Add inherited types macro parameter

Sources/Spyable/Spyable.swift

@@ -134,7 +134,11 @@
 /// - The generated spy class name is suffixed with `Spy` (e.g., `ServiceProtocolSpy`).
 ///
 @attached(peer, names: suffixed(Spy))
-public macro Spyable(behindPreprocessorFlag: String? = nil, accessLevel: SpyAccessLevel? = nil) =
+public macro Spyable(
+  behindPreprocessorFlag: String? = nil,
+  accessLevel: SpyAccessLevel? = nil,
+  inheritedTypes: String? = nil
+) =
   #externalMacro(
     module: "SpyableMacro",
     type: "SpyableMacro"

Sources/SpyableMacro/Extractors/Extractor.swift

@@ -145,6 +145,46 @@ struct Extractor {
   func extractAccessLevel(from protocolDeclSyntax: ProtocolDeclSyntax) -> DeclModifierSyntax? {
     protocolDeclSyntax.modifiers.first(where: \.name.isAccessLevelSupportedInProtocol)
   }
+
+  func extractInheritedTypes(
+    from attribute: AttributeSyntax,
+    in context: some MacroExpansionContext
+  ) -> String? {
+    guard case let .argumentList(argumentList) = attribute.arguments else {
+      // No arguments are present in the attribute.
+      return nil
+    }
+
+    let inheritedTypesArgument = argumentList.first { argument in
+      argument.label?.text == "inheritedTypes"
+    }
+
+    guard let inheritedTypesArgument else {
+      // The `inheritedTypes` argument is missing.
+      return nil
+    }
+
+    let segments = inheritedTypesArgument.expression
+       .as(StringLiteralExprSyntax.self)?
+       .segments
+
+     guard let segments,
+       segments.count == 1,
+       case let .stringSegment(literalSegment)? = segments.first
+     else {
+       // The `inheritedTypes` argument's value is not a static string literal.
+       context.diagnose(
+         Diagnostic(
+           node: attribute,
+           message: SpyableDiagnostic.behindPreprocessorFlagArgumentRequiresStaticStringLiteral,
+           highlights: [Syntax(inheritedTypesArgument.expression)]
+         )
+       )
+       return nil
+     }
+
+     return literalSegment.content.text
+  }
 }
 
 extension TokenSyntax {

Tests/SpyableMacroTests/Macro/UT_SpyableMacro.swift

@@ -555,4 +555,38 @@ final class UT_SpyableMacro: XCTestCase {
       macros: sut
     )
   }
+
+  func testMacroWithParameterToMakeGeneratedSpyConformToAnotherProtocol() {
+    let baseProtocolDeclaration = """
+    protocol BaseProtocol {
+        func baseMethod()
+    }
+
+    class BaseClass: BaseProtocol {
+        func baseMethod() {}
+    }
+
+    """
+
+    let protocolDeclaration = "protocol MyProtocol: BaseProtocol {}"
+
+    assertMacroExpansion(
+      """
+      \(baseProtocolDeclaration)
+      @Spyable(inheritedTypes: "BaseClass")
+      \(protocolDeclaration)
+      """,
+      expandedSource: """
+        \(baseProtocolDeclaration)
+
+        \(protocolDeclaration)
+
+        class MyProtocolSpy: MyProtocol, @unchecked Sendable, BaseClass {
+            init() {
+            }
+        }
+        """,
+      macros: sut
+    )
+  }
 }