VersionedFile.walk deprecated?

[Martin Pool]

On 12/04/2006, at 10:55 PM, Aaron Bentley wrote:

> Martin Pool wrote:
>> Just to expand on what I said before - the problem with walk() is   
>> that
>> it returns all lines in the history of the file, even those  which  
>> are
>> irrelevant to the two versions we're trying to merge.   Touching  
>> them is
>> not just specific to weave storage, but an  undesirable consequence,
>> since we spend time walking lines we can't  possibly use.
>
> Okay, but with weaves, we always have to read the weave from
> top-to-bottom anyhow, I think.

Right - what I meant was that there's no sense paying this cost on  
non-weave VersionedFiles.

>> We can make a plan_merge for knits which does something similar, but
>> only deals with lines which can possibly be in the output.  It   
>> requires
>> annotated knits.  It should work like this:
>>
>>   Do a two-way diff between the two versions to be merged.   
>> Within  the
>> difference regions, we need to determine whether each line is   
>> unborn,
>> live, or killed in the other side.  Taking the lines from the
>> left-hand-side conflict region first, get the line origins.
>
> Depending on the costs involved, it might be worthwile to diff the
> annotated version, to reduce false matches.

Doing that would give you a result that's more similar to that of  
weave merge.  Whether those results are subjectively better or not  
may vary from case to case.

Possibly a good tradeoff would be to use a strict Patience diff,  
without falling back to difflib diff; then we'll align only on lines  
that are unique in each file, even if their apparent origin is  
different.

> An interesting thought.  Are you thinking of
> http://revctrl.org/MarkMerge and the way it distinguishes between  
> choices?

Yes, that sort of thing.  If the user gets a conflict and resolves  
it, then they have made a new decision in that area, even if they  
didn't introduce any new lines.  It's a bit more like the case  
described as a motivation here

   http://revctrl.org/EdgeVersioning

-- 
Martin