improve sourcemap performance

lib/map-generator.js

@@ -17,6 +17,10 @@ class MapGenerator {
     this.opts = opts
     this.css = cssString
     this.usesFileUrls = !this.mapOpts.from && this.mapOpts.absolute
+
+    this.memoizedFileURLs = new Map()
+    this.memoizedPaths = new Map()
+    this.memoizedURLs = new Map()
   }
 
   addAnnotation() {
@@ -241,18 +245,22 @@ class MapGenerator {
   }
 
   path(file) {
-    if (file.indexOf('<') === 0) return file
-    if (/^\w+:\/\//.test(file)) return file
     if (this.mapOpts.absolute) return file
+    if (file.charCodeAt(0) === 60 /* `<` */) return file
+    if (/^\w+:\/\//.test(file)) return file
+    let cached = this.memoizedPaths.get(file)
+    if (cached) return cached
 
     let from = this.opts.to ? dirname(this.opts.to) : '.'
 
     if (typeof this.mapOpts.annotation === 'string') {
       from = dirname(resolve(from, this.mapOpts.annotation))
     }
 
-    file = relative(from, file)
-    return file
+    let path = relative(from, file)
+    this.memoizedPaths.set(file, path)
+
+    return path
   }
 
   previous() {
@@ -318,8 +326,14 @@ class MapGenerator {
   }
 
   toFileUrl(path) {
+    let cached = this.memoizedFileURLs.get(path)
+    if (cached) return cached
+
     if (pathToFileURL) {
-      return pathToFileURL(path).toString()
+      let fileURL = pathToFileURL(path).toString()
+      this.memoizedFileURLs.set(path, fileURL)
+
+      return fileURL
     } else {
       throw new Error(
         '`map.absolute` option is not available in this PostCSS build'
@@ -328,10 +342,17 @@ class MapGenerator {
   }
 
   toUrl(path) {
+    let cached = this.memoizedURLs.get(path)
+    if (cached) return cached
+
     if (sep === '\\') {
       path = path.replace(/\\/g, '/')
     }
-    return encodeURI(path).replace(/[#?]/g, encodeURIComponent)
+
+    let url = encodeURI(path).replace(/[#?]/g, encodeURIComponent)
+    this.memoizedURLs.set(path, url)
+
+    return url
   }
 }