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LDoc, a Lua Documentation Tool

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Introduction

LDoc is a software documentation tool which automatically generates API documentation out of source code comments (doc comments). It is mainly targeted at Lua and documenting Lua APIs, but it can also parse C with according doc comments for documenting Lua modules implemented in C.

It is mostly compatible with LuaDoc, except that certain workarounds are no longer needed. For instance, it is not so married to the idea that Lua modules should be defined using the module function; this is not only a matter of taste since this has been deprecated in Lua 5.2.

Otherwise, the output is very similar, which is no accident since the HTML templates are based directly on LuaDoc. You can ship your own customized templates and style sheets with your own project (also see Graham Hannington's documentation for Lua for z/OS). LDoc comes with three extra themes; 'pale' for those who like whitespace, 'one' for one-column output, and 'fixed' for a fixed navigation bar down the left side.

You have an option to use Markdown to process the documentation, which means no ugly HTML is needed in doc comments. C/C++ extension modules may be documented in a similar way, although function names cannot be inferred from the code itself.

LDoc can provide integrated documentation, with traditional function comments, any documents in Markdown format, and specified source examples. Lua source in examples and the documents will be prettified.

Although there are a fair number of command-line options, the preferred route is to write a config.ld configuration file in Lua format. By convention, if LDoc is simply invoked as ldoc . it will read this file first. In this way, the aim is to make it very easy for end-users to build your documentation using this simple command.

Commenting Conventions

LDoc follows the conventions established by Javadoc and later by LuaDoc to document the modules, functions, tables and types ("classes") of your API.

Doc comments

Only 'doc comments' are parsed; these can be started with at least 3 hyphens, or by a empty comment line with at least 3 hyphens:

--- summary.
-- Description; this can extend over
-- several lines

-----------------
-- This will also do.

You can also use Lua block comments:

--[[--
    Summary. A description
    ...;
]]

Any module or script must start with a doc comment; any other files are ignored and a warning issued. The only exception is if the module starts with an explicit module statement.

If your coding standards require a boilerplate copyright notice, then the -B flag or boilerplate=true will make LDoc ignore the first comment of each module.

Common commenting patterns like '---- (text) -----' are exempted, since they are often used for programmer-facing documentation.

Doing modules the Lua 5.1 way

As an alternative to using the 'module' tag as described previously, you can still start your modules the Lua 5.1 way:

--- solvers for common equations.
module("solvers", package.seeall)

However, the 'module' function is deprecated in Lua 5.2 and it is increasingly common to see less 'magic' ways of creating modules, as seen in the description of the 'module' tag previously with the explicitly returned module table.

Repeating tags

Tags like 'param' and 'return' can be specified multiple times, whereas a type tag like 'function' can only occur once in a comment.

The basic rule is that a single doc comment can only document one entity.

Local module name

It is common to use a local name for a module when declaring its contents. In this case the 'alias' tag can tell LDoc that these functions do belong to the module:

--- another test.
-- @module test2
-- @alias M

local M = {}

-- first test.
function M.one()
..
end

return M

M and _M are used commonly enough that LDoc will recognize them as aliases automatically, but 'alias' allows you to use any identifier.

LDoc tries to deduce the function name and the formal parameter names from examining the code after the doc comment. It also recognizes the 'unsugared' way of defining functions as explicit assignment to a variable:

--- second test.
M.two = function(...) ... end

Local functions

Apart from exported functions, a module usually contains local functions. By default, LDoc does not include these in the documentation, but they can be enabled using the --all flag, or all=true in config.ld. They can be documented just like 'public' functions:

--- it's clear that boo is local from context.
local function boo(...) .. end

local foo

--- we need to give a hint here for foo
-- @local here
function foo(...) .. end

Alternative way of specifying tags

Since 1.3, LDoc allows the use of colons instead of @.

--- a simple function.
-- string: name person's name
-- int: age age of person
-- !person: person object
-- treturn: ?string
-- function check(name,age)

However, you must either use the --colon flag or set colon=true in your config.ld.

In this style, types may be used directly if prefixed with '!' or '?' (for type-or-nil)

(see @{colon.lua})

Sections

LDoc supports explicit sections. By default, the implicit sections correspond to the pre-existing types in a module: 'Functions', 'Tables' and 'Fields' (There is another default section 'Local Functions' which only appears if LDoc is invoked with the --all flag.) But new sections can be added; the first mechanism is when you @{Adding_new_Tags|define a new type} (say 'macro'). Then a new section ('Macros') is created to contain these types.

There is also a way to declare ad-hoc sections using the @section tag. The need occurs when a module has a lot of functions that need to be put into logical sections.

--- File functions.
-- Useful utilities for opening foobar format files.
-- @section file

--- open a file
...

--- read a file
...

--- Encoding operations.
-- Encoding foobar output in different ways.
-- @section encoding

...

A section doc-comment has the same structure as a normal doc-comment; the summary is used as the new section title, and the description will be output at the start of the function details for that section; the name is not used, but must be unique.

Sections appear under 'Contents' on the left-hand side. See the winapi documentation for an example of how this looks.

