Support Option in from_dynamic.

CHANGELOG.md

@@ -9,6 +9,11 @@ Compiler requirement
 
 * Minimum compiler version is bumped to 1.51.
 
+Bug fixes
+---------
+
+* `from_dynamic` now supports deserializing `Option`.
+
 Enhancements
 ------------
 

src/serde/de.rs

@@ -365,8 +365,15 @@ impl<'de> Deserializer<'de> for &mut DynamicDeserializer<'de> {
         self.type_error()
     }
 
-    fn deserialize_option<V: Visitor<'de>>(self, _: V) -> Result<V::Value, Box<EvalAltResult>> {
-        self.type_error()
+    fn deserialize_option<V: Visitor<'de>>(
+        self,
+        visitor: V,
+    ) -> Result<V::Value, Box<EvalAltResult>> {
+        if self.value.is::<()>() {
+            visitor.visit_none()
+        } else {
+            visitor.visit_some(self)
+        }
     }
 
     fn deserialize_unit<V: Visitor<'de>>(self, visitor: V) -> Result<V::Value, Box<EvalAltResult>> {

tests/serde.rs

@@ -746,3 +746,32 @@ fn test_serde_json() -> serde_json::Result<()> {
 
     Ok(())
 }
+
+#[test]
+#[cfg(not(feature = "no_object"))]
+fn test_serde_optional() -> Result<(), Box<EvalAltResult>> {
+    #[derive(Debug, Clone, PartialEq, Eq, Deserialize)]
+    struct TestStruct {
+        foo: Option<char>,
+    }
+
+    let mut engine = Engine::new();
+    engine.register_type_with_name::<TestStruct>("TestStruct");
+
+    let r = engine.eval::<Dynamic>("#{ foo: 'a' }")?;
+
+    assert_eq!(
+        from_dynamic::<TestStruct>(&r)?,
+        TestStruct { foo: Some('a') }
+    );
+
+    let r = engine.eval::<Dynamic>("#{ foo: () }")?;
+
+    assert_eq!(from_dynamic::<TestStruct>(&r)?, TestStruct { foo: None });
+
+    let r = engine.eval::<Dynamic>("#{ }")?;
+
+    assert_eq!(from_dynamic::<TestStruct>(&r)?, TestStruct { foo: None });
+
+    Ok(())
+}