add flatten adjacently tagged enum test

Author: haifengkao

Sources/MacroCodableKit/Macros/TaggedAnnotations.swift

@@ -29,7 +29,7 @@ public enum TaggedCodableCaseStyle {
 /// ```json
 /// {"intent": "SCROLL"}
 /// ```
-@attached(extension, conformances: Decodable, Encodable, names: named(CodingKeys), named(init(from:)), named(encode(to:)))
+@attached(extension, conformances: Decodable, Encodable, names: arbitrary)
 public macro TaggedCodable() = #externalMacro(module: "Macro", type: "TaggedCodableMacro")
 
 /// Specifies the discriminator key name and case-name transformation style

Tests/MacroCodableKitTests/TaggedEnum/TaggedEnumFlattenTests.swift

@@ -0,0 +1,69 @@
+import Foundation
+import MacroCodableKit
+import XCTest
+
+// MARK: - Types
+
+@TaggedCodable
+@CodedAt("type", caseStyle: .screamingSnakeCase)
+@ContentAt("params")
+private enum Command {
+    case ping
+    case fetch(url: String)
+}
+
+// Case A: @AllOfCodable with a single TaggedCodable property
+@AllOfCodable
+private struct EnvelopeAllOf {
+    let command: Command
+}
+
+// Case B: plain @Codable (control group — expected to nest)
+@Codable
+private struct EnvelopeCodable {
+    let command: Command
+}
+
+// MARK: - Tests
+
+final class TaggedEnumFlattenTests: XCTestCase {
+
+    private let encoder: JSONEncoder = {
+        let e = JSONEncoder()
+        e.outputFormatting = [.sortedKeys]
+        return e
+    }()
+
+    // Expected: {"params":{"url":"https://example.com"},"type":"FETCH"}
+    // i.e. type + params are sibling keys at the top level
+    func test_allOf_flattens_taggedEnum() throws {
+        let value = EnvelopeAllOf(command: .fetch(url: "https://example.com"))
+        let data = try encoder.encode(value)
+        let json = String(data: data, encoding: .utf8)!
+
+        let obj = try JSONSerialization.jsonObject(with: data) as! [String: Any]
+
+        // Should be flat — "type" and "params" at root, no extra nesting
+        XCTAssertEqual(obj["type"] as? String, "FETCH",
+                       "Expected 'type' as sibling key, got: \(json)")
+        let params = obj["params"] as? [String: Any]
+        XCTAssertEqual(params?["url"] as? String, "https://example.com",
+                       "Expected 'params' as sibling key, got: \(json)")
+        XCTAssertNil(obj["command"] as? [String: Any],
+                     "Should NOT be nested object under 'command'")
+    }
+
+    // Control: @Codable nests under "command" key as expected
+    func test_codable_nests_taggedEnum() throws {
+        let value = EnvelopeCodable(command: .fetch(url: "https://example.com"))
+        let data = try encoder.encode(value)
+        let json = String(data: data, encoding: .utf8)!
+
+        let obj = try JSONSerialization.jsonObject(with: data) as! [String: Any]
+
+        // Should be nested under "command"
+        let nested = obj["command"] as? [String: Any]
+        XCTAssertNotNil(nested, "Expected nesting under 'command', got: \(json)")
+        XCTAssertEqual(nested?["type"] as? String, "FETCH")
+    }
+}