Guidelines:Modules
Overview
Modules are Lua scripts for making templates using a full-fledged programming language. You can ask questions about Zelda Wiki modules in #wiki-tech on Discord.
Templates
Modules exist as a means to create more complex templates. In order to contribute to modules, you must first understand how templates are used. You should also know to create a basic template without modules to get a sense of when Lua scripts are needed and why.
Getting Started
In order to contribute to modules, you'll need to learn basic programming in Lua. You'll also need to know the specifics of Lua scripting on MediaWiki.
Lua for Beginners
There are many excellent online resources designed to teach programming fundamentals... But not in Lua. Fortunately, Lua is a relatively small language. Jump in and try to learn through the Exercises.
If you would prefer more guided lessons, try Codeacademy's Python 2 course or Khan Academy's Intro to JavaScript. Lua is closer to Python than to JavaScript, but Khan Academy's course has the benefit of video talk-throughs. Learning JavaScript would allow you to build Gadgets or write personal modifications to the wiki's interface.
If you would prefer a book, try An Introduction to Programming in Go by Caleb Doxsey. Due to the nature of Go, this book teaches more general-purpose computing fundamentals than what you would need for writing wiki modules. Were you to pursue programming beyond the wiki, those concepts would likely serve you well.
Lua for Developers
If you already have some programming experience in other languages, read Learn Lua in 15 minutes.
Note the following in particular:
| Particularities | Further reading |
|---|---|
tables are the only built-in object type. Any use of the term "array" actually refers to a table with integer keys.
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|
Generally arrays are 1-indexed as opposed to 0-indexed.
local tbl = {"foo"}
tbl[1]
> "foo"
|
|
|
|
The length operator for a table is #.
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|
Tables, nil, and the # operator don't interact the way similar constructs do in other languages.
#{ nil, nil, "foo" }
> 3
local tbl = {}
tbl[3] = "foo"
#tbl
> 0
tbl[1] = "bar"
#tbl
> 1
tbl[2] = "baz"
#tbl
> 3
Generally, "array" functions only look at the consecutive indices starting from 1. |
Scribunto
- For a broader and more in-depth guide, see Gamepedia Help Wiki.
- See also the full Scribunto/Lua reference manual.
Scribunto is the name of the extension that enables Lua modules. The Lua on you see on MediaWiki is almost the same as standard Lua except for some changes to library functions and packages. The main difference is in how Lua scripts are invoked.
#invoke
The #invoke parser function is what bridges the gap between templates and module scripts. For example, the transcluded content of Template:Game Rating is as follows:
{{#invoke:Game Rating|Main}}
This invokes Module:Game Rating, which could looks something like:
A page can invoke any function that is a field on the module's export table. The export table is the table object returned by the module, which is named p by convention (short for "package").
In the above example, Main and color are the functions in the export table. Only Main can be used by Template:Game Rating via #invoke. The rating function can be used by other modules (see require below).
By convention, Zelda Wiki uses UpperCamelCase to indicate functions meant for #invoke, and lowerCamelCase for all other functions.
args
Functions called via #invoke are passed a Frame object.
frame.argsis a table of the arguments to#invoke. (There are none in the above example.)frame:getParent().argsis a table of the arguments to the template.- Example: If a page has
{{Game Rating|ESRB|E}}, thenframe:getParent().args[1]evaluates to the stringESRBfor that invocation.
- Example: If a page has
The # operator and most other table functions don't work on frame.args.
require
A module can import another module and use its exported functions. This is done with the require function.
For example, Module:Release imports Module:Region to get flags from a region code.
mw
Scribunto pre-loads several MediaWiki-related libraries as the mw object. The following libraries are of note, in addition to the base functions:
| Library | Usage example |
|---|---|
mw.text
|
Module:List |
mw.title
|
Module:Subpage List |
mw.html
|
Module:Infobox |
Debugging
- See also gphelp:Extension:Scribunto#Debugging
You should never be in a situation where you're blindly submitting code and hoping that it works. The first two exercises of these guidelines cover how to debug with previewing, logging, and the debug console.
Always ensure that your code does not produce script errors. Please fix or revert any changes that do. Keep an eye on Category:Articles using invalid arguments in template calls as well.
Testing and Documentation
When coding a module, the best page to preview is often the corresponding template's documentation. If it exists, the page should have usage examples for every available feature. In fact, an effective way to write modules is actually to write the documentation examples before the code itself. When you're writing the actual code, previewing that documentation page will tell you if your code is working—and will give you material to debug with if it isn't. The practice of writing test cases before the code is called test-driven development.
