Add missing property name to the "property missing" error message (#206)

Author: knutwalker

lib/src/types/serde/element.rs

@@ -46,13 +46,23 @@ pub enum ElementDataValue<'de> {
 
 pub struct ElementDataDeserializer<'de, T> {
     data: T,
+    field_name: Option<&'static str>,
     _lifetime: PhantomData<&'de ()>,
 }
 
 impl<'de, T: ElementData<'de>> ElementDataDeserializer<'de, T> {
     pub fn new(data: T) -> Self {
         Self {
             data,
+            field_name: None,
+            _lifetime: PhantomData,
+        }
+    }
+
+    pub fn with_field_name(data: T, field_name: &'static str) -> Self {
+        Self {
+            data,
+            field_name: Some(field_name),
             _lifetime: PhantomData,
         }
     }
@@ -77,7 +87,7 @@ impl<'de, T: ElementData<'de>> ElementDataDeserializer<'de, T> {
             (
                 BorrowedStr(f),
                 properties.and_then(|p| p.get(f)).map_or_else(
-                    || AdditionalData::Element(self.data),
+                    || AdditionalData::Element(self.data, f),
                     |v| AdditionalData::Property(v),
                 ),
             )
@@ -270,7 +280,7 @@ impl<'de, T: ElementData<'de>> Deserializer<'de> for ElementDataDeserializer<'de
     where
         V: Visitor<'de>,
     {
-        Err(DeError::PropertyMissingButRequired)
+        Err(DeError::PropertyMissingButRequired(self.field_name))
     }
 }
 
@@ -490,7 +500,7 @@ impl<'de> IntoDeserializer<'de, DeError> for BorrowedStr<'de> {
 #[derive(Copy, Clone, Debug)]
 enum AdditionalData<'de, T> {
     Property(&'de BoltType),
-    Element(T),
+    Element(T, &'static str),
 }
 
 enum AdditionalDataDeserializer<'de, T> {
@@ -544,9 +554,9 @@ impl<'de, T: ElementData<'de>> IntoDeserializer<'de, DeError> for AdditionalData
             AdditionalData::Property(v) => {
                 AdditionalDataDeserializer::Property(v.into_deserializer())
             }
-            AdditionalData::Element(v) => {
-                AdditionalDataDeserializer::Element(ElementDataDeserializer::new(v))
-            }
+            AdditionalData::Element(v, field_name) => AdditionalDataDeserializer::Element(
+                ElementDataDeserializer::with_field_name(v, field_name),
+            ),
         }
     }
 }

lib/src/types/serde/error.rs

@@ -56,13 +56,14 @@ pub enum DeError {
     NoSuchProperty,
 
     #[error(
-        "The property is missing but the deserializer still expects a value. \
+        "{} is missing but the deserializer still expects a value. \
         If you have an optional property with a default value, you need to \
         use an Option<T> instead (the default attribute does not work in \
         this particular instance). If you meant to extract additional data \
-        other than properties, you need to use the appropriate struct wrapper."
+        other than properties, you need to use the appropriate struct wrapper.",
+        property_missing_msg(.0)
     )]
-    PropertyMissingButRequired,
+    PropertyMissingButRequired(Option<&'static str>),
 
     #[error("{0}")]
     Other(String),
@@ -74,6 +75,13 @@ pub enum DeError {
     DateTimeOutOfBounds(&'static str),
 }
 
+fn property_missing_msg(field_name: &Option<&'static str>) -> String {
+    match field_name {
+        Some(field_name) => format!("The property `{}`", field_name),
+        None => "A property".to_owned(),
+    }
+}
+
 /// `Unexpected` represents an unexpected invocation of any one of the `Visitor`
 /// trait methods.
 ///
@@ -254,3 +262,23 @@ impl Error for DeError {
         Self::Other(msg.to_string())
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn error_message_for_missing_property() {
+        let message = "The property `frobnicate` is missing";
+
+        assert!(DeError::PropertyMissingButRequired(Some("frobnicate"))
+            .to_string()
+            .starts_with(message),);
+
+        let message = "A property is missing";
+
+        assert!(DeError::PropertyMissingButRequired(None)
+            .to_string()
+            .starts_with(message));
+    }
+}

lib/src/types/serde/node.rs

@@ -308,7 +308,10 @@ mod tests {
 
         let node = test_node();
         let actual = node.to::<Person>().unwrap_err();
-        assert!(matches!(actual, DeError::PropertyMissingButRequired));
+        assert!(matches!(
+            actual,
+            DeError::PropertyMissingButRequired(Some("favorite_rust_crate"))
+        ));
     }
 
     #[test]