🎑 tygo

Tygo is a tool for generating Typescript typings from Golang source files that just works.

It preserves comments, understands constants and also supports non-struct type expressions. It's perfect for generating equivalent types for a Golang REST API to be used in your front-end codebase.

🚀 Now supports Golang 1.18 generic types, struct inheritance

Installation

# Go >= 1.17
go install github.com/gzuidhof/tygo@latest
# Go < 1.17:
go install github.com/gzuidhof/tygo

Example

Golang input file

// Comments are kept :)
type ComplexType map[string]map[uint16]*uint32

type UserRole = string
const (
	UserRoleDefault UserRole = "viewer"
	UserRoleEditor  UserRole = "editor" // Line comments are also kept
)

type UserEntry struct {
	// Instead of specifying `tstype` we could also declare the typing
	// for uuid.NullUUID in the config file.
	ID uuid.NullUUID `json:"id" tstype:"string | null"`

	Preferences map[string]struct {
		Foo uint32 `json:"foo"`
		// An unknown type without a `tstype` tag or mapping in the config file
		// becomes `any`
		Bar uuid.UUID `json:"bar"`
	} `json:"prefs"`

	MaybeFieldWithStar *string  `json:"address"`
	Nickname           string   `json:"nickname,omitempty"`
	Role               UserRole `json:"role"`

	Complex    ComplexType `json:"complex"`
	unexported bool        // Unexported fields are omitted
	Ignored    bool        `tstype:"-"` // Fields with - are omitted too
}

type ListUsersResponse struct {
	Users []UserEntry `json:"users"`
}

Typescript output

/**
 * Comments are kept :)
 */
export type ComplexType = {
  [key: string]: {
    [key: number /* uint16 */]: number /* uint32 */ | undefined;
  };
};
export type UserRole = string;
export const UserRoleDefault: UserRole = "viewer";
export const UserRoleEditor: UserRole = "editor"; // Line comments are also kept
export interface UserEntry {
  /**
   * Instead of specifying `tstype` we could also declare the typing
   * for uuid.NullUUID in the config file.
   */
  id: string | null;
  prefs: {
    [key: string]: {
      foo: number /* uint32 */;
      /**
       * An unknown type without a `tstype` tag or mapping in the config file
       * becomes `any`
       */
      bar: any /* uuid.UUID */;
    };
  };
  address?: string;
  nickname?: string;
  role: UserRole;
  complex: ComplexType;
}
export interface ListUsersResponse {
  users: UserEntry[];
}

For a real baptism by fire example, here is a Gist with output for the Go built-in net/http and time package.

Usage

Option A: CLI (recommended)

Create a file tygo.yaml in which you specify which packages are to be converted and any special type mappings you want to add.

packages:
  - path: "github.com/gzuidhof/tygo/examples/bookstore"
    type_mappings:
      time.Time: "string /* RFC3339 */"
      null.String: "null | string"
      null.Bool: "null | boolean"
      uuid.UUID: "string /* uuid */"
      uuid.NullUUID: "null | string /* uuid */"

Then run

tygo generate

The output Typescript file will be next to the Go source files.

Option B: Library-mode

config := &tygo.Config{
  Packages: []*tygo.PackageConfig{
      &tygo.PackageConfig{
          Path: "github.com/gzuidhof/tygo/examples/bookstore",
      },
  },
}
gen := tygo.New(config)
err := gen.Generate()

Config

# You can specify more than one package
packages:
  # The package path just like you would import it in Go
  - path: "github.com/my/package"

    # Where this output should be written to.
    # If you specify a folder it will be written to a file `index.ts` within that folder. By default it is written into the Golang package folder.
    output_path: "webapp/api/types.ts"

    # Customize the indentation (use \t if you want tabs)
    indent: "    "

    # Specify your own custom type translations, useful for custom types, `time.Time` and `null.String`.
    # Be default unrecognized types will be `any`.
    type_mappings:
      time.Time: "string"
      my.Type: "SomeType"

    # This content will be put at the top of the output Typescript file, useful for importing custom types.
    frontmatter: |
      "import {SomeType} from "../lib/sometype.ts"

    # Filenames of Go source files that should not be included
    # in the output.
    exclude_files:
      - "private_stuff.go"

See also the source file tygo/config.go.

Type hints through tagging

You can tag struct fields with tstype to specify their output Typescript type.

