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
#require serve
setting up repo
$ hg init test
$ cd test
$ echo a > a
$ hg ci -Ama
adding a
$ hg rm a
$ hg ci -mdel
set up hgweb
$ hg serve -n test -p $HGPORT -d --pid-file=hg.pid -A access.log -E errors.log
$ cat hg.pid >> $DAEMON_PIDS
revision
$ get-with-headers.py localhost:$HGPORT 'rev/tip'
200 Script output follows
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en-US">
<head>
<link rel="icon" href="/static/hgicon.png" type="image/png" />
<meta name="robots" content="index, nofollow" />
<link rel="stylesheet" href="/static/style-paper.css" type="text/css" />
<script type="text/javascript" src="/static/mercurial.js"></script>
<title>test: c78f6c5cbea9</title>
</head>
<body>
<div class="container">
<div class="menu">
<div class="logo">
<a href="https://mercurial-scm.org/">
<img src="/static/hglogo.png" alt="mercurial" /></a>
</div>
<ul>
<li><a href="/shortlog/tip">log</a></li>
<li><a href="/graph/tip">graph</a></li>
<li><a href="/tags">tags</a></li>
<li><a href="/bookmarks">bookmarks</a></li>
<li><a href="/branches">branches</a></li>
</ul>
<ul>
<li class="active">changeset</li>
<li><a href="/raw-rev/tip">raw</a></li>
<li><a href="/file/tip">browse</a></li>
</ul>
<ul>
</ul>
<ul>
<li><a href="/help">help</a></li>
</ul>
</div>
<div class="main">
<h2 class="breadcrumb"><a href="/">Mercurial</a> </h2>
<h3>
changeset 1:<a href="/rev/c78f6c5cbea9">c78f6c5cbea9</a>
<span class="phase">draft</span> <span class="branchhead">default</span> <span class="tag">tip</span>
</h3>
<form class="search" action="/log">
<p><input name="rev" id="search1" type="text" size="30" value="" /></p>
<div id="hint">Find changesets by keywords (author, files, the commit message), revision
number or hash, or <a href="/help/revsets">revset expression</a>.</div>
</form>
<div class="description">del</div>
<table id="changesetEntry">
<tr>
<th class="author">author</th>
<td class="author">test</td>
</tr>
<tr>
<th class="date">date</th>
<td class="date age">Thu, 01 Jan 1970 00:00:00 +0000</td>
</tr>
<tr>
<th class="author">parents</th>
<td class="author"><a href="/rev/cb9a9f314b8b">cb9a9f314b8b</a> </td>
</tr>
<tr>
<th class="author">children</th>
<td class="author"></td>
</tr>
<tr>
<th class="files">files</th>
<td class="files">a </td>
</tr>
<tr>
<th class="diffstat">diffstat</th>
<td class="diffstat">
1 files changed, 0 insertions(+), 1 deletions(-)
<a id="diffstatexpand" class="diffstattoggle" href="#">[<tt>+</tt>]</a>
<div id="diffstatdetails" style="display:none;">
<a class="diffstattoggle" href="#">[<tt>-</tt>]</a>
<table class="diffstat-table stripes2"> <tr>
<td class="diffstat-file"><a href="#l1.1">a</a></td>
<td class="diffstat-total" align="right">1</td>
<td class="diffstat-graph">
<span class="diffstat-add" style="width:0.0%;"> </span>
<span class="diffstat-remove" style="width:100.0%;"> </span>
</td>
</tr>
</table>
</div>
</td>
</tr>
</table>
<div class="overflow">
<div class="sourcefirst linewraptoggle">line wrap: <a class="linewraplink" href="#">on</a></div>
<div class="sourcefirst"> line diff</div>
<div class="stripes2 diffblocks">
<div class="bottomline inc-lineno"><pre class="sourcelines wrap">