Arguably a module writer should not write such very long modules, but it is not the job of the documentation tool to limit the programmer!

A specialized kind of section is type: it is used for documenting classes. The functions (or fields) within a type section are considered to be the methods of that class.

--- A File class.
-- @type File

....
--- get the modification time.
-- @return standard time since epoch
function File:mtime()
...
end

(In an ideal world, we would use the word 'class' instead of 'type', but this would conflict with the LuaDoc class tag.)

A section continues until the next section is found, @section end, or end of file.

You can put items into implicit sections using @within. This allows you to put adjacent functions in different sections, so that you are not forced to order your code in a particular way.

With 1.4, there is another option for documenting classes, which is the top-level type classmod. It is intended for larger classes which are implemented within one module, and the advantage that methods can be put into sections.

Sometimes a module may logically span several files, which can easily happen with large There will be a master module with name 'foo' and other files which when required add functions to that module. If these files have a @submodule tag, their contents will be placed in the master module documentation. However, a current limitation is that the master module must be processed before the submodules.

See the tests/submodule example for how this works in practice.

Which files are processed?

By default, LDoc will process any file ending in '.lua' or '.luadoc' in a specified directory; you may point it to a single file as well. A 'project' usually consists of many modules in one or more packages. The generated index.html will point to the generated documentation for each of these modules.

If only one module or script is documented for a project, then the index.html generated contains the documentation for that module, since an index pointing to one module would be redundant.

LDoc has a two-layer hierarchy; underneath the project, there are modules, scripts, classes (containing code) and examples and 'topics' (containing documentation). These then contain items like functions, tables, sections, and so forth.

If you want to document scripts, then use @script instead of @module. New with 1.4 is @classmod which is a module which exports a single class.

See References

@see is used to reference other parts of the documentation, and @usage can provide examples of use; there can be multiple such tags:

---------
-- split a string in two.
-- @param s the string
-- @param delim the delimiter (default space)
-- @return first part
-- @return second part
-- @usage local hello,world = split2("hello world")
-- @see split
function split2(s,delim) ... end

Here it's assumed that 'split' is a function defined in the same module. If you wish to link to a function in another module, then the reference has to be qualified.

References to methods use a colon: myclass:method; this is for instance how you would refer to members of a @type section.

The example at tests/complex shows how @see references are interpreted:

complex.util.parse
complex.convert.basic
complex.util
complex.display
complex

You may of course use the full name of a module or function, but can omit the top-level namespace - e.g. can refer to the module util and the function display.display_that directly. Within a module, you can directly use a function name, e.g. in display you can say display_this.

What applies to functions also applies to any module-level item like tables. New module-level items can be defined and they will work according to these rules.

If a reference is not found within the project, LDoc checks to see if it is a reference to a Lua standard function or table, and links to the online Lua manual. So references like 'table.concat' are handled sensibly.

References may be made inline using the @{\ref} syntax. This may appear anywhere in the text, and is more flexible than @see. In particular, it provides one way to document the type of a parameter or return value when that type has a particular structure:

------
-- extract standard variables.
-- @param s the string
-- @return @{\\stdvars}
function extract_std(s) ... end

------
-- standard variables.
-- Use @{\\extract_std} to parse a string containing variables,
-- and @{\\pack_std} to make such a string.
-- @field length
-- @field duration
-- @field viscosity
-- @table stdvars

@{\ref} is very useful for referencing your API from code samples and readme text.

The link text can be changed from the default by the extended syntax `@{\ref|text}.

You can also put references in backticks, like \stdvars``. This is commonly used in Markdown to indicate code, so it comes naturally when writing documents. The difference is that the backticked expression does not have to be a reference and then will appear in code style; with @ references you will get a warning for unrecognized symbols and the result will be rendered as '???'.

It is controlled by the configuration variable backtick_references or the backtick format; the default is true if you use Markdown in your project, but can be specified explicitly in config.ld.

To quote such references so they won't be expanded, say @{\ref}.

Custom @see References

It's useful to define how to handle references external to a project. For instance, in the luaposix project we wanted to have man references to the corresponding C function:

------------
-- raise a signal on this process.
-- @see raise(3)
-- @int nsig
-- @return integer error cod
function raise (nsig)
end

These see references always have this particular form, and the task is to turn them into online references to the Linux manpages. So in config.ld we have:

local upat = "http://www.kernel.org/doc/man-pages/online/pages/man%s/%s.%s.html"

custom_see_handler('^([%w_]+)%((%d)%)$',function(name,section)
    local url = upat:format(section,name,section)
    local name = name .. '(' ..section..')'
    return name, url
end)

^([%w_]+)%((%d)%)$ both matches the pattern and extracts the name and its section. Then it's a simple matter of building up the appropriate URL. The function is expected to return link text and link source and the patterns are checked before LDoc tries to resolve project references. So it is best to make them match as exactly as possible.

Module Tags

LDoc requires you to have a module doc comment. If your code style requires license blocks that might look like doc comments, then set boilerplate=true in your configuration and they will be skipped.

