chore: import from #1875

Author: indietyp

libs/deer/src/impls/core.rs

@@ -4,5 +4,6 @@ mod bool;
 mod floating;
 mod integral;
 mod non_zero;
+mod option;
 mod string;
 mod unit;

libs/deer/src/impls/core/option.rs

@@ -0,0 +1,53 @@
+use core::marker::PhantomData;
+
+use error_stack::{Result, ResultExt};
+
+use crate::{
+    error::{DeserializeError, VisitorError},
+    Deserialize, Deserializer, Document, OptionalVisitor, Reflection, Schema,
+};
+
+struct OptionVisitor<T>(PhantomData<fn() -> *const T>);
+
+impl<'de, T: Deserialize<'de>> OptionalVisitor<'de> for OptionVisitor<T> {
+    type Value = Option<T>;
+
+    fn expecting(&self) -> Document {
+        Self::Value::reflection()
+    }
+
+    fn visit_none(self) -> Result<Self::Value, VisitorError> {
+        Ok(None)
+    }
+
+    fn visit_null(self) -> Result<Self::Value, VisitorError> {
+        Ok(None)
+    }
+
+    fn visit_some<D>(self, deserializer: D) -> Result<Self::Value, VisitorError>
+    where
+        D: Deserializer<'de>,
+    {
+        T::deserialize(deserializer)
+            .change_context(VisitorError)
+            .map(Some)
+    }
+}
+
+pub struct OptionReflection<T: ?Sized>(PhantomData<fn() -> *const T>);
+
+impl<T: Reflection + ?Sized> Reflection for OptionReflection<T> {
+    fn schema(doc: &mut Document) -> Schema {
+        // TODO: how?!
+        todo!()
+    }
+}
+
+impl<'de, T: Deserialize<'de>> Deserialize<'de> for Option<T> {
+    type Reflection = OptionReflection<T::Reflection>;
+
+    fn deserialize<D: Deserializer<'de>>(de: D) -> Result<Self, DeserializeError> {
+        de.deserialize_optional(OptionVisitor(PhantomData))
+            .change_context(DeserializeError)
+    }
+}