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01/04 — 2020
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<h1>
Rapid Refactoring With Vim
</h1>
<div class="post-text">
<p>Last weekend, I was tasked with refactoring the 96 unit tests on <a href="https://github.com/ruma/ruma-events/pull/70">ruma-events</a> to use strictly typed json objects using <code>serde_json::json!</code> instead of raw strings. It was rather painless thanks to vim :)</p>
<p>Here’s a small sample of what had to be done (note the lines prefixed with the arrow):</p>
<div class="sourceCode" id="cb1"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb1-1"><a href="#cb1-1" aria-hidden="true"></a>→ <span class="kw">use</span> <span class="pp">serde_json::</span><span class="op">{</span>from_str<span class="op">};</span></span>
<span id="cb1-2"><a href="#cb1-2" aria-hidden="true"></a> </span>
<span id="cb1-3"><a href="#cb1-3" aria-hidden="true"></a> <span class="at">#[</span>test<span class="at">]</span></span>
<span id="cb1-4"><a href="#cb1-4" aria-hidden="true"></a> <span class="kw">fn</span> deserialize() <span class="op">{</span></span>
<span id="cb1-5"><a href="#cb1-5" aria-hidden="true"></a> <span class="pp">assert_eq!</span>(</span>
<span id="cb1-6"><a href="#cb1-6" aria-hidden="true"></a>→ <span class="pp">from_str::</span><span class="op"><</span>Action<span class="op">></span>(<span class="st">r#"{"set_tweak": "highlight"}"#),</span></span>
<span id="cb1-7"><a href="#cb1-7" aria-hidden="true"></a><span class="st"> Action::SetTweak(Tweak::Highlight { value: true })</span></span>
<span id="cb1-8"><a href="#cb1-8" aria-hidden="true"></a><span class="st"> );</span></span>
<span id="cb1-9"><a href="#cb1-9" aria-hidden="true"></a><span class="st"> }</span></span></code></pre></div>
<p>had to be converted to:</p>
<div class="sourceCode" id="cb2"><pre class="sourceCode rust"><code class="sourceCode rust"><span id="cb2-1"><a href="#cb2-1" aria-hidden="true"></a>→ <span class="kw">use</span> <span class="pp">serde_json::</span><span class="op">{</span>from_value<span class="op">};</span></span>
<span id="cb2-2"><a href="#cb2-2" aria-hidden="true"></a> </span>
<span id="cb2-3"><a href="#cb2-3" aria-hidden="true"></a> <span class="at">#[</span>test<span class="at">]</span></span>
<span id="cb2-4"><a href="#cb2-4" aria-hidden="true"></a> <span class="kw">fn</span> deserialize() <span class="op">{</span></span>
<span id="cb2-5"><a href="#cb2-5" aria-hidden="true"></a> <span class="pp">assert_eq!</span>(</span>
<span id="cb2-6"><a href="#cb2-6" aria-hidden="true"></a>→ <span class="pp">from_value::</span><span class="op"><</span>Action<span class="op">></span>(<span class="pp">json!</span>(<span class="op">{</span><span class="st">"set_tweak"</span><span class="op">:</span> <span class="st">"highlight"</span><span class="op">}</span>))<span class="op">,</span></span>
<span id="cb2-7"><a href="#cb2-7" aria-hidden="true"></a> <span class="pp">Action::</span>SetTweak(<span class="pp">Tweak::</span>Highlight <span class="op">{</span> value<span class="op">:</span> <span class="cn">true</span> <span class="op">}</span>)</span>
<span id="cb2-8"><a href="#cb2-8" aria-hidden="true"></a> )<span class="op">;</span></span>
<span id="cb2-9"><a href="#cb2-9" aria-hidden="true"></a> <span class="op">}</span></span></code></pre></div>
<h3 id="the-arglist">The arglist</h3>
<p>For the initial pass, I decided to handle imports, this was a simple find and replace operation, done to all the files containing tests. Luckily, modules (and therefore files) containing tests in Rust are annotated with the <code>#[cfg(test)]</code> attribute. I opened all such files:</p>
<div class="sourceCode" id="cb3"><pre class="sourceCode bash"><code class="sourceCode bash"><span id="cb3-1"><a href="#cb3-1" aria-hidden="true"></a><span class="co"># `grep -l pattern files` lists all the files</span></span>
<span id="cb3-2"><a href="#cb3-2" aria-hidden="true"></a><span class="co"># matching the pattern</span></span>
<span id="cb3-3"><a href="#cb3-3" aria-hidden="true"></a></span>
<span id="cb3-4"><a href="#cb3-4" aria-hidden="true"></a><span class="ex">vim</span> <span class="va">$(</span><span class="fu">grep</span> -l <span class="st">'cfg\(test\)'</span> ./**/*.rs<span class="va">)</span></span>
<span id="cb3-5"><a href="#cb3-5" aria-hidden="true"></a></span>
<span id="cb3-6"><a href="#cb3-6" aria-hidden="true"></a><span class="co"># expands to something like:</span></span>
<span id="cb3-7"><a href="#cb3-7" aria-hidden="true"></a><span class="ex">vim</span> push_rules.rs room/member.rs key/verification/lib.rs</span></code></pre></div>
<p>Starting vim with more than one file at the shell prompt populates the arglist. Hit <code>:args</code> to see the list of files currently ready to edit. The square [brackets] indicate the current file. Navigate through the arglist with <code>:next</code> and <code>:prev</code>. I use tpope’s vim-unimpaired <a href="#fn1" class="footnote-ref" id="fnref1" role="doc-noteref"><sup>1</sup></a>, which adds <code>]a</code> and <code>[a</code>, mapped to <code>:next</code> and <code>:prev</code>.</p>
