fix: concat performance

src/utils/safe-stringify.ts

@@ -0,0 +1,34 @@
+const replacer = (key: string, value: unknown) => {
+  if (typeof value === 'object') {
+    if (key === 'globalThis') {
+      return '[globalThis]';
+    }
+    if (key === 'global') {
+      return '[global]';
+    }
+    if (key === 'GLOBAL') {
+      return '[GLOBAL]';
+    }
+    if (key === 'process') {
+      return '[process]';
+    }
+    if (key === 'win32') {
+      // path.win32
+      return '[win32]';
+    }
+    if (key === 'posix') {
+      // path.posix
+      return '[posix]';
+    }
+  }
+  if (typeof value === 'function') {
+    return '[Function]';
+  }
+  if (typeof value === 'bigint') {
+    return '[bigint]';
+  }
+  return value;
+};
+export function safeStringify(obj: unknown) {
+  return JSON.stringify(obj, replacer);
+}

src/utils/static-eval.ts

@@ -1,29 +1,38 @@
+import { safeStringify } from './safe-stringify';
 import { EvaluatedValue, StaticValue, ConditionalValue, Node } from './types';
-import { URL } from 'url';
-type Walk = (node: Node) => EvaluatedValue;
+type Walk = (node: Node) => Promise<EvaluatedValue>;
 type State = { computeBranches: boolean; vars: Record<string, any> };
 
+const walkCache = new Map<string, EvaluatedValue>();
+
 export async function evaluate(
-  ast: Node,
-  vars = {},
-  computeBranches = true,
+  ast: Readonly<Node>,
+  vars: Readonly<Record<string, string>> = {},
+  computeBranches: Readonly<boolean> = true,
 ): Promise<EvaluatedValue> {
   const state: State = {
     computeBranches,
     vars,
   };
+  const stateCacheKey = safeStringify(state);
   return walk(ast);
 
   // walk returns:
   // 1. Single known value: { value: value }
   // 2. Conditional value: { test, then, else }
   // 3. Unknown value: undefined
-  function walk(node: Node) {
+  async function walk(node: Node) {
+    const walkCacheKey = stateCacheKey + safeStringify(node);
+    let result = walkCache.get(walkCacheKey);
+    if (result) {
+      return result;
+    }
     const visitor = visitors[node.type];
     if (visitor) {
-      return visitor.call(state, node, walk);
+      result = await visitor.call(state, node, walk);
     }
-    return undefined;
+    walkCache.set(walkCacheKey, result);
+    return result;
   }
 }
 
@@ -359,7 +368,7 @@ const visitors: Record<
       if (typeof obj.value === 'string' && node.property.name === 'concat') {
         return {
           value: {
-            [FUNCTION]: (...args: string[]) => obj.value.concat(args),
+            [FUNCTION]: (...args: string[]) => obj.value.concat(...args),
           },
         };
       }

test/unit.test.js

@@ -8,6 +8,8 @@ const stat = gracefulFS.promises.stat;
 const readlink = gracefulFS.promises.readlink;
 const readFile = gracefulFS.promises.readFile;
 
+jest.setTimeout(5_000);
+
 global._unit = true;
 
 const nodeGypTests = [
@@ -139,6 +141,7 @@ for (const { testName, isRoot } of unitTests) {
         // Ignore.
       }
 
+      const startTime = Date.now();
       const { fileList, reasons } = await nodeFileTrace(
         inputFileNames.map((file) => join(unitPath, file)),
         {
@@ -166,6 +169,9 @@ for (const { testName, isRoot } of unitTests) {
         },
       );
 
+      const totalTime = Date.now() - startTime;
+      expect(totalTime).toBeLessThan(1000);
+
       const normalizeFilesRoot = (f) =>
         (isRoot ? relative(join('./', __dirname, '..'), f) : f).replace(
           /\\/g,

test/unit/string-concat-chain/input.js

@@ -0,0 +1,24 @@
+var str = './lib/'
+  .concat('1')
+  .concat('_', '2')
+  .concat('_', '3')
+  .concat('_', '4')
+  .concat('_', '5')
+  .concat('_', '6')
+  .concat('_', '7')
+  .concat('_', '8')
+  .concat('_', '9')
+  .concat('_', '10')
+  .concat('_', '11')
+  .concat('_', '12')
+  .concat('_', '13')
+  .concat('_', '14')
+  .concat('_', '15')
+  .concat('_', '16')
+  .concat('_', '17')
+  .concat('_', '18')
+  .concat('_', '19')
+  .concat('_', '20')
+  .concat('.js');
+
+require(str);

test/unit/string-concat-chain/lib/1_2_3_4_5_6_7_8_9_10_11_12_13_14_15_16_17_18_19_20.js

@@ -0,0 +1 @@
+module.exports = { file: 'file' }

test/unit/string-concat-chain/output.js

@@ -0,0 +1,5 @@
+[
+  "package.json",
+  "test/unit/string-concat-chain/input.js",
+  "test/unit/string-concat-chain/lib/1_2_3_4_5_6_7_8_9_10_11_12_13_14_15_16_17_18_19_20.js"
+]