From 12423e16b7df39b2bf995efd1376ba4b6ef41e02 Mon Sep 17 00:00:00 2001
From: Aaron O'Mullan <aaron.omullan@gmail.com>
Date: Fri, 7 Jan 2022 13:07:58 +0100
Subject: [PATCH] fix(serde_v8): support #[serde(default)] (#13300)

---
 serde_v8/src/de.rs   | 66 ++++++++++++++------------------------------
 serde_v8/tests/de.rs | 16 +++++++++++
 2 files changed, 36 insertions(+), 46 deletions(-)

diff --git a/serde_v8/src/de.rs b/serde_v8/src/de.rs
index 44f94b2d6e1e07..24023b05dde9a9 100644
--- a/serde_v8/src/de.rs
+++ b/serde_v8/src/de.rs
@@ -375,7 +375,7 @@ impl<'de, 'a, 'b, 's, 'x> de::Deserializer<'de>
     // Regular struct
     let obj = v8::Local::<v8::Object>::try_from(self.input)
       .map_err(|_| Error::ExpectedObject)?;
-    let map = ObjectAccess {
+    let struct_access = StructAccess {
       fields,
       obj,
       pos: 0,
@@ -383,7 +383,7 @@ impl<'de, 'a, 'b, 's, 'x> de::Deserializer<'de>
       _cache: None,
     };
 
-    visitor.visit_map(map)
+    visitor.visit_seq(struct_access)
   }
 
   /// To be compatible with `serde-json`, we expect enums to be:
@@ -511,7 +511,7 @@ impl<'de> de::MapAccess<'de> for MapAccess<'_, '_, '_> {
   }
 }
 
-struct ObjectAccess<'a, 'b, 's> {
+struct StructAccess<'a, 'b, 's> {
   obj: v8::Local<'a, v8::Object>,
   scope: &'b mut v8::HandleScope<'s>,
   fields: &'static [&'static str],
@@ -519,57 +519,31 @@ struct ObjectAccess<'a, 'b, 's> {
   _cache: Option<&'b mut KeyCache>,
 }
 
-fn str_deserializer(s: &str) -> de::value::StrDeserializer<Error> {
-  de::IntoDeserializer::into_deserializer(s)
-}
-
-impl<'de, 'a, 'b, 's> de::MapAccess<'de> for ObjectAccess<'a, 'b, 's> {
+impl<'de> de::SeqAccess<'de> for StructAccess<'_, '_, '_> {
   type Error = Error;
 
-  fn next_key_seed<K: de::DeserializeSeed<'de>>(
-    &mut self,
-    seed: K,
-  ) -> Result<Option<K::Value>> {
-    Ok(match self.fields.get(self.pos) {
-      Some(&field) => Some(seed.deserialize(str_deserializer(field))?),
-      None => None,
-    })
-  }
-
-  fn next_value_seed<V: de::DeserializeSeed<'de>>(
+  fn next_element_seed<T: de::DeserializeSeed<'de>>(
     &mut self,
-    seed: V,
-  ) -> Result<V::Value> {
+    seed: T,
+  ) -> Result<Option<T::Value>> {
     if self.pos >= self.fields.len() {
-      return Err(Error::LengthMismatch);
+      return Ok(None);
     }
-    let field = self.fields[self.pos];
+
+    let pos = self.pos;
     self.pos += 1;
-    let key = v8_struct_key(self.scope, field).into();
-    let v8_val = self.obj.get(self.scope, key).unwrap();
-    let mut deserializer = Deserializer::new(self.scope, v8_val, None);
-    seed.deserialize(&mut deserializer)
-  }
 
-  fn next_entry_seed<
-    K: de::DeserializeSeed<'de>,
-    V: de::DeserializeSeed<'de>,
-  >(
-    &mut self,
-    kseed: K,
-    vseed: V,
-  ) -> Result<Option<(K::Value, V::Value)>> {
-    if self.pos >= self.fields.len() {
-      return Ok(None);
+    let field = self.fields[pos];
+    let key = v8_struct_key(self.scope, field).into();
+    let val = self.obj.get(self.scope, key).unwrap();
+    let mut deserializer = Deserializer::new(self.scope, val, None);
+    match seed.deserialize(&mut deserializer) {
+      Ok(val) => Ok(Some(val)),
+      // Fallback to Ok(None) for #[serde(Default)] at cost of error quality ...
+      // TODO(@AaronO): double check that there's no better solution
+      Err(_) if val.is_undefined() => Ok(None),
+      Err(e) => Err(e),
     }
-    let field = self.fields[self.pos];
-    self.pos += 1;
-    Ok(Some((kseed.deserialize(str_deserializer(field))?, {
-      let key = v8_struct_key(self.scope, field).into();
-      let v8_val = self.obj.get(self.scope, key).unwrap();
-      let mut deserializer = Deserializer::new(self.scope, v8_val, None);
-      vseed.deserialize(&mut deserializer)?
-    })))
   }
 }
 
diff --git a/serde_v8/tests/de.rs b/serde_v8/tests/de.rs
index fee532518635fe..da850b579f71f9 100644
--- a/serde_v8/tests/de.rs
+++ b/serde_v8/tests/de.rs
@@ -271,3 +271,19 @@ detest!(de_bigint_i64, i64, "BigInt(-(2**59))", -(1 << 59));
 
 defail!(defail_struct, MathOp, "123", |e| e
   == Err(Error::ExpectedObject));
+
+#[derive(PartialEq, Debug, Deserialize)]
+pub struct SomeThing {
+  pub a: String,
+  #[serde(default)]
+  pub b: String,
+}
+detest!(
+  de_struct_defaults,
+  SomeThing,
+  "({ a: 'hello' })",
+  SomeThing {
+    a: "hello".into(),
+    b: "".into()
+  }
+);