[vcpkg] how to disable default features

[rib]

This is essentially a duplicate of #11097 (closed) since the answer there didn't appear to work for me.

I'm trying to build ffmpeg with with the gpl feature disabled. ffmpeg has over 30 features and to start with I wasn't sure how to get the list of default features so I ended up running ./vcpkg install ffmpeg waiting for the output that showed that it was actually building/installing:
ffmpeg[avcodec,avdevice,avfilter,avformat,avresample,core,gpl,postproc,swresample,swscale]:x64-windows

I then stopped the build, copy & pasted the list of default features (except removing gpl), and ran:

.\vcpkg install ffmpeg[avcodec,avdevice,avfilter,avformat,avresample,core,postproc,swresample,swscale]:x64-windows

I still see Building package ffmpeg[avcodec,avdevice,avfilter,avformat,avresample,core,gpl,postproc,swresample,swscale]:x64-windows... in the output - so it looks like it's still including the gpl feature?

[vicroms]

I looked into ffmpeg's control file and the postproc feature has a declared dependency on gpl. I don't know enough about ffmpeg to know if that dependency is correct.

You can manually modify the CONTROL file to remove the dependency, as there is now way to remove a feature that is required upon by another feature or package.

vcpkg/ports/ffmpeg/CONTROL

Lines 35 to 37 in 254bd8f

	Feature: postproc
	Build-Depends: ffmpeg[core,gpl]
	Description: Postproc support in ffmpeg

[rib]

Ah, ok, yeah it looks like that feature is a gpl feature itself.

In this case what's really desired is that I want the default features minus anything that depends on the gpl feature.

vcpkg is making it pretty hard to configure ffmpeg features here since I need to explicitly inspect the heirachy of dependencies and subtract anything depending on gpl. Ideally there could be some syntax like -gpl (as mentioned in #11097) that could solve this automatically. Any time there's an update to the ffmpeg package I currently need to remember to re-check the heirachy of dependencies to manually subtract gpl dependent features.

Thanks for helping me understand what's going on.

[vicroms]

@rib Thanks for the report.