This comment does not have to have an explicit @module tag and LDoc continues to respect the use of module().

There are three types of 'modules' (i.e. 'project-level'); module, a library loadable with require(), script, a program, and classmod which is a class implemented in a single module.

There are some tags which are only useful in module comments: author,copyright, license and release. These are presented in a special Info section in the default HTML output.

The @usage tag has a somewhat different presentation when used in modules; the text is presented formatted as-is in a code font. If you look at the script ldoc in this documentation, you can see how the command-line usage is shown. Since coding is all about avoiding repetition and the out-of-sync issues that arise, the @usage tag can appear later in the module, before a long string. For instance, the main script of LDoc is ldoc.lua and you will see that the usage tag appears on line 36 before the usage string presented as help.

@export is another module tag that is usually 'detached'. It is for supporting modules that wish to explicitly export their functions @{three.lua|at the end}. In that example, both question and answer are local and therefore private to the module, but answer has been explicitly exported. (If you invoke LDoc with the -a flag on this file, you will see the documentation for the unexported function as well.)

@set is a powerful tag which assigns a configuration variable to a value just for this module. Saying @set no_summary=true in a module comment will temporarily disable summary generation when the template is expanded. Generally configuration variables that effect template expansion are modifiable in this way. For instance, if you wish that the contents of a particular module be sorted, then @set sort=true will do it just for that module.

Adding new Tags

LDoc tries to be faithful to LuaDoc, but provides some extensions. Aliases for tags can be defined, and new types declared.

--- zero function. Two new ldoc features here; item types
-- can be used directly as tags, and aliases for tags
-- can be defined in config.ld.
-- @function zero_fun
-- @p k1 first
-- @p k2 second

Here an alias for 'param' has been defined. If a file config.ld is found in the source, then it will be loaded as Lua data. For example, the configuration for the above module provides a title and defines an alias for 'param':

title = "testmod docs"
project = "testmod"
alias("p","param")

Extra tag types can be defined:

new_type("macro","Macros")

And then used as any other type:

-----
-- A useful macro. This is an example of a custom type.
-- @macro first_macro
-- @see second_function

This will also create a new module section called 'Macros'.

If your new type has arguments or fields, then specify the name:

new_type("macro","Macros",false,"param")

(The third argument means that this is not a project level tag)

Then you may say:

-----
-- A macro with arguments.
-- @macro second_macro
-- @param x the argument

And the arguments will be displayed under the subsection 'param'

Inferring more from Code

The qualified name of a function will be inferred from any function keyword following the doc comment. LDoc goes further with this kind of code analysis, however.

Instead of:

--- first table.
-- @table one
-- @field A alpha
-- @field B beta
M.one = {
    A = 1,
    B = 2;
}

you can write:

--- first table
-- @table one
M.one = {
    A = 1, -- alpha
    B = 2; -- beta
}

Similarly, function parameter comments can be directly used:

------------
-- third function. Can also provide parameter comments inline,
-- provided they follow this pattern.
function mod1.third_function(
    alpha, -- correction A
    beta, -- correction B
    gamma -- factor C
    )
    ...
end

As always, explicit tags can override this behaviour if it is inappropriate.

Extension modules written in C

LDoc can process C/C++ files:

/***
Create a table with given array and hash slots.
@function createtable
@param narr initial array slots, default 0
@param nrec initial hash slots, default 0
@return the new table
*/
static int l_createtable (lua_State *L) {
....

Both /** and /// are recognized as starting a comment block. Otherwise, the tags are processed in exactly the same way. It is necessary to specify that this is a function with a given name, since this cannot be reliably be inferred from code. Such a file will need a module comment, which is treated exactly as in Lua.

An unknown extension can be associated with a language using a call like add_language_extension('lc','c') in config.ld. (Currently the language can only be 'c' or 'lua'.)

An LDoc feature which is particularly useful for C extensions is module merging. If several files are all marked as @module lib then a single module lib is generated, containing all the docs from the separate files. For this, use merge=true.

See @{mylib.c} for the full example.

Moonscript Support

1.4 introduces basic support for Moonscript. Moonscript module conventions are just the same as Lua, except for an explicit class construct. @{List.moon} shows how @classmod can declare modules that export one class, with metamethods and methods put implicitly into a separate section.

Basic Usage

For example, to process all files in the 'lua' directory:

$ ldoc lua
output written to doc/

Thereafter the doc directory will contain index.html which points to individual modules in the modules subdirectory. The --dir flag can specify where the output is generated, and will ensure that the directory exists. The output structure is like LuaDoc: there is an index.html and the individual modules are in the modules subdirectory. This applies to all project-level types, so that you can also get scripts, examples and topics directories.

If your modules use module(...) then the module name has to be deduced. If ldoc is run from the root of the package, then this deduction does not need any help - e.g. if your package was foo then ldoc foo will work as expected. If we were actually in the foo directory then ldoc -b .. . will correctly deduce the module names. An example would be generating documentation for LuaDoc itself:

$ ldoc -b .. /path/to/luadoc

Without the -b setting the base of the package to the parent of the directory, implicit modules like luadoc.config will be incorrectly placed in the global namespace.

