bug#28727: Profiles with intentionally out of date packages are upgraded to the newest version

[Ben Woodcroft]

Hi,

I have a profile with python@2 in it, and running 'guix package -u' 
updates it to python@3, which isn't what I want. I cannot run 'guix 
package -i python@2 -u' because then it tries to install both python@2 
and python@3, which conflicts.

I can workaround this using 'guix package -u; guix package -i python@2'. 
That isn't ideal (wasteful downloading of substitute, extra entries in 
the generations list, etc), but is workable for me, making this a low 
priority bug for me.

Ideally, I would expect that because I specified python@2 first, guix 
should not try to install python@3. However, this difficult because IIUC 
the packages which were specified to be included are not stored 
anywhere, and I suppose it would entail changes to the manifest format 
also. So, how to handle this?

Thanks, ben