<p>All that’s left to do is the find and replace, for which we will be using vim’s <code>argdo</code>, applying a substitution to every file in the arglist:</p>
<pre><code>:argdo s/from_str/from_value/g</code></pre>
<h3 id="the-quickfix-list">The quickfix list</h3>
<p>Next up, replacing <code>r#" ... "#</code> with <code>json!( ... )</code>. I couldn’t search and replace that trivially, so I went with a macro call <a href="#fn2" class="footnote-ref" id="fnref2" role="doc-noteref"><sup>2</sup></a> instead, starting with the cursor on ‘r’, represented by the caret, in my attempt to breakdown the process:</p>
<pre><code>BUFFER: r#" ... "#;
^
ACTION: vllsjson!(
BUFFER json!( ... "#;
^
ACTION: <esc>$F#
BUFFER: json!( ... "#;
^
ACTION: vhs)<esc>
BUFFER: json!( ... );</code></pre>
<p>Here’s the recorded <a href="#fn3" class="footnote-ref" id="fnref3" role="doc-noteref"><sup>3</sup></a> macro in all its glory: <code>vllsjson!(<esc>$F#vhs)<esc></code>.</p>
<p>Great! So now we just go ahead, find every occurrence of <code>r#</code> and apply the macro right? Unfortunately, there were more than a few occurrences of raw strings that had to stay raw strings. Enter, the quickfix list.</p>
<p>The idea behind the quickfix list is to jump from one position in a file to another (maybe in a different file), much like how the arglist lets you jump from one file to another.</p>
<p>One of the easiest ways to populate this list with a bunch of positions is to use <code>vimgrep</code>:</p>
<pre><code># basic usage
:vimgrep pattern files
# search for raw strings
:vimgrep 'r#' ./**/*.rs</code></pre>
<p>Like <code>:next</code> and <code>:prev</code>, you can navigate the quickfix list with <code>:cnext</code> and <code>:cprev</code>. Every time you move up or down the list, vim indicates your index:</p>
<pre><code>(1 of 131): r#"{"set_tweak": "highlight"}"#;</code></pre>
<p>And just like <code>argdo</code>, you can <code>cdo</code> to apply commands to <em>every</em> match in the quickfix list:</p>
<pre><code>:cdo norm! @q</code></pre>
<p>But, I had to manually pick out matches, and it involved some button mashing.</p>
<h3 id="external-filtering">External Filtering</h3>
<p>Some code reviews later, I was asked to format all the json inside the <code>json!</code> macro. All you have to do is pass a visual selection through a pretty json printer. Select the range to be formatted in visual mode, and hit <code>:</code>, you will notice the command line displaying what seems to be gibberish:</p>
<pre><code>:'<,'></code></pre>
<p><code>'<</code> and <code>'></code> are <em>marks</em> <a href="#fn4" class="footnote-ref" id="fnref4" role="doc-noteref"><sup>4</sup></a>. More specifically, they are marks that vim sets automatically every time you make a visual selection, denoting the start and end of the selection.</p>
<p>A range is one or more line specifiers separated by a <code>,</code>:</p>
<pre><code>:1,7 lines 1 through 7
:32 just line 32
:. the current line
:.,$ the current line to the last line
:'a,'b mark 'a' to mark 'b'</code></pre>
<p>Most <code>:</code> commands can be prefixed by ranges. <code>:help usr_10.txt</code> for more on that.</p>
<p>Alright, lets pass json through <code>python -m json.tool</code>, a json formatter that accepts <code>stdin</code> (note the use of <code>!</code> to make use of an external program):</p>
<pre><code>:'<,'>!python -m json.tool</code></pre>
<p>Unfortunately that didn’t quite work for me because the range included some non-json text as well, a mix of regex and macros helped fix that. I think you get the drift.</p>
<p>Another fun filter I use from time to time is <code>:!sort</code>, to sort css attributes, or <code>:!uniq</code> to remove repeated imports.</p>
<section class="footnotes" role="doc-endnotes">
<hr />
<ol>
<li id="fn1" role="doc-endnote"><p>https://github.com/tpope/vim-unimpaired It also handles various other mappings, <code>]q</code> and <code>[q</code> to navigate the quickfix list for example<a href="#fnref1" class="footnote-back" role="doc-backlink">↩︎</a></p></li>
<li id="fn2" role="doc-endnote"><p><code>:help recording</code><a href="#fnref2" class="footnote-back" role="doc-backlink">↩︎</a></p></li>
<li id="fn3" role="doc-endnote"><p>When I’m recording a macro, I prefer starting out by storing it in register <code>q</code>, and then copying it over to another register if it works as intended. I think of <code>qq</code> as ‘quick record’.<a href="#fnref3" class="footnote-back" role="doc-backlink">↩︎</a></p></li>
<li id="fn4" role="doc-endnote"><p><code>:help mark-motions</code><a href="#fnref4" class="footnote-back" role="doc-backlink">↩︎</a></p></li>
</ol>
</section>
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<p>I'm Akshay, I go by nerd or nerdypepper on the internet.</p>
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