For new-style modules, that don't use module(), it is recommended that the module comment has an explicit @module PACKAGE.NAME. If it does not, then ldoc will still attempt to deduce the module name, but may need help with --package/-b as above.

A special case is if you simply say 'ldoc .'. Then there must be a config.ld file available in the directory, and it can specify the file:

file = "mymod.lua"
title = "mymod documentation"
description = "mymod does some simple but useful things"

file can of course point to a directory, just as with the --file option. This mode makes it particularly easy for the user to build the documentation, by allowing you to specify everything explicitly in the configuration.

In config.ld, file may be a Lua table, containing file names or directories; if it has an exclude field then that will be used to exclude files from the list, for example {'examples', exclude = {'examples/slow.lua'}}.

A particular configuration file can be specified with the -c flag. Configuration files don't have to contain a file field, but in that case LDoc does need an explicit file on the command line. This is useful if you have some defaults you wish to apply to all of your docs.

Markdown Support

format = 'markdown' can be used in your config.ld and will be used to process summaries and descriptions; you can also use the -f flag. This requires a markdown processor. LDoc knows how to use:

markdown.lua a pure Lua processor by Niklas Frykholm. For convenience, LDoc comes with a copy of markdown.lua.
lua-discount, a faster alternative (installed with luarocks install lua-discount). lua-discount uses the C discount Markdown processor which has more features than the pure Lua version, such as PHP-Extra style tables.
lunamark, another pure Lua processor, faster than markdown, and with extra features (luarocks install lunamark).
commonmark via cmark-lua, a Lua wrapper around the fast libcmark C library (luarocks install cmark)

You can request the processor you like with format = 'markdown|discount|lunamark|commonmark|plain|backticks', and LDoc will attempt to use it. If it can't find it, it will look for one of the other markdown processors; the original markdown.lua ships with LDoc, although it's slow for larger documents.

Even with the default of 'plain' some minimal processing takes place, in particular empty lines are treated as line breaks. If the 'backticks' formatter is used, then it's equivalent to using process_backticks=true in config.ld and backticks will be expanded into documentation links like @{\ref} and converted into <code>ref</code> otherwise.

This formatting applies to all of a project, including any readmes and so forth. You may want Markdown for this 'narrative' documentation, but not for your code comments. plain=true will switch off formatting for code.

Processing Single Modules

--output can be used to give the output file a different name. This is useful for the special case when a single module file is specified. Here an index would be redundant, so the single HTML file generated contains the module documentation.

$ ldoc mylib.lua --> results in doc/index.html
$ ldoc --output mylib mylib.lua --> results in doc/mylib.html
$ ldoc --output mylib --dir html mylib.lua --> results in html/mylib.html

The default sections used by LDoc are 'Functions', 'Tables' and 'Fields', corresponding to the built-in types 'function', 'table' and 'field'. If config.ld contains something like new_type("macro","Macros") then this adds a new section 'Macros' which contains items of 'macro' type - 'macro' is registered as a new valid tag name. The default template then presents items under their corresponding section titles, in order of definition.

Getting Help about a Module

There is an option to simply dump the results of parsing modules. Consider the C example `tests/example/mylib.c':

``console $ ldoc --dump mylib.c

module: mylib A sample C extension. Demonstrates using ldoc's C/C++ support. Can either use /// or /*** */ etc.

function createtable(narr, nrec) Create a table with given array and hash slots. narr initial array slots, default 0 nrec initial hash slots, default 0

function solve(a, b, c) Solve a quadratic equation. a coefficient of x^2 b coefficient of x c constant return {"first root","second root"}


This is useful to quickly check for problems; here we see that `createable` did not have a
return tag.