Custom type mapping

// Golang input

type Book struct {
	Title    string    `json:"title"`
	Genre    string    `json:"genre" tstype:"'novel' | 'crime' | 'fantasy'"`
}

// Typescript output

export interface Book {
  title: string;
  genre: "novel" | "crime" | "fantasy";
}

Alternative

You could use the frontmatter field in the config to inject export type Genre = "novel" | "crime" | "fantasy" at the top of the file, and use tstype:"Genre". I personally prefer that as we may use the Genre type more than once.

Required fields

Pointer type fields usually become optional in the Typescript output, but sometimes you may want to require it regardless.

You can add ,required to the tstype tag to mark a pointer type as required.

// Golang input
type Nicknames struct {
	Alice   *string `json:"alice"`
	Bob     *string `json:"bob" tstype:"BobCustomType,required"`
	Charlie *string `json:"charlie" tstype:",required"`
}

// Typescript output
export interface Nicknames {
  alice?: string;
  bob: BobCustomType;
  charlie: string;
}

Readonly fields

Sometimes a field should be immutable, you can add ,readonly to the tstype tag to mark a field as readonly.

// Golang input
type Cat struct {
	Name    string `json:"name,readonly"`
	Owner   string `json:"owner"`
}

// Typescript output
export interface Cat {
  readonly name: string;
  owner: string;
}

Inheritance

Tygo supports interface inheritance. To extend an inlined struct, use the tag tstype:",extends" on struct fields you wish to extend. Only struct types can be extended.

Struct pointers are optionally extended using Partial<MyType>. To mark these structs as required, use the tag tstype:",extends,required".

Named struct fields can also be extended.

Example usage here

// Golang input
import "example.com/external"

type Base struct {
	Name string `json:"name"`
}

type Base2[T string | int] struct {
	ID T `json:"id"`
}

type OptionalPtr struct {
	Field string `json:"field"`
}

type Other[T int] struct {
	*Base                  `       tstype:",extends,required"`
	Base2[T]               `       tstype:",extends"`
	*OptionalPtr           `       tstype:",extends"`
	external.AnotherStruct `       tstype:",extends"`
	OtherValue             string `                  json:"other_value"`
}

// Typescript output
export interface Base {
  name: string;
}

export interface Base2<T extends string | number /* int */> {
  id: T;
}

export interface OptionalPtr {
  field: string;
}

export interface Other<T extends number /* int */>
  extends Base,
    Base2<T>,
    Partial<OptionalPtr>,
    external.AnotherStruct {
  other_value: string;
}

Generics

Tygo supports generic types (Go version >= 1.18) out of the box.

// Golang input
type UnionType interface {
	uint64 | string
}

type ABCD[A, B string, C UnionType, D int64 | bool] struct {
	A A `json:"a"`
	B B `json:"b"`
	C C `json:"c"`
	D D `json:"d"`
}

// Typescript output
export type UnionType = number /* uint64 */ | string;

export interface ABCD<
  A extends string,
  B extends string,
  C extends UnionType,
  D extends number /* int64 */ | boolean
> {
  a: A;
  b: B;
  c: C;
  d: D;
}

YAML support

Tygo supports generating typings for YAML-serializable objects that can be understood by Go apps. By default, Tygo will respect yaml Go struct tags, in addition to json, but it will not apply any transformations to untagged fields. However, the default behavior of the popular gopkg.in/yaml.v2 package for Go structs without tags is to downcase the struct field names. To emulate this behavior, one can use the flavor configuration option:

packages:
  - path: "github.com/my/package"
    output_path: "webapp/api/types.ts"
    flavor: "yaml"

// Golang input
type Foo struct {
	TaggedField string `yaml:"custom_field_name_in_yaml"`
    UntaggedField string
}

// Typescript output
export interface Foo {
  custom_field_name_in_yaml: string;
  untaggedfield: string;
}

Related projects

typescriptify-golang-structs: Probably the most popular choice. The downside of this package is that it relies on reflection rather than parsing, which means that certain things can't be kept such as comments without adding a bunch of tags to your structs. The CLI generates a Go file which is then executed and reflected on, and its library requires you to manually specify all types that should be converted.
go2ts: A transpiler with a web interface, this project was based off this project. It's perfect for quick one-off transpilations. There is no CLI, no support for const and there are no ways to customize the output.

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License

MIT

gzuidhof/tygo

gzuidhof

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