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use proc_macro2::{Span, TokenStream};
use quote::ToTokens;
use syn::parse::{Parse, ParseStream};
use syn::{Attribute, Error, Expr, Fields, Result, Stmt, Token, Visibility};
use crate::emit::Kind;
pub enum Input {
Enum(syn::ItemEnum),
Match(syn::ExprMatch),
Struct(syn::ItemStruct),
Let(syn::ExprMatch),
}
impl Input {
pub fn kind(&self) -> Kind {
match self {
Input::Enum(_) => Kind::Enum,
Input::Match(_) => Kind::Match,
Input::Struct(_) => Kind::Struct,
Input::Let(_) => Kind::Let,
}
}
}
impl Parse for Input {
fn parse(input: ParseStream) -> Result<Self> {
let ahead = input.fork();
let _ = ahead.call(Attribute::parse_outer)?;
if ahead.peek(Token![match]) {
let expr = match input.parse()? {
Expr::Match(expr) => expr,
_ => unreachable!("expected match"),
};
return Ok(Input::Match(expr));
}
if ahead.peek(Token![let]) {
let stmt = match input.parse()? {
Stmt::Local(stmt) => stmt,
_ => unreachable!("expected let"),
};
let init = match stmt.init {
Some((_, init)) => *init,
None => return Err(unexpected()),
};
let expr = match init {
Expr::Match(expr) => expr,
_ => return Err(unexpected()),
};
return Ok(Input::Let(expr));
}
let _: Visibility = ahead.parse()?;
if ahead.peek(Token![enum]) {
return input.parse().map(Input::Enum);
} else if ahead.peek(Token![struct]) {
let input: syn::ItemStruct = input.parse()?;
if let Fields::Named(_) = &input.fields {
return Ok(Input::Struct(input));
}
}
Err(unexpected())
}
}
impl ToTokens for Input {
fn to_tokens(&self, tokens: &mut TokenStream) {
match self {
Input::Enum(item) => item.to_tokens(tokens),
Input::Struct(item) => item.to_tokens(tokens),
Input::Match(expr) | Input::Let(expr) => expr.to_tokens(tokens),
}
}
}
fn unexpected() -> Error {
let span = Span::call_site();
let msg = "expected enum, struct, or match expression";
Error::new(span, msg)
}
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