LDoc takes this idea of data dumping one step further. If used with the `-m` flag it will
look up an installed Lua module and parse it. If it has been marked up in LuaDoc-style then
you will get a handy summary of the contents:

```console
$ ldoc -m pl.pretty
----
module: pl.pretty       Pretty-printing Lua tables.
* read(s) - read a string representation of a Lua table.
* write(tbl, space, not_clever) - Create a string representation of a Lua table.

* dump(t, ...) - Dump a Lua table out to a file or stdout.

You can specify a fully qualified function to get more information:

$ ldoc -m pl.pretty.write

function        write(tbl, space, not_clever)
create a string representation of a Lua table.
tbl      {table} Table to serialize to a string.
space    {string} (optional) The indent to use.
                Defaults to two spaces.
not_clever       {bool} (optional) Use for plain output, e.g {['key']=1}.
                Defaults to false.

LDoc knows about the basic Lua libraries, so that it can be used as a handy console reference:

$ ldoc -m assert

function        assert(v, message)
Issues an error when the value of its argument `v` is false (i.e.,
    nil or false); otherwise, returns all its arguments.
`message` is an error
    message; when absent, it defaults to "assertion failed!"
v
message

Thanks to Mitchell's Textadept project, LDoc has a set of .luadoc files for all the standard tables, plus LuaFileSystem and LPeg.

$ ldoc -m lfs.lock

function        lock(filehandle, mode, start, length)
Locks a file or a part of it.
This function works on open files; the file
    handle should be specified as the first argument. The string mode could be
    either r (for a read/shared lock) or w (for a write/exclusive lock). The
    optional arguments start and length can be used to specify a starting point
    and its length; both should be numbers.
    Returns true if the operation was successful; in case of error, it returns
    nil plus an error string.
filehandle
mode
start
length

Anatomy of a LDoc-generated Page

winapi can be used as a good example of a module that uses extended LDoc features.

The navigation section down the left has several parts:

The project name (project in the config)
A project description (description)
Contents of the current page
Modules listing all the modules in this project

Note that description will be passed through Markdown, if it has been specified for the project. This gives you an opportunity to make lists of links, etc; any '##' headers will be formatted like the other top-level items on the navigation bar.

Contents is automatically generated. It will contain any explicit sections as well as the usual categories: 'Functions', 'Tables' and 'Fields'. For a documentation page, the subtitles become the sections shown here.

Modules will appear for any project providing Lua libraries; there may also be a 'Scripts' section if the project contains Lua scripts. For example, LuaMacro has a driver script luam in this section. The builtin module only defines macros, which are defined as a custom tag type[?].

The content section on the right shows:

The module summary and description
The contents summary, per section as above
The detailed documentation for each item

As before, the description can use Markdown. The summary contains the contents of each section as a table, with links to the details. This is where the difference between an item's summary and an item's description is important; the first will appear in the contents summary. The item details show the item name and its summary again, followed by the description. There are then sections for the following tags: 'param', 'usage', 'return' and 'see' in that order. (For tables, 'Fields' is used instead of 'Parameters' but internally fields of a table are stored as the 'param' tag.)

By default, the items appear in the order of declaration within their section. If sort=true then they will be sorted alphabetically. (This can be set per-module with @{Module_Tags|@set}.)

You can of course customize the default template, but there are some parameters that can control what the template will generate. Setting one=true in your configuration file will give a one-column layout, which can be easier to use as a programming reference. You can suppress the contents summary with no_summary.

If you don't like the usual top-level names, like 'Module' and 'Topics', you can override these with kind_names in config.ld. For instance, in Penlight I use kind_names={topic='Manual',module='Libraries'}

Customizing the Page

A basic customization is to override the default UTF-8 encoding using charset. For instance, Brazilian software would find it useful to put charset='ISO-8859-1' in config.ld, or use the @charset tag for individual files.

Setting no_return_or_parms to true will suppress the display of 'param' and 'return' tags. This may appeal to programmers who dislike the traditional @tag soup xDoc style and prefer to comment functions just with a description. This is particularly useful when using Markdown in a stylized way to specify arguments:

---------
-- This extracts the shortest common substring from the strings _s1_ and _s2_
function M.common_substring(s1,s2)

Here I've chosen to italicise parameter names; the main thing is to be consistent.

This style is close to the Python documentation standard, especially when used with no_summary.

It is also very much how the Lua documentation is ordered. For instance, this configuration file formats the built-in documentation for the Lua global functions in a way which is close to the original:

project = 'Lua'
description = 'Lua Standard Libraries'
file = {'ldoc/builtin',exclude = {'ldoc/builtin/globals.lua'}}
no_summary = true
no_return_or_parms = true
format = 'discount'

Generally, using Markdown gives you the opportunity to structure your documentation in any way you want; particularly if using lua-discount and its table syntax; the desired result can often be achieved then by using a custom style sheet.

Examples

It has been long known that documentation generated just from the source is not really adequate to explain how to use a library. People like reading narrative documentation, and they like looking at examples. Previously I found myself dealing with source-generated and writer-generated documentation using different tools, and having to match these up.

LDoc allows for source examples to be included in the documentation. For example, see the online documentation for winapi. The function utf8_expand has a @see reference to 'testu.lua' and following that link gives you a pretty-printed version of the code.

