The SingleMainWindow key added to osu!.desktop in #145 has been added to the Desktop Entry Specification in version 1.5 [1]. appimagetool was using an older version of desktop-file-validate that only understood version 1.0 [2], thus leading to deployment failure.
To fix, update appimagetool from release 13 to the continuous build to receive the upstream fixes from [2], as well as explicitly specify the Desktop Entry Specification version in the osu!.desktop file template.
The
SingleMainWindowkey added toosu!.desktopin #145 has been added to the Desktop Entry Specification in version 1.5 [1].appimagetoolwas using an older version ofdesktop-file-validatethat only understood version 1.0 [2], thus leading to deployment failure.To fix, update
appimagetoolfrom release 13 to the continuous build to receive the upstream fixes from [2], as well as explicitly specify the Desktop Entry Specification version in theosu!.desktopfile template.