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
# A B
#
# 3 4 3
# |\/| |\
# |/\| | \
# 1 2 1 2
# \ / \ /
# 0 0
#
# if the result of the merge of 1 and 2
# is the same in 3 and 4, no new manifest
# will be created and the manifest group
# will be empty during the pull
#
# (plus we test a failure where outgoing
# wrongly reported the number of csets)
$ hg init a
$ cd a
$ touch init
$ hg ci -A -m 0
adding init
$ touch x y
$ hg ci -A -m 1
adding x
adding y
$ hg update 0
0 files updated, 0 files merged, 2 files removed, 0 files unresolved
$ touch x y
$ hg ci -A -m 2
adding x
adding y
created new head
$ hg merge 1
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hg ci -A -m m1
$ hg update -C 1
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg merge 2
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hg ci -A -m m2
created new head
$ cd ..
$ hg clone -r 3 a b
adding changesets
adding manifests
adding file changes
added 4 changesets with 3 changes to 3 files
new changesets 5fcb73622933:d15a0c284984
updating to branch default
3 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg clone -r 4 a c
adding changesets
adding manifests
adding file changes
added 4 changesets with 3 changes to 3 files
new changesets 5fcb73622933:1ec3c74fc0e0
updating to branch default
3 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg -R a outgoing b
comparing with b
searching for changes
changeset: 4:1ec3c74fc0e0
tag: tip
parent: 1:79f9e10cd04e
parent: 2:8e1bb01c1a24
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: m2
$ hg -R a outgoing c
comparing with c
searching for changes
changeset: 3:d15a0c284984
parent: 2:8e1bb01c1a24
parent: 1:79f9e10cd04e
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: m1
$ hg -R b outgoing c
comparing with c
searching for changes
changeset: 3:d15a0c284984
tag: tip
parent: 2:8e1bb01c1a24
parent: 1:79f9e10cd04e
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: m1
$ hg -R c outgoing b
comparing with b
searching for changes
changeset: 3:1ec3c74fc0e0
tag: tip
parent: 1:79f9e10cd04e
parent: 2:8e1bb01c1a24
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: m2
$ hg -R b pull a
pulling from a
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 0 changes to 0 files (+1 heads)
new changesets 1ec3c74fc0e0
(run 'hg heads' to see heads, 'hg merge' to merge)
$ hg -R c pull a
pulling from a
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 0 changes to 0 files (+1 heads)
new changesets d15a0c284984
(run 'hg heads' to see heads, 'hg merge' to merge)