feat: add InterfaceToType mutation to convert interfaces to type aliases (#52)

* feat: add InterfaceToType mutation to convert interfaces to type aliases

This mutation converts TypeScript interfaces to type aliases with object literals:
- interface User { name: string } -> type User = { name: string }
- Supports generic interfaces with type parameters
- Adds TypeLiteralNode expression type and corresponding bindings
- Includes test data and TypeScript engine support
- Adds TypeIntersection expression and corresponding bindings

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Steven Masley <stevenmasley@gmail.com>

Author: 3 people

bindings/bindings.go

@@ -99,6 +99,10 @@ func (b *Bindings) ToTypescriptExpressionNode(ety ExpressionType) (*goja.Object,
 		siObj, err = b.ArrayLiteral(ety)
 	case *OperatorNodeType:
 		siObj, err = b.OperatorNode(ety)
+	case *TypeLiteralNode:
+		siObj, err = b.TypeLiteralNode(ety)
+	case *TypeIntersection:
+		siObj, err = b.TypeIntersection(ety)
 	default:
 		return nil, xerrors.Errorf("unsupported type for field type: %T", ety)
 	}
@@ -703,3 +707,64 @@ func (b *Bindings) EnumDeclaration(e *Enum) (*goja.Object, error) {
 
 	return obj, nil
 }
+
+func (b *Bindings) TypeLiteralNode(node *TypeLiteralNode) (*goja.Object, error) {
+	typeLiteralF, err := b.f("typeLiteralNode")
+	if err != nil {
+		return nil, err
+	}
+
+	var members []interface{}
+	for _, member := range node.Members {
+		v, err := b.PropertySignature(member)
+		if err != nil {
+			return nil, err
+		}
+
+		// Add field comments if they exist
+		if len(member.FieldComments) > 0 {
+			for _, text := range member.FieldComments {
+				v, err = b.Comment(Comment{
+					SingleLine:      true,
+					Text:            text,
+					TrailingNewLine: false,
+					Node:            v,
+				})
+				if err != nil {
+					return nil, fmt.Errorf("comment field %q: %w", member.Name, err)
+				}
+			}
+		}
+
+		members = append(members, v)
+	}
+
+	res, err := typeLiteralF(goja.Undefined(), b.vm.NewArray(members...))
+	if err != nil {
+		return nil, xerrors.Errorf("call typeLiteralNode: %w", err)
+	}
+
+	return res.ToObject(b.vm), nil
+}
+
+func (b *Bindings) TypeIntersection(node *TypeIntersection) (*goja.Object, error) {
+	intersectionF, err := b.f("intersectionType")
+	if err != nil {
+		return nil, err
+	}
+
+	var types []interface{}
+	for _, t := range node.Types {
+		v, err := b.ToTypescriptExpressionNode(t)
+		if err != nil {
+			return nil, fmt.Errorf("intersection type: %w", err)
+		}
+		types = append(types, v)
+	}
+
+	res, err := intersectionF(goja.Undefined(), b.vm.NewArray(types...))
+	if err != nil {
+		return nil, xerrors.Errorf("call intersectionType: %w", err)
+	}
+	return res.ToObject(b.vm), nil
+}

bindings/expressions.go

@@ -181,3 +181,18 @@ type EnumMember struct {
 
 func (*EnumMember) isNode()           {}
 func (*EnumMember) isExpressionType() {}
+
+// TypeLiteralNode represents an object type literal like { name: string }
+type TypeLiteralNode struct {
+	Members []*PropertySignature
+}
+
+func (*TypeLiteralNode) isNode()           {}
+func (*TypeLiteralNode) isExpressionType() {}
+
+type TypeIntersection struct {
+	Types []ExpressionType
+}
+
+func (*TypeIntersection) isNode()           {}
+func (*TypeIntersection) isExpressionType() {}

bindings/walk/walk.go

@@ -59,13 +59,17 @@ func Walk(v Visitor, node bindings.Node) {
 	case *bindings.LiteralType:
 		// noop
 	case *bindings.Null:
-	// noop
+		// noop
 	case *bindings.HeritageClause:
 		walkList(v, n.Args)
 	case *bindings.OperatorNodeType:
 		Walk(v, n.Type)
 	case *bindings.EnumMember:
 		Walk(v, n.Value)
+	case *bindings.TypeLiteralNode:
+		walkList(v, n.Members)
+	case *bindings.TypeIntersection:
+		walkList(v, n.Types)
 	default:
 		panic(fmt.Sprintf("convert.Walk: unexpected node type %T", n))
 	}

config/mutations.go

@@ -107,7 +107,7 @@ func TrimEnumPrefix(ts *guts.Typescript) {
 
 // EnumAsTypes uses types to handle enums rather than using 'enum'.
 // An enum will look like:
-//  type EnumString = "bar" | "baz" | "foo" | "qux";
+// type EnumString = "bar" | "baz" | "foo" | "qux";
 func EnumAsTypes(ts *guts.Typescript) {
 	ts.ForEach(func(key string, node bindings.Node) {
 		enum, ok := node.(*bindings.Enum)
@@ -142,7 +142,7 @@ func EnumAsTypes(ts *guts.Typescript) {
 // )
 // const MyEnums: string = ["foo", "bar"] <-- this is added
 // TODO: Enums were changed to use proper enum types. This should be
-//   updated to support that. EnumLists only works with EnumAsTypes used first.
+// updated to support that. EnumLists only works with EnumAsTypes used first.
 func EnumLists(ts *guts.Typescript) {
 	addNodes := make(map[string]bindings.Node)
 	ts.ForEach(func(key string, node bindings.Node) {
@@ -342,6 +342,47 @@ func (v *notNullMaps) Visit(node bindings.Node) walk.Visitor {
 	return v
 }
 
