Rollup config error on dynamic import during library build

Type of Issue

[x ] Bug Report
[ ] Feature Request

Description

This bug relates to building angular library which uses dynamic imports. Consider building foo library with the command ng build foo. When the library contains a file (service in my case), which uses dynamic import, the build will fail throwing error below.

Error: You must set "output.dir" instead of "output.file" when generating multiple chunks.
    at error (c:\Development\rollup-test\node_modules\rollup\dist\rollup.js:3410:30)
    at normalizeOutputOptions (c:\Development\rollup-test\node_modules\rollup\dist\rollup.js:17107:13)
    at getOutputOptions (c:\Development\rollup-test\node_modules\rollup\dist\rollup.js:16865:24)
    at Object.write (c:\Development\rollup-test\node_modules\rollup\dist\rollup.js:16957:43)
    at Object. (c:\Development\rollup-test\node_modules\ng-packagr\lib\flatten\rollup.js:46:22)
    at Generator.next ()
    at fulfilled (c:\Development\rollup-test\node_modules\ng-packagr\lib\flatten\rollup.js:4:58)

How To Reproduce

See details about how to reproduce at this post: https://github.com/angular/angular-cli/issues/14444#issue-444906345

[raphael22]

I agree with @blemaire. In a plugin context you want the library to be autonomous. Even more when you deal with non routed lazy-loaded component.

If you take my exemple in earlier post, why a plugin button which call a modal could not take the responsability of it ? THIS look like a bad pattern to me.

[kingfolk]

The issue may come from https://github.com/ng-packagr/ng-packagr/blob/master/src/lib/flatten/rollup.ts#L69 when there is dynamic import, rollup will try to use output.dir instead of output.file to build multiple bundles.

For me, the library I am trying to build is not entirely depends on Angular. So I just use typescript-library-starte and override the https://github.com/alexjoverm/typescript-library-starter/blob/master/rollup.config.ts#L15 to output.dir then will have the following issue https://github.com/rollup/rollup/issues/2072 which just says umd bundle format is not compatible for dynamic import. As I googled what that means, one of github issue says IIFE and UMD formats are (purposefully) self-contained https://github.com/lukeed/navaid/issues/5#issuecomment-488540276

It seems a lot of effort to make umd support dynamic import. For now I guess the best way right now is to support rollup build multiple bundles and add a ng-packagr option to disable umd build.