Format crates comparison

This document tracks feature parity across all facet format crates.

Legend:

✅ = Fully supported with tests
🟡 = Partial support or untested
🚫 = Not supported
➖ = Not applicable to this format

Note: msgp = facet-msgpack (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-rs)	View
facet-yaml	SD	Text	Event-based (saphyr)	View
facet-toml	SD	Text	DOM (toml_edit)	🚫
facet-msgpack	SD	Binary	Event-based (custom)	🚫
facet-asn1	S	Binary	(Custom)	🚫
facet-xdr	S	Binary	(Custom)	🚫
facet-args	D	CLI	(Custom)	🚫
facet-urlencoded	D	Text	(Custom)	🚫
facet-csv	S	Text	(Custom)	🚫

Scalar Types

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

String Types

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

Lists, Sets, and Maps

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

Compound Types

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

Smart Pointers

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

External Types

Type	json	kdl	yaml	toml	msgp	asn1	xdr	args	urlenc	csv
`chrono`	✅	🟡	✅	🚫	🟡	🚫	🚫	🚫	🚫	🚫
`time`	✅	🟡	✅	🚫	🟡	🚫	🚫	🚫	🚫	🚫
`jiff`	✅	🟡	🟡	🚫	🟡	🚫	🚫	🚫	🚫	🚫
`uuid`	✅	🟡	🟡	🟡	🟡	🚫	🚫	🚫	🚫	🚫
`ulid`	✅	🟡	🟡	🟡	🟡	🚫	🚫	🚫	🚫	🚫
`camino`	✅	🟡	🟡	🟡	🟡	🚫	🚫	🚫	🚫	🚫
`ordered-float`	✅	🟡	🟡	🟡	🟡	🚫	🚫	🚫	🚫	🚫
`bytes`	✅	🟡	🟡	🟡	✅	✅	✅	🚫	🚫	🚫

Struct Types

Type	json	kdl	yaml	toml	msgp	asn1	xdr	args	urlenc	csv
Named structs	✅	✅	✅	✅	✅	✅	✅	✅	✅	✅
Tuple structs	✅	✅	✅	✅	✅	✅	✅	🟡	🟡	✅
Unit structs	✅	✅	✅	✅	✅	✅	✅	✅	🟡	🟡

Enum Representations

Tagging Strategies

Representation	json	kdl	yaml	toml	msgp	asn1	xdr	args	urlenc	csv
Externally tagged (default)	✅	✅	✅	✅	✅	✅	✅	➖	➖	➖
Internally tagged (`tag=`)	✅	🟡	✅	🚫	🟡	🚫	🚫	➖	➖	➖
Adjacently tagged (`tag+content`)	✅	🟡	✅	🚫	🟡	🚫	🚫	➖	➖	➖
Untagged	✅	🟡	✅	🚫	🟡	🚫	🚫	➖	➖	➖

Examples (JSON):

// Externally tagged: { "Variant": "value" }
// Internally tagged: { "type": "Variant", "data": "value" }  
// Adjacently tagged: { "tag": "Variant", "content": "value" }

Attributes

Attribute	json	kdl	yaml	toml	msgp	asn1	xdr	args	urlenc	csv
`rename`	✅	✅	✅	✅	✅	🟡	🟡	✅	✅	🟡
`rename_all`	✅	✅	✅	✅	✅	🟡	🟡	✅	🟡	🟡
`default`	✅	✅	✅	✅	✅	🟡	🟡	✅	✅	🟡
`skip_serializing`	✅	✅	✅	🟡	🟡	🟡	🟡	➖	➖	🟡
`skip_deserializing`	✅	✅	✅	🟡	🟡	➖	➖	🟡	🟡	➖
`skip_serializing_if`	✅	🟡	🟡	🟡	🟡	🟡	🟡	➖	➖	🟡
`transparent`	✅	✅	✅	🟡	✅	🟡	🟡	🟡	🟡	🟡
`flatten`	✅	✅	✅	🚫	🚫	🚫	🚫	🚫	🚫	🚫
`deny_unknown_fields`	✅	✅	🟡	🟡	✅	➖	➖	🚫	✅	➖
`deserialize_with`	✅	✅	🟡	🟡	🟡	➖	➖	🟡	🟡	➖
`serialize_with`	✅	🟡	🟡	🟡	🟡	🟡	🟡	➖	➖	🟡
`type_tag` (KDL-specific)	➖	✅	➖	➖	➖	➖	➖	➖	➖	➖

Diagnostics

Feature	json	kdl	yaml	toml	msgp	asn1	xdr	args	urlenc	csv
`miette::Diagnostic`	✅	✅	✅	🟡	🚫	🚫	🚫	✅	🚫	🚫
`Spanned<T>` wrapper	✅	✅	✅	🚫	🚫	🚫	🚫	✅	🚫	🚫
Solver integration	✅	✅	🟡	🚫	🚫	🚫	🚫	🚫	🚫	🚫
"Did you mean?" suggestions	✅	✅	🚫	🚫	🚫	🚫	🚫	🚫	🚫	🚫

Advanced Features

Feature	json	kdl	yaml	toml	msgp	asn1	xdr	args	urlenc	csv
Nested flatten	✅	✅	🟡	🚫	🚫	🚫	🚫	🚫	🚫	🚫
Multiple flattened enums	✅	✅	🟡	🚫	🚫	🚫	🚫	🚫	🚫	🚫
Value-based disambiguation	✅	✅	🟡	🚫	🚫	🚫	🚫	🚫	🚫	🚫

no_std Support

Feature	json	kdl	yaml	toml	msgp	asn1	xdr	args	urlenc	csv
`no_std` + `alloc`	✅	✅	✅ (deser)	✅	🟡	✅	✅	🟡	🟡	🟡
Serialization	✅	✅	🚫 (needs std)	✅	✅	✅	✅	➖	➖	✅
Deserialization	✅	✅	✅	✅	✅	➖	➖	🟡	🟡	➖