test: add actual benchmark comparing eager vs targeted file loading

The benchmark test now measures both approaches with timing:
- Eager: loads all files from all tsconfigs (500+ files)
- Targeted: loads only the requested config file (1 file)
- Comparison test asserts targeted is faster and loads fewer files

Author: Alp

tests/benchmark.test.ts

@@ -1,7 +1,8 @@
 import * as path from 'node:path';
 import {Project} from 'ts-morph';
-import {test, expect} from 'vitest';
-import {ensureSourceFileInProject} from '../src/cli/ts-project';
+import {describe, test, expect} from 'vitest';
+import {addSourceFilesFromTsConfigSafe, ensureSourceFileInProject} from '../src/cli/ts-project';
+import {discoverAllTsConfigs} from '../src/cli/tsconfig';
 
 const fixtureRoot = path.resolve(
   __dirname,
@@ -12,28 +13,85 @@ const schemaConfigFile = path.resolve(
   'benchmarks/synthetic-monorepo/schema/drizzle-zero.config.ts',
 );
 
-test(
-  'project only loads the explicitly added file, not all tsconfig files',
-  {timeout: 120_000},
-  async () => {
+describe('file loading performance', {timeout: 120_000}, () => {
+  test('eager loading pulls in all files from all tsconfigs', async () => {
+    const start = performance.now();
+
+    const allTsConfigPaths = await discoverAllTsConfigs(fixtureRoot);
     const project = new Project({
       tsConfigFilePath: fixtureRoot,
       skipAddingFilesFromTsConfig: true,
     });
+    for (const tsConfigPath of allTsConfigPaths) {
+      addSourceFilesFromTsConfigSafe({tsProject: project, tsConfigPath});
+    }
+
+    const eagerTime = performance.now() - start;
+    const eagerFileCount = project.getSourceFiles().length;
+
+    console.log(`Eager: ${eagerFileCount} files in ${eagerTime.toFixed(1)}ms`);
+
+    // Eager should load all fixture files (500+)
+    expect(eagerFileCount).toBeGreaterThan(400);
+  });
 
+  test('targeted loading only loads the requested file', async () => {
+    const start = performance.now();
+
+    const project = new Project({
+      tsConfigFilePath: fixtureRoot,
+      skipAddingFilesFromTsConfig: true,
+    });
     ensureSourceFileInProject({
       tsProject: project,
       filePath: schemaConfigFile,
       debug: false,
     });
 
-    const fileCount = project.getSourceFiles().length;
+    const lazyTime = performance.now() - start;
+    const lazyFileCount = project.getSourceFiles().length;
 
-    console.log(`Files loaded: ${fileCount}`);
+    console.log(`Targeted: ${lazyFileCount} files in ${lazyTime.toFixed(1)}ms`);
 
-    // Regression guard: only the config file (and possibly a few resolved
-    // dependencies) should be loaded. If someone accidentally re-introduces
-    // eager loading, this will catch it.
-    expect(fileCount).toBeLessThan(10);
-  },
-);
+    // Only the config file should be loaded
+    expect(lazyFileCount).toBeLessThan(10);
+  });
+
+  test('targeted loading is faster than eager loading', async () => {
+    // Eager
+    const eagerStart = performance.now();
+    const allTsConfigPaths = await discoverAllTsConfigs(fixtureRoot);
+    const eagerProject = new Project({
+      tsConfigFilePath: fixtureRoot,
+      skipAddingFilesFromTsConfig: true,
+    });
+    for (const tsConfigPath of allTsConfigPaths) {
+      addSourceFilesFromTsConfigSafe({tsProject: eagerProject, tsConfigPath});
+    }
+    const eagerTime = performance.now() - eagerStart;
+    const eagerFileCount = eagerProject.getSourceFiles().length;
+
+    // Targeted (current default)
+    const lazyStart = performance.now();
+    const lazyProject = new Project({
+      tsConfigFilePath: fixtureRoot,
+      skipAddingFilesFromTsConfig: true,
+    });
+    ensureSourceFileInProject({
+      tsProject: lazyProject,
+      filePath: schemaConfigFile,
+      debug: false,
+    });
+    const lazyTime = performance.now() - lazyStart;
+    const lazyFileCount = lazyProject.getSourceFiles().length;
+
+    const speedup = eagerTime / lazyTime;
+
+    console.log(`Eager:    ${eagerFileCount} files in ${eagerTime.toFixed(1)}ms`);
+    console.log(`Targeted: ${lazyFileCount} files in ${lazyTime.toFixed(1)}ms`);
+    console.log(`Speedup:  ${speedup.toFixed(1)}x faster`);
+
+    expect(lazyFileCount).toBeLessThan(eagerFileCount);
+    expect(lazyTime).toBeLessThan(eagerTime);
+  });
+});