What Lua scripting means for Wikimedia and open source

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Yesterday we flipped a switch: editors can now use Lua, an innovative programming language, to generate sections of wiki pages on all our sites. We’d like to talk about what this means for the open source community at large, for Wikimedians, and for our future.

Why we did this

In the old wikitext templating system, this is part of Template:Citation/core. Any Wikipedia article citing a source will cause our CPUs to run through this instructionset. With Lua, we’ll be able to replace this.

When we started digging into the causes of slow pageload times a few years ago, we saw that our CPUs ate a lot of time interpreting templates — useful bits of markup that programmatically told MediaWiki to reuse little bits of text. Templates are everywhere on our sites. Good Wikipedia articles heavily use the citation templates, for instance, and you’ve seen the ubiquitous infoboxes on every biography. In fact, editors can write code to generate substantial portions of wiki pages. Hit “View source” sometime to see how.
But, because we’d never planned for wikitext to become a programming language, these templates were terribly inefficient and hacky — they didn’t even have recursion or loops — and were terrible for performance. When you edit a complex article like Tulsi Gabbard, with scores of citations, it can take up to 30 seconds to parse and display the page. Even as we worked to improve performance via caching, query profiling, new hardware, and other common means, we sometimes had to advise our community to remove functionality from a particular template so pages would render faster.
This wouldn’t do. It was a terrible experience for our users and especially hard for our editors, who had to wait for a multi-second roundtrip after every “how would this page look?” preview.
So our staffers and volunteers worked on Scribunto (from the Latin for “they shall write”), a MediaWiki extension to allow editors to embed Lua scripts instead of wikitext for templating. And volunteers and Foundation staffers have already started identifying pages that are slow to render and converting the most inefficient templates. We have 488,731 templates on English Wikipedia alone right now. The process of turning many of those into Lua scripts is going to affect everyone who reads our sites — and the Scribunto project has already started giving back to the Lua community.

Us and Lua

For instance, our engineer Brad Jorsch wrote mw.ustring.lua, a Unicode module reusable by other Lua developers. This library is good news for people who write templates in non-Latin characters, and for anyone who wants a version of Lua’s standard String library where the methods operate on characters in UTF-8 encoded strings rather than bytes.
And with Scribunto, we empower those frustrated Wikimedians who have been spending years breaking their knuckles making amazing things in wikitext; as they learn how much easier it is to script in Lua, we hope they’ll be able to use those skills in their hobbies, schools, and workplaces. They’ll join forces with the graduates of Codecademy, World of Warcraft, and the other communities that teach anyone to program. New programmers with basic knowledge of computer science who want to do something real with their new skills will find that Lua scripting on Wikimedia sites is a logical next step for them. Our implementation only differs slightly from standard Lua.
And since Scribunto is an extension that any MediaWiki administrator can install, we hope the MediaWiki administrators out there will enjoy using Lua to more easily customize their wikis for their users.

Structured data and new ways to display it

Scribunto lays the foundations for exciting work to come when the Wikidata structured data project comes further online (the Wikidata interface is still in development and being deployed in phases). We know that Lua will be an attractive way to integrate Wikidata information into pages, and we hope a lot of (currently) unstructured data will get structured, helping new applications emerge.
Now that Lua and Wikidata are more mature, we can look forward to enabling more functionality and plugging in more libraries. And as we continue deploying Wikidata, people will make interesting improvements that we currently can’t predict. For instance, right now, each citation is hard to programmatically dissect; the Cite template takes many unstructured parameters (“author1,” “author2,” etc.) We structure these arguments by convention, but the data’s not structured as CS folks would have it, and can’t be queried via APIs, remixed, and so on.

Excerpt of Coordinates module
A screenshot of part of the new Coordinates module, written in Lua by User:Dragons flight. Note that, with Lua, we can actually use proper conditionals.

But in the future, we could have citations stored in Wikidata and then put together onto article pages using Lua, or even assembled into other various reasonable forms (automatically generated bibliographies?) using Lua, and it will be more easy for Zotero users to discover. That’s just one example; on all our sites over the next few years, things will change from the status quo in a user-visible way. The old math and geography templates were inefficient and hard to hack; once rewritten, they’ll run faster and perhaps editors will use them more. We might see galleries, automatic data analyses, better annotated maps, and various other interesting processes and queries embedded in Wikimedia pages.

