Implement Decode, Encode and Type for Box, Arc, Cow and Rc (#3674)

* feat: implement Decode,Encode,Type for Box,Arc,Cow

* feat implement Encode,Type for Rc

* feat: implement Decode for Rc

* chore: make tests more concise

* chore: use macro's

* chore: remove conflicting impls

* chore: more macro's

* Relax Sized bound for Decode, Encode

* update unit tests

* fixes after review

* add comment in `Decode` impl

* add comment about `ToOwned` trait bound

* add comment explaining why decoding to `Cow::Owned` was chosen

* Remove unnecessary Decode impls

Author: joeydewaal

sqlx-core/src/decode.rs

@@ -1,5 +1,9 @@
 //! Provides [`Decode`] for decoding values from the database.
 
+use std::borrow::Cow;
+use std::rc::Rc;
+use std::sync::Arc;
+
 use crate::database::Database;
 use crate::error::BoxDynError;
 
@@ -77,3 +81,60 @@ where
         }
     }
 }
+
+macro_rules! impl_decode_for_smartpointer {
+    ($smart_pointer:tt) => {
+        impl<'r, DB, T> Decode<'r, DB> for $smart_pointer<T>
+        where
+            DB: Database,
+            T: Decode<'r, DB>,
+        {
+            fn decode(value: <DB as Database>::ValueRef<'r>) -> Result<Self, BoxDynError> {
+                Ok(Self::new(T::decode(value)?))
+            }
+        }
+
+        impl<'r, DB> Decode<'r, DB> for $smart_pointer<str>
+        where
+            DB: Database,
+            &'r str: Decode<'r, DB>,
+        {
+            fn decode(value: <DB as Database>::ValueRef<'r>) -> Result<Self, BoxDynError> {
+                let ref_str = <&str as Decode<DB>>::decode(value)?;
+                Ok(ref_str.into())
+            }
+        }
+
+        impl<'r, DB> Decode<'r, DB> for $smart_pointer<[u8]>
+        where
+            DB: Database,
+            Vec<u8>: Decode<'r, DB>,
+        {
+            fn decode(value: <DB as Database>::ValueRef<'r>) -> Result<Self, BoxDynError> {
+                // The `Postgres` implementation requires this to be decoded as an owned value because
+                // bytes can be sent in text format.
+                let bytes = <Vec<u8> as Decode<DB>>::decode(value)?;
+                Ok(bytes.into())
+            }
+        }
+    };
+}
+
+impl_decode_for_smartpointer!(Arc);
+impl_decode_for_smartpointer!(Box);
+impl_decode_for_smartpointer!(Rc);
+
+// implement `Decode` for Cow<T> for all SQL types
+impl<'r, 'a, DB, T> Decode<'r, DB> for Cow<'a, T>
+where
+    DB: Database,
+    // `ToOwned` is required here to satisfy `Cow`
+    T: ToOwned + ?Sized,
+    <T as ToOwned>::Owned: Decode<'r, DB>,
+{
+    fn decode(value: <DB as Database>::ValueRef<'r>) -> Result<Self, BoxDynError> {
+        // See https://github.com/launchbadge/sqlx/pull/3674#discussion_r2008611502 for more info
+        // about why decoding to a `Cow::Owned` was chosen.
+        <<T as ToOwned>::Owned as Decode<DB>>::decode(value).map(Cow::Owned)
+    }
+}

sqlx-core/src/encode.rs

@@ -1,6 +1,9 @@
 //! Provides [`Encode`] for encoding values for the database.
 