<span id="l1.1" class="minusline">--- a/a Thu Jan 01 00:00:00 1970 +0000</span><a href="#l1.1"></a>
<span id="l1.2" class="plusline">+++ /dev/null Thu Jan 01 00:00:00 1970 +0000</span><a href="#l1.2"></a>
<span id="l1.3" class="atline">@@ -1,1 +0,0 @@</span><a href="#l1.3"></a>
<span id="l1.4" class="minusline">-a</span><a href="#l1.4"></a></pre></div>
</div>
</div>
</div>
</div>
</body>
</html>
diff removed file
$ get-with-headers.py localhost:$HGPORT 'diff/tip/a'
200 Script output follows
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en-US">
<head>
<link rel="icon" href="/static/hgicon.png" type="image/png" />
<meta name="robots" content="index, nofollow" />
<link rel="stylesheet" href="/static/style-paper.css" type="text/css" />
<script type="text/javascript" src="/static/mercurial.js"></script>
<title>test: a diff</title>
</head>
<body>
<div class="container">
<div class="menu">
<div class="logo">
<a href="https://mercurial-scm.org/">
<img src="/static/hglogo.png" alt="mercurial" /></a>
</div>
<ul>
<li><a href="/shortlog/tip">log</a></li>
<li><a href="/graph/tip">graph</a></li>
<li><a href="/tags">tags</a></li>
<li><a href="/bookmarks">bookmarks</a></li>
<li><a href="/branches">branches</a></li>
</ul>
<ul>
<li><a href="/rev/tip">changeset</a></li>
<li><a href="/file/tip">browse</a></li>
</ul>
<ul>
<li><a href="/file/tip/a">file</a></li>
<li><a href="/file/tip/a">latest</a></li>
<li class="active">diff</li>
<li><a href="/comparison/tip/a">comparison</a></li>
<li><a href="/annotate/tip/a">annotate</a></li>
<li><a href="/log/tip/a">file log</a></li>
<li><a href="/raw-file/tip/a">raw</a></li>
</ul>
<ul>
<li><a href="/help">help</a></li>
</ul>
</div>
<div class="main">
<h2 class="breadcrumb"><a href="/">Mercurial</a> </h2>
<h3>
diff a @ 1:<a href="/rev/c78f6c5cbea9">c78f6c5cbea9</a>
<span class="phase">draft</span> <span class="branchhead">default</span> <span class="tag">tip</span>
</h3>
<form class="search" action="/log">
<p><input name="rev" id="search1" type="text" size="30" value="" /></p>
<div id="hint">Find changesets by keywords (author, files, the commit message), revision
number or hash, or <a href="/help/revsets">revset expression</a>.</div>
</form>
<div class="description">del</div>
<table id="changesetEntry">
<tr>
<th>author</th>
<td>test</td>
</tr>
<tr>
<th>date</th>
<td class="date age">Thu, 01 Jan 1970 00:00:00 +0000</td>
</tr>
<tr>
<th>parents</th>
<td><a href="/file/cb9a9f314b8b/a">cb9a9f314b8b</a> </td>
</tr>
<tr>
<th>children</th>
<td></td>
</tr>
</table>
<div class="overflow">
<div class="sourcefirst linewraptoggle">line wrap: <a class="linewraplink" href="#">on</a></div>
<div class="sourcefirst"> line diff</div>
<div class="stripes2 diffblocks">
<div class="bottomline inc-lineno"><pre class="sourcelines wrap">
<span id="l1.1" class="minusline">--- a/a Thu Jan 01 00:00:00 1970 +0000</span><a href="#l1.1"></a>
<span id="l1.2" class="plusline">+++ /dev/null Thu Jan 01 00:00:00 1970 +0000</span><a href="#l1.2"></a>
<span id="l1.3" class="atline">@@ -1,1 +0,0 @@</span><a href="#l1.3"></a>
<span id="l1.4" class="minusline">-a</span><a href="#l1.4"></a></pre></div>
</div>
</div>
</div>
</div>
</body>
</html>
$ cd ..