From dee945d3151b8af85fbafb643b06f76432d5a4c9 Mon Sep 17 00:00:00 2001
From: Matt Lewis <hello@mattlewis.me>
Date: Tue, 5 Sep 2023 13:14:02 +0100
Subject: [PATCH] perf: cache results of fs.stat call for each build to improve
 incremental performance

---
 src/cache.ts  | 18 ++++++++++++------
 src/plugin.ts |  7 +++++--
 2 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/src/cache.ts b/src/cache.ts
index 15023bb..d1d27aa 100644
--- a/src/cache.ts
+++ b/src/cache.ts
@@ -5,8 +5,14 @@ import {promises as fsp, Stats} from 'fs'
 type OnLoadCallback = (args: OnLoadArgs) => (OnLoadResult | Promise<OnLoadResult>)
 type PluginLoadCallback = (path: string) => (OnLoadResult | Promise<OnLoadResult>)
 
-function collectStats(watchFiles): Promise<Stats[]> {
-  return Promise.all(watchFiles.map(filename => fsp.stat(filename)))
+function collectStats(watchFiles: string[], fsStatCache: Map<string, Stats>): Promise<Stats[]> {
+  return Promise.all(watchFiles.map(async filename => {
+    if (!fsStatCache.has(filename)) {
+      const stats = await fsp.stat(filename)
+      fsStatCache.set(filename, stats)
+    }
+    return fsStatCache.get(filename) as Stats
+  }))
 }
 
 function maxMtimeMs(stats: Stats[]) {
@@ -23,7 +29,7 @@ function getCache(options: SassPluginOptions): Map<string, CachedResult> | undef
   }
 }
 
-export function useCache(options: SassPluginOptions = {}, loadCallback: PluginLoadCallback): OnLoadCallback {
+export function useCache(options: SassPluginOptions = {}, fsStatCache: Map<string, Stats>, loadCallback: PluginLoadCallback): OnLoadCallback {
   const cache = getCache(options)
   if (cache) {
     return async ({path}: OnLoadArgs) => {
@@ -31,7 +37,7 @@ export function useCache(options: SassPluginOptions = {}, loadCallback: PluginLo
         let cached = cache.get(path)
         if (cached) {
           let watchFiles = cached.result.watchFiles!
-          let stats = await collectStats(watchFiles)
+          let stats = await collectStats(watchFiles, fsStatCache)
           for (const {mtimeMs} of stats) {
             if (mtimeMs > cached.mtimeMs) {
               cached.result = await loadCallback(watchFiles[0])
@@ -42,7 +48,7 @@ export function useCache(options: SassPluginOptions = {}, loadCallback: PluginLo
         } else {
           let result = await loadCallback(path)
           cached = {
-            mtimeMs: maxMtimeMs(await collectStats(result.watchFiles)),
+            mtimeMs: maxMtimeMs(await collectStats(result.watchFiles!, fsStatCache)),
             result
           }
           cache.set(path, cached)
@@ -59,4 +65,4 @@ export function useCache(options: SassPluginOptions = {}, loadCallback: PluginLo
   } else {
     return ({path}) => loadCallback(path)
   }
-}
\ No newline at end of file
+}
diff --git a/src/plugin.ts b/src/plugin.ts
index a91d9b4..e29def4 100755
--- a/src/plugin.ts
+++ b/src/plugin.ts
@@ -31,7 +31,7 @@ export function sassPlugin(options: SassPluginOptions = {}): Plugin {
 
   return {
     name: 'sass-plugin',
-    setup({initialOptions, onResolve, onLoad, resolve}) {
+    setup({initialOptions, onResolve, onLoad, resolve, onStart}) {
 
       options.loadPaths = Array.from(new Set([
         ...options.loadPaths || modulesPaths(initialOptions.absWorkingDir),
@@ -49,6 +49,9 @@ export function sassPlugin(options: SassPluginOptions = {}): Plugin {
         })
       }
 
+      const fsStatCache = new Map()
+      onStart(() => fsStatCache.clear())
+
       const transform = options.transform ? options.transform.bind(options) : null
 
       const cssChunks: Record<string, string | Uint8Array | undefined> = {}
@@ -71,7 +74,7 @@ export function sassPlugin(options: SassPluginOptions = {}): Plugin {
 
       const renderSync = createRenderer(options, options.sourceMap ?? sourcemap)
 
-      onLoad({filter: options.filter ?? DEFAULT_FILTER}, useCache(options, async path => {
+      onLoad({filter: options.filter ?? DEFAULT_FILTER}, useCache(options, fsStatCache, async path => {
         try {
           let {cssText, watchFiles, warnings} = renderSync(path)
           if (!warnings) {