Conditional Compilation

Directives pick code by target and mode. They work at three levels: declarations, statements and expressions. Non-matching branches never reach resolve and typecheck.

Directives

Directive	Values	Description
@os	linux, windows, darwin, freebsd, android, wasip1	Target OS
@arch	x86_64, aarch64, i686, wasm32, wasm64	Target CPU
@env	gnu, musl, msvc, android	Target environment
@target	full triple	Exact target triple
@family	unix, windows, wasm	Platform family
@debug	none	Debug mode
@release	none	Release mode

Values with | mean OR. Directives chain with else:

@os[linux] {
  fn platform() i32 {
    return 1;
  }
}
else @os[windows] {
  fn platform() i32 {
    return 2;
  }
}
else {
  fn platform() i32 {
    return 3;
  }
}

Statements flatten inline, expressions pick a branch value:

@os[linux] {
  @println("linux");
}

let threads = @debug { 1 } else { 8 };

Variables

@var[...] becomes a literal for the current target:

Variable	Literal
@var[os]	string
@var[arch]	string
@var[env]	string
@var[target]	string
@var[family]	string
@var[debug]	bool
@var[release]	bool

fn main() {
  let os = @var[os];
  let arch = @var[arch];

  @println("You're on: {} {}", os, arch);
}