+// InterfaceToType converts all interfaces to type aliases.
+// interface User { name: string } --> type User = { name: string }
+func InterfaceToType(ts *guts.Typescript) {
+	ts.ForEach(func(key string, node bindings.Node) {
+		intf, ok := node.(*bindings.Interface)
+		if !ok {
+			return
+		}
+
+		// Create a type literal node to represent the interface structure
+		var typeLiteral bindings.ExpressionType = &bindings.TypeLiteralNode{
+			Members: intf.Fields,
+		}
+
+		// If the interface has heritage (extends/implements), create an intersection type.
+		// The output of an intersection type is equivalent to extending multiple interfaces.
+		if len(intf.Heritage) > 0 {
+			var intersection []bindings.ExpressionType
+			intersection = make([]bindings.ExpressionType, 0, len(intf.Heritage)+1)
+			for _, heritage := range intf.Heritage {
+				for _, arg := range heritage.Args {
+					intersection = append(intersection, arg)
+				}
+			}
+			intersection = append(intersection, typeLiteral)
+			typeLiteral = &bindings.TypeIntersection{
+				Types: intersection,
+			}
+		}
+
+		// Replace the interface with a type alias
+		ts.ReplaceNode(key, &bindings.Alias{
+			Name:       intf.Name,
+			Modifiers:  intf.Modifiers,
+			Type:       typeLiteral,
+			Parameters: intf.Parameters,
+			Source:     intf.Source,
+		})
+	})
+}
+
 func isGoEnum(n bindings.Node) (*bindings.Alias, *bindings.UnionType, bool) {
 	al, ok := n.(*bindings.Alias)
 	if !ok {

convert_test.go

@@ -123,6 +123,8 @@ func TestGeneration(t *testing.T) {
 						mutations = append(mutations, config.NullUnionSlices)
 					case "TrimEnumPrefix":
 						mutations = append(mutations, config.TrimEnumPrefix)
+					case "InterfaceToType":
+						mutations = append(mutations, config.InterfaceToType)
 					default:
 						t.Fatal("unknown mutation, add it to the list:", m)
 					}

testdata/interfacetotype/interfacetotype.go

@@ -0,0 +1,32 @@
+package codersdk
+
+type Score[T int | float32 | float64] struct {
+	Points T   `json:"points"`
+	Level  int `json:"level"`
+}
+
+type User[T comparable] struct {
+	ID       T      `json:"id"`
+	Name     string `json:"name"`
+	Email    string `json:"email"`
+	IsActive bool   `json:"is_active"`
+}
+
+type Player[ID comparable, P int | float32 | float64] struct {
+	User[ID]
+	Score[P]
+
+	X int `json:"x"`
+	Y int `json:"y"`
+}
+
+type Address struct {
+	Street  string `json:"street"`
+	City    string `json:"city"`
+	Country string `json:"country"`
+}
+
+type GenericContainer[T any] struct {
+	Value T   `json:"value"`
+	Count int `json:"count"`
+}

testdata/interfacetotype/interfacetotype.ts

@@ -0,0 +1,36 @@
+// Code generated by 'guts'. DO NOT EDIT.
+
+// From codersdk/interfacetotype.go
+export type Address = {
+    street: string;
+    city: string;
+    country: string;
+};
+
+export type Comparable = string | number | boolean;
+
+// From codersdk/interfacetotype.go
+export type GenericContainer<T extends any> = {
+    value: T;
+    count: number;
+};
+
+// From codersdk/interfacetotype.go
+export type Player<ID extends Comparable, P extends number> = User<ID> & Score<P> & {
+    x: number;
+    y: number;
+};
+
+// From codersdk/interfacetotype.go
+export type Score<T extends number> = {
+    points: T;
+    level: number;
+};
+
+// From codersdk/interfacetotype.go
+export type User<T extends Comparable> = {
+    id: T;
+    name: string;
+    email: string;
+    is_active: boolean;
+};

testdata/interfacetotype/mutations

@@ -0,0 +1 @@
+InterfaceToType,ExportTypes,ReadOnly

typescript-engine/dist/main.js

@@ -11,7 +11,7 @@
 // https://astexplorer.net/
 
 import * as ts from "typescript";
-import {Identifier, Modifier, ModifierSyntaxKind, StringLiteral} from "typescript";
+import {Identifier, IntersectionTypeNode, Modifier, ModifierSyntaxKind, StringLiteral, TypeNode} from "typescript";
 
 type modifierKeys = FilterKeys<typeof ts.SyntaxKind, ModifierSyntaxKind>;
 export function modifier(name: modifierKeys | ts.Modifier): Modifier {
@@ -279,6 +279,16 @@ export function typeOperatorNode(
   return ts.factory.createTypeOperatorNode(ts.SyntaxKind[operator], node);
 }
 
+export function typeLiteralNode(
+  members: ts.TypeElement[]
+): ts.TypeLiteralNode {
+  return ts.factory.createTypeLiteralNode(members);
+}
+
+export function intersectionType(types:TypeNode[]): ts.IntersectionTypeNode {
+  return ts.factory.createIntersectionTypeNode(types);
+}
+
 module.exports = {
   modifier: modifier,
   identifier: identifier,
@@ -305,6 +315,8 @@ module.exports = {
   variableDeclarationList: variableDeclarationList,
   arrayLiteral: arrayLiteral,
   typeOperatorNode: typeOperatorNode,
+  typeLiteralNode: typeLiteralNode,
+  intersectionType: intersectionType,
   enumDeclaration: enumDeclaration,
   enumMember: enumMember,
 };