Fix serde-rs#1495: Do not buffer content of the internally tagged enu…

…ms if tag is the first field failures (2): newtype_unit newtype_unit_struct
Mingun · Oct 21, 2024 · 19b34f6 · 19b34f6
1 parent 032dbfc
commit 19b34f6
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Showing 3 changed files with 19 additions and 29 deletions.
diff --git a/serde/src/private/de.rs b/serde/src/private/de.rs
@@ -223,8 +223,7 @@ mod content {
     /// # Parameters
     /// - `map`: map that will be drained
     /// - `tag_name`: name of tag in the `#[serde(tag = "tag_name")]` attribute
-    /// - `tag`: tag, if first value in map was a tag
-    /// - `vec`: placeholder for all other key-value pairs
+    /// - `first_key`: the first key already fetched from the map
     ///
     /// # Returns
     /// A tuple with two values:
@@ -237,13 +236,17 @@ mod content {
     pub fn drain_map<'de, T, A>(
         mut map: A,
         tag_name: &'static str,
-        mut tag: Option<T>,
-        mut vec: Vec<(Content<'de>, Content<'de>)>,
+        first_key: Content<'de>,
     ) -> Result<(T, ContentDeserializer<'de, A::Error>), A::Error>
     where
         T: Deserialize<'de>,
         A: MapAccess<'de>,
     {
+        let mut tag = None;
+        let mut vec =
+            Vec::with_capacity(size_hint::cautious::<(Content, Content)>(map.size_hint()));
+
+        vec.push((first_key, tri!(map.next_value())));
         while let Some(key) = tri!(map.next_key_seed(TagOrContentVisitor::new(tag_name))) {
             match key {
                 TagOrContent::Tag => {

diff --git a/serde_derive/src/de.rs b/serde_derive/src/de.rs
@@ -1440,26 +1440,22 @@ fn deserialize_internally_tagged_enum(
             where
                 __M: _serde::de::MapAccess<#delife>,
             {
-                let mut __vec = _serde::__private::Vec::with_capacity(
-                    _serde::de::MapAccess::size_hint(&__map).unwrap_or(0)
-                );
-
+                // Read the first field. If it is a tag, immediately deserialize the typed data.
+                // Otherwise, we collect everything until we find the tag, and then deserialize
+                // using ContentDeserializer.
                 match _serde::de::MapAccess::next_key_seed(
                     &mut __map, _serde::__private::de::TagOrContentVisitor::new(#tag)
                 )? {
                     _serde::__private::Some(_serde::__private::de::TagOrContent::Tag) => {
                         let __tag = _serde::de::MapAccess::next_value(&mut __map)?;
-                        let (__tag, __deserializer) = _serde::__private::de::drain_map(
-                            __map, #tag, _serde::__private::Some(__tag), __vec
-                        )?;
 
-                        Self::visit(__tag, __deserializer)
+                        Self::visit(__tag, _serde::de::value::MapAccessDeserializer::new(__map))
                     },
                     _serde::__private::Some(_serde::__private::de::TagOrContent::Content(__key)) => {
-                        let __val = _serde::de::MapAccess::next_value(&mut __map)?;
-                        __vec.push((__key, __val));
+                        // Drain map to Content::Map, convert it to ContentDeserializer
+                        // Special handling for tag key -- search them and return as separate result
                         let (__tag, __deserializer) = _serde::__private::de::drain_map(
-                            __map, #tag, _serde::__private::None, __vec
+                            __map, #tag, __key
                         )?;
 
                         Self::visit(__tag, __deserializer)

diff --git a/test_suite/tests/expand/expanded.rs b/test_suite/tests/expand/expanded.rs
@@ -1770,9 +1770,6 @@ mod expand {
                         where
                             __M: _serde::de::MapAccess<'de>,
                         {
-                            let mut __vec = _serde::__private::Vec::with_capacity(
-                                _serde::de::MapAccess::size_hint(&__map).unwrap_or(0),
-                            );
                             match _serde::de::MapAccess::next_key_seed(
                                 &mut __map,
                                 _serde::__private::de::TagOrContentVisitor::new("tag"),
@@ -1781,24 +1778,18 @@ mod expand {
                                     _serde::__private::de::TagOrContent::Tag,
                                 ) => {
                                     let __tag = _serde::de::MapAccess::next_value(&mut __map)?;
-                                    let (__tag, __deserializer) = _serde::__private::de::drain_map(
-                                        __map,
-                                        "tag",
-                                        _serde::__private::Some(__tag),
-                                        __vec,
-                                    )?;
-                                    Self::visit(__tag, __deserializer)
+                                    Self::visit(
+                                        __tag,
+                                        _serde::de::value::MapAccessDeserializer::new(__map),
+                                    )
                                 }
                                 _serde::__private::Some(
                                     _serde::__private::de::TagOrContent::Content(__key),
                                 ) => {
-                                    let __val = _serde::de::MapAccess::next_value(&mut __map)?;
-                                    __vec.push((__key, __val));
                                     let (__tag, __deserializer) = _serde::__private::de::drain_map(
                                         __map,
                                         "tag",
-                                        _serde::__private::None,
-                                        __vec,
+                                        __key,
                                     )?;
                                     Self::visit(__tag, __deserializer)
                                 }