Add opencv as a core dependency package?

[dstansby]

Comment:

I've just been testing https://github.com/conda-forge/sunpy-feedstock, which now depends on opencv for testing. We have run up against the error in this issue: #321.

The conda-forge docs say (https://conda-forge.org/docs/maintainer/adding_pkgs.html#avoid-external-dependencies):

As a general rule: all dependencies have to be packaged by conda-forge as well. This is necessary to assure ABI compatibility for all our packages.
There are only a few exceptions to this rule:
Some dependencies have to be satisfied with CDT packages (see Core Dependency Tree Packages (CDTs)).

From reading the conda-forge docs it seems like opencv should be packaged as a Core Dependency Tree Package, not a normal feedstock package. To avoid the libGL linking error should opencv be added as a Core Dependency Tree package instead of living here as a normal feedstock?

[hmaarrfk]

I think the conversion here #293 is relevant.

[hmaarrfk]

I'm going to close this since I think 293 is the relevant issue. let me know if you disagree.