I know nothing about a prepackaged package called ‘XXXX’, …

Short explanation: an OS dependency is listed by one of the packages, but no definition exists in one of the osdeps files.

Long explanation: XXXX is listed as an operating system dependency by one of the packages that you requested to build. Two solutions: (i) the package should not depend on it, and you should modify the package’s manifest.xml file. (ii) the package should depend on it and you should list the OS package in the relevant osdeps file

XXX depends on YYY, which is excluded from the build

The layout requires the XXX package to be built, but this package depends on YYY and YYY has explicitly been excluded from the build.

There are two cases.

In the first case, the package has been listed in the exclude_packages section of autoproj/manifest. So, you will have to find out why and either remove it from there, or add XXX to the same section.

In the second case, the package is disabled on your operating system version. This is done in the package set’s autobuild files by using the not_on and only_on statements. You will have to either exclude the XXX package as well (either by including it in the same not_on/only_on block, or by adding it to the exclude_packages section of autoproj/manifest), or to make it so that YYY builds on your OS, an thus remove it from the not_on/only_on block.