The line in the config.ld that enables this is:

examples = {'examples', exclude = {'examples/slow.lua'}}

That is, all files in the examples folder are to be pretty-printed, except for slow.lua which is meant to be called from one of the examples. To link to an example, use a reference like @{\testu.lua} which resolves to 'examples/testu.lua.html'.

Examples may link back to the API documentation, for instance the example input.lua has a @{\spawn_process} inline reference.

By default, LDoc uses a built-in Lua code 'prettifier'. Reference links are allowed in comments, and also in code if they're enclosed in backticks. Lua and C are known languages.

lxsh can be used (available from LuaRocks) if you want something more powerful. pretty='lxsh' will cause lxsh to be used, if available.

Sometimes the best examples you have are your source files. prettify_files=true will prettify all sources, and generate per-function links to the source.

Readme files

Like all good Github projects, Winapi has a readme.md:

readme = "readme.md"

This goes under the 'Topics' global section; the 'Contents' of this document is generated from the second-level (##) headings of the readme.

Readme files are always processed with the current Markdown processor, but may also contain @{\ref} references back to the documentation and to example files. Any symbols within backticks will be expanded as references, if possible. As with doc comments, a link to a standard Lua function like @{\os.execute} will work as well. Any code sections will be pretty-printed as Lua, unless the first indented line is '@plain'. (See the source for this readme to see how it's used.)

Another name for readme is topics, which is more descriptive. From LDoc 1.2, readme/topics can be a list of documents. These act as a top-level table-of-contents for your documentation. Currently, if you want them in a particular order, then use names like 01-introduction.md etc, which sort appropriately.

The first line of a document may be a Markdown # title. If so, then LDoc will regard the next level as the subheadings, normally second-level ##. But if the title is already second-level, then third-level headings will be used ###, and so forth. The implication is that the first heading must be top-level relative to the headings that follow, and must start at the first line.

A reference like @{\string.upper} is unambiguous, and will refer to the online Lua manual. In a project like Penlight, it can get tedious to have to write out fully qualified names like @{\pl.utils.printf}. The first simplification is to use the package field to resolve unknown references, which in this case is 'pl'. (Previously we discussed how package is used to tell LDoc where the base package is in cases where the module author wishes to remain vague, but it does double-duty here.) A further level of simplification comes from the @lookup directive in documents, which must start at the first column on its own line. For instance, if I am talking about pl.utils, then I can say @lookup utils and thereafter references like @{\printf} will resolve correctly.

If you look at the source for this document, you will see a @lookup doc.md which allows direct references to sections like @{Readme_files|this} with @{\Readme_files|this}.

Remember that the default is for references in backticks to be resolved; unlike @ references, it is not an error if the reference cannot be found.

The sections of a document (the second-level headings) are also references. This particular section you are reading can be referred to as @{\doc.md.Readme_files} - the rule is that any non-alphabetic character is replaced by an underscore.

Any indented blocks are assumed to be Lua, unless their first line is @plain. New with 1.4 is github-markdown-style fenced code blocks, which start with three backticks optionally followed by a language. The code continues until another three backticks is found: the language can be c, cpp or cxx for C/C++, anything else is Lua.

Tag Modifiers

Ay tag may have tag modifiers. For instance, you may say @param[type=number] and this associates the modifier type with value number with this particular param tag. A shorthand has been introduced for this common case, which is @tparam <type> <parmname> <comment>; in the same way @treturn is defined.

This is useful for larger projects where you want to provide the argument and return value types for your API, in a structured way that can be easily extracted later.

These types can be combined, so that "?string|number" means "either a string or a number"; "?string" is short for "?|nil|string". However, for this last case you should usually use the opt modifier discussed below.

There is a useful function for creating new tags that can be used in config.ld:

tparam_alias('string','string')

That is, @string will now have the same meaning as "@tparam string"; this also applies to the optional type syntax "?|T1|T2".

From 1.3, the following standard type aliases are predefined:

string
number
int
bool Lua 'boolean' type
func 'function' (using 'function' would conflict with the type)
tab 'table'
thread

When using 'colon-style' (@{colon.lua}) it's possible to directly use types by prepending them with '!'; '?' is also naturally understood.

The exact form of <type> is not defined, but here is one suggested scheme:

number -- a plain type
Bonzo -- a known type; a reference link will be generated
{string,number} -- a 'list' tuple of two values, built from type expressions
{A=string,N=number} -- a 'struct', ditto (But it's often better to create a named table and refer to it)
{Bonzo,...} -- an array of Bonzo objects
{[string]=Bonzo,...} -- a map of Bonzo objects with string keys
Array(Bonzo) -- (assuming that Array is a container type)

The alias function within configuration files has been extended so that alias tags can be defined as a tag plus a set of modifiers. So tparam is defined as:

alias('tparam',{'param',modifiers={type="$1"}})

As an extension, you're allowed to use @param tags in table definitions. This makes it possible to use type aliases like @string to describe fields, since they will expand to 'param'.

Another modifier understood by LDoc is opt. For instance,

---- testing [opt]
-- @param one
-- @param[opt] two
-- @param three
-- @param[opt] four
function fun (one,two,three,four)
end
----> displayed as: fun (one [, two], three [, four])

A more typical Lua API would have a chain of optional arguments, like so:

---- a chain of options
-- @param one
-- @param[opt] two
-- @param[optchain] three
-- @param[optchain] four
function fun (one,two,three,four)
end
