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meson.build(5) File Formats Manual meson.build(5)

meson.build - a build system dsl

The meson dsl is a dynamically typed language, similar to other interpreted languages like python and ruby. All objects are immutable. Functions cannot be defined, only built-in functions are available.

•STRUCTURE - overview of source and project layout
•TYPES - information on all primitive types
•SYNTAX - description of syntax and keywords

All meson projects must have a file called `meson.build` at the project root. This is the root build file. This file must have a call to the `project()` function as its first statement. Additional `meson.build` files may reside in any subdirectories of the project. These build files are then executed with the `subdir()` function.

The meson build system dsl contains most of the common types that would be expected:

•booleans (written as `true` and `false`)
•integers
•strings
•arrays
•dictionaries

Booleans are either `true` or `false`.

OPERATORS

•`and` - logical and
•`or` - logical or
•`not` - logical and

You can specify an integer literal using decimal, hexadecimal, octal, and binary.

int_1 = 1
int_42 = 42
int_255 = 0xFF
int_493 = 0o755
int_1365 = 0b10101010101

All common arithmetic operations are implemented for integers: addition, subtraction, division, multiplication, and modulo.

OPERATORS

•`*` - multiplication
•`/` - integer division
•`%` - modulo (remainder)
•`+` - addition
•`-` - subtraction
•`==` - equal to
•`!=` - not equal to
•`<` - less than
•`>` - greater than
•`<=` - less than or equal to
•`>=` - greater than or equal to

Strings in Meson are declared with single quotes. `` is the escape character.

The full list of escape sequences is:

•`\` Backslash
•`'` Single quote
•`a` Bell
•`b` Backspace
•`f` Formfeed
•`n` Newline
•`r` Carriage Return
•`t` Horizontal Tab
•`v` Vertical Tab
•`ooo` Character with octal value ooo, up to 3 digits long
•`xhh` Character with hex value hh
•`uxxxx` Character with 16-bit hex value xxxx
•`Uxxxxxxxx` Character with 32-bit hex value xxxxxxxx
•`N{name}` Character named name in Unicode database

Multi-line strings are surrounded by 3 consecutive quotes. These are raw strings that do not support the escape sequences listed above.

Format strings are expressed by a placing leading `f` before the first opening quote. Inside of a format string, sequences of the form `@[a-z_]+@` will be substituted with the value of the matching variable.

name = 'Alice'
# prints "Hello Alice"
message(f'Hello @name@')

OPERATORS

•`+` - concatenate two strings
•`/` - concatenate two strings as if `join_paths()` was called
•`[n]` - access the character at index `n`
•`==` - equal to
•`!=` - not equal to

Arrays are delimited by brackets. An array can contain an arbitrary number of objects of any type.

OPERATORS

•`+` - If the rhs operand is an array, it will be joined to the lhs array. If it is a scalar, it will be appended to the lhs array.
•`[n]` - access the object at index `n`
•`<obj> in <array>` - check if object `obj` is in `array`
•`<obj> in <array>` - check if object `obj` is not in `array`
•`==` - equal to
•`!=` - not equal to

Dictionaries are delimited by curly braces. A dictionary can contain an arbitrary number of key: value pairs. Keys are required to be strings, but values can be objects of any type. Dictionaries are immutable and do not have a guaranteed order.

OPERATORS

•`+` - merge two dictionaries. In case of a conflicting key, the value from the rhs dictionary will be taken.
•`[key]` - access the object with key `key`
•`<key> in <dict>` - check if key `key` is in `dict`
•`<key> not in <dict>` - check if key `key` is not in `dict`
•`==` - equal to
•`!=` - not equal to

A meson build file is composed of statements, which are terminated by newlines. Other than the statement-terminating newline, white space has no syntactic meaning.

A comment starts with the `#` character and extends until the end of the line.

A variable can contain a value of any type, and does not need to be predeclared.

var1 = 'hello'
var2 = 102

One important difference in how variables work in the dsl is that all objects are immutable. When you see an operation which appears like a mutation, actually a new object is created and assigned to the name.

var1 = [1, 2, 3]
var2 = var1
var2 += [4]
# var2 is now [1, 2, 3, 4]
# var1 is still [1, 2, 3]

Builtin functions are called by their name followed by parenthesis containing optional, comma-separated arguments. Arguments are either positional or keyword. Keyword arguments are expressed using the keyword without quotes, followed by a colon.

foo()
foo('bar')
foo('bar', baz: true)

Method calls are expressed by a `.` followed by the same function call syntax as above.

foo.bar()
foo.bar('baz', qux: false)

For a complete list of functions and methods, please see `meson-reference(3)`.

Start an if statement with the `if` keyword followed by a boolean expression. Further conditions can be expressed using the `elif` keyword followed by a boolean expression. The `else` keyword can be used to handle the case when no conditions are matched. An if statement is terminated with the `endif` keyword.

if conditon1
elif condition2
else condition3
endif

To loop over values in an iterable, use the `foreach` keyword followed by a comma separated list of names to assign the values of the iterable to, a colon, and an iterable expression. Only arrays and dictionaries are iterable. A foreach statement is terminated with the `endforeach` keyword.

Arrays have one value to assign to.

foreach value : array
	foo(value)
endforeach

Dictionaries have one two values to assign to.

foreach key, value : dictionary
	foo(key)
	bar(value)
endforeach

Inside a `foreach` block you may use the `break` and `continue` keywords. `break` exits the loop immediately. `continue` skips the rest of the current iteration.

meson-reference(3) meson(1) muon(1)

2023-01-22