🔧 fix: handle strict union check

Author: SaltyAom

CHANGELOG.md

@@ -1,3 +1,7 @@
+# 0.2.4 - 26 Nov 2025
+Improvement:
+- handle strict union check
+
 # 0.2.3 - 5 Nov 2025
 Bug fix:
 - [#24](https://github.com/elysiajs/exact-mirror/pull/24) bracket handling in fields

example/index.ts

@@ -3,26 +3,31 @@ import createMirror from '../src/index'
 
 import { TypeCompiler } from '@sinclair/typebox/compiler'
 
-const shape = t.Object({
-	total: t
-		.Transform(t.Number())
-		.Decode((x) => x)
-		.Encode((x) => x),
-	user: t.Object({
-		username: t.String()
-	}),
-})
+const SchemaA = t.Object(
+	{ foo: t.Number() },
+	{
+		additionalProperties: false
+	}
+)
+const SchemaB = t.Object(
+	{ foo: t.Number(), baz: t.Boolean() },
+	{
+		additionalProperties: false
+	}
+)
+const UnionSchema = t.Union([SchemaA, SchemaB])
+const OmittedUnionSchema = t.Omit(UnionSchema, ['baz'])
+
+const shape = OmittedUnionSchema
 
-const value = {
-	total: 1,
-	user: { username: 'Bob', secret: 'shhh' }
-} satisfies typeof shape.static
+const value = { baz: true, foo: 1 } satisfies typeof shape.static
 
 const mirror = createMirror(shape, {
-	TypeCompiler,
-	sanitize: (a) => a
+	TypeCompiler
 })
 
+console.log(mirror.toString())
+
 console.dir(mirror(value), {
 	depth: null
 })

package.json

@@ -1,6 +1,6 @@
 {
 	"name": "exact-mirror",
-	"version": "0.2.3",
+	"version": "0.2.4",
 	"description": "Mirror exact value to TypeBox/OpenAPI model",
 	"license": "MIT",
 	"scripts": {

src/index.ts

@@ -254,6 +254,10 @@ const handleUnion = (
 		return type
 	}
 
+	// some type require cleaning before checking
+	// e.g. object with `additionalProperties: false`
+	let cleanThenCheck = ''
+
 	for (let i = 0; i < schemas.length; i++) {
 		let type = unwrapRef(schemas[i])
 
@@ -277,16 +281,26 @@ const handleUnion = (
 				parentIsOptional: true
 			}
 		)}}\n`
+
+		cleanThenCheck +=
+			(i ? '' : 'let ') +
+			'tmp=' +
+			mirror(type, property, {
+				...instruction,
+				recursion: instruction.recursion + 1,
+				parentIsOptional: true
+			}) +
+			`\nif(d.unions[${ui}][${i}].Check(tmp))return tmp\n`
 	}
 
+	if (cleanThenCheck) v += cleanThenCheck
+
 	// unknown type, return as-is (this is a default intended behavior)
 	// because it's expected that exact-mirror input should always be a correct value
 	// returning an incorrect value then later checked is expected
-	v +=
-		`return ${instruction.removeUnknownUnionType ? 'undefined' : property}` +
-		`})()`
+	v += `return ${instruction.removeUnknownUnionType ? 'undefined' : property}`
 
-	return v
+	return v + `})()`
 }
 
 const mirror = (

test/union.test.ts

@@ -214,4 +214,35 @@ describe('Union', () => {
 			value
 		)
 	})
+
+	it('handle clean then check', () => {
+		const SchemaA = t.Object(
+			{ foo: t.Number() },
+			{
+				additionalProperties: false
+			}
+		)
+		const SchemaB = t.Object(
+			{ foo: t.Number(), baz: t.Boolean() },
+			{
+				additionalProperties: false
+			}
+		)
+		const UnionSchema = t.Union([SchemaA, SchemaB])
+		const OmittedUnionSchema = t.Omit(UnionSchema, ['baz'])
+
+		const shape = OmittedUnionSchema
+
+		const value = { foo: 1 } satisfies typeof shape.static
+
+		isEqual(
+			shape,
+			{
+				// @ts-ignore
+				baz: true,
+				foo: 1
+			},
+			value
+		)
+	})
 })