feat: handle unnamed union type constraints

Author: Emyrk

convert.go

@@ -997,6 +997,20 @@ func (ts *Typescript) typescriptType(ty types.Type) (parsedType, error) {
 	case *types.Alias:
 		// TODO: Verify this is correct.
 		return ts.typescriptType(ty.Underlying())
+	case *types.Union:
+		allTypes := make([]bindings.ExpressionType, 0, ty.Len())
+		for i := 0; i < ty.Len(); i++ {
+			constraintType, err := ts.typescriptType(ty.Term(i).Type())
+			if err != nil {
+				return parsedType{}, xerrors.Errorf("union %q: %w", ty.String(), err)
+			}
+			allTypes = append(allTypes, constraintType.Value)
+		}
+		return parsedType{
+			Value:          bindings.Union(allTypes...),
+			TypeParameters: nil,
+			RaisedComments: nil,
+		}, nil
 	}
 
 	// These are all the other types we need to support.

testdata/union/union.go

@@ -0,0 +1,5 @@
+package union
+
+type UnionConstraint[T string | int64] struct {
+	Value T
+}

testdata/union/union.ts

@@ -0,0 +1,6 @@
+// Code generated by 'guts'. DO NOT EDIT.
+
+// From union/union.go
+export interface UnionConstraint<T extends string | number> {
+    readonly Value: T;
+}