fix(bind): allow serialization of Some(_) and None values (as the inner value and NULL respectively)

src/sql/mod.rs

@@ -184,20 +184,27 @@ mod tests {
         );
     }
 
+    #[test]
+    fn option_as_null() {
+        let mut sql = SqlBuilder::new("SELECT 1 FROM test WHERE a = ?");
+        sql.bind_arg(None::<u32>);
+        assert_eq!(sql.finish().unwrap(), r"SELECT 1 FROM test WHERE a = NULL");
+    }
+
+    #[test]
+    fn option_as_value() {
+        let mut sql = SqlBuilder::new("SELECT 1 FROM test WHERE a = ?");
+        sql.bind_arg(Some(1u32));
+        assert_eq!(sql.finish().unwrap(), r"SELECT 1 FROM test WHERE a = 1");
+    }
+
     #[test]
     fn failures() {
         let mut sql = SqlBuilder::new("SELECT 1");
         sql.bind_arg(42);
         let err = sql.finish().unwrap_err();
         assert!(err.to_string().contains("all arguments are already bound"));
 
-        let mut sql = SqlBuilder::new("SELECT ?");
-        sql.bind_arg(None::<u32>);
-        let err = sql.finish().unwrap_err();
-        assert!(err
-            .to_string()
-            .contains("invalid argument: serialize_none is unsupported"));
-
         let mut sql = SqlBuilder::new("SELECT ?fields");
         sql.bind_fields::<Unnamed>();
         let err = sql.finish().unwrap_err();

src/sql/ser.rs

@@ -86,7 +86,6 @@ impl<'a, W: Write> Serializer for SqlSerializer<'a, W> {
     unsupported!(
         serialize_map(Option<usize>) -> Result<Impossible>,
         serialize_bytes(&[u8]),
-        serialize_none,
         serialize_unit,
         serialize_unit_struct(&'static str),
     );
@@ -141,7 +140,13 @@ impl<'a, W: Write> Serializer for SqlSerializer<'a, W> {
 
     #[inline]
     fn serialize_some<T: Serialize + ?Sized>(self, _value: &T) -> Result {
-        Err(SqlSerializerError::Unsupported("serialize_some"))
+        _value.serialize(self)
+    }
+
+    #[inline]
+    fn serialize_none(self) -> std::result::Result<Self::Ok, Self::Error> {
+        self.writer.write_str("NULL")?;
+        Ok(())
     }
 
     #[inline]
@@ -340,8 +345,8 @@ mod tests {
     fn it_fails_on_unsupported() {
         let mut out = String::new();
         assert!(write_arg(&mut out, &std::collections::HashMap::<u32, u32>::new()).is_err());
-        assert!(write_arg(&mut out, &None::<u32>).is_err());
-        assert!(write_arg(&mut out, &Some(42)).is_err());
+        assert!(write_arg(&mut out, &None::<u32>).is_ok());
+        assert!(write_arg(&mut out, &Some(42)).is_ok());
         assert!(write_arg(&mut out, &()).is_err());
 
         #[derive(Serialize)]