[RFC] Bug 440952: "be more helpful when attempting to branch a shared repo"

[Brian de Alwis]

Bug 440952 is based on a complaint where a user tried to branch from a  
repository directory.  Bzr's error message was pretty opaque: the  
problem was that the location provided was a repository, not a branch.

I was recently hit a similar situation, and was sufficiently annoyed  
that I thought I'd try to hack out a solution (lp:~slyguy/bzr/ 
bug-440952).  This solution modifies BranchFormat.find_format() to try  
opening the provided location as a repository having determined that  
the location is not a branch.  If it is a repository, the resulting  
NotBranchError's extra field (now exposed from the superclass) is set  
to "location is a repository"; this string is only shown to the user,  
and thus preserves the calling requirements of find_format().

My approach does mean that two transport probes will now be made when  
the location is not a branch. My initial approach was to modify the  
relevant command definitions in builtin.py, but this requires  
modifying every possible command beyond the obvious 'branch' and  
'checkout', and is somewhat error-prone (when I realized I had  
forgotten about 'missing').  I'm not sure what impact of changing  
find_format(), but I guessed find_format() is only called a couple of  
times per invocation.

Comments or suggestions?

Brian.

-- 
"Amusement to an observing mind is study." - Benjamin Disraeli