java2swift: add non-optional-returning as function to JavaClassMacro

Sources/JavaKit/Macros.swift

@@ -37,7 +37,8 @@
   named(javaThis),
   named(javaEnvironment),
   named(init(javaHolder:)),
-  named(JavaSuperclass)
+  named(JavaSuperclass),
+  named(`as`)
 )
 @attached(extension, conformances: AnyJavaObject)
 @attached(peer)
@@ -73,7 +74,8 @@ public macro JavaClass(
   named(javaThis),
   named(javaEnvironment),
   named(init(javaHolder:)),
-  named(JavaSuperclass)
+  named(JavaSuperclass),
+  named(`as`)
 )
 @attached(extension, conformances: AnyJavaObject)
 public macro JavaInterface(_ fullClassName: String, extends: (any AnyJavaObject.Type)?...) =

Sources/JavaKitMacros/JavaClassMacro.swift

@@ -87,13 +87,21 @@ extension JavaClassMacro: MemberMacro {
       }
       """
 
+    let nonOptionalAs: DeclSyntax = """
+      /// Casting to ``\(raw: superclass)`` will never be nil because ``\(raw: className.split(separator: ".").last!)`` extends it.
+      public func `as`(_: \(raw: superclass).Type) -> \(raw: superclass) {
+          return \(raw: superclass)(javaHolder: javaHolder)
+      }
+      """
+
     return [
       fullJavaClassNameMember,
       superclassTypealias,
       javaHolderMember,
       javaThisMember,
       javaEnvironmentMember,
       initMember,
+      nonOptionalAs,
     ]
   }
 }

Tests/JavaKitMacroTests/JavaClassMacroTests.swift

@@ -78,6 +78,11 @@ class JavaKitMacroTests: XCTestCase {
             public init(javaHolder: JavaObjectHolder) {
                 self.javaHolder = javaHolder
             }
+
+            /// Casting to ``JavaObject`` will never be nil because ``HelloWorld`` extends it.
+            public func `as`(_: JavaObject.Type) -> JavaObject {
+                return JavaObject(javaHolder: javaHolder)
+            }
         }
       """,
       macros: Self.javaKitMacros