+use std::borrow::Cow;
 use std::mem;
+use std::rc::Rc;
+use std::sync::Arc;
 
 use crate::database::Database;
 use crate::error::BoxDynError;
@@ -129,3 +132,71 @@ macro_rules! impl_encode_for_option {
         }
     };
 }
+
+macro_rules! impl_encode_for_smartpointer {
+    ($smart_pointer:ty) => {
+        impl<'q, T, DB: Database> Encode<'q, DB> for $smart_pointer
+        where
+            T: Encode<'q, DB>,
+        {
+            #[inline]
+            fn encode(
+                self,
+                buf: &mut <DB as Database>::ArgumentBuffer<'q>,
+            ) -> Result<IsNull, BoxDynError> {
+                <T as Encode<DB>>::encode_by_ref(self.as_ref(), buf)
+            }
+
+            #[inline]
+            fn encode_by_ref(
+                &self,
+                buf: &mut <DB as Database>::ArgumentBuffer<'q>,
+            ) -> Result<IsNull, BoxDynError> {
+                <&T as Encode<DB>>::encode(self, buf)
+            }
+
+            #[inline]
+            fn produces(&self) -> Option<DB::TypeInfo> {
+                (**self).produces()
+            }
+
+            #[inline]
+            fn size_hint(&self) -> usize {
+                (**self).size_hint()
+            }
+        }
+    };
+}
+
+impl_encode_for_smartpointer!(Arc<T>);
+impl_encode_for_smartpointer!(Box<T>);
+impl_encode_for_smartpointer!(Rc<T>);
+
+impl<'q, T, DB: Database> Encode<'q, DB> for Cow<'q, T>
+where
+    T: Encode<'q, DB>,
+    T: ToOwned,
+{
+    #[inline]
+    fn encode(self, buf: &mut <DB as Database>::ArgumentBuffer<'q>) -> Result<IsNull, BoxDynError> {
+        <&T as Encode<DB>>::encode_by_ref(&self.as_ref(), buf)
+    }
+
+    #[inline]
+    fn encode_by_ref(
+        &self,
+        buf: &mut <DB as Database>::ArgumentBuffer<'q>,
+    ) -> Result<IsNull, BoxDynError> {
+        <&T as Encode<DB>>::encode_by_ref(&self.as_ref(), buf)
+    }
+
+    #[inline]
+    fn produces(&self) -> Option<DB::TypeInfo> {
+        <&T as Encode<DB>>::produces(&self.as_ref())
+    }
+
+    #[inline]
+    fn size_hint(&self) -> usize {
+        <&T as Encode<DB>>::size_hint(&self.as_ref())
+    }
+}

sqlx-core/src/types/mod.rs

@@ -17,6 +17,8 @@
 //! To represent nullable SQL types, `Option<T>` is supported where `T` implements `Type`.
 //! An `Option<T>` represents a potentially `NULL` value from SQL.
 
+use std::{borrow::Cow, rc::Rc, sync::Arc};
+
 use crate::database::Database;
 use crate::type_info::TypeInfo;
 
@@ -251,3 +253,38 @@ impl<T: Type<DB>, DB: Database> Type<DB> for Option<T> {
         ty.is_null() || <T as Type<DB>>::compatible(ty)
     }
 }
+
+macro_rules! impl_type_for_smartpointer {
+    ($smart_pointer:ty) => {
+        impl<T, DB: Database> Type<DB> for $smart_pointer
+        where
+            T: Type<DB> + ?Sized,
+        {
+            fn type_info() -> DB::TypeInfo {
+                <T as Type<DB>>::type_info()
+            }
+
+            fn compatible(ty: &DB::TypeInfo) -> bool {
+                <T as Type<DB>>::compatible(ty)
+            }
+        }
+    };
+}
+
+impl_type_for_smartpointer!(Arc<T>);
+impl_type_for_smartpointer!(Box<T>);
+impl_type_for_smartpointer!(Rc<T>);
+
+impl<T, DB: Database> Type<DB> for Cow<'_, T>
+where
+    // `ToOwned` is required here to satisfy `Cow`
+    T: Type<DB> + ToOwned + ?Sized,
+{
+    fn type_info() -> DB::TypeInfo {
+        <T as Type<DB>>::type_info()
+    }
+
+    fn compatible(ty: &DB::TypeInfo) -> bool {
+        <T as Type<DB>>::compatible(ty)
+    }
+}

sqlx-mysql/src/types/bytes.rs

@@ -1,3 +1,5 @@
+use std::borrow::Cow;
+
 use crate::decode::Decode;
 use crate::encode::{Encode, IsNull};
 use crate::error::BoxDynError;
@@ -40,28 +42,12 @@ impl<'r> Decode<'r, MySql> for &'r [u8] {
     }
 }
 
