Merge pull request swiftlang#72024 from belkadan/protocol-extension-default-arguments-test-case

Test existing behavior of default arguments in protocol extensions

Author: Azoy

test/Interpreter/protocol_extensions.swift

@@ -374,3 +374,25 @@ extension String: Addable {}
 ProtocolExtensionTestSuite.test("MarkerProtocolExtensions") {
     expectTrue("hello".increment(this: 11) == 111)
 }
+
+protocol DefaultArgumentsInExtension {
+    func foo(a: Int, b: Int) -> (Int, Int)
+}
+extension DefaultArgumentsInExtension {
+    func foo(a: Int, b: Int = 1) -> (Int, Int) {
+        self.foo(a: a * 10, b: b * 10)
+    }
+}
+struct DefaultArgumentsInExtensionImpl: DefaultArgumentsInExtension {
+    func foo(a: Int, b: Int) -> (Int, Int) {
+        (a * 2, b * 2)
+    }
+}
+
+ProtocolExtensionTestSuite.test("DefaultArgumentsInExtension") {
+    let instance = DefaultArgumentsInExtensionImpl()
+    expectEqual((4, 6), instance.foo(a: 2, b: 3))
+    expectEqual((4, 6), (instance as any DefaultArgumentsInExtension).foo(a: 2, b: 3))
+    expectEqual((40, 20), instance.foo(a: 2))
+    expectEqual((40, 20), (instance as any DefaultArgumentsInExtension).foo(a: 2))
+}