Further simplify deserialization

src/event_id.rs

@@ -7,13 +7,10 @@ use std::{
 
 #[cfg(feature = "diesel")]
 use diesel::sql_types::Text;
-use serde::{
-    de::{Error as SerdeError, Expected, Unexpected},
-    Deserialize, Deserializer, Serialize, Serializer,
-};
+use serde::{Deserialize, Deserializer, Serialize, Serializer};
 use url::Host;
 
-use crate::{display, error::Error, generate_localpart, parse_id};
+use crate::{deserialize_id, display, error::Error, generate_localpart, parse_id};
 
 /// A Matrix event ID.
 ///
@@ -155,10 +152,7 @@ impl<'de> Deserialize<'de> for EventId {
     where
         D: Deserializer<'de>,
     {
-        String::deserialize(deserializer).and_then(|v| {
-            EventId::try_from(&v as &str)
-                .map_err(|_| SerdeError::invalid_value(Unexpected::Str(&v), &ExpectedEventId))
-        })
+        deserialize_id(deserializer, "a Matrix event ID as a string")
     }
 }
 
@@ -189,14 +183,6 @@ impl<'a> TryFrom<&'a str> for EventId {
     }
 }
 
-struct ExpectedEventId;
-
-impl Expected for ExpectedEventId {
-    fn fmt(&self, formatter: &mut Formatter<'_>) -> FmtResult {
-        write!(formatter, "a Matrix event ID as a string")
-    }
-}
-
 #[cfg(test)]
 mod tests {
     use std::convert::TryFrom;

src/lib.rs

@@ -14,9 +14,13 @@
 #[cfg_attr(feature = "diesel", macro_use)]
 extern crate diesel;
 
-use std::fmt::{Formatter, Result as FmtResult};
+use std::{
+    convert::TryFrom,
+    fmt::{Formatter, Result as FmtResult},
+};
 
 use rand::{distributions::Alphanumeric, thread_rng, Rng};
+use serde::de::{self, Deserialize as _, Deserializer, Unexpected};
 use url::Url;
 
 pub use url::Host;
@@ -112,3 +116,16 @@ fn parse_id(required_sigil: char, id: &str) -> Result<(&str, Host, u16), Error>
 
     Ok((localpart, host, port))
 }
+
+/// Deserializes any type of id using the provided TryFrom implementation.
+///
+/// This is a helper function to reduce the boilerplate of the Deserialize implementations.
+fn deserialize_id<'de, D, T>(deserializer: D, expected_str: &str) -> Result<T, D::Error>
+where
+    D: Deserializer<'de>,
+    T: for<'a> TryFrom<&'a str>,
+{
+    String::deserialize(deserializer).and_then(|v| {
+        T::try_from(&v).map_err(|_| de::Error::invalid_value(Unexpected::Str(&v), &expected_str))
+    })
+}

src/room_alias_id.rs

@@ -7,13 +7,10 @@ use std::{
 
 #[cfg(feature = "diesel")]
 use diesel::sql_types::Text;
-use serde::{
-    de::{Error as SerdeError, Expected, Unexpected},
-    Deserialize, Deserializer, Serialize, Serializer,
-};
+use serde::{Deserialize, Deserializer, Serialize, Serializer};
 use url::Host;
 
-use crate::{display, error::Error, parse_id};
+use crate::{deserialize_id, display, error::Error, parse_id};
 
 /// A Matrix room alias ID.
 ///
@@ -80,10 +77,7 @@ impl<'de> Deserialize<'de> for RoomAliasId {
     where
         D: Deserializer<'de>,
     {
-        String::deserialize(deserializer).and_then(|v| {
-            RoomAliasId::try_from(&v as &str)
-                .map_err(|_| SerdeError::invalid_value(Unexpected::Str(&v), &ExpectedRoomAliasId))
-        })
+        deserialize_id(deserializer, "a Matrix room alias ID as a string")
     }
 }
 
@@ -105,14 +99,6 @@ impl<'a> TryFrom<&'a str> for RoomAliasId {
     }
 }
 
-struct ExpectedRoomAliasId;
-
-impl Expected for ExpectedRoomAliasId {
-    fn fmt(&self, formatter: &mut Formatter<'_>) -> FmtResult {
-        write!(formatter, "a Matrix room alias ID as a string")
-    }
-}
-
 #[cfg(test)]
 mod tests {
     use std::convert::TryFrom;

src/room_id.rs

@@ -7,13 +7,10 @@ use std::{
 
 #[cfg(feature = "diesel")]
 use diesel::sql_types::Text;
-use serde::{
-    de::{Error as SerdeError, Expected, Unexpected},
-    Deserialize, Deserializer, Serialize, Serializer,
-};
+use serde::{Deserialize, Deserializer, Serialize, Serializer};
 use url::Host;
 
-use crate::{display, error::Error, generate_localpart, parse_id};
+use crate::{deserialize_id, display, error::Error, generate_localpart, parse_id};
 
 /// A Matrix room ID.
 ///
@@ -95,10 +92,7 @@ impl<'de> Deserialize<'de> for RoomId {
     where
         D: Deserializer<'de>,
     {
-        String::deserialize(deserializer).and_then(|v| {
-            RoomId::try_from(&v as &str)
-                .map_err(|_| SerdeError::invalid_value(Unexpected::Str(&v), &ExpectedRoomId))
-        })
+        deserialize_id(deserializer, "a Matrix room ID as a string")
     }
 }
 
