forked from wezm/wezm.net
98 lines
4.2 KiB
Markdown
98 lines
4.2 KiB
Markdown
+++
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title = "Neovim Versus the 28Mb XML File"
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date = 2020-01-26T10:47:41+10:00
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draft = true
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# [extra]
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# updated = 2019-07-01T22:40:53+10:00
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+++
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I had occasion recently to open and navigate a 28Mb XML file. This proved a
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challenge for Neovim's syntax highlighting, which prompted me to see how some
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other editors handled the file. In this post I want to expand on the problem a
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bit more and explore ways in which the task can be handled without the need to
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switch to another editor.
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<!-- more -->
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It all started withe the following [tweet](https://twitter.com/wezm/status/1219759981441871875?s=20):
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> Battle of the editors! It's 2020, on a 12c/24t Ryzen 9 system with 16Gb of RAM, which Linux text editor can open, syntax highlight, and provide folding for a 28Mb XML file?
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>
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> Not Neovim, VS Code, or CLion. Sublime did. gedit opened and highlighted it but doesn't support folding.
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<table>
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<tr>
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<td><a href="neovim.png"><img src="neovim.png" /></a></td>
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<td><a href="clion.png"><img src="clion.png" /></a></td>
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</tr>
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<tr>
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<td><a href="vscode.png"><img src="vscode.png" /></a></td>
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<td><a href="sublime.png"><img src="sublime.png" /></a></td>
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</tr>
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</table>
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It wasn't meant to shame any editors or highlight any particular editor's
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superiority. Mostly I thought it was interesting — opening a large but not
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ridiculously sized file proved to be a challenge for several professional
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editors running on a modern, fairly high-end desktop computer.
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{% aside(title="Want to see how your editor handles the file?", float="right") %}
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You can [download it](https://files.wezm.net/twitter/NotoColorEmoji.ttx.bz2),
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just be sure to uncompress it first.
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{% end %}
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I use Neovim for most text editing, except Rust where I use CLion and it will
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take a lot more than a once in a decade experience with one file to make me
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switch editors. The XML file in question was produced by the `ttx`
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tool. This tool generates an XML representation of a font file. It can also
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convert the XML back into a font file. I was interested in navigating to a
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specific element in the file and examining its children. I was not interested
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in the children's children.
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I opened the file in Neovim (which happens instantaneously despite the size).
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My planned workflow was to jump to the `CBLC` element and use folding to
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collapse the child elements. However, when I navigated to the `CBLC` element
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(98% through the file) the syntax highlighting disappeared and the following
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message was shown in the status line:
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> 'redrawtime' exceeded, syntax highlighting disabled
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`:set redrawtime` tells me it is set to 2000 (2 seconds), which is the default
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value. Additionally I have `foldmethod=syntax` so with syntax highlighting
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disabled I lose the automatic folding too (or so I thought…).
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So how might the task be completed? We can increase `redrawtime`. Turns out it needs to be `10000`
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for it not to disable syntax highlighting. And there is of course a nearly 10s delay when redrawing
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now. However, folding still doesn't work.
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It turns out there is a setting that's required to enable syntax based folding for xml:
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```vim
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let g:xml_syntax_folding=1
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```
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If I turn this on and reopen the file, the syntax highlighting remains on but every movement
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is excruciatingly slow — I imagine this is why it's not enabled by default.
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So what else can we try? Well Neovim lets us navigate the file fine, the size
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is only an issue for syntax highlighting and folding. If we make the
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amount of text we're dealing with smaller everything should work.
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We can navigate to the `CBLC` element with `/CBLC`, the syntax highlighting
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turns off but we can still use the [tag text object][text-objects] to yank the `CBLC` element
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and its children to a new buffer: `yat` (yank outside tag) followed by `:enew`
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to open a new buffer and `p` to paste. Now we have a much smaller subset to
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deal with (3121 lines). If we enable `xml_syntax_folding` in this smaller buffer it now
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works as expected and it perfectly responsive:
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```vim
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:let g:xml_syntax_folding=1
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:set ft=xml
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```
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The kicker is that there's actually one one child `strike` element of the `CBLC` element — I was
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expecting more. With this knowledge the folding wasn't really needed. Nonetheless I learnt some
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things. 🤓
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[text-objects]: https://neovim.io/doc/user/motion.html#at
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