[embedded] Add a embedded Swift + typed throw test showcasing that we avoid existentials

Author: kubamracek

test/embedded/throw-typed.swift

@@ -0,0 +1,95 @@
+// RUN: %target-run-simple-swift(%S/Inputs/print.swift -enable-experimental-feature Embedded -enable-experimental-feature TypedThrows -parse-as-library -runtime-compatibility-version none -wmo -Xfrontend -disable-objc-interop) | %FileCheck %s
+
+// REQUIRES: executable_test
+// REQUIRES: optimized_stdlib
+// REQUIRES: VENDOR=apple
+// REQUIRES: OS=macosx
+
+public enum MyError : Error, Equatable {
+  case a
+  case b
+  case c(Int)
+}
+
+extension Int : Error {}
+
+public func throwing(which: Int) throws(MyError) -> Int {
+  if which == 0 {
+    throw MyError.a
+  } else if which == 1 {
+    throw MyError.b
+  } else if which == 2 {
+    throw MyError.c(42)
+  }
+
+  return 123
+}
+
+public func throwing2() throws(Int) {
+  throw 42
+}
+
+public func catching() {
+  do {
+    try throwing(which: 0)
+  } catch let e as MyError {
+    print(e == .a ? "OK1" : "???")
+  }
+
+  do {
+    try throwing(which: 1)
+  } catch let e as MyError where e == .b {
+    print(e == .b ? "OK2" : "???")
+  } catch {
+    print("???")
+  }
+
+  do {
+    try throwing(which: 2)
+  } catch let e as MyError where e == .b {
+    print("???")
+  } catch {
+    print("OK3")
+  }
+
+  do {
+    try throwing(which: 2)
+  } catch let e as MyError {
+    if case .c(let n) = e {
+      print(n == 42 ? "OK4" : "???") 
+    } else {
+      print("???")
+    }
+  } catch {
+    print("???")
+  }
+
+  do {
+    try throwing(which: 3)
+    print("OK5")
+  } catch {
+    print("???")
+  }
+
+  do {
+    try throwing2()
+  } catch {
+    print(error == 42 ? "OK6" : "???")
+  }
+}
+
+@main
+struct Main {
+  static func main() {
+    catching()
+  }
+}
+
+// CHECK: OK1
+// CHECK: OK2
+// CHECK: OK3
+// CHECK: OK4
+// CHECK: OK5
+// CHECK: OK6
+
+// CHECK-NOT: ???