🌴 Kailua
Kailua is an experimental type checker and integrated development environment (IDE) for the Lua programming language (currently only Lua 5.1 is supported).
THIS IS VERY EXPERIMENTAL PROJECT AND NO WARRANTY OR SUPPORT IS PROVIDED!
Installation and Usage
Kailua can be used as a standalone checker or an IDE plugin.
Standalone Checker
To install a standalone checker, install Rust first (1.15 or later required), then type the following:
cargo install kailua
You can run kailua check <path to the entry point>
now.
You can also run kailua check <path to the directory>
, if you have kailua.json
or .vscode/kailua.json
in that directory. See the following section on the configuration format.
Visual Studio Code
Caution: Currently the extension only works in Windows due to the packaging issue.
Kailua can be used as an IDE support for Visual Studio Code. Install Kailua by typing ext install kailua
from the Quick Launch (Ctrl-P
).
You will see a warning that the configuration file is missing when you open a folder containing Lua codes. You need it for real-time checking.
You can either create .vscode/kailua.json
by hand, or search "Kailua" from the Command Palette (Ctrl-Shift-P
) to edit one.
The following content is required for .vscode/kailua.json
, in case you are editing it by hand:
{
// Unlike a normal JSON, a comment or a stray comma is allowed.
"start_path": "<path to the entry point>",
// You can also put the following:
//
//"package_path": "<the value of `package.path`, determined from assignments if missing>",
//"package_cpath": "<the value of `package.cpath`, determined from assignments if missing>",
}
You need to reload the current window (Ctrl-R
or Cmd-R
) to apply the configuration.
Your First Kailua Code
Once you've set the entry point, you can write your first Kailua code:
--# open lua51
print
Play a bit with this code to see which errors Kailua can detect.
Supported IDE Functions
-
Real-time syntax checking (for all files).
-
Real-time type checking, starting from given start path.
-
Auto-completions for names and fields.
-
Help for function signatures.
-
Help for types of most subexpressions on hover.
-
Go to definition for local and global names.
-
Mass renaming of local and global names.
Kailua the Language
Special Comments
Kailua is a subset of valid Lua code---you don't need any transpilation or compilation. The additional annotations are described in special comments:
-
--: <type>
describes the type(s) of preceding item(s).It is valid anywhere a new name can be possibly defined:
local
(either individual names or statement),function
(arguments),for
(individual names) and assignment (either individual names or statement).When used right after the name, for the ease of typing, you can put a comma or closing parenthesis before the type like this:
For the common case of defining multiple names you can put types after the statement. In this case types are delimited by commas.
-
--> <type>
describes the type(s) of function returns.It is valid only after the closing parenthesis of function arguments. It is valid to put
--:
(for the last argument) and-->
in the same line. -
--v function(<name>: <type> ...) [--> <type>]
describes a function type.It is valid before the
function
keyword (yes, also for anonymous functions). This is equivalent to--:
and-->
, but much more readable. All names should be identical to the corresponding declarations. Variadic arguments can be written as...: <type>
at the end of arguments. Multiple returns need parentheses.The general rule of the thumb is that all functions have to be typed with either
--v
or--:/-->
unless it is obvious from the preceding context. This allows you to write a code likef(function(a, b) ... end)
, but only whenf
is known to accept such a function. -
--v method(<name>: <type> ...) [--> <type>]
describes a method type.It is same to
function
, but for declarations likefunction A:b(...)
. Kailua tries to infer the type ofself
, and if it's not possible you should usefunction A.b(self, ...)
and--v function(...)
instead for the clarity. -
--# ...
is a special directive for the type checker.The most important directive is
--# open <built-in library name>
, which loads the corresponding built-in names and also implicitly specifies what language variant is currently in use. The only supported name so far islua51
, for the vanilla Lua 5.1. It is recommended to put it to the first non-comment line in the entry point.--# type [local | global] <name> = <type>
can be used to declare a type alias. There are three flavors of typa alises:local
is locally scoped (much likelocal
statements),global
is globally scoped (much likeA = ...
