Right now, unpack silently ignores unsupported files, e.g.: unpack simutrans_coalwagonfix.rar: file format not recognized. Ignoring. This makes sense in default_src_unpack() but I dare say passing an unsupported file explicitly to 'unpack' should be an error.
I suppose the simplest way of doing that would be to modify the spec to say something like 'does the equivalent of calling unpack with filenames from ${A} that are recognized as supported archives'.
From #gentoo-pms: <@ulm> if it cannot unpack ${A} then it's not a default situation <@mgorny> ulm: ebuilds quite often fetch auxiliary files like images or uncompressed patches or .. <@mgorny> maybe a compromise would be having 'unpack' fail if none of the files were recognized <@mgorny> and succeed if at least one was unpacked <@ulm> yeah, that would also be possible
