---
slug: release-notes/typespec-0-57
title: 0.57 - June 2024
releaseDate: 2024-06-10
version: "0.57"
---

:::caution
This release contains deprecations and breaking changes
:::

## Values In TypeSpec

Decorators often expect some sort of configuration to be passed as an argument. In version `0.51.0` we introduced the `valueof` keyword to constrain a decorator or template parameter to be a value, however this was limited to string, numeric and boolean values.
When dealing with more complex decorators or free form data, one had to use a model type to represent the data. Unfortunately, this approach was difficult for decorator authors to handle reliably and required somewhat sophisticated validation to avoid some common pitfalls that couldn't be prevented through type system constraints.

In this release we introduce a new concept to TypeSpec: values. This includes new syntax for declaring object and array values, scalar constructors, and `const` declarations.

### Object values

Object values can be declared with the `#{}` syntax.

```tsp
const user = #{ name: "Bob", age: 48, address: #{ city: "London" } };
```

### Array values

Array values can be declared with the `#[]` syntax.

```tsp
const users = #["Bob", "Frank"];
```

### `const`

Const declares a variable that holds a value, and can optionally specify a type.

```tsp
const name = "Bob";
const name: string = "Bob";
```

### Scalar constructors

Scalars can define custom values with scalar value constructors. Scalars which don't extend a base type like `string`, `number` or `boolean` can define a constructor.

```tsp
scalar ipV4 {
  init fromInt(value: int32);
}
const ip: ipV4 = ipV4.fromInt(3232235776);
```

[See values doc for more info](https://typespec.io/docs/language-basics/values)

## Breaking changes

- [#3022](https://github.com/microsoft/typespec/pull/3022) Addition of new `const` keyword means using `const` as a property name or decorator name will result in an error. This can be fixed by wrapping the property in backtick.

```tsp
model Test {
  // error
  const: string;

  // correct
  `const`: string;

}
```

## Deprecations

### @typespec/compiler

- [#3022](https://github.com/microsoft/typespec/pull/3022) Using a tuple type as a value is deprecated. Tuple types in contexts where values are expected must be updated to be array values instead. A codefix is provided to automatically convert tuple types into array values.

```tsp
model Test {
  // Deprecated
  values: string[] = ["a", "b", "c"];

  // Correct
  values: string[] = #["a", "b", "c"];
}
```

- [#3022](https://github.com/microsoft/typespec/pull/3022) Using a model type as a value is deprecated. Model types in contexts where values are expected must be updated to be object values instead. A codefix is provided to automatically convert model types into object values.

```tsp
model Test {
  // Deprecated
  user: {
    name: string;
  } = {
    name: "System";
  };

  // Correct
  user: {
    name: string;
  } = #{ name: "System" };
}
```

- [#3022](https://github.com/microsoft/typespec/pull/3022) Decorator API: Legacy marshalling logic

With the introduction of values, the decorator marshalling behavior has changed in some cases. This behavior is opt-in by setting the `valueMarshalling` package flag to `"new"`, but will be the default behavior in future versions. It is strongly recommended to adopt this new behavior as soon as possible.

Example:

```tsp
extern dec multipleOf(target: numeric | Reflection.ModelProperty, value: valueof numeric);
```

Will now emit a deprecated warning because `value` is of type `valueof string` which would marshall to `Numeric` under the new logic but as `number` previously.

To opt-in you can add the following to your library js/ts files.

```ts
export const $flags = definePackageFlags({
  decoratorArgMarshalling: "new",
});
```

## Features

### @typespec/compiler

- [#3280](https://github.com/microsoft/typespec/pull/3280) Support completion for Model with extended properties

  Example

  ```tsp
  model Device {
    name: string;
    description: string;
  }

  model Phone extends Device {
    ┆
  } | [name]
    | [description]
  ```

- [#3280](https://github.com/microsoft/typespec/pull/3280) Support completion for object values and model expression properties.

  Example

  ```tsp
  model User {
    name: string;
    age: int32;
    address: string;
  }

  const user: User = #{name: "Bob", ┆}
                                    | [age]
                                    | [address]
  ```

- [#3375](https://github.com/microsoft/typespec/pull/3375) Allow `@` to be escaped in doc comment with `\`
- [#3022](https://github.com/microsoft/typespec/pull/3022) Add syntax for declaring values. [See docs](https://typespec.io/docs/language-basics/values).

