can
+ * be keyed without calling `JSON.stringify`, which dominates short-circuit
+ * cache lookups. Falls back to `JSON.stringify` for any other shape so keys
+ * remain compatible with previously cached `BufferedMaps` entries.
+ * @param {undefined | MapOptions | Options} options options
+ * @returns {string} cache key
+ */
+const getCacheKey = (options) => {
+	if (!options) return CACHE_KEY_EMPTY;
+	const columns = options.columns;
+	if (
+		/** @type {Options} */ (options).source === undefined &&
+		/** @type {Options} */ (options).finalSource === undefined &&
+		/** @type {MapOptions} */ (options).module === undefined
+	) {
+		if (columns === undefined) return CACHE_KEY_EMPTY;
+		return columns ? CACHE_KEY_COLUMNS_TRUE : CACHE_KEY_COLUMNS_FALSE;
+	}
+	return JSON.stringify(options);
+};
+
 /**
  * @typedef {object} CachedData
  * @property {boolean=} source source
@@ -294,7 +322,7 @@ class CachedSource extends Source {
 	 * @returns {SourceAndMap} source and map
 	 */
 	sourceAndMap(options) {
-		const key = options ? JSON.stringify(options) : "{}";
+		const key = getCacheKey(options);
 		const cacheEntry = this._cachedMaps.get(key);
 		// Look for a cached map
 		if (cacheEntry !== undefined) {
@@ -332,7 +360,7 @@ class CachedSource extends Source {
 	 * @returns {GeneratedSourceInfo} generated source info
 	 */
 	streamChunks(options, onChunk, onSource, onName) {
-		const key = options ? JSON.stringify(options) : "{}";
+		const key = getCacheKey(options);
 		if (
 			this._cachedMaps.has(key) &&
 			(this._cachedBuffer !== undefined || this._cachedSource !== undefined)
@@ -379,7 +407,7 @@ class CachedSource extends Source {
 	 * @returns {RawSourceMap | null} map
 	 */
 	map(options) {
-		const key = options ? JSON.stringify(options) : "{}";
+		const key = getCacheKey(options);
 		const cacheEntry = this._cachedMaps.get(key);
 		if (cacheEntry !== undefined) {
 			return this._getMapFromCacheEntry(cacheEntry);
