bdiff: balance recursion to avoid quadratic behavior (issue4704)
For highly structured files like JSON or XML dumps with large numbers
of duplicate lines (eg braces) and isolated matching lines, bdiff
could find large numbers of equally good spans. Because it prefers
earlier matches, this would result in pathologically unbalance
recursion that resulted in quadratic performance.
This patch makes it prefer matches closer to the middle that tend to
balance recursion. This change improves the speed of a pathological
test case from 1100s to 9s.
Included is a smaller test that has a roughly 50x safety margin on the
performance it accepts. It's likely to fail on pure builds because
difflib also has a recursion-balancing problem.
Failed qimport of patches from files should cleanup by recording successfully
imported patches in series file.
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init repo
$ cd repo
$ echo a > a
$ hg ci -Am'add a'
adding a
$ cat >b.patch<<EOF
> diff --git a/a b/a
> --- a/a
> +++ b/a
> @@ -1,1 +1,2 @@
> a
> +b
> EOF
empty series
$ hg qseries
qimport valid patch followed by invalid patch
$ hg qimport b.patch fakepatch
adding b.patch to series file
abort: unable to read file fakepatch
[255]
valid patches before fail added to series
$ hg qseries
b.patch
$ hg pull -q -r 0 . # update phase
$ hg qimport -r 0
abort: revision 0 is not mutable
(see "hg help phases" for details)
[255]
$ cd ..