perf(@angular/build): traverse AST with iterative post-order walker in i18n inliner

Replace the oxc-parser Visitor class in the i18n inliner worker with a lightweight, non-recursive post-order AST walker based on visitorKeys.

oxc-parser's Visitor class caches visitor callback objects in a module-global array across invocations, which causes all per-request MagicString instances, source code buffers, and diagnostics closures to be retained for the lifetime of the worker thread. In multi-locale builds, this leads to continuous heap accumulation and out-of-memory errors on memory-constrained CI runners.

The custom walker uses an iterative two-pass array traversal on the V8 heap to guarantee bottom-up evaluation without recursion or stack overflow risks. This ensures nested $localize template expressions are transformed and written to MagicString before outer templates evaluate their expressions, while eliminating all module-global caching and memory retention across file transformations.

Author: clydin

packages/angular/build/src/tools/esbuild/i18n-inliner-worker.ts

@@ -7,11 +7,12 @@
  */
 
 import remapping, { type DecodedSourceMap, type SourceMapInput } from '@ampproject/remapping';
+import type { Node } from '@oxc-project/types';
 import { MagicString } from 'magic-string';
 import assert from 'node:assert';
 import { deserialize } from 'node:v8';
 import { workerData } from 'node:worker_threads';
-import { Visitor, parseSync } from 'oxc-parser';
+import { parseSync, visitorKeys } from 'oxc-parser';
 
 /**
  * The options passed to the inliner for each file request
@@ -180,6 +181,51 @@ async function loadLocalizeTools(): Promise<LocalizeUtilityModule> {
   return localizeToolsModule;
 }
 
+/**
+ * Traverses ESTree AST nodes in post-order (bottom-up) without recursion.
+ * Bottom-up traversal ensures that nested `$localize` expressions are transformed and
+ * written to MagicString before outer containing templates are evaluated.
+ *
+ * @param root The root AST node to traverse.
+ * @param onExit Callback invoked on each AST node in post-order.
+ */
+function walkAstPostOrder(root: Node, onExit: (node: Node) => void): void {
+  const traverseStack: Node[] = [root];
+  const postOrderNodes: Node[] = [];
+
+  while (traverseStack.length > 0) {
+    const current = traverseStack.pop();
+    if (!current) {
+      continue;
+    }
+
+    postOrderNodes.push(current);
+
+    const keys = visitorKeys[current.type];
+    if (keys) {
+      for (let i = 0; i < keys.length; i++) {
+        const child = (current as unknown as Record<string, Node | Node[]>)[keys[i]];
+        if (child && typeof child === 'object') {
+          if (Array.isArray(child)) {
+            for (let j = 0; j < child.length; j++) {
+              const item = child[j];
+              if (item && typeof item === 'object') {
+                traverseStack.push(item);
+              }
+            }
+          } else {
+            traverseStack.push(child);
+          }
+        }
+      }
+    }
+  }
+
+  for (let i = postOrderNodes.length - 1; i >= 0; i--) {
+    onExit(postOrderNodes[i]);
+  }
+}
+
 /**
  * Transforms a JavaScript file using OXC and Magic-String to inline the request locale and translation.
  * @param code A string containing the JavaScript code to transform.
@@ -206,13 +252,12 @@ async function transformWithOxc(
   const { Diagnostics, translate } = await loadLocalizeTools();
   const diagnostics = new Diagnostics();
 
-  const visitor = new Visitor({
-    Literal(node) {
+  walkAstPostOrder(program, (node) => {
+    if (node.type === 'Literal') {
       if (typeof node.value === 'string' && node.value === '___NG_LOCALE_INSERT___') {
         magicString.overwrite(node.start, node.end, JSON.stringify(options.locale));
       }
-    },
-    'TaggedTemplateExpression:exit'(node) {
+    } else if (node.type === 'TaggedTemplateExpression') {
       if (node.tag.type === 'Identifier' && node.tag.name === '$localize') {
         const cooked = node.quasi.quasis.map((q) => q.value.cooked);
         const raw = node.quasi.quasis.map((q) => q.value.raw);
@@ -252,11 +297,9 @@ async function transformWithOxc(
 
         magicString.overwrite(node.start, node.end, replacement);
       }
-    },
+    }
   });
 
-  visitor.visit(program);
-
   const outputCode = magicString.toString();
   let outputMap;
   if (map && magicString.hasChanged()) {

packages/angular/build/src/tools/esbuild/i18n-inliner_spec.ts

@@ -274,4 +274,25 @@ describe('I18nInliner', () => {
 
     expect(findFile(outputFiles, 'other.js').text).toBe('export const answer = 42;\n');
   });
+
+  it('inlines nested $localize calls in post-order', async () => {
+    const source =
+      'export const msg = $localize`:@@outer:You selected ${$localize`:@@inner:Apple`} for delivery.`;\n';
+    const { outputFiles, errors, warnings } = await createInliner([
+      browserFile('main.js', source),
+    ]).inlineForLocale('fr', {
+      inner: translationFor('Pomme'),
+      outer: {
+        messageParts: ['Vous avez sélectionné ', ' pour la livraison.'],
+        placeholderNames: ['PH'],
+        text: 'Vous avez sélectionné {$PH} pour la livraison.',
+      },
+    });
+
+    expect(errors).toEqual([]);
+    expect(warnings).toEqual([]);
+    expect(findFile(outputFiles, 'main.js').text).toBe(
+      'export const msg = `Vous avez sélectionné ${"Pomme"} pour la livraison.`;\n',
+    );
+  });
 });