Format crates comparison

This document tracks feature parity across all facet format crates.

Legend:

Note: msgp = facet-msgpack, pcrd = facet-postcard (shortened for column width)

Overview

Note: S = Serialization, D = Deserialization

Crate	Direction	Format Type	Parser	Showcase
facet-json	SD	Text	Event-based (custom)	View
facet-kdl	SD	Text (node-based)	DOM (kdl)	View
facet-yaml	SD	Text	Event-based (saphyr-parser)	View
facet-toml	SD	Text	Event-based (toml_parser)	View
facet-xml	SD	Text	Event-based (quick-xml)	🚫
facet-msgpack	SD	Binary	Event-based (custom)	🚫
facet-postcard	SD	Binary	Event-based (custom)	🚫
facet-asn1	S	Binary	(Custom)	🚫
facet-xdr	S	Binary	(Custom)	🚫
facet-args	D	CLI	(Custom)	View
facet-urlencoded	D	Text	form_urlencoded	🚫
facet-csv	S	Text	(Custom)	🚫

Type	json	kdl	yaml	toml	xml	msgp	pcrd	asn1	xdr	args	urlenc	csv
`bool`	✅	✅	✅	✅	🟡	✅	✅	✅	✅	✅	🚫	✅
`u8..u64`	✅	✅	✅	✅	🟡	✅	✅	✅	✅	✅	✅	✅
`i8..i64`	✅	✅	✅	✅	🟡	✅	✅	✅	✅	✅	🚫	✅
`u128/i128`	✅	🟡	✅	🟡	🟡	🟡	✅	🟡	🟡	🟡	🟡	🟡
`f32/f64`	✅	✅	✅	✅	🟡	🚫	✅	✅	✅	✅	🚫	✅
`char`	🚫	🟡	✅	🟡	🟡	✅	✅	🟡	🟡	🚫	🚫	✅
NonZero integers	✅	🟡	🟡	🚫	🟡	🟡	🚫	🚫	🚫	🟡	🟡	✅

All formats support String, &str (with best-effort borrowing), and Cow<str>.

Type	json	kdl	yaml	toml	xml	msgp	pcrd	asn1	xdr	args	urlenc	csv
`Vec<T>`	✅	✅	✅	✅	✅	✅	✅	✅	✅	✅	🚫	🚫
`[T; N]` (arrays)	✅	🟡	✅	✅	🟡	✅	✅	✅	✅	🟡	🚫	🚫
`HashSet<T>`	✅	✅	✅	🚫	🟡	🚫	✅	🟡	🚫	🚫	🚫	🚫
`BTreeSet<T>`	✅	✅	✅	🚫	🟡	🚫	✅	🟡	🚫	🚫	🚫	🚫
`HashMap<K, V>`	✅	🟡	✅	✅	🟡	✅	✅	🟡	🚫	🚫	🚫	🚫
`BTreeMap<K, V>`	✅	🟡	✅	✅	🟡	🟡	✅	🟡	🚫	🚫	🚫	🚫
Non-string map keys	✅	🚫	✅	🚫	🚫	✅	✅	🚫	🚫	➖	➖	➖

Type	json	kdl	yaml	toml	xml	msgp	pcrd	asn1	xdr	args	urlenc	csv
`Option<T>`	✅	✅	✅	✅	✅	✅	✅	🟡	✅	✅	🚫	✅
`Result<T, E>`	🚫	🟡	🟡	🚫	🚫	🚫	🟡	🚫	🚫	🚫	🚫	🚫

Type	json	kdl	yaml	toml	xml	msgp	pcrd	asn1	xdr	args	urlenc	csv
`Box<T>`	✅	✅	✅	🚫	🟡	🟡	✅	🟡	🟡	🟡	🚫	🟡
`Rc<T>`	✅	✅	✅	🚫	🟡	🟡	✅	🟡	🟡	🟡	🚫	🟡
`Arc<T>`	✅	✅	✅	🚫	🟡	🟡	✅	🟡	🟡	🟡	🚫	🟡

Attribute	json	kdl	yaml	toml	xml	msgp	pcrd	asn1	xdr	args	urlenc	csv
`opaque`	✅	✅	🚫	🚫	✅	🚫	🚫	🚫	🚫	🚫	🚫	🚫
`proxy`	✅	✅	🚫	🚫	✅	🚫	🚫	🚫	🚫	🚫	🚫	🚫