----> displayed as: fun (one [, two [, three [, four]]])

This is a bit tedious to type, so the rule is that a series of 'opt' modifiers will be interpreted as 'opt','optchain'.... . If you want to be explicit, then do convert_opt=true in your config.ld.

If a value is given for optthen LDoc can present this as the default value for this optional argument.

This modifier can also be used with typed param aliases.

--- a function with typed args.
-- If the Lua function has varargs, then
-- you may document an indefinite number of extra arguments!
-- @string name person's name
-- @int age
-- @string[opt='gregorian'] calendar optional calendar
-- @int[opt=0] offset optional offset
-- @treturn string
function one (name,age,...)
end
----> displayed as: one (name, age [, calendar='gregorian' [, offset=0]])

(See @{four.lua})

An experimental feature in 1.4 allows different 'return groups' to be defined. There may be multiple @return tags, and the meaning of this is well-defined, since Lua functions may return multiple values. However, being a dynamic language it may return a single value if successful and two values (nil,an error message) if there is an error. This is in fact the convention for returning 'normal' errors (like 'file not found') as opposed to parameter errors (like 'file must be a string') that are often raised as errors.

Return groups allow a documenter to specify the various possible return values of a function, by specifying number modifiers. All return tags with the same digit modifier belong together as a group:

-----
-- function with return groups.
-- @return[1] result
-- @return[2] nil
-- @return[2] error message
function mul1() ... end

This is the first function in @{multiple.lua}, and the output shows how return groups are presented, with an Or between the groups.

This is rather clumsy, and so there is a shortcut, the @error tag which achieves the same result, with helpful type information.

Currently the type,opt and <digit> modifiers are the only ones known and used by LDoc when generating HTML output. However, any other modifiers are allowed and are available for use with your own templates or for extraction by your own tools.

Fields allowed in `config.ld`

Same meaning as the corresponding parameters:

file a file or directory containing sources. In config.ld this can also be a table of files and directories.
project name of project, used as title in top left
title page title, default 'Reference'
package explicit base package name; also used for resolving references in documents
all show local functions, etc as well in the docs
format markup processor, can be 'plain' (default), 'markdown' or 'discount'
output output name (default 'index')
dir directory for output files (default 'doc')
colon use colon style, instead of @ tag style
boilerplate ignore first comment in all source files (e.g. license comments)
ext extension for output (default 'html')
one use a one-column layout
style, template: together these specify the directories for the style and and the template. In config.ld they may also be true, meaning use the same directory as the configuration file.
merge allow documentation from different files to be merged into modules without explicit @submodule tag

These only appear in the configuration file:

description a short project description used under the project title
full_description when you really need a longer project description
examples a directory or file: can be a table
readme or topics readme files (to be processed with Markdown)
pretty code prettify 'lua' (default) or 'lxsh'
prettify_files prettify the source as well and make links to it; if its value is "show" then also index the source files.
charset use if you want to override the UTF-8 default (also @charset in files)
sort set if you want all items in alphabetical order
no_return_or_parms don't show parameters or return values in output
no_lua_ref stop obsessively trying to create references to standard Lua libraries
backtick_references whether references in backticks will be resolved. Happens by default when using Markdown. When explicit will expand non-references in backticks into <code> elements
plain set to true if format is set but you don't want code comments processed
wrap set to true if you want to allow long names to wrap in the summaries
manual_url(url) point to an alternative or local location for the Lua manual, e.g. 'manual_url file:///D:/dev/lua/projects/lua-5.1.4/doc/manual.html'. Remember it is a function!
no_summary suppress the Contents summary
custom_tags define some new tags, which will be presented after the function description. The format is {<name>,[title=<name>,}{hidden=false,}{format=nil}}. For instance custom_tags={'remark',title='Remarks'} will add a little Remarks section to the docs for any function containing this tag. format can be a function - if not present the default formatter will be used, e.g. Markdown
custom_see_handler(pat,handler) function that filters see-references

custom_display_name_handler(item, default_handler) function that formats an item's name. The arguments are the item and the default function used to format the name. For example, to show an icon or label beside any function tagged with a certain tag:

-- define a @callback tag:
custom_tags = { { 'callback', hidden = true } }

-- show a label beside functions tagged with @callback.
custom_display_name_handler = function(item, default_handler)
if item.type == 'function' and item.tags.callback then
    return item.name .. ' [callback]'
end
return default_handler(item)
end

not_luadoc set to true if the docs break LuaDoc compatibility
no_space_before_args set to true if you do not want a space between a function's name and its arguments.
template_escape overrides the usual '#' used for Lua code in templates. This needs to be changed if the output format is Markdown, for instance.
user_keywords A list of keywords that will be marked in "prettified" code. Useful if you want to display your own functions in a special way. Each keyword may be styled differently (using CSS). Only works when pretty is set to 'lua' (the default).
postprocess_html function that allows a last-minute modification to the produced HTML page. The arguments are the raw HTML that's intended to be written out (a string), and the module object. The string this function returns will be what's actually gets written out.
favicon A link to an image that browser's will display as each page's icon.

Available functions are:

import(obj) exposes Lua object obj to config.ld (enabled with --unsafe_no_sandbox)
alias(a,tag) provide an alias a for the tag tag, for instance p as short for param
