no-custom-classname: perf optimization

Author: XantreDev

lib/util/cssFiles.js

@@ -3,12 +3,17 @@
 const fg = require('fast-glob');
 const fs = require('fs');
 const postcss = require('postcss');
-const removeDuplicatesFromArray = require('./removeDuplicatesFromArray');
 
-let previousGlobsResults = [];
+const classRegexp = /\.([^\.\,\s\n\:\(\)\[\]\'~\+\>\*\\]*)/gim;
+
 let lastUpdate = null;
 let classnamesFromFiles = [];
 
+/**
+ * @type {Map<string, number}
+ */
+const prevEditedTimestamp = new Map()
+
 /**
  * Read CSS files and extract classnames
  * @param {Array} patterns Glob patterns to locate files
@@ -17,27 +22,56 @@ let classnamesFromFiles = [];
  */
 const generateClassnamesListSync = (patterns, refreshRate = 5_000) => {
   const now = new Date().getTime();
-  const files = fg.sync(patterns, { suppressErrors: true });
-  const newGlobs = previousGlobsResults.flat().join(',') != files.flat().join(',');
   const expired = lastUpdate === null || now - lastUpdate > refreshRate;
-  if (newGlobs || expired) {
-    previousGlobsResults = files;
-    lastUpdate = now;
-    let detectedClassnames = [];
-    for (const file of files) {
-      const data = fs.readFileSync(file, 'utf-8');
-      const root = postcss.parse(data);
-      root.walkRules((rule) => {
-        const regexp = /\.([^\.\,\s\n\:\(\)\[\]\'~\+\>\*\\]*)/gim;
-        const matches = [...rule.selector.matchAll(regexp)];
-        const classnames = matches.map((arr) => arr[1]);
-        detectedClassnames.push(...classnames);
-      });
-      detectedClassnames = removeDuplicatesFromArray(detectedClassnames);
+
+  if (!expired) {
+    return classnamesFromFiles;
+  }
+  const files = fg.sync(patterns, { suppressErrors: true, stats: true });
+  lastUpdate = now;
+
+  /**
+   * @type {Set<string}
+   */
+  const detectedClassnames = new Set();
+  /**
+   * @type {Set<string>}
+   */
+  const filesSet = new Set();
+  for (const { path: file, stats } of files) {
+    filesSet.add(file);
+    if (!stats) {} 
+    // file is not changed -> we do need to do extra work
+    else if (prevEditedTimestamp.get(file) === stats.mtimeMs) {
+      continue;
+    } else {
+      prevEditedTimestamp.set(file, stats.mtimeMs);
     }
-    classnamesFromFiles = detectedClassnames;
+    const data = fs.readFileSync(file, 'utf-8');
+    const root = postcss.parse(data);
+    root.walkRules((rule) => {
+      for (const match of rule.selector.matchAll(classRegexp)) {
+        detectedClassnames.add(match[1]);
+      }
+    });
   }
-  return classnamesFromFiles;
+  // avoiding memory leak
+  {
+    /**
+     * @type {string[]}
+     */
+    const keysToDelete = []
+    for (const cachedFilePath of prevEditedTimestamp.keys()) {
+      if (!filesSet.has(cachedFilePath)) {
+        keysToDelete.push(cachedFilePath);
+      }
+    }
+    for (const key of keysToDelete) {
+      prevEditedTimestamp.delete(key);
+    }
+ }
+  classnamesFromFiles = [...detectedClassnames];
+  return classnamesFromFiles
 };
 
 module.exports = generateClassnamesListSync;