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use proc_macro2::{Delimiter, Group, Span, TokenStream, TokenTree};
use quote::{format_ident, quote, ToTokens};
use std::iter::FromIterator;
use syn::parse::{Nothing, ParseStream};
use syn::{
braced, bracketed, parenthesized, token, Attribute, Error, Ident, Index, LitInt, LitStr,
Result, Token,
};
pub struct Attrs<'a> {
pub display: Option<Display<'a>>,
pub source: Option<&'a Attribute>,
pub backtrace: Option<&'a Attribute>,
pub from: Option<&'a Attribute>,
pub transparent: Option<Transparent<'a>>,
}
#[derive(Clone)]
pub struct Display<'a> {
pub original: &'a Attribute,
pub fmt: LitStr,
pub args: TokenStream,
pub has_bonus_display: bool,
}
#[derive(Copy, Clone)]
pub struct Transparent<'a> {
pub original: &'a Attribute,
pub span: Span,
}
pub fn get(input: &[Attribute]) -> Result<Attrs> {
let mut attrs = Attrs {
display: None,
source: None,
backtrace: None,
from: None,
transparent: None,
};
for attr in input {
if attr.path.is_ident("error") {
parse_error_attribute(&mut attrs, attr)?;
} else if attr.path.is_ident("source") {
require_empty_attribute(attr)?;
if attrs.source.is_some() {
return Err(Error::new_spanned(attr, "duplicate #[source] attribute"));
}
attrs.source = Some(attr);
} else if attr.path.is_ident("backtrace") {
require_empty_attribute(attr)?;
if attrs.backtrace.is_some() {
return Err(Error::new_spanned(attr, "duplicate #[backtrace] attribute"));
}
attrs.backtrace = Some(attr);
} else if attr.path.is_ident("from") {
if !attr.tokens.is_empty() {
continue;
}
if attrs.from.is_some() {
return Err(Error::new_spanned(attr, "duplicate #[from] attribute"));
}
attrs.from = Some(attr);
}
}
Ok(attrs)
}
fn parse_error_attribute<'a>(attrs: &mut Attrs<'a>, attr: &'a Attribute) -> Result<()> {
syn::custom_keyword!(transparent);
attr.parse_args_with(|input: ParseStream| {
if let Some(kw) = input.parse::<Option<transparent>>()? {
if attrs.transparent.is_some() {
return Err(Error::new_spanned(
attr,
"duplicate #[error(transparent)] attribute",
));
}
attrs.transparent = Some(Transparent {
original: attr,
span: kw.span,
});
return Ok(());
}
let display = Display {
original: attr,
fmt: input.parse()?,
args: parse_token_expr(input, false)?,
has_bonus_display: false,
};
if attrs.display.is_some() {
return Err(Error::new_spanned(
attr,
"only one #[error(...)] attribute is allowed",
));
}
attrs.display = Some(display);
Ok(())
})
}
fn parse_token_expr(input: ParseStream, mut begin_expr: bool) -> Result<TokenStream> {
let mut tokens = Vec::new();
while !input.is_empty() {
if begin_expr && input.peek(Token![.]) {
if input.peek2(Ident) {
input.parse::<Token![.]>()?;
begin_expr = false;
continue;
}
if input.peek2(LitInt) {
input.parse::<Token![.]>()?;
let int: Index = input.parse()?;
let ident = format_ident!("_{}", int.index, span = int.span);
tokens.push(TokenTree::Ident(ident));
begin_expr = false;
continue;
}
}
begin_expr = input.peek(Token![break])
|| input.peek(Token![continue])
|| input.peek(Token![if])
|| input.peek(Token![in])
|| input.peek(Token![match])
|| input.peek(Token![mut])
|| input.peek(Token![return])
|| input.peek(Token![while])
|| input.peek(Token![+])
|| input.peek(Token![&])
|| input.peek(Token![!])
|| input.peek(Token![^])
|| input.peek(Token![,])
|| input.peek(Token![/])
|| input.peek(Token![=])
|| input.peek(Token![>])
|| input.peek(Token![<])
|| input.peek(Token![|])
|| input.peek(Token![%])
|| input.peek(Token![;])
|| input.peek(Token![*])
|| input.peek(Token![-]);
let token: TokenTree = if input.peek(token::Paren) {
let content;
let delimiter = parenthesized!(content in input);
let nested = parse_token_expr(&content, true)?;
let mut group = Group::new(Delimiter::Parenthesis, nested);
group.set_span(delimiter.span);
TokenTree::Group(group)
} else if input.peek(token::Brace) {
let content;
let delimiter = braced!(content in input);
let nested = parse_token_expr(&content, true)?;
let mut group = Group::new(Delimiter::Brace, nested);
group.set_span(delimiter.span);
TokenTree::Group(group)
} else if input.peek(token::Bracket) {
let content;
let delimiter = bracketed!(content in input);
let nested = parse_token_expr(&content, true)?;
let mut group = Group::new(Delimiter::Bracket, nested);
group.set_span(delimiter.span);
TokenTree::Group(group)
} else {
input.parse()?
};
tokens.push(token);
}
Ok(TokenStream::from_iter(tokens))
}
fn require_empty_attribute(attr: &Attribute) -> Result<()> {
syn::parse2::<Nothing>(attr.tokens.clone())?;
Ok(())
}
impl ToTokens for Display<'_> {
fn to_tokens(&self, tokens: &mut TokenStream) {
let fmt = &self.fmt;
let args = &self.args;
tokens.extend(quote! {
write!(__formatter, #fmt #args)
});
}
}