Path" argument must be of type string or an instance of Buffer or URL. Received an instance of Promise

[CedricEtchepare]

My project is currently using Angular 20 and "single-spa-angular 9.0.0".
I wanted tu upgrade my project to Angular 21 but I noticed that its not compatible anymore with single-spa-angular
So Im trying to use "single-spa-community/angular 21.0.0" but I have the following issue when i am doing "npm run start"

An unhandled exception occurred: The "path" argument must be of type string or an instance of Buffer or URL. Received an instance of Promise.

I tried to fix that in the index.js of the library (in the getProjectNameFromAngularJson method) :

const angularJsonPath = (0, find_up_1.findUp)(['angular.json', '.angular.json', 'workspace.json'], process.cwd());

I tried a quick equivalent without findup but less flexible on the files locations and it works :

const path = require('path'); 
const possibleFiles = ['angular.json', '.angular.json', 'workspace.json'];
const angularJsonPath = possibleFiles
     .map(file => path.join(process.cwd(), file))
     .find(file => fs.existsSync(file)); 

Have you ever seen this issue ?

[bjuhr]

In Angular CLI 21.2.x, the findUp utility was refactored.
findUp is now async (returns a Promise), and the previous synchronous implementation was moved to a new function called findUpSync.

Refactor commit:
angular/angular-cli@8ba6967

Because single-spa-angular still calls findUp synchronously, this breaks when using Angular CLI 21.2.x. In Angular CLI 21.1.x, findUp was still synchronous, so everything worked as expected.

Expected fix

In libs/single-spa-community-angular/webpack/index.ts, the call to findUp should be updated to either:

• use findUpSync, or
• handle the new async return value

A patch release for the 21.2.x compatibility range would resolve this.

Temporary workaround

Until a fix is released, I’m temporarily monkey‑patching Angular CLI’s findUp inside my webpack config so that single-spa-angular sees the synchronous version again:

const singleSpaAngularWebpack = require('single-spa-angular/lib/webpack').default;

module.exports = (angularWebpackConfig, options) => {
  const findUpModule = require('@angular/cli/src/utilities/find-up');

  // Save originals
  const originalFindUp = findUpModule.findUp;
  const originalFindUpSync = findUpModule.findUpSync;

  // Patch: make findUp behave synchronously again
  findUpModule.findUp = findUpModule.findUpSync;

  let singleSpaWebpackConfig;

  try {
    singleSpaWebpackConfig = singleSpaAngularWebpack(angularWebpackConfig, options);
  } finally {
    // Restore original functions
    findUpModule.findUp = originalFindUp;
    findUpModule.findUpSync = originalFindUpSync;
  }

  return singleSpaWebpackConfig;
};

This keeps the patch isolated to the single-spa-angular webpack factory and avoids affecting other Angular CLI usage in the same workspace.