-impl Type<MySql> for Box<[u8]> {
-    fn type_info() -> MySqlTypeInfo {
-        <&[u8] as Type<MySql>>::type_info()
-    }
-
-    fn compatible(ty: &MySqlTypeInfo) -> bool {
-        <&[u8] as Type<MySql>>::compatible(ty)
-    }
-}
-
 impl Encode<'_, MySql> for Box<[u8]> {
     fn encode_by_ref(&self, buf: &mut Vec<u8>) -> Result<IsNull, BoxDynError> {
         <&[u8] as Encode<MySql>>::encode(self.as_ref(), buf)
     }
 }
 
-impl<'r> Decode<'r, MySql> for Box<[u8]> {
-    fn decode(value: MySqlValueRef<'r>) -> Result<Self, BoxDynError> {
-        <&[u8] as Decode<MySql>>::decode(value).map(Box::from)
-    }
-}
-
 impl Type<MySql> for Vec<u8> {
     fn type_info() -> MySqlTypeInfo {
         <[u8] as Type<MySql>>::type_info()
@@ -83,3 +69,9 @@ impl Decode<'_, MySql> for Vec<u8> {
         <&[u8] as Decode<MySql>>::decode(value).map(ToOwned::to_owned)
     }
 }
+
+impl Encode<'_, MySql> for Cow<'_, [u8]> {
+    fn encode_by_ref(&self, buf: &mut Vec<u8>) -> Result<IsNull, BoxDynError> {
+        <&[u8] as Encode<MySql>>::encode(self.as_ref(), buf)
+    }
+}

sqlx-mysql/src/types/str.rs

@@ -1,11 +1,12 @@
+use std::borrow::Cow;
+
 use crate::decode::Decode;
 use crate::encode::{Encode, IsNull};
 use crate::error::BoxDynError;
 use crate::io::MySqlBufMutExt;
 use crate::protocol::text::{ColumnFlags, ColumnType};
 use crate::types::Type;
 use crate::{MySql, MySqlTypeInfo, MySqlValueRef};
-use std::borrow::Cow;
 
 impl Type<MySql> for str {
     fn type_info() -> MySqlTypeInfo {
@@ -46,28 +47,12 @@ impl<'r> Decode<'r, MySql> for &'r str {
     }
 }
 
-impl Type<MySql> for Box<str> {
-    fn type_info() -> MySqlTypeInfo {
-        <&str as Type<MySql>>::type_info()
-    }
-
-    fn compatible(ty: &MySqlTypeInfo) -> bool {
-        <&str as Type<MySql>>::compatible(ty)
-    }
-}
-
 impl Encode<'_, MySql> for Box<str> {
     fn encode_by_ref(&self, buf: &mut Vec<u8>) -> Result<IsNull, BoxDynError> {
         <&str as Encode<MySql>>::encode(&**self, buf)
     }
 }
 
-impl<'r> Decode<'r, MySql> for Box<str> {
-    fn decode(value: MySqlValueRef<'r>) -> Result<Self, BoxDynError> {
-        <&str as Decode<MySql>>::decode(value).map(Box::from)
-    }
-}
-
 impl Type<MySql> for String {
     fn type_info() -> MySqlTypeInfo {
         <str as Type<MySql>>::type_info()
@@ -90,16 +75,6 @@ impl Decode<'_, MySql> for String {
     }
 }
 
