[gentoo-user] ebuild is trying to download a tarball instead of using git

[Jack]

I want to try some changes to an ebuild in the dotnet overlay.  So, I  
copied /var/lib/layman/dotnet/dev-lang/mono/mono-9999.ebuild into  
/usr/local/portage/dev-lang/mono.  I cd into that directory, and run  
"ebuild mono-9999.ebuild manifest" and it fails because it tries to  
download mono-9999.tar.bz2, which obviously doesn't exist anywhere.   
There is no SRC_URI in the ebuild, just  
"EGIT_REPO_URI="git://github.com/mono/${PN}.git".  Also, I notice there  
is no Manifest file (or no DIST line) for any 9999 ebuild - and that  
seems true in the main tree and also overlays.  Trying "ebuild  
mono-9999.ebuild prepare" complains that the digest is missing.  So  
does "emerge mono-9999.ebuild" although it complains that a file (the  
ebuild itself) is not listed in the manifest.

So - if a manifest entry is not needed for a live/9999 ebuild, why is  
portage (ebuild or emerge) failing to work without one, and why is it  
trying to download a tarball, even without any SRC_URI in the ebuild?

Jack