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.
$ unset HGUSER
$ EMAIL="My Name <myname@example.com>"
$ export EMAIL
$ hg init test
$ cd test
$ touch asdf
$ hg add asdf
$ hg commit -m commit-1
$ hg tip
changeset: 0:53f268a58230
tag: tip
user: My Name <myname@example.com>
date: Thu Jan 01 00:00:00 1970 +0000
summary: commit-1
$ unset EMAIL
$ echo 1234 > asdf
$ hg commit -u "foo@bar.com" -m commit-1
$ hg tip
changeset: 1:3871b2a9e9bf
tag: tip
user: foo@bar.com
date: Thu Jan 01 00:00:00 1970 +0000
summary: commit-1
$ echo "[ui]" >> .hg/hgrc
$ echo "username = foobar <foo@bar.com>" >> .hg/hgrc
$ echo 12 > asdf
$ hg commit -m commit-1
$ hg tip
changeset: 2:8eeac6695c1c
tag: tip
user: foobar <foo@bar.com>
date: Thu Jan 01 00:00:00 1970 +0000
summary: commit-1
$ echo 1 > asdf
$ hg commit -u "foo@bar.com" -m commit-1
$ hg tip
changeset: 3:957606a725e4
tag: tip
user: foo@bar.com
date: Thu Jan 01 00:00:00 1970 +0000
summary: commit-1
$ echo 123 > asdf
$ echo "[ui]" > .hg/hgrc
$ echo "username = " >> .hg/hgrc
$ hg commit -m commit-1
abort: no username supplied
(use 'hg config --edit' to set your username)
[255]
# test alternate config var
$ echo 1234 > asdf
$ echo "[ui]" > .hg/hgrc
$ echo "user = Foo Bar II <foo2@bar.com>" >> .hg/hgrc
$ hg commit -m commit-1
$ hg tip
changeset: 4:6f24bfb4c617
tag: tip
user: Foo Bar II <foo2@bar.com>
date: Thu Jan 01 00:00:00 1970 +0000
summary: commit-1
# test prompt username
$ cat > .hg/hgrc <<EOF
> [ui]
> askusername = True
> EOF
$ echo 12345 > asdf
$ hg commit --config ui.interactive=False -m ask
enter a commit username:
no username found, using '[^']*' instead (re)
$ hg rollback -q
$ hg commit --config ui.interactive=True -m ask <<EOF
> Asked User <ask@example.com>
> EOF
enter a commit username: Asked User <ask@example.com>
$ hg tip
changeset: 5:84c91d963b70
tag: tip
user: Asked User <ask@example.com>
date: Thu Jan 01 00:00:00 1970 +0000
summary: ask
# test no .hg/hgrc (uses generated non-interactive username)
$ echo space > asdf
$ rm .hg/hgrc
$ hg commit -m commit-1 2>&1
no username found, using '[^']*' instead (re)
$ echo space2 > asdf
$ hg commit -u ' ' -m commit-1
transaction abort!
rollback completed
abort: empty username!
[255]
# don't add tests here, previous test is unstable
$ cd ..