small nag about mime apps spec

[Ryan Lortie]

hi,

I have a small nag about the mime apps spec that has been bothering me
for a while:

The interaction between [Default Applications] and [Removed
Applications] at a higher level is strange.

In particular, what happens if we have
/usr/share/applications/mimeapps.list advertising that gedit.desktop is
the default for text/plain but then the user has recorded a [Removed
Applications] in their ~/.config/mimeapps.list.

The text in the spec is this:

"""
Note as well that the default application for a given type can be an
application that is not associated with this type (ie: neither by
MimeType= or an added association, or even in the case that the
association was specifically removed). Such configurations should be
regarded as unusual, however, and implementations should not write
mimeapps.list files that create this circumstance.
"""

We considered that it would be "unusual" to get into this situation but
I don't think we fully thought-out specifically how to avoid this
situation.  In order to avoid it, we'd have to ensure that when removing
the formerly default app for a given file type, we'd need to add a new
default app to the user's mimeapps config.  How do we chose such an app?
 Random?  Second place after the removed app?  What if there is no 2nd
app?

In retrospect, I'd like to modify the specification to require that an
app is valid for a given type in order to be considered as a default. 
This would mean that removing an association would also cause an app to
stop being considered as the default and would let us avoid this strange
wording about "regarded as unusual".

As a caveat, it would add a slight complication to the code for deciding
the default app.

Thoughts?