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Library is not compatible with Ivy

See original GitHub issue

I installed the latest version of @fullcalendar/angular (5.11.0) in an Angular 13 application. I have an error building the application using ngc and Webpack.

Reproduce the error

I have created a repository with a minimal Angular 13 project to reproduce the issue: https://github.com/AlessandroSomma/fullcalendar-angular-13

Steps to reproduce:

clone the repository
run npm install
run npm start or npm run build
see the error

Details

Error logged:

node_modules/@fullcalendar/angular/lib/fullcalendar.module.d.ts:2:22 - error NG6002: Appears in the NgModule.imports of AppModule, but could not be resolved to an NgModule class.

This likely means that the library (@fullcalendar/angular) which declares FullCalendarModule has not been processed correctly by ngcc, or is not compatible with Angular Ivy. Check if a newer version of the library is available, and update if so. Also consider checking with the library's authors to see if the library is expected to be compatible with Ivy.

Use ngcc before building will fix the issue but in my situation it would be difficult to use it because of package manager. Also using it in the test project a warning is logged:

Processing legacy "View Engine" libraries:
- @fullcalendar/angular [fesm2015/esm2015] (git+https://github.com/fullcalendar/fullcalendar-angular.git)
- @fullcalendar/angular [esm2015/esm2015] (git+https://github.com/fullcalendar/fullcalendar-angular.git)
- @fullcalendar/angular [main/umd] (git+https://github.com/fullcalendar/fullcalendar-angular.git)
Encourage the library authors to publish an Ivy distribution.