Revive for..of optimization

resources/build-npm.ts

@@ -6,6 +6,8 @@ import ts from 'typescript';
 
 import { changeExtensionInImportPaths } from './change-extension-in-import-paths.js';
 import { inlineInvariant } from './inline-invariant.js';
+import { optimizeArrayDestructuring } from './optimize-array-destructuring.js';
+import { optimizeForOf } from './optimize-for-of.js';
 import {
   prettify,
   readPackageJSON,
@@ -145,6 +147,7 @@ function emitTSFiles(options: {
 
   const tsProgram = ts.createProgram(['src/index.ts'], tsOptions, tsHost);
   const tsResult = tsProgram.emit(undefined, undefined, undefined, undefined, {
+    before: [optimizeForOf(tsProgram), optimizeArrayDestructuring()],
     after: [changeExtensionInImportPaths({ extension }), inlineInvariant],
   });
   assert(

resources/optimize-array-destructuring.ts

@@ -0,0 +1,36 @@
+import ts from 'typescript';
+
+export function optimizeArrayDestructuring() {
+  const transformer: ts.TransformerFactory<ts.SourceFile> = (context) => {
+    const { factory } = context;
+
+    return (sourceFile: ts.SourceFile): ts.SourceFile => {
+      const visitor = (node: ts.Node): ts.Node => {
+        if (ts.isArrayBindingPattern(node)) {
+          const elements = node.elements
+            .map((el, i) => {
+              if (!el.getText()) {
+                return undefined;
+              }
+              return { key: String(i), name: el.getText() };
+            })
+            .filter(Boolean) as Array<{ key: string; name: string }>;
+
+          const objectBindingPattern = factory.createObjectBindingPattern(
+            elements.map((el) => {
+              const key = factory.createIdentifier(el.key);
+              const name = factory.createIdentifier(el.name);
+              return factory.createBindingElement(undefined, key, name);
+            }),
+          );
+          return objectBindingPattern;
+        }
+
+        return ts.visitEachChild(node, visitor, context);
+      };
+      return ts.visitNode(sourceFile, visitor) as ts.SourceFile;
+    };
+  };
+
+  return transformer;
+}