), and no modifier indicates that the type is exported from the current file and they should be locally visible afterrequire
. Only local types can be in the inner scopes. Unlike variable names, inner type names should not overwrite outer names.--# assume [global] <name>: <type>
overrides the type for given name. Theglobal
keyword forces the global assignment, otherwise a new scope is created likelocal
statements. It is useful for sidestepping the checker issue, but it is also highly unsafe. Use at your own risk.More directives are likely to come.
The equal kind of special comments can span multiple lines.
--# type Date = {
--# hour: integer;
--# min: integer;
--# sec: integer;
--# }
Types
The following basic types are recognized:
-
nil
,boolean
(orbool
),number
,string
,function
,userdata
,thread
,table
for primitive Lua types. -
integer
(orint
) for a check-time integral subset ofnumber
. (In the future, in the Lua 5.3 mode or later, it will be also recognized as primitive.) -
true
orfalse
, integer and string literals are valid subtypes ofboolean
,integer
andstring
, respectively. -
The table type is divided into four useful cases.
Importantly, first two cases are not automatically inferred from the use and should be explicitly annotated like
local tab = {} --: vector<integer>
.-
vector<T>
for a table with consecutive integer keys. -
map<Key, Value>
for a homogeneous associative table. -
{ key1: T1, key2: T2 }
for records, whose keys are strings and fixed at the check time. You can use semicolons in place of commas.Explicitly declared records are "inextensible" by default, meaning that the list of fields is complete and cannot be altered. You can make it extensible by putting
...
at the end of fields; this allows a lazy initialization of records liketable.field = 'string'
. On the other hands, a normal Lua table is implicitly typed as extensible records, only made inextensible when required. -
{ T1, T2, T3 }
for tuples, whose keys are consecutive integers. Otherwise they are similar to records.
-
-
function(Arg, ...)
orfunction(Arg, ...) --> Ret
for functions.Ret
can be multiple types, in which case you need parentheses (function(vector<T>, integer) --> (integer, string)
). Arguments can be named likefunction(a: string, b: number)
. -
T | T | ...
for union types. They are mostly useful for literal types (e.g."read" | "write" | "execute"
). Kailua has very limited support for checking other kinds of union types. -
any
has no type information.--# assume
is the only way to make it useful. -
WHATEVER
(note the case) is a hole that the type checker always accepts.map<integer, WHATEVER>
andmap<WHATEVER, string>
are compatible;map<integer, WHATEVER>
andmap<string, string>
are not. As this thwarts the basic of type checking, use at your own risk.
The Kailua types are by default not checked for nil
. That is, you can assign nil
to integer
but you can also add two integer
s; the valid Kailua code can still result in a runtime error therefore. This restriction was required for making a practical type checker without changing the source programming language.
You can opt in two other nil
-handling modes if you need to make it explicit. As they are (transitively) freely assignable, consider them more a machine-readable documentation.
-
T?
also acceptsnil
but it is aware that it can containnil
. Twointeger?
s cannot be added. It also allows for missing fields and missing arguments (they are not allowed otherwise): the type{a: integer?, b: integer}
can contain either{a = 42, b = 54}
or{b = 54}
, but not{a = 42}
. -
T!
guarantees that it cannot containnil
.
Also, the table values are always T
or T?
(for the obvious reason).
Finally, types for the names and table values can optionally have a const
prefix. You cannot modify the innard of const
types: map<integer, const vector<string>>
. You can still assign to them (otherwise this type won't be useful at all).
Avoiding the type checker
As annotating everything is not practical, Kailua supports two ways to avoid the type checking with more localized guarantees:
-
--v [NO_CHECK] function(...)
disables the type checking for the following function.Kailua essentially believes the specified function type, which can be no longer omitted.
-
You can override what file to check by having
.kailua
files.When
require()
was used with a check-time string Kailua makes use ofpackage.path
andpackage.cpath
set. Forpackage.path
, it will tryF.kailua
first before reading a fileF
. Forpackage.cpath
, it will alwaysF.kailua
asF
would be probably binary. (Note that this will normally result in two extensions.lua.kailua
unless you have a sole?
in the search paths.).kailua
files would frequently use--# assume
as you should assume that the original code has given types.
See Also
The internal documentation is available in a different file.
License
Kailua is dual-licensed under the MIT license and Apache license 2.0 at your option. By contributing to Kailua you agree that your contributions will be licensed under these two licenses.