@@ -120,14 +114,6 @@ impl<'a> TryFrom<&'a str> for RoomId {
     }
 }
 
-struct ExpectedRoomId;
-
-impl Expected for ExpectedRoomId {
-    fn fmt(&self, formatter: &mut Formatter<'_>) -> FmtResult {
-        write!(formatter, "a Matrix room ID as a string")
-    }
-}
-
 #[cfg(test)]
 mod tests {
     use std::convert::TryFrom;

src/room_id_or_room_alias_id.rs

@@ -7,12 +7,11 @@ use std::{
 
 #[cfg(feature = "diesel")]
 use diesel::sql_types::Text;
-use serde::{
-    de::{Error as SerdeError, Expected, Unexpected},
-    Deserialize, Deserializer, Serialize, Serializer,
-};
+use serde::{Deserialize, Deserializer, Serialize, Serializer};
 
-use crate::{display, error::Error, room_alias_id::RoomAliasId, room_id::RoomId, validate_id};
+use crate::{
+    deserialize_id, display, error::Error, room_alias_id::RoomAliasId, room_id::RoomId, validate_id,
+};
 
 /// A Matrix room ID or a Matrix room alias ID.
 ///
@@ -83,11 +82,10 @@ impl<'de> Deserialize<'de> for RoomIdOrAliasId {
     where
         D: Deserializer<'de>,
     {
-        String::deserialize(deserializer).and_then(|v| {
-            RoomIdOrAliasId::try_from(&v as &str).map_err(|_| {
-                SerdeError::invalid_value(Unexpected::Str(&v), &ExpectedRoomIdOrAliasId)
-            })
-        })
+        deserialize_id(
+            deserializer,
+            "a Matrix room ID or room alias ID as a string",
+        )
     }
 }
 
@@ -120,14 +118,6 @@ impl<'a> TryFrom<&'a str> for RoomIdOrAliasId {
     }
 }
 
-struct ExpectedRoomIdOrAliasId;
-
-impl Expected for ExpectedRoomIdOrAliasId {
-    fn fmt(&self, formatter: &mut Formatter<'_>) -> FmtResult {
-        write!(formatter, "a Matrix room ID or room alias ID as a string")
-    }
-}
-
 #[cfg(test)]
 mod tests {
     use std::convert::TryFrom;

src/room_version_id.rs

@@ -7,12 +7,9 @@ use std::{
 
 #[cfg(feature = "diesel")]
 use diesel::sql_types::Text;
-use serde::{
-    de::{Error as SerdeError, Expected, Unexpected},
-    Deserialize, Deserializer, Serialize, Serializer,
-};
+use serde::{Deserialize, Deserializer, Serialize, Serializer};
 
-use crate::error::Error;
+use crate::{deserialize_id, error::Error};
 
 /// Room version identifiers cannot be more than 32 code points.
 const MAX_CODE_POINTS: usize = 32;
@@ -154,10 +151,7 @@ impl<'de> Deserialize<'de> for RoomVersionId {
     where
         D: Deserializer<'de>,
     {
-        String::deserialize(deserializer).and_then(|v| {
-            RoomVersionId::try_from(&v as &str)
-                .map_err(|_| SerdeError::invalid_value(Unexpected::Str(&v), &ExpectedRoomVersionId))
-        })
+        deserialize_id(deserializer, "a Matrix room version ID as a string")
     }
 }
 
@@ -187,14 +181,6 @@ impl<'a> TryFrom<&'a str> for RoomVersionId {
     }
 }
 
-struct ExpectedRoomVersionId;
-
-impl Expected for ExpectedRoomVersionId {
-    fn fmt(&self, formatter: &mut Formatter<'_>) -> FmtResult {
-        write!(formatter, "a Matrix room version ID as a string")
-    }
-}
-
 #[cfg(test)]
 mod tests {
     use std::convert::TryFrom;

src/user_id.rs

@@ -7,13 +7,10 @@ use std::{
 
 #[cfg(feature = "diesel")]
 use diesel::sql_types::Text;
-use serde::{
-    de::{Error as SerdeError, Expected, Unexpected},
-    Deserialize, Deserializer, Serialize, Serializer,
-};
+use serde::{Deserialize, Deserializer, Serialize, Serializer};
 use url::Host;
 
-use crate::{display, error::Error, generate_localpart, parse_id};
+use crate::{deserialize_id, display, error::Error, generate_localpart, parse_id};
 
 /// A Matrix user ID.
 ///
@@ -99,10 +96,7 @@ impl<'de> Deserialize<'de> for UserId {
     where
         D: Deserializer<'de>,
     {
-        String::deserialize(deserializer).and_then(|v| {
-            UserId::try_from(&v as &str)
-                .map_err(|_| SerdeError::invalid_value(Unexpected::Str(&v), &ExpectedUserId))
-        })
+        deserialize_id(deserializer, "a Matrix user ID as a string")
     }
 }
 
@@ -133,14 +127,6 @@ impl<'a> TryFrom<&'a str> for UserId {
     }
 }
 
-struct ExpectedUserId;
-
-impl Expected for ExpectedUserId {
-    fn fmt(&self, formatter: &mut Formatter<'_>) -> FmtResult {
-        write!(formatter, "a Matrix user ID as a string")
-    }
-}
-
 #[cfg(test)]
 mod tests {
     use std::convert::TryFrom;