add_language_extension(ext,lang) here lang may be either 'c' or 'lua', and ext is an extension to be recognized as this language
add_section
new_type(tag,header,project_level) used to add new tags, which are put in their own section header. They may be 'project level'.
tparam_alias(name,type) for instance, you may wish that Object becomes a new tag alias that means @tparam Object.
custom_see_handler(pattern,handler). If a reference matches pattern, then the extracted values will be passed to handler. It is expected to return link text and a suitable URI. (This match will happen before default processing.)

Importing Lua Objects

The import function is available to gain access to built-in Lua functions & objects.

local print = import("print")
local string = import("string")

for _, s in ipairs({string.split("Hello world!")}) do
	print(s)
end

Annotations and Searching for Tags

Annotations are special tags that can be used to keep track of internal development status. The known annotations are 'todo', 'fixme' and 'warning'. They may occur in regular function/table doc comments, or on their own anywhere in the code.

--- Testing annotations
-- @module annot1
...
--- first function.
-- @todo check if this works!
function annot1.first ()
    if boo then

    end
    --- @fixme what about else?
end

Although not currently rendered by the template as HTML, they can be extracted by the --tags command, which is given a comma-separated list of tags to list.

D:\dev\lua\LDoc\tests> ldoc --tags todo,fixme annot1.lua
d:\dev\lua\ldoc\tests\annot1.lua:14: first: todo check if this works!
d:\dev\lua\ldoc\tests\annot1.lua:19: first-fixme1: fixme what about else?

Generating HTML

LDoc, like LuaDoc, generates output HTML using a template, in this case ldoc/html/ldoc_ltp.lua. This is expanded by the powerful but simple preprocessor devised originally by Rici Lake which is now part of Lake](http://lua-users.org/wiki/SlightlyLessSimpleLuaPreprocessor) which is now part of Penlight. There are two rules - any line starting with '#' is Lua code, which can also be embedded with '$(...)'.

<h2>Contents</h2>
<ul>
# for kind,items in module.kinds() do
<li><a href="#$(no_spaces(kind))">$(kind)</a></li>
# end
</ul>

This is then styled with ldoc.css. Currently the template and stylesheet is very much based on LuaDoc, so the results are mostly equivalent; the main change that the template has been more generalized. The default location (indicated by '!') is the directory of ldoc_ltp.lua.

You will notice that the built-in templates and stylesheets end in .lua; this is simply to make it easier for LDoc to find them. Where you are customizing one or both of the template and stylesheet, they will have their usual extensions.

You may customize how you generate your documentation by specifying an alternative style sheet and/or template, which can be deployed with your project. The parameters are --style and --template, which give the directories where ldoc.css and ldoc.ltp are to be found. If config.ld contains these variables, they are interpreted slightly differently; if they are true, then it means 'use the same directory as config.ld'; otherwise they must be a valid directory relative to the ldoc invocation.

An example of fully customized documentation is tests/example/style: this is what you could call 'minimal Markdown style' where there is no attempt to tag things (except emphasizing parameter names). The narrative alone can to be sufficient, if it is written well.

There are three other stylesheets available in LDoc since 1.4; the first is ldoc_one.css which is what you get from one=true and the second is ldoc_pale.css. This is a lighter theme which might give some relief from the heavier colours of the default. You can use this style with style="!pale" or -s !pale. See the Lake documentation as an example of its use. With 1.4.3 there is also the style='!fixed' where the left navigation panel is fixed and does not scroll with the rest of the document; you may find this assists navigation in complex modules and documents.

Of course, there's no reason why LDoc must always generate HTML. --ext defines what output extension to use; this can also be set in the configuration file. So it's possible to write a template that converts LDoc output to LaTex, for instance. The separation of processing and presentation makes this kind of new application possible with LDoc.

From 1.4, LDoc has some limited support for generating Markdown output, although only for single files currently. Use --ext md for this. 'ldoc/html/ldoc_md_ltp.lua' defines the template for Markdown, but this can be overridden with template as above. It's another example of minimal structure, and provides a better place to learn about these templates than the rather elaborate default HTML template.

Internal Data Representation

The --dump flag gives a rough text output on the console. But there is a more customizeable way to process the output data generated by LDoc, using the --filter parameter. This is understood to be a fully qualified function (module + name). For example, try

$ ldoc --filter pl.pretty.dump mylib.c

to see a raw dump of the data. (Simply using dump as the value here would be a shorthand for pl.pretty.dump.) This is potentially very powerful, since you may write arbitrary Lua code to extract the information you need from your project.

For instance, a file custom.lua like this:

return {
    filter = function (t)
        for _, mod in ipairs(t) do
            print(mod.type,mod.name,mod.summary)
        end
    end
}

Can be used like so:

~/LDoc/tests/example$ ldoc --filter custom.filter mylib.c
module  mylib   A sample C extension.

The basic data structure is straightforward: it is an array of 'modules' (project-level entities, including scripts) which each contain an item array (functions, tables and so forth).

For instance, to find all functions which don't have a @return tag:

return {
    filter = function (t)
        for _, mod in ipairs(t) do
            for _, item in ipairs(mod.items) do
            if item.type == 'function' and not item.ret then
                print(mod.name,item.name,mod.file,item.lineno)
            end
            end
        end
    end
}

The internal naming is not always so consistent; ret corresponds to @return, and params corresponds to @param. item.params is an array of the function parameters, in order; it is also a map from these names to the individual descriptions of the parameters.

item.modifiers is a table where the keys are the tags and the values are arrays of modifier tables. The standard tag aliases tparam and treturn attach a type modifier to their tags.