Comment 4 for bug 1878709

I have run into same issue. The following build dependencies are not available on focal (the version constraints are higher than the available package versions in focal):

- golang-github-gophercloud-gophercloud-dev (>= 0.3.0~):

 $ apt-cache show golang-github-gophercloud-gophercloud-dev
 Package: golang-github-gophercloud-gophercloud-dev
 Architecture: all
 Version: 0.0~git20180917.45f1c769-1
 ...

- golang-github-prometheus-alertmanager-dev (>= 0.18.0~):

 $ apt-cache show golang-github-prometheus-alertmanager-dev
 Package: golang-github-prometheus-alertmanager-dev
 Architecture: all
 Version: 0.15.3+ds-3ubuntu1
 ...

- golang-github-prometheus-client-golang-dev (>= 1.2.1~):

 $ apt-cache show golang-github-prometheus-client-golang-dev
 Package: golang-github-prometheus-client-golang-dev
 Architecture: amd64
 Version: 0.9.2-0ubuntu3
 ...

I suggest to use opensource build tool BLDR, which always builds in clean environment based on the Build-dependencies in the control file and this errors could be avoided easily:

 bldr build ubuntu:focal

[1] https://github.com/OneIdentity/bldr
[2] https://pypi.org/project/bldr/