Switch to new serializer

Fixes tafia#252
Fixes tafia#280
Fixes tafia#287
Fixes tafia#343
Fixes tafia#346
Fixes tafia#361
Partially addresses tafia#368
Fixes tafia#429
Fixes tafia#430

Fixes all tests

Co-authored-by: Daniel Alley <dalley@redhat.com>

Changelog.md

@@ -14,11 +14,24 @@
 
 ### Bug Fixes
 
+- [#490]: Ensure that serialization of map keys always produces valid XML names.
+  In particular, that means that maps with numeric and numeric-like keys (for
+  example, `"42"`) no longer can be serialized because [XML name] cannot start
+  from a digit
+
 ### Misc Changes
 
 - [#490]: Removed `$unflatten=` special prefix for fields for serde (de)serializer, because:
   - it is useless for deserializer
   - serializer was rewritten and does not require it anymore
+
+  This prefix allowed you to serialize struct field as an XML element and now
+  replaced by a more thoughtful system explicitly indicating that a field should
+  be serialized as an attribute by prepending `@` character to its name
+- [#490]: Removed `$primitive=` prefix. That prefix allowed you to serialize struct
+  field as an attribute instead of an element and now replaced by a more thoughtful
+  system explicitly indicating that a field should be serialized as an attribute
+  by prepending `@` character to its name
 - [#490]: In addition to the `$value` special name for a field a new `$text`
   special name was added:
   - `$text` is used if you want to map field to text content only. No markup is
@@ -31,6 +44,7 @@
   Refer to [documentation] for details.
 
 [#490]: https://github.com/tafia/quick-xml/pull/490
+[XML name]: https://www.w3.org/TR/xml11/#NT-Name
 [documentation]: https://docs.rs/quick-xml/0.27.0/quick_xml/de/index.html#difference-between-text-and-value-special-names
 
 ## 0.26.0 -- 2022-10-23

README.md

@@ -132,23 +132,6 @@ struct Foo {
 
 Read about the difference in the [documentation](https://docs.rs/quick-xml/latest/quick_xml/de/index.html#difference-between-text-and-value-special-names).
 
-### Serializing unit variants as primitives
-
-The `$primitive` prefix lets you serialize enum variants without associated values (internally referred to as _unit variants_) as primitive strings rather than self-closing tags. Consider the following definitions:
-
-```rust,ignore
-enum Foo {
-    #[serde(rename = "$primitive=Bar")]
-    Bar
-}
-
-struct Root {
-    foo: Foo
-}
-```
-
-Serializing `Root { foo: Foo::Bar }` will then yield `<Root foo="Bar"/>` instead of `<Root><Bar/></Root>`.
-
 ### Performance
 
 Note that despite not focusing on performance (there are several unnecessary copies), it remains about 10x faster than serde-xml-rs.

src/de/mod.rs

@@ -356,7 +356,6 @@ use std::num::NonZeroUsize;
 pub(crate) const TEXT_KEY: &str = "$text";
 /// Data represented by any XML markup inside
 pub(crate) const VALUE_KEY: &str = "$value";
-pub(crate) const PRIMITIVE_PREFIX: &str = "$primitive=";
 
 /// Simplified event which contains only these variants that used by deserializer
 #[derive(Debug, PartialEq, Eq)]