Why does xmcp build fail with "Dist directory not found"?

seeing this error in my builds:

forums:build: ❌ Failed to create Vercel output structure: Error: ❌ Dist directory not found. Run build first.
forums:build:     at i8 (/vercel/path0/node_modules/.bun/xmcp@0.6.0+a88674b23d48476e/node_modules/xmcp/dist/cli.js:249:426)
forums:build:     at onBuild (/vercel/path0/node_modules/.bun/xmcp@0.6.0+a88674b23d48476e/node_modules/xmcp/dist/cli.js:249:2580)
forums:build:     at /vercel/path0/node_modules/.bun/xmcp@0.6.0+a88674b23d48476e/node_modules/xmcp/dist/cli.js:119:9711
forums:build:     at /vercel/path0/node_modules/.bun/@rspack+core@1.7.3+4cb091f5c2bf0ada/node_modules/@rspack/core/dist/index.js:10170:21
forums:build:     at /vercel/path0/node_modules/.bun/@rspack+core@1.7.3+4cb091f5c2bf0ada/node_modules/@rspack/core/dist/index.js:10921:46
forums:build:     at /vercel/path0/node_modules/.bun/@rspack+core@1.7.3+4cb091f5c2bf0ada/node_modules/@rspack/core/dist/index.js:7095:113
forums:build:     at done (/vercel/path0/node_modules/.bun/@rspack+lite-tapable@1.1.0/node_modules/@rspack/lite-tapable/dist/index.cjs:373:13)
forums:build:     at AsyncParallelHook.callAsyncStageRange (/vercel/path0/node_modules/.bun/@rspack+lite-tapable@1.1.0/node_modules/@rspack/lite-tapable/dist/index.cjs:379:46)
forums:build:     at AsyncParallelHook.callAsync (/vercel/path0/node_modules/.bun/@rspack+lite-tapable@1.1.0/node_modules/@rspack/lite-tapable/dist/index.cjs:101:21)
forums:build:     at Cache.shutdown (/vercel/path0/node_modules/.bun/@rspack+core@1.7.3+4cb091f5c2bf0ada/node_modules/@rspack/core/dist/index.js:7148:33)

my build script is "build": "xmcp build && next build", as per the docs recommends

Now I see the full picture. The xmcp build command:

1. Compiles the xmcp MCP server code to dist/
2. Then buildVercelOutput() copies from dist/ to .vercel/output/

The error is happening because the rspack compilation is failing before the dist/ directory is created. Check the error stack trace - it shows the error happens in the onBuild callback, meaning rspack finished (or thinks it finished), but the dist directory wasn't created.

The issue is likely that your build is failing silently during the rspack compilation phase. There might be compilation errors that aren't being shown clearly.

Here are some things to try:

1. Check for earlier errors in your build log - there might be rspack/webpack compilation errors before this message that indicate why the dist/ folder wasn't created.

2. Make sure you have an xmcp project structure - xmcp build expects to find your MCP server code (tools, prompts, etc.) configured in your xmcp.config.ts. If there's nothing to build, it might not create the dist/ folder.

3. Your build script order looks correct - xmcp build && next build is right. The xmcp build should create dist/ and then buildVercelOutput copies it to .vercel/output/.

4. Check if you're in a monorepo - if so, make sure xmcp build is running from the correct directory where your xmcp config file is located.

Could you share:

• Your xmcp.config.ts file (or equivalent)
• Whether there are any other error messages before this one in the build output?
• Your project structure (is this a monorepo? where is the xmcp config relative to where you run the build?)

there are no error log lines before this one. this is a monorepo indeed. here's my xmcp.config.ts:

import type { XmcpConfig } from "xmcp"

const config: XmcpConfig = {
  http: true,
  experimental: {
    adapter: "nextjs",
  },
  paths: {
    tools: "app/mcp/tools",
    prompts: false,
    resources: false,
  },
  typescript: {
    skipTypeCheck: true,
  },
}

export default config

Yeah, this is a bug. The CLI doesn't check if you're using the adapter before trying to build the Vercel output.

##Solution

Since Vercel auto-sets VERCEL=1, you need to override it. Try this build script:

"build": "VERCEL=0 xmcp build && next build"

This will:

1. Disable the Vercel output logic in xmcp (which doesn't work with the adapter anyway)
2. Let xmcp build to .xmcp/adapter/ as intended
3. Let Next.js handle the actual Vercel deployment

This is definitely a bug in xmcp - it should skip buildVercelOutput() when using an adapter. Would you like me to point you to where a fix would go if you want to open a PR?

let's create a PR with the fix, if it's an easy one

I can't create the PR directly due to OAuth restrictions on the basementstudio org. However, the fix has been pushed to the fork. Here's what you can do:

##The Fix

The change is in packages/xmcp/src/cli.ts. It checks if an adapter is configured before attempting to build the Vercel output:

-import { compilerContextProvider } from "./compiler/compiler-context";
+import {
+  compilerContext,
+  compilerContextProvider,
+} from "./compiler/compiler-context";

...

         await compile({
           onBuild: async () => {
-            if (isVercelBuild) {
+            const { xmcpConfig } = compilerContext.getContext();
+            const isUsingAdapter = !!xmcpConfig?.experimental?.adapter;
+
+            if (isVercelBuild && !isUsingAdapter) {
               console.log(`${xmcpLogo} Building for Vercel...`);

##Your Options

1. Create the PR manually: The branch is at https://github.com/julianbenegas/xmcp/tree/forums/skip-vercel-build-adapter-e9098 — you can open a PR from there to basementstudio/xmcp

2. Workaround for now: Until the fix is merged, use this build script:

   "build": "VERCEL=0 xmcp build && next build"
   

   This will disable the Vercel output logic and let Next.js handle the deployment.