appstream-util doesn't compare versions correctly

[scx]

It seems that appstream-util doesn't compare versions correctly, which leads to incorrect validation of AppData files.

$ appstream-util --version
Version:    0.7.13

$ appstream-util vercmp "Build 9half" "Build 10"
Build 9half > Build 10
$ appstream-util vercmp "Build 9.5" "Build 10"
Build 9.5 > Build 10
$ appstream-util vercmp "Build 9+" "Build 10"
Build 9+ > Build 10
$ appstream-util vercmp "Build 9a" "Build 10"
Build 9a > Build 10
$ appstream-util vercmp "Build 9" "Build 10"
Build 9 > Build 10

$ appstream-util vercmp "9half" "10"
9half > 10
$ appstream-util vercmp "9.5" "10"
9.5 > 10
$ appstream-util vercmp "9+" "10"
9+ > 10
$ appstream-util vercmp "9a" "10"
9a > 10
$ appstream-util vercmp "9" "10"
9 < 10

As you can see, only the last result is correct. The problem occurs in both Freedesktop 1.6 and 18.08.

Please compare this with the rpmdev-vercmp on RHEL 7:

$ rpm -q --qf "%{VERSION}\n" rpmdevtools
8.3

$ rpmdev-vercmp "Build 9half" "Build 10"
Build 9half < Build 10
$ rpmdev-vercmp "Build 9.5" "Build 10"
Build 9.5 < Build 10
$ rpmdev-vercmp "Build 9+" "Build 10"
Build 9+ < Build 10
$ rpmdev-vercmp "Build 9a" "Build 10"
Build 9a < Build 10
$ rpmdev-vercmp "Build 9" "Build 10"
Build 9 < Build 10

$ rpmdev-vercmp "9half" "10"
9half < 10
$ rpmdev-vercmp "9.5" "10"
9.5 < 10
$ rpmdev-vercmp "9+" "10"
9+ < 10
$ rpmdev-vercmp "9a" "10"
9a < 10
$ rpmdev-vercmp "9" "10"
9 < 10

[TingPing]

I see you already reported it in the correct place: https://github.com/hughsie/appstream-glib/issues/270

[scx]

I think you should consider temporarily disabling AppData validation, because currently the build will fail even if the data is correct.