fix: esbuild md loader

.changeset/tangy-candles-cover.md

@@ -0,0 +1,6 @@
+---
+"@workflow/builders": patch
+"@workflow/next": patch
+---
+
+Support esbuild loaders

packages/builders/src/base-builder.ts

@@ -128,6 +128,7 @@ export abstract class BaseBuilder {
         logLevel: 'silent',
         // External packages that should not be bundled during discovery
         external: this.config.externalPackages || [],
+        loader: this.config.esbuildLoaders,
       });
     } catch (_) {}
 
@@ -364,6 +365,7 @@ export abstract class BaseBuilder {
         '.mjs',
         '.cjs',
       ],
+      loader: this.config.esbuildLoaders,
       // Inline source maps for better stack traces in step execution.
       // Steps execute in Node.js context and inline sourcemaps ensure we get
       // meaningful stack traces with proper file names and line numbers when errors
@@ -537,6 +539,7 @@ export abstract class BaseBuilder {
         '.mjs',
         '.cjs',
       ],
+      loader: this.config.esbuildLoaders,
       plugins: [
         createSwcPlugin({
           mode: 'workflow',
@@ -718,6 +721,7 @@ export const POST = workflowEntrypoint(workflowCode);`;
         '.mjs',
         '.cjs',
       ],
+      loader: this.config.esbuildLoaders,
       plugins: [createSwcPlugin({ mode: 'client' })],
     });
 

packages/builders/src/types.ts

@@ -1,3 +1,5 @@
+import type { Loader } from 'esbuild';
+
 export const validBuildTargets = [
   'standalone',
   'vercel-build-output-api',
@@ -27,6 +29,9 @@ interface BaseWorkflowConfig {
 
   // Optional prefix for debug files (e.g., "_" for Astro to ignore them)
   debugFilePrefix?: string;
+
+  // Custom esbuild loaders for non-standard file extensions (e.g., { '.md': 'text' })
+  esbuildLoaders?: Record<string, Loader>;
 }
 
 /**

packages/next/src/index.ts

@@ -1,3 +1,4 @@
+import type { Loader } from 'esbuild';
 import type { NextConfig } from 'next';
 import semver from 'semver';
 import { getNextBuilder } from './builder.js';
@@ -11,13 +12,16 @@ export function withWorkflow(
       ) => Promise<NextConfig>),
   {
     workflows,
+    esbuildLoaders,
   }: {
     workflows?: {
       local?: {
         port?: number;
         dataDir?: string;
       };
     };
+    /** Custom esbuild loaders for non-standard file extensions (e.g., { '.md': 'text' }) */
+    esbuildLoaders?: Record<string, Loader>;
   } = {}
 ) {
   if (!process.env.VERCEL_DEPLOYMENT_ID) {
@@ -137,6 +141,7 @@ export function withWorkflow(
           'client-only',
           ...(nextConfig.serverExternalPackages || []),
         ],
+        esbuildLoaders,
       });
 
       await workflowBuilder.build();

workbench/nextjs-turbopack/md.d.ts

@@ -0,0 +1,4 @@
+declare module '*.md' {
+  const content: string;
+  export default content;
+}

workbench/nextjs-turbopack/next.config.ts

@@ -4,7 +4,19 @@ import { withWorkflow } from 'workflow/next';
 const nextConfig: NextConfig = {
   /* config options here */
   serverExternalPackages: ['@node-rs/xxhash'],
+  turbopack: {
+    rules: {
+      '*.md': {
+        loaders: ['raw-loader'],
+        as: '*.js',
+      },
+    },
+  },
 };
 
 // export default nextConfig;
-export default withWorkflow(nextConfig);
+export default withWorkflow(nextConfig, {
+  esbuildLoaders: {
+    '.md': 'text',
+  },
+});

workbench/nextjs-turbopack/package.json

@@ -42,6 +42,7 @@
     "@types/react-dom": "^19",
     "@vercel/blob": "2.0.0",
     "@workflow/world-postgres": "workspace:*",
+    "raw-loader": "4.0.2",
     "tailwindcss": "^4",
     "typescript": "catalog:"
   }

workbench/nextjs-turbopack/workflows/11_custom_loader.md

@@ -0,0 +1,7 @@
+# Test Prompt
+
+This is a test markdown file to verify the esbuildLoaders feature works.
+
+## Instructions
+- Step 1: Do something
+- Step 2: Do something else

workbench/nextjs-turbopack/workflows/11_custom_loader.ts

@@ -0,0 +1,23 @@
+/**
+ * Test for custom esbuild loaders feature.
+ * Verifies that non-standard file extensions (like .md) can be imported
+ * when configured via esbuildLoaders in withWorkflow options.
+ */
+import PROMPT from '@/workflows/11_custom_loader.md';
+
+async function logPrompt(): Promise<string> {
+  'use step';
+
+  console.log('Loaded prompt:', PROMPT.slice(0, 50));
+
+  return PROMPT;
+}
+
+export async function customLoader() {
+  'use workflow';
+
+  const prompt = await logPrompt();
+  console.log('Custom loader test completed. Prompt length:', prompt.length);
+
+  return { success: true, promptLength: prompt.length };
+}