encoding: fix trim() to be O(n) instead of O(n^2)
`encoding.trim()` iterated over the possible lengths smaller than the
input and created a slice for each. It then calculated the column
width of the result, which is of course O(n), so the overall algorithm
was O(n). This patch rewrites it to iterate over the unicode
characters, keeping track of the length so far. Also, the old
algorithm started from the end of the string, which made it much worse
when the input is large and the limit is small (such as the typical 72
we pass to it).
You can time it by running something like this:
```
time python3 -c 'from mercurial.utils import stringutil; print(stringutil.ellipsis(b"0123456789" * 1000, 5))'
```
That drops from 4.05 s to 83 ms with this patch (and most of that is
of course startup time).
Differential Revision: https://phab.mercurial-scm.org/D12089
$ 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
[50]
# don't add tests here, previous test is unstable
$ cd ..