Macro define_attr_grammar 

macro_rules! define_attr_grammar {
    ($($grammar:tt)*) => { ... };
}

Define an attribute grammar with type-safe parsing.

This macro generates:

• The attribute types (enum + structs)
• A __parse_attr! macro for parsing attribute tokens
• Re-exports for the necessary proc-macros

Example

facet::define_attr_grammar! {
    pub enum Attr {
        /// Skip this field entirely
        Skip,
        /// Rename to a different name
        Rename(&'static str),
        /// Database column configuration
        Column(Column),
    }

    pub struct Column {
        /// Override the database column name
        pub name: Option<&'static str>,
        /// Mark as primary key
        pub primary_key: bool,
    }
}

This generates an Attr enum and Column struct with the specified fields, along with a __parse_attr! macro that can parse attribute syntax like:

• skip → Attr::Skip
• rename("users") → Attr::Rename("users")
• column(name = "user_id", primary_key) → Attr::Column(Column { name: Some("user_id"), primary_key: true })

Supported Field Types

Grammar Type	Rust Type	Syntax
bool	bool	flag or flag = true
&'static str	&'static str	name = "value"
Option<&'static str>	Option<&'static str>	name = "value" (optional)
Option<bool>	Option<bool>	flag = true (optional)