Add regression test for issue #2792

test_suite/tests/regression/issue2792.rs

@@ -0,0 +1,16 @@
+#![allow(dead_code)] // we do not read enum fields
+use serde_derive::Deserialize;
+
+#[derive(Deserialize)]
+#[serde(deny_unknown_fields)]
+pub enum A {
+    B {
+        c: String,
+    },
+    D {
+        #[serde(flatten)]
+        e: E,
+    },
+}
+#[derive(Deserialize)]
+pub struct E {}