Do not allocate unnecessary

Each consumer of MapAccess should consume it fully, so in the end `read_to_end`
actually read only one End tag which name already matches the start name, because
we use reader that checks that

Author: Mingun

Changelog.md

@@ -37,6 +37,7 @@ MSRV bumped to 1.56! Crate now uses Rust 2021 edition.
 - [#649]: Make features linkable and reference them in the docs.
 - [#619]: Allow to raise application errors in `ElementWriter::write_inner_content`
   (and newly added `ElementWriter::write_inner_content_async` of course).
+- [#662]: Get rid of some allocations during serde deserialization.
 
 [#545]: https://github.com/tafia/quick-xml/pull/545
 [#580]: https://github.com/tafia/quick-xml/issues/580
@@ -47,6 +48,7 @@ MSRV bumped to 1.56! Crate now uses Rust 2021 edition.
 [#651]: https://github.com/tafia/quick-xml/pull/651
 [#660]: https://github.com/tafia/quick-xml/pull/660
 [#661]: https://github.com/tafia/quick-xml/pull/661
+[#662]: https://github.com/tafia/quick-xml/pull/662
 
 
 ## 0.30.0 -- 2023-07-23

src/de/map.rs

@@ -289,9 +289,14 @@ where
                     seed.deserialize(de).map(Some)
                 }
                 // Stop iteration after reaching a closing tag
-                DeEvent::End(e) if e.name() == self.start.name() => Ok(None),
-                // This is a unmatched closing tag, so the XML is invalid
-                DeEvent::End(e) => Err(DeError::UnexpectedEnd(e.name().as_ref().to_owned())),
+                // The matching tag name is guaranteed by the reader if our
+                // deserializer implementation is correct
+                DeEvent::End(e) => {
+                    debug_assert_eq!(self.start.name(), e.name());
+                    // Consume End
+                    self.de.next()?;
+                    Ok(None)
+                }
                 // We cannot get `Eof` legally, because we always inside of the
                 // opened tag `self.start`
                 DeEvent::Eof => Err(DeError::UnexpectedEof),

src/de/mod.rs

@@ -2785,13 +2785,7 @@ where
         V: Visitor<'de>,
     {
         match self.next()? {
-            DeEvent::Start(e) => {
-                let name = e.name().as_ref().to_vec();
-                let map = ElementMapAccess::new(self, e, fields)?;
-                let value = visitor.visit_map(map)?;
-                self.read_to_end(QName(&name))?;
-                Ok(value)
-            }
+            DeEvent::Start(e) => visitor.visit_map(ElementMapAccess::new(self, e, fields)?),
             DeEvent::End(e) => Err(DeError::UnexpectedEnd(e.name().as_ref().to_owned())),
             DeEvent::Text(_) => Err(DeError::ExpectedStart),
             DeEvent::Eof => Err(DeError::UnexpectedEof),