Standard library

A file imports each std name it uses, from the module that holds it:

import { HashMap, Set } from "@alloy/std/collections"
import { Serialize, Deserialize } from "@alloy/std/serde"

@derive(Serialize, Deserialize)
struct Save
    coins: number
end

local owners = new HashMap<<string, Save>>()

The modules:

@alloy/std/collections  HashMap Set BitSet Queue Heap Array Symbol
@alloy/std/iter         Iter
@alloy/std/result       Result Ok Err
@alloy/std/async        Future Scope
@alloy/std/signal       Signal SignalConnection Signalish
@alloy/std/traits       Display Debug Clone Default Eq PartialEq Ord Add Sub Mul Div
@alloy/std/serde        Serialize Deserialize
@alloy/std/types        Partial Readonly Sink
@alloy/std/roblox       R15Character R6Character Attributes

@alloy/std alone holds every name, and import * as c from "@alloy/std/collections" binds a module, so c.HashMap reads the value and the type. An alias, import { HashMap as Map }, binds the name under the alias. An import writes nothing to the output: the emit reaches every std name through the runtime, so an import and an ambient name compile to the same Luau.

The names the language owns need no import: Future, Result, Ok, Err, Array, and the traits of @alloy/std/traits. A keyword, a literal, or an operator writes them: async returns a Future, try gives a Result, [ ] builds an Array, and ==, <, +, and tostring call the traits.

[std] globals sets the rest:

alloy.tomlalloy.toml

[std]
globals = "none"               # the default: a file imports each name
# globals = "all"              # every std name is ambient
# globals = ["Signal", "Iter"]  # these names are ambient

A name the file does not reach reports an ImportError that names the line to write, once per name. alloy flux --fix writes every missing import. The editor offers the same fix, and a completion of a std name writes its import.