Object and array values

```tsp
@dummy(#{
  name: "John",
  age: 48,
  address: #{ city: "London" }
  aliases: #["Bob", "Frank"]
})
```

Scalar constructors

```tsp
scalar utcDateTime {
  init fromISO(value: string);
}

model DateRange {
  minDate: utcDateTime = utcDateTime.fromISO("2024-02-15T18:36:03Z");
}
```

- [#3527](https://github.com/microsoft/typespec/pull/3527) Add support for `@prop` doc comment tag to describe model properties
- [#3460](https://github.com/microsoft/typespec/pull/3460) Hide deprecated items from completion list
- [#3462](https://github.com/microsoft/typespec/pull/3462) Linter `all` rulesets is automatically created if not explicitly provided
- [#3533](https://github.com/microsoft/typespec/pull/3533) More logs and traces are added for diagnostic and troubleshooting in TypeSpec language server
- [#3422](https://github.com/microsoft/typespec/pull/3422) Formatter: Indent or dedent multiline strings to the current indentation

### @typespec/http

- [#3342](https://github.com/microsoft/typespec/pull/3342) Add new multipart handling. Using `@multipartBody` with `HttpPart<Type, Options>`. See [multipart docs](https://typespec.io/docs/next/libraries/http/multipart) for more information.

  ```tsp
  op upload(
    @header contentType: "multipart/mixed",
    @multipartBody body: {
      name: HttpPart<string>;
      avatar: HttpPart<bytes>[];
    },
  ): void;
  ```

- [#3462](https://github.com/microsoft/typespec/pull/3462) Use new compiler automatic `all` ruleset instead of explicitly provided one

### @typespec/openapi3

- [#3022](https://github.com/microsoft/typespec/pull/3022) Add support for new object and array values as default values (e.g. `decimals: decimal[] = #[123, 456.7];`)

### @typespec/html-program-viewer

- [#3022](https://github.com/microsoft/typespec/pull/3022) Add support for values

### @typespec/json-schema

- [#3557](https://github.com/microsoft/typespec/pull/3557) Add support for @oneOf decorator.

### typespec-vs

- [#3461](https://github.com/microsoft/typespec/pull/3461) Support Arm64

### typespec-vscode

- [#3533](https://github.com/microsoft/typespec/pull/3533) Enhance logging and trace

1.  Support "Developer: Set Log Level..." command to filter logs in TypeSpec output channel
2.  Add "typespecLanguageServer.trace.server" config for whether and how to send the traces from TypeSpec language server to client. (It still depends on client to decide whether to show these traces based on the configured Log Level.)
3.  More logs and traces are added for diagnostic and troubleshooting

- [#3385](https://github.com/microsoft/typespec/pull/3385) Add 'TypeSpec: Show Output Channel' command in VSCode extension

## Bug Fixes

### @typespec/compiler

- [#3399](https://github.com/microsoft/typespec/pull/3399) Preserve leading whitespace in fenced blocks in doc comments
- [#3522](https://github.com/microsoft/typespec/pull/3522) Fix EINVAL error when running `tsp code install`
- [#3371](https://github.com/microsoft/typespec/pull/3371) Numeric not handling trailing zeros and causing freeze(e.g. `const a = 100.0`)
- [#3451](https://github.com/microsoft/typespec/pull/3451) Emitter framework: fix losing context when referencing circular types
- [#3517](https://github.com/microsoft/typespec/pull/3517) Fix application of `@param` doc tag on operation create with `op is` to override upstream doc
- [#3488](https://github.com/microsoft/typespec/pull/3488) Add `PickProperties` type to dynamically select a subset of a model

### @typespec/http

- [#3022](https://github.com/microsoft/typespec/pull/3022) Update Flow Template to make use of the new array values

### @typespec/versioning

- [#3292](https://github.com/microsoft/typespec/pull/3292) Add `@madeRequired` decorator
- [#3022](https://github.com/microsoft/typespec/pull/3022) Update to support new value types
- [#3409](https://github.com/microsoft/typespec/pull/3409) Using `@removed` on member types and `@added` on containing type could result in errors
- [#3255](https://github.com/microsoft/typespec/pull/3255) If a property were marked with @added on a later version, the logic that said it was originally added on the first version was erroneously removed, resulting in incorrect projections.

### @typespec/rest

- [#3022](https://github.com/microsoft/typespec/pull/3022) Update types to support new values in TypeSpec

### @typespec/openapi3

- [#3342](https://github.com/microsoft/typespec/pull/3342) Add support for new multipart constructs in http library
- [#3574](https://github.com/microsoft/typespec/pull/3574) Emit diagnostic when an invalid type is used as a property instead of crashing.

### @typespec/protobuf

- [#3022](https://github.com/microsoft/typespec/pull/3022) Update to support new value types
- [#3561](https://github.com/microsoft/typespec/pull/3561) Corrected cross-package reference behavior in some buggy cases.
-

### @typespec/json-schema

- [#3398](https://github.com/microsoft/typespec/pull/3398) Fix decorators application for union variants
- [#3022](https://github.com/microsoft/typespec/pull/3022) Update to support new value types
- [#3430](https://github.com/microsoft/typespec/pull/3430) The emitted JSON Schema now doesn't make root schemas for TypeSpec types which do not have the @jsonSchema decorator or are contained in a namespace with that decorator. Instead, such schemas are put into the $defs of any root schema which references them, and are referenced using JSON Pointers.
