Hello OpenProject team,

I’m setting up the development environment for OpenProject v16.5.1, and I’ve encountered a frontend build error that seems related to Angular version compatibility.

What I did

1. Cloned the repository and checked out the release/16.5.1 branch:

git clone https://github.com/opf/openproject.git
cd openproject
git checkout release/16.5.1

1. Ran the setup and migrations:

bin/setup_dev
bundle exec rake db:migrate

1. Tried to build the frontend manually and through Rails assets:

cd frontend
npm install
npm run build

1. or

RAILS_ENV=development bundle exec rake assets:precompile

The problem

Both methods fail with the following message:

Error: Could not find the '@angular-builders/custom-esbuild:application' builder's node package.
rake aborted!
Failed to compile angular frontend: 1
Tasks: TOP => assets:precompile => assets:compile_environment => assets:prepare_op => assets:angular

When I checked, the @angular-builders/custom-esbuild@16.x version does not exist on npm.
The latest version (20.x) only supports Angular 17+ or 20+, but OpenProject 16.5.1 uses Angular 16.2.12.

My question

• Is there an official workaround for this in OpenProject 16.5.1?

• Should I replace the builder in frontend/angular.json with @angular-devkit/build-angular:browser, or is there another supported approach?

• If OpenProject 16.5.1 truly depends on Angular 17+, should I upgrade Angular manually for the build to succeed?

Any guidance from the maintainers or other developers who’ve built OpenProject 16.5.1 locally would be very helpful.

Thank you.

Environment