add a test

src/test/codegen/set-discriminant-invalid.rs

@@ -0,0 +1,43 @@
+// compile-flags: -C opt-level=0
+#![crate_type = "lib"]
+
+pub enum ApiError {}
+#[allow(dead_code)]
+pub struct TokioError {
+    b: bool,
+}
+pub enum Error {
+    Api {
+        source: ApiError,
+    },
+    Ethereum,
+    Tokio {
+        source: TokioError,
+    },
+}
+struct Api;
+impl IntoError<Error> for Api
+{
+    type Source = ApiError;
+    // CHECK-LABEL: @into_error
+    // CHECK: unreachable
+    // Also check the next two instructions to make sure we do not match against `unreachable`
+    // elsewhere in the code (e.g., in the closure bode).
+    // CHECK-NEXT: load
+    // CHECK-NEXT: ret
+    #[no_mangle]
+    fn into_error(self, error: Self::Source) -> Error {
+        Error::Api {
+            source: (|v| v)(error),
+        }
+    }
+}
+
+pub trait IntoError<E>
+{
+    /// The underlying error
+    type Source;
+
+    /// Combine the information to produce the error
+    fn into_error(self, source: Self::Source) -> E;
+}