You should also write module documentation for any Lua function meant to be used by other modules. Module documentation can double as automated unit tests via the expect property. If the output of the function does not equal what is expected, the page is added to Category:Modules with failing tests.
Utility Modules
A utility module is a library-type module meant to be used by other modules, rather than being invoked by a template. Most template-facing modules use at least one of these:
A list of utility modules is available at Category:Utility Modules. Leverage utility modules as much as possible so that the wiki's codebase stays DRY.
Exercises
Try the available exercises to test and develop your understanding of Lua, Scribunto, and Zelda Wiki's utilities.
Style
Once you are able to produce working code, make sure it adheres to Zelda Wiki's coding standards.
Strings
| Default to double quotes | |
|---|---|
|
local foo = "foo"
local bar = '<span class="baz">bar</span>'
|
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local foo = 'foo'
|
Errors
| Template calls must not throw script errors on purpose. Use warnings and error categories instead. | |
|---|---|
|
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function(foo)
if not foo then
mw.addWarning("'foo' is required.")
return "[[Category:Pages with Invalid Arguments]]"
end
local bar = foo.bar
...
end
Module:UtilsArg can help with this. |
|
|
function(foo)
local bar = foo.bar -- throws an error if foo is nil
...
end
|
|
|
function(foo)
if not foo then
error("foo cannot be nil")
end
local bar = foo.bar
...
end
|
Performance Optimization
High-usage modules may require additional effort for them to work well at scale. "High usage" can mean one of two things:
1. Modules used many times per page
One example is Module:Term. Some pages invoke this module 300+ times.
The Lua processing time quickly adds up in these cases, so the modules must be as fast as possible to avoid slowing down wiki page processing. Total Lua processing time on a page must be less than 7 seconds—any Lua code running after that is aborted and manifests as a script error. Ideally, Lua processing time should be less than 1 second.
What you can do:
- Use the Profiler to find out what's slowing down a module.
- Follow Module:Documentation#Performance Optimization.
- Follow https://dev.fandom.com/wiki/Lua_templating/Optimisation
2. Modules used on many pages
Examples: FileInfo, Franchise, UtilsArg.
Every time such a module is updated, every page that uses it (directly or indirectly) must be updated. This can set off a large job queue. When there are many active jobs in the queue, any changes to other templates (high-usage or no) may take several hours to propagate to all the pages that use them. The same goes for Special:ReplaceText operations, which are also sent to the back of the job queue.
What you can do:
- Put high-usage functions in separate modules.
- Minimize the number of imports in high-usage modules.
A case study: Module:File used to contain the #invoke functions for Template:FileInfo and Template:File Redirect as well as utility functions for image thumbnails. As a result, the module was linked on nearly every page on the wiki (~50,000 for all articles and files). Changing the code for file redirects would create a job queue for all these pages even though file redirects only number a few hundred. The solution to this problem was to create three separate modules: Module:File for rendering image thumbnails, Module:FileInfo for file descriptions, and Module:FileInfo/File Redirect for file redirects. This way, changes to any module function would only affect the pages that actually use them.
Profiling
Our MediaWiki installation comes with a Lua Profiler which indicates how much time and memory Lua takes up when loading a page on the wiki. It will also show the top ten Lua functions which contribute the most time usage.
To generate a profiler report, preview a page on the wiki. The report is located at the bottom of the page under the editing area, in the Parser profiling data: section which may be collapsed by default. It looks something like this:
| Lua time usage | 1.253/7.000 seconds | |
|---|---|---|
| Lua memory usage | 15,186,425/52,428,800 bytes | |
| Lua Profile | ||
| Scribunto_LuaSandboxCallback::query | 200 ms | 14.7% |
| recursiveClone <mwInit.lua:41> | 200 ms | 14.7% |
| Scribunto_LuaSandboxCallback::preprocess | 140 ms | 10.3% |
| Scribunto_LuaSandboxCallback::get | 120 ms | 8.8% |
| ? | 100 ms | 7.4% |
| init <Module:UtilsTable/Inspect> | 60 ms | 4.4% |
| init <Module:UtilsString> | 60 ms | 4.4% |
| Scribunto_LuaSandboxCallback::newTitle | 60 ms | 4.4% |
| Scribunto_LuaSandboxCallback::callParserFunction | 60 ms | 4.4% |
| init <Module:UtilsArg> | 40 ms | 2.9% |
| [others] | 320 ms | 23.5% |
The Lua Profile section only appears when total Lua time usage on the page is above 1000ms (1 second).
