[PATCH 3 of 5 V3] copies: refactor checkcopies() into a top level method

[Durham Goode]

On 5/9/13 12:44 PM, "Kevin Bullock" <kbullock+mercurial at ringworld.org>
wrote:

>On 8 May 2013, at 6:24 PM, Durham Goode wrote:
>
>> +def checkcopies(ctx, f, m1, m2, ca, limit, diverge, copy, fullcopy):
>> +    """
>> +    check possible copies of f from m1 to m2
>> +
>> +    ctx = function accepting (filename, node) that returns a filectx.
>> +    f = the filename to check
>> +    m1 = the source manifest
>> +    m2 = the destination manifest
>> +    ca = the changectx of the common ancestor
>> +    limit = the rev number to not search beyond
>> +    diverge = record all diverges in this dict
>> +    copy = record all non-divergent copies in this dict
>> +    fullcopy = record all copies in this dict
>> +    """
>
>Since the last 3 of these are essentially out params, can we just return
>them in a tuple?

The function is called once per file that is different between the m1 and
m2, which could be quite a lot of calls. If I construct a new
diverge/copy/fullcopy each time it would be a lot of allocations, and I'd
have to merge them into the master diverge/copy/fullcopy instances after
each call.  The diverge one in particular is a pain because it's a
dictionary with list values, so I couldn't just call dict.update()

I figured it's better to avoid the overhead in this case.