fix(next): derive workflow project root

.changeset/next-root-detection.md

@@ -0,0 +1,5 @@
+---
+"@workflow/next": patch
+---
+
+Derive the workflow builder project root from Next.js workspace root configuration.

packages/next/src/index.test.ts

@@ -123,6 +123,31 @@ describe('withWorkflow builder config', () => {
     });
   });
 
+  it('derives projectRoot from the nearest pnpm workspace root', async () => {
+    const repoRoot = mkdtempSync(join(realTmpDir, 'workflow-next-root-'));
+    const appRoot = join(repoRoot, 'apps/web');
+    mkdirSync(appRoot, { recursive: true });
+    writeFile(join(repoRoot, 'pnpm-workspace.yaml'), 'packages: []\n');
+    process.chdir(appRoot);
+
+    try {
+      const config = withWorkflow({});
+
+      await config('phase-production-build', {
+        defaultConfig: {},
+      });
+
+      expect(builderConfigs[0]).toMatchObject({
+        projectRoot: repoRoot,
+        moduleSpecifierRoot: appRoot,
+        workingDir: appRoot,
+      });
+    } finally {
+      process.chdir(originalCwd);
+      rmSync(repoRoot, { recursive: true, force: true });
+    }
+  });
+
   it.each([
     'phase-production-build',
     'phase-development-server',

packages/next/src/index.ts

@@ -1,6 +1,6 @@
 import { copyFileSync, mkdirSync, statSync } from 'node:fs';
 import { copyFile, mkdir, readFile } from 'node:fs/promises';
-import { dirname, isAbsolute, join } from 'node:path';
+import { dirname, isAbsolute, join, resolve } from 'node:path';
 import type { NextConfig } from 'next';
 import semver from 'semver';
 import { getNextBuilder } from './builder.js';
@@ -16,7 +16,6 @@ const VERCEL_WORLD_SERVER_EXTERNAL_PACKAGES = [
   VERCEL_WORLD_PACKAGE,
   ...VERCEL_WORLD_DEPENDENCY_PACKAGES,
 ];
-
 const useWorkflowPattern = /^\s*(['"])use workflow\1;?\s*$/m;
 const useStepPattern = /^\s*(['"])use step\1;?\s*$/m;
 const workflowSerdeImportPattern = /from\s+(['"])@workflow\/serde\1/;
@@ -232,6 +231,31 @@ function fileExists(path: string): boolean {
   }
 }
 
+function resolveNextProjectRoot(
+  nextConfig: NextConfig,
+  workingDir: string
+): string {
+  if (nextConfig.outputFileTracingRoot) {
+    return isAbsolute(nextConfig.outputFileTracingRoot)
+      ? nextConfig.outputFileTracingRoot
+      : resolve(workingDir, nextConfig.outputFileTracingRoot);
+  }
+
+  let current = resolve(workingDir);
+
+  while (true) {
+    if (fileExists(join(current, 'pnpm-workspace.yaml'))) {
+      return current;
+    }
+
+    const parent = dirname(current);
+    if (parent === current) {
+      return workingDir;
+    }
+    current = parent;
+  }
+}
+
 function getWorkflowManifestCopyPaths({
   projectDir,
   distDir,
@@ -442,7 +466,9 @@ export function withWorkflow(
       nextConfig.turbopack.rules = {};
     }
     const existingRules = nextConfig.turbopack.rules as any;
-    const nextVersion = resolveNextVersion(process.cwd());
+    const workingDir = process.cwd();
+    const nextVersion = resolveNextVersion(workingDir);
+    const projectRoot = resolveNextProjectRoot(nextConfig, workingDir);
     const supportsTurboCondition = semver.gte(nextVersion, 'v16.0.0');
 
     const shouldWatch = process.env.NODE_ENV === 'development';
@@ -474,9 +500,9 @@ export function withWorkflow(
               'jsx',
               'js',
             ],
-            projectRoot: nextConfig.outputFileTracingRoot,
-            moduleSpecifierRoot: process.cwd(),
-            workingDir: process.cwd(),
+            projectRoot,
+            moduleSpecifierRoot: workingDir,
+            workingDir,
             distDir,
             diagnosticsDir: `${distDir}/diagnostics`,
             buildTarget: 'next',