Open for change

Wikimedians have been writing wikitext templates for years, and doing hard, astounding, unexpected things with them for readers to enjoy. But the steep learning curve drove contributors away. With Lua, a genuine programming language, people now have a deeper and more useful foundation to build upon. And for years, power users on our sites have customized their experiences with JavaScript/CSS Gadgets and user scripts, but those are basically one level above skins preferences; other people won’t stumble upon your hacks in the process of reading an article.
So, now is the first time that the Wikimedia site maintainers have enabled real coding that affects all readers. We’re letting people program Wikipedia unsupervised. Anyone can write a chunk of code to be included in an article that will be seen by millions of people, often without much review. We are taking our “anyone can edit” maxim one big step forward.
If someone doesn’t like the load time of a webpage, they can now actually improve it themselves. Just as we crowdsourced building Wikipedia, now we’re crowdsourcing bits of infrastructure improvement. And this kind of massively multiplayer, crowdsourced performance improvement is uniquely us.
Wikitext templates could do a lot of things, but Lua does them better and faster, and now mere mortals can do it. We’re aiming to help our users learn to program, to empower themselves, and to help each other and help our readers.
We hope you’ll join us.
Sumana Harihareswara, Engineering Community Manager

Archive notice: This is an archived post from blog.wikimedia.org, which operated under different editorial and content guidelines than Diff.

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I have a main template (used multiple times per page and on 40% of all my pages) which includes many other simplier templates.
Would Lua be worth it?

Subfader, I think it’s worth a try. Dragons flight has tested replacing some wikitext templates with Lua and found very significant performance improvements.
To preview and test a converted template, try Special:TemplateSandbox on your wiki. With it, you can preview a page using sandboxed versions of templates and modules, allowing for easy testing before you make the new template live.

Great work! I hope everyone will enjoy Lua template.

This is really exciting news on several fronts. It should improve Wikipedia in multiple ways (but likely with a cost of providing additional attack vectors.) People who have programming skills should enjoy better productivity and lower frustration while editing Wikipedia. Perhaps most exciting is how many people will have a gentle and practical introduction to programming because of this.

Zak, thanks for the comment. Indeed it’s very exciting for the reasons you mentioned! And I agree that giving people a gentle and practical introduction to programming is ultra-promising.
We’ve done our best to put Lua code in a sandbox, partially to reduce the threat surface. Check out how Lua-via-Scribunto differs from standard Lua; we’ve removed a few functions or packages for security reasons. But as always, if anyone finds a security vulnerability in MediaWiki or one of Wikimedia’s web sites, we ask them to directly e-mail security@wikimedia.org with details.

Will we be able to use lua for generating/modifying SVG too? It would be very helpful for maps and graphs.

Where do I see an example page with lua invocations?

Yuv, our earlier blog post has some links to examples and tutorials and the template sandbox. Check out the basic “hello, world!” instructions, then look at Brad Jorsch’s short presentation for a basic example of how to convert a wikitext template into a Lua module. After that, try Tim Starling’s tutorial.

The Wikimedia Foundation hosted a one-hour presentation this week (video recording available) in which people from the WMF and the Lua community gave an intro to Lua and explained how to use it on Wikimedia projects. (We’re working on copying the video to Commons.)

Pengo: Thanks for your question.
At this time, no.
It was brought up in one of our brainstorming sessions that generating images from Lua is something that could be added, since with Lua we can provide a general-purpose image library rather than the extremely-special-purpose things like EasyTimeline, but it’s not on the roadmap at this time.

Pengo: The problem with using Lua for SVGs is the need to either write to file (if SVGs are served as PNGs) or generate cross-browser compatible, safe, resource-limited SVG files to serve directly. Both present similar (and deep) difficulties, I’m afraid, which suggests to me that Lua-d SVGs won’t be happening any time soon.

Great work! I think this will be a huge advancement for MediaWiki.

I may well have missed some comment on this point (my apologies if so), but are there any restrictions in place to cope with any deliberately bad Lua scripting, e.g. if someone tries to create some form of repeating loop that uses resources (CPU, memory or maybe creates a giant page) effectively as a form of a DoS attack?

Neil, as I understand it, there is a limit of 10 seconds of CPU time. I’m not sure about other limits.

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