fix(@schematics/angular): preserve the workspace build version during migration

packages/schematics/angular/migrations/use-application-builder/migration.ts

@@ -19,6 +19,7 @@ import {
   DependencyType,
   ExistingBehavior,
   addDependency,
+  getDependency,
   removeDependency,
 } from '../../utility/dependency';
 import { JSONFile } from '../../utility/json-file';
@@ -270,10 +271,13 @@ function updateProjects(tree: Tree, context: SchematicContext) {
       }
 
       // Add direct @angular/build dependencies and remove @angular-devkit/build-angular
+      const buildAngularVersion =
+        getDependency(tree, '@angular-devkit/build-angular')?.version ??
+        latestVersions.AngularBuild;
       rules.push(
-        addDependency('@angular/build', latestVersions.DevkitBuildAngular, {
+        addDependency('@angular/build', buildAngularVersion, {
           type: DependencyType.Dev,
-          existing: ExistingBehavior.Replace,
+          existing: ExistingBehavior.Skip,
         }),
         removeDependency('@angular-devkit/build-angular'),
       );

packages/schematics/angular/migrations/use-application-builder/migration_spec.ts

@@ -9,6 +9,7 @@
 import { JsonObject } from '@angular-devkit/core';
 import { EmptyTree } from '@angular-devkit/schematics';
 import { SchematicTestRunner, UnitTestTree } from '@angular-devkit/schematics/testing';
+import { latestVersions } from '../../utility/latest-versions';
 import { Builders, ProjectType, WorkspaceSchema } from '../../utility/workspace-models';
 
 function createWorkSpaceConfig(tree: UnitTestTree) {
@@ -450,6 +451,49 @@ describe(`Migration to use the application builder`, () => {
     expect(devDependencies['postcss']).toBeUndefined();
   });
 
+  it('should reuse the installed builder version when migrating to "@angular/build"', async () => {
+    tree.overwrite(
+      '/package.json',
+      JSON.stringify({
+        devDependencies: {
+          '@angular-devkit/build-angular': '~18.2.20',
+        },
+      }),
+    );
+
+    const newTree = await schematicRunner.runSchematic(schematicName, {}, tree);
+
+    const { devDependencies } = JSON.parse(newTree.readContent('/package.json'));
+    expect(devDependencies['@angular/build']).toBe('~18.2.20');
+    expect(devDependencies['@angular-devkit/build-angular']).toBeUndefined();
+  });
+
+  it('should use the latest "@angular/build" version when no builder is installed', async () => {
+    const newTree = await schematicRunner.runSchematic(schematicName, {}, tree);
+
+    const { devDependencies } = JSON.parse(newTree.readContent('/package.json'));
+    expect(devDependencies['@angular/build']).toBe(latestVersions.AngularBuild);
+    expect(devDependencies['@angular-devkit/build-angular']).toBeUndefined();
+  });
+
+  it('should preserve an existing "@angular/build" version when migrating', async () => {
+    tree.overwrite(
+      '/package.json',
+      JSON.stringify({
+        devDependencies: {
+          '@angular-devkit/build-angular': '~18.2.20',
+          '@angular/build': '~18.2.10',
+        },
+      }),
+    );
+
+    const newTree = await schematicRunner.runSchematic(schematicName, {}, tree);
+
+    const { devDependencies } = JSON.parse(newTree.readContent('/package.json'));
+    expect(devDependencies['@angular/build']).toBe('~18.2.10');
+    expect(devDependencies['@angular-devkit/build-angular']).toBeUndefined();
+  });
+
   it('it should not add esModuleInterop and moduleResolution when module is preserve', async () => {
     tree.overwrite(
       'tsconfig.json',