perf: Speed up dev prefix generation for long file paths (#1466)

.changeset/lemon-colts-allow.md

@@ -0,0 +1,5 @@
+---
+'@vanilla-extract/css': patch
+---
+
+Speed up dev prefix generation for long file paths

packages/css/package.json

@@ -124,6 +124,7 @@
     "dedent": "^1.5.3",
     "deep-object-diff": "^1.1.9",
     "deepmerge": "^4.2.2",
+    "lru-cache": "^10.4.3",
     "media-query-parser": "^2.0.2",
     "modern-ahocorasick": "^1.0.0",
     "picocolors": "^1.0.0"

packages/css/src/getDebugFileName.test.ts

@@ -0,0 +1,45 @@
+import { getDebugFileName } from './getDebugFileName';
+
+const testCases = [
+  {
+    name: 'longPath',
+    input:
+      'node_modules/.pnpm/[email protected]_@[email protected][email protected][email protected]_re_ctndskkf4y74v2qksfjwfz6ezy/node_modules/braid-design-system/dist/lib/components/ButtonDir/Button.css.mjs',
+    expected: 'Button',
+  },
+  {
+    name: 'emojiPath',
+    input: 'node_modules/my_package/dist/👨‍👩‍👦Test🎉Dir👨‍🚀/Test🎉File👨‍🚀.css.ts',
+    expected: 'Test🎉File👨‍🚀',
+  },
+  {
+    name: 'loneSurrogates',
+    input: 'node_modules/my_package/dist/Test\uD801Dir/Test\uDC01File.css.ts',
+    expected: 'Test\uDC01File',
+  },
+  {
+    name: 'noExtension',
+    input: 'node_modules/my_package/dist/TestDir/TestFile',
+    expected: '',
+  },
+  {
+    name: 'singleFileSparator',
+    input: 'src/Button.css.ts',
+    expected: 'Button',
+  },
+  {
+    name: 'noDir',
+    input: 'myFile.css.ts',
+    expected: 'myFile',
+  },
+];
+
+describe('getDebugFileName', () => {
+  testCases.forEach(({ name, input, expected }) => {
+    it(name, () => {
+      const result = getDebugFileName(input);
+
+      expect(result).toStrictEqual(expected);
+    });
+  });
+});

packages/css/src/getDebugFileName.ts

@@ -0,0 +1,73 @@
+import { LRUCache } from 'lru-cache';
+
+const getLastSlashBeforeIndex = (path: string, index: number) => {
+  let pathIndex = index - 1;
+
+  while (pathIndex >= 0) {
+    if (path[pathIndex] === '/') {
+      return pathIndex;
+    }
+
+    pathIndex--;
+  }
+
+  return -1;
+};
+
+/**
+ * Assumptions:
+ * - The path is always normalized to use posix file separators (/) (see `addFileScope`)
+ * - The path is always relative to the project root, i.e. there will never be a leading slash (see `addFileScope`)
+ * - As long as `.css` is there, we have a valid `.css.*` file path, because otherwise there wouldn't
+ *   be a file scope to begin with
+ *
+ * The LRU cache we use can't cache undefined/null values, so we opt to return an empty string,
+ * rather than using a custom Symbol or something similar.
+ */
+const _getDebugFileName = (path: string): string => {
+  let file: string;
+
+  const lastIndexOfDotCss = path.lastIndexOf('.css');
+
+  if (lastIndexOfDotCss === -1) {
+    return '';
+  }
+
+  const lastSlashIndex = getLastSlashBeforeIndex(path, lastIndexOfDotCss);
+  file = path.slice(lastSlashIndex + 1, lastIndexOfDotCss);
+
+  // There are no slashes, therefore theres no directory to extract
+  if (lastSlashIndex === -1) {
+    return file;
+  }
+
+  let secondLastSlashIndex = getLastSlashBeforeIndex(path, lastSlashIndex - 1);
+  // If secondLastSlashIndex is -1, it means that the path looks like `directory/file.css.ts`,
+  // in which case dir will still be sliced starting at 0, which is what we want
+  const dir = path.slice(secondLastSlashIndex + 1, lastSlashIndex);
+
+  const debugFileName = file !== 'index' ? file : dir;
+
+  return debugFileName;
+};
+
+const memoizedGetDebugFileName = () => {
+  const cache = new LRUCache<string, string>({
+    max: 500,
+  });
+
+  return (path: string) => {
+    const cachedResult = cache.get(path);
+
+    if (cachedResult) {
+      return cachedResult;
+    }
+
+    const result = _getDebugFileName(path);
+    cache.set(path, result);
+
+    return result;
+  };
+};
+
+export const getDebugFileName = memoizedGetDebugFileName();

packages/css/src/identifier.ts

@@ -2,6 +2,7 @@ import hash from '@emotion/hash';
 
 import { getIdentOption } from './adapter';
 import { getAndIncrementRefCounter, getFileScope } from './fileScope';
+import { getDebugFileName } from './getDebugFileName';
 
 function getDevPrefix({
   debugId,
@@ -15,13 +16,11 @@ function getDevPrefix({
   if (debugFileName) {
     const { filePath } = getFileScope();
 
-    const matches = filePath.match(
-      /(?<dir>[^\/\\]*)?[\/\\]?(?<file>[^\/\\]*)\.css\.(ts|js|tsx|jsx|cjs|mjs)$/,
-    );
+    const debugFileName = getDebugFileName(filePath);
 
-    if (matches && matches.groups) {
-      const { dir, file } = matches.groups;
-      parts.unshift(file && file !== 'index' ? file : dir);
+    // debugFileName could be an empty string
+    if (debugFileName) {
+      parts.unshift(debugFileName);
     }
   }