fix(@angular/build): do not mark Babel _defineProperty helper function as pure

Fixes #29145

Author: jsaguet

packages/angular/build/src/tools/babel/plugins/pure-toplevel-functions.ts

@@ -32,6 +32,18 @@ function isTslibHelperName(name: string): boolean {
   return tslibHelpers.has(originalName);
 }
 
+const babelHelpers = new Set<string>(['_defineProperty']);
+
+/**
+ * Determinates whether an identifier name matches one of the Babel helper function names.
+ *
+ * @param name The identifier name to check.
+ * @returns True, if the name matches a Babel helper name; otherwise, false.
+ */
+function isBabelHelperName(name: string): boolean {
+  return babelHelpers.has(name);
+}
+
 /**
  * A babel plugin factory function for adding the PURE annotation to top-level new and call expressions.
  *
@@ -53,9 +65,12 @@ export default function (): PluginObj {
         ) {
           return;
         }
-        // Do not annotate TypeScript helpers emitted by the TypeScript compiler.
-        // TypeScript helpers are intended to cause side effects.
-        if (callee.isIdentifier() && isTslibHelperName(callee.node.name)) {
+        // Do not annotate TypeScript helpers emitted by the TypeScript compiler or Babel helpers.
+        // They are intended to cause side effects.
+        if (
+          callee.isIdentifier() &&
+          (isTslibHelperName(callee.node.name) || isBabelHelperName(callee.node.name))
+        ) {
           return;
         }
 

packages/angular/build/src/tools/babel/plugins/pure-toplevel-functions_spec.ts

@@ -130,6 +130,18 @@ describe('pure-toplevel-functions Babel plugin', () => {
     `),
   );
 
+  it(
+    'does not annotate _defineProperty function',
+    testCaseNoChange(`
+      class LanguageState {}
+      _defineProperty(
+        LanguageState,
+        'property',
+        'value'
+      );
+    `),
+  );
+
   it(
     'does not annotate object literal methods',
     testCaseNoChange(`