-impl Type<MySql> for Cow<'_, str> {
-    fn type_info() -> MySqlTypeInfo {
-        <&str as Type<MySql>>::type_info()
-    }
-
-    fn compatible(ty: &MySqlTypeInfo) -> bool {
-        <&str as Type<MySql>>::compatible(ty)
-    }
-}
-
 impl Encode<'_, MySql> for Cow<'_, str> {
     fn encode_by_ref(&self, buf: &mut Vec<u8>) -> Result<IsNull, BoxDynError> {
         match self {
@@ -108,9 +83,3 @@ impl Encode<'_, MySql> for Cow<'_, str> {
         }
     }
 }
-
-impl<'r> Decode<'r, MySql> for Cow<'r, str> {
-    fn decode(value: MySqlValueRef<'r>) -> Result<Self, BoxDynError> {
-        value.as_str().map(Cow::Borrowed)
-    }
-}

sqlx-postgres/src/types/bytes.rs

@@ -1,3 +1,5 @@
+use std::borrow::Cow;
+
 use crate::decode::Decode;
 use crate::encode::{Encode, IsNull};
 use crate::error::BoxDynError;
@@ -80,15 +82,6 @@ fn text_hex_decode_input(value: PgValueRef<'_>) -> Result<&[u8], BoxDynError> {
         .map_err(Into::into)
 }
 
-impl Decode<'_, Postgres> for Box<[u8]> {
-    fn decode(value: PgValueRef<'_>) -> Result<Self, BoxDynError> {
-        Ok(match value.format() {
-            PgValueFormat::Binary => Box::from(value.as_bytes()?),
-            PgValueFormat::Text => Box::from(hex::decode(text_hex_decode_input(value)?)?),
-        })
-    }
-}
-
 impl Decode<'_, Postgres> for Vec<u8> {
     fn decode(value: PgValueRef<'_>) -> Result<Self, BoxDynError> {
         Ok(match value.format() {
@@ -110,3 +103,9 @@ impl<const N: usize> Decode<'_, Postgres> for [u8; N] {
         Ok(bytes)
     }
 }
+
+impl Encode<'_, Postgres> for Cow<'_, [u8]> {
+    fn encode_by_ref(&self, buf: &mut PgArgumentBuffer) -> Result<IsNull, BoxDynError> {
+        <&[u8] as Encode<Postgres>>::encode(self.as_ref(), buf)
+    }
+}

sqlx-postgres/src/types/str.rs

@@ -24,26 +24,6 @@ impl Type<Postgres> for str {
     }
 }
 
-impl Type<Postgres> for Cow<'_, str> {
-    fn type_info() -> PgTypeInfo {
-        <&str as Type<Postgres>>::type_info()
-    }
-
-    fn compatible(ty: &PgTypeInfo) -> bool {
-        <&str as Type<Postgres>>::compatible(ty)
-    }
-}
-
-impl Type<Postgres> for Box<str> {
-    fn type_info() -> PgTypeInfo {
-        <&str as Type<Postgres>>::type_info()
-    }
-
-    fn compatible(ty: &PgTypeInfo) -> bool {
-        <&str as Type<Postgres>>::compatible(ty)
-    }
-}
-
 impl Type<Postgres> for String {
     fn type_info() -> PgTypeInfo {
         <&str as Type<Postgres>>::type_info()
@@ -129,18 +109,6 @@ impl<'r> Decode<'r, Postgres> for &'r str {
     }
 }
 
-impl<'r> Decode<'r, Postgres> for Cow<'r, str> {
-    fn decode(value: PgValueRef<'r>) -> Result<Self, BoxDynError> {
-        Ok(Cow::Borrowed(value.as_str()?))
-    }
-}
-
-impl<'r> Decode<'r, Postgres> for Box<str> {
-    fn decode(value: PgValueRef<'r>) -> Result<Self, BoxDynError> {
-        Ok(Box::from(value.as_str()?))
-    }
-}
-
 impl Decode<'_, Postgres> for String {
     fn decode(value: PgValueRef<'_>) -> Result<Self, BoxDynError> {
         Ok(value.as_str()?.to_owned())