Add test case

Author: DougGregor

test/Unsafe/safe.swift

@@ -0,0 +1,48 @@
+// RUN: %target-typecheck-verify-swift -enable-experimental-feature AllowUnsafeAttribute -enable-experimental-feature WarnUnsafe -print-diagnostic-groups
+
+// REQUIRES: swift_feature_AllowUnsafeAttribute
+// REQUIRES: swift_feature_WarnUnsafe
+
+@unsafe
+func unsafeFunction() { }
+
+@unsafe
+struct UnsafeType { } // expected-note{{unsafe struct 'UnsafeType' declared here}}
+
+@safe(unchecked)
+func f() {
+  unsafeFunction()
+}
+
+@safe(unchecked, message: "I was careful")
+func g() {
+  unsafeFunction()
+}
+
+// expected-note@+2{{mark the enclosing global function 'h' '@unsafe' to allow it to use unsafe constructs}}
+@safe(unchecked, message: "I was careful")
+func h(_: UnsafeType) { // expected-warning{{reference to unsafe struct 'UnsafeType' [Unsafe]}}
+  unsafeFunction()
+}
+
+// Parsing issues
+@safe // expected-error{{expected '(' in 'safe' attribute}}
+func bad1() { }
+
+@safe() // expected-error{{'@safe' attribute must be written as '@safe(unchecked)'}}
+func bad2() { }
+
+@safe(blah) // expected-error{{'@safe' attribute must be written as '@safe(unchecked)'}}
+func bad3() { }
+
+@safe(5) // expected-error{{'@safe' attribute must be written as '@safe(unchecked)'}}
+func bad4() { }
+
+@safe(unchecked, blah) // expected-error{{unknown option 'blah' for attribute 'safe'}}
+func bad5() { }
+
+@safe(unchecked, message) // expected-error{{expected ':' after label 'message'}}
+func bad6() { }
+
+@safe(unchecked, message: "a\(b)") // expected-error{{message cannot be an interpolated string literal}}
+func bad7() { }