Unify handling of unit and unit structs in ContentDeserializer

Author: Mingun

serde/src/private/de.rs

@@ -1318,9 +1318,24 @@ mod content {
         where
             V: Visitor<'de>,
         {
+            // Covered by tests/test_enum_internally_tagged.rs
+            //      newtype_unit
             match self.content {
-                Content::Unit => visitor.visit_unit(),
-
+                // As a special case, allow deserializing untagged newtype
+                // variant containing unit struct.
+                //
+                //     #[derive(Deserialize)]
+                //     struct Info;
+                //
+                //     #[derive(Deserialize)]
+                //     #[serde(tag = "topic")]
+                //     enum Message {
+                //         Info(Info),
+                //     }
+                //
+                // We want {"topic":"Info"} to deserialize even though
+                // ordinarily unit structs do not deserialize from empty map/seq.
+                //
                 // Allow deserializing newtype variant containing unit.
                 //
                 //     #[derive(Deserialize)]
@@ -1331,7 +1346,8 @@ mod content {
                 //
                 // We want {"result":"Success"} to deserialize into Response<()>.
                 Content::Map(ref v) if v.is_empty() => visitor.visit_unit(),
-                _ => Err(self.invalid_type(&visitor)),
+                Content::Seq(ref v) if v.is_empty() => visitor.visit_unit(),
+                _ => self.deserialize_any(visitor),
             }
         }
 
@@ -1343,25 +1359,9 @@ mod content {
         where
             V: Visitor<'de>,
         {
-            match self.content {
-                // As a special case, allow deserializing untagged newtype
-                // variant containing unit struct.
-                //
-                //     #[derive(Deserialize)]
-                //     struct Info;
-                //
-                //     #[derive(Deserialize)]
-                //     #[serde(tag = "topic")]
-                //     enum Message {
-                //         Info(Info),
-                //     }
-                //
-                // We want {"topic":"Info"} to deserialize even though
-                // ordinarily unit structs do not deserialize from empty map/seq.
-                Content::Map(ref v) if v.is_empty() => visitor.visit_unit(),
-                Content::Seq(ref v) if v.is_empty() => visitor.visit_unit(),
-                _ => self.deserialize_any(visitor),
-            }
+            // Covered by tests/test_enum_internally_tagged.rs
+            //      newtype_unit_struct
+            self.deserialize_unit(visitor)
         }
 
         fn deserialize_newtype_struct<V>(