Crate mf2_model 

mf2-model — the Unicode MessageFormat 2 (MF2) interchange data model as Rust types, plus the identities and error kinds every Rust MF2 crate shares and the Frontend trait a parser implements.

The data model’s structs mirror the specification’s message.json field for field, and code builds them by literal; a later MF2 that defines a new structure adds a variant, which is why the enums are #[non_exhaustive].

• MsgId, Dir — identities shared with the catalog and the runtime.
• is_name_start, is_name_char — the ABNF’s name classes, shared by the two frontends.
• ErrorKind, ErrorClass, Span, Diagnostic, Diagnostics — the 13 error kinds of the WG test suite plus two, and how a frontend reports them.
• Message and everything below it — the specification’s interchange data model, one-to-one.
• Parsed, Frontend — the parser boundary.

Values are kept as written: nothing in this crate normalizes. Names exclude the bidi marks the syntax allows around them (spec, “Names and Identifiers”); equality is exact (bytewise), which is what the round-trip properties of the conformance tests need. Normalization belongs to comparison (validation in mf2-syntax) and to catalog encoding.

#![no_std] + alloc, no dependencies by default. Features: serde (JSON that validates against the specification’s message.json) and suite-names (error kinds ↔ the suite’s strings). The client wasm links only MsgId, Dir and ErrorKind.

The user guide

The Rust MF2 book is the user guide: how the crates fit together, web and native applications, the command line, and what 2.x promises. An application formatting messages starts at mf2; this crate is for tools that work on the data model itself, with mf2-syntax.

Structs

Attributes

The attributes of an expression or markup, in source order; a None value is the spec’s true (an attribute written without a value).

CatchAllKey

The catch-all key. Its value lets other formats keep an identifier; it is always None from MF2 syntax, where the key is written *.

Diagnostic

One reported error. Made with Diagnostic::new; a later version may add fields.

Diagnostics

The errors a frontend or validator reported, in the order reported.

FunctionExpression

An expression with a function and no operand.

FunctionRef

A function reference: its identifier and options.

InputDeclaration

.input {$name …}: binds an external variable, optionally through a function.

Literal

A literal: its cooked value (escapes processed). Whether it was quoted is not data-model information and is not kept.

LiteralExpression

An expression whose operand is a literal.

LocalDeclaration

.local $name = {…}: binds a local variable to an expression.

Markup

Markup: {#name …}, {#name … /} or {/name …}.

MsgId

A message id: which message of a build’s catalogs. tr! and the generated module make them; an application compares, hashes and passes them, and never builds one from a number.

Options

The options of a function or markup, in source order.

Parsed

The result of parsing one message.

Pattern

A pattern: a sequence of parts with no empty Text and no two adjacent Text parts (Pattern::push merges and drops accordingly).

PatternMessage

A message without selectors: declarations and one pattern.

SelectMessage

A message with a matcher: declarations, selectors and variants.

Span

A byte range in the source: start ≤ end ≤ len, both on char boundaries.

VariableExpression

An expression whose operand is a variable.

VariableRef

A variable reference, by name (without the $ sigil).

Variant

A variant: one key per selector, and a pattern.

Enums

Declaration

A declaration.

Dir

Text direction.

ErrorClass

The category of an ErrorKind (spec/errors.md).

ErrorKind

The kind of an MF2 error: the 13 error types of the WG test suite (test/README.md, “Error Codes”) plus Unsupported Operation and the umbrella Message Function Error of spec/errors.md.

Expression

An expression: an operand with an optional function, or a function alone.

Key

A variant key.

MarkupKind

The three forms of markup.

Message

A message: a single pattern, or a selection among variants.

OptionValue

An option’s value: a literal or a variable.

PatternPart

One element of a Pattern.

Traits

Frontend

A parser from MF2 source to the data model.

Functions

is_name_char

name-char = name-start / DIGIT / "-" / ".".

is_name_start

name-start: an ASCII letter, +, _, or a non-ASCII character that is not whitespace, a bidi control, a surrogate, a private-use character or a noncharacter.

split_identifier

Splits an identifier at its namespace separator: "ns:name" → (Some("ns"), "name"), "name" → (None, "name"). A name cannot contain :, so the first colon is the separator.