libopencv-dev doesn't install when specifying arm64 from an amd64 system

[Brian Lee]

Ubuntu release: 20.04.3 LTS

apt-cache policy libopencv-dev output:
libopencv-dev:
  Installed: (none)
  Candidate: 4.2.0+dfsg-5
  Version table:
     4.2.0+dfsg-5 500
        500 http://archive.ubuntu.com/ubuntu focal/universe amd64 Packages

I attempted to "apt-get install libopencv-dev:arm64" from an amd64 system (it's a docker image, but I don't think that should affect anything) for the purposes of cross-compiling. The error I get is:

#13 471.4 Some packages could not be installed. This may mean that you have
#13 471.4 requested an impossible situation or if you are using the unstable
#13 471.4 distribution that some required packages have not yet been created
#13 471.4 or been moved out of Incoming.
#13 471.4 The following information may help to resolve the situation:
#13 471.4
#13 471.4 The following packages have unmet dependencies:
#13 471.5 libopencv-dev:arm64 : Depends: libopencv4.2-java:arm64 (= 4.2.0+dfsg-5) but it is not installable
#13 471.5 Recommends: opencv-data:arm64 but it is not installable
#13 471.5 E: Unable to correct problems, you have held broken packages.

I believe this is because libopencv4.2-java is not an arch-specific package (architecture is listed as "all"), and the "arm64" specification is throwing things off. Note the same issue for opencv-data, but that's just a "recommends", and so is not actually breaking anything for me.

As a band-aid, I going the "equivs" route to build a empty libopencv4.2-java:arm64 and libopencv4.2-java:armhf packages to technically satisfy the dependency since I'm not actually using those packages, but that's oh-so-hacky. Is there a better work-around until this gets fixed?

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.