[PATCH 2 of 3] merge: introduce method to minimize merge regions

[Ryan McElroy]

On 2/10/2016 00:40, Ryan McElroy wrote:
> # HG changeset patch
> # User Ryan McElroy <rmcelroy at fb.com>
> # Date 1455063667 28800
> #      Tue Feb 09 16:21:07 2016 -0800
> # Node ID 51558e81358f58eb82c8a09d5cc3663e12619f7c
> # Parent  d520165147534eabfd95d66df6f176809a4c5b03
> merge: introduce method to minimize merge regions
>
> In the next diff, we will use this to trim down the start and end of conflict
> regions where the A and B sides both made the same changes.
>
> diff --git a/mercurial/simplemerge.py b/mercurial/simplemerge.py
> --- a/mercurial/simplemerge.py
> +++ b/mercurial/simplemerge.py
> @@ -269,6 +269,45 @@ class Merge3Text(object):
>                   ia = aend
>                   ib = bend
>   
> +    def minimize(self, merge_regions):
> +        """Trim conflict regions of lines where A and B sides match.
> +
> +        Lines where both A and B have made the same changes at the begining
> +        or the end of each merge region are eliminated from the conflict
> +        region and are instead considered the same.
> +        """
> +        for region in merge_regions:
> +            if region[0] != "conflict":
> +                yield region
> +                continue
> +            issue, z1, z2, a1, a2, b1, b2 = region
> +            alen = a2 - a1
> +            blen = b2 - b1
> +
> +            # find matches at the front
> +            ii = 0
> +            while ii < alen and ii < blen and \
> +                  self.a[a1 + ii] == self.b[b1 + ii]:
> +                ii += 1
> +            startmatches = ii
> +
> +            # find matches at the end
> +            ii = 0
> +            while ii < alen and ii < blen and \
> +                  self.a[a2 - ii - 1] == self.b[b2 - ii - 1]:
> +                ii += 1
> +            endmatches = ii
> +
> +            if startmatches > 0:
> +                yield 'same', a1, a1 + startmatches
> +
> +            yield ('conflict', z1, z2,
> +                    a1 + startmatches, a2 - endmatches,
> +                    b1 + startmatches, b2 - endmatches)
> +
> +            if endmatches > 0:
> +                yield 'same', a2 - startmatches, a2

Whoops, this should be a2 - endmatches

Thanks to Jun Wu for giving me some test cases that uncovered this bug. 
I'll send out a v2 with the fix.

> +
>       def find_sync_regions(self):
>           """Return a list of sync regions, where both descendants match the base.
>   
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