It appears to be a bug in previous versions of ngx-build-plus. where it was enabled by default https://github.com/manfredsteyer/ngx-build-plus/blob/8e58880a279d329934a1c7e556b9cac6523ea284/lib/src/browser/schema.json#L246

License extraction is not intended to be used for incremental builds. Following the above, it appears that there is no action needed from the Angular team.

Thanks everyone for chiming in.

With the help of @alan-agius4 I got to a point where the rebuild is only ~3seconds; we needed to set "extractLicenses": false to disable license extraction. We are yet to figure out why that would have been enabled, as it should be disabled by default.

Thanks @sod, that’s super helpful.

In fact it’s what I have done using the reproduction and there’s a couple things to share here:

the ngc incremental build took 17s, most of which was type-checking. ngc doesn’t do incremental type-checking so each rebuild incurs the full cost. The Angular compiler was actually not adding much overhead here.

The CLI does have incremental type checking in rebuilds (since 11.1, coincidentally) and it’s a lot better in that case. Unfortunately, the CLI adds Webpack bundling, circular dependencies checks and bundle source-maps. Those steps add quite a bit of overhead.

Disabling source maps and the circular dependency check improves the times quite a bit. This can be done by extending the build configuration in angular.json using the following two flags:

            "showCircularDependencies": false,
            "sourceMap": false,

I can’t say whether it’s acceptable for these features to be disabled; for the circular dependencies plugin I’d suggest to have it at least enabled for prod builds; or perhaps introduce a dedicated “fast” configuration with those options configured.

Even with those flags, the rebuild is still ~10s. Most time (~80%) is spent in Webpack chunk plugins; that looks rather inefficient but I haven’t yet determined what could be done here.

@sod No I have all styles in dedicated theme files. Don’t use styles in components (sometimes but very simple).