// Copyright 2018 Syn Developers
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
use std;
use std::fmt::{self, Display};
use std::iter::FromIterator;
use proc_macro2::{
Delimiter, Group, Ident, LexError, Literal, Punct, Spacing, Span, TokenStream, TokenTree,
};
use buffer::Cursor;
/// The result of a Syn parser.
pub type Result<T> = std::result::Result<T, Error>;
/// Error returned when a Syn parser cannot parse the input tokens.
///
/// Refer to the [module documentation] for details about parsing in Syn.
///
/// [module documentation]: index.html
///
/// *This type is available if Syn is built with the `"parsing"` feature.*
#[derive(Debug, Clone)]
pub struct Error {
span: Span,
message: String,
}
impl Error {
/// Usually the [`ParseStream::error`] method will be used instead, which
/// automatically uses the correct span from the current position of the
/// parse stream.
///
/// Use `Error::new` when the error needs to be triggered on some span other
/// than where the parse stream is currently positioned.
///
/// [`ParseStream::error`]: struct.ParseBuffer.html#method.error
///
/// # Example
///
/// ```
/// #[macro_use]
/// extern crate syn;
///
/// use syn::{Ident, LitStr};
/// use syn::parse::{Error, ParseStream, Result};
///
/// // Parses input that looks like `name = "string"` where the key must be
/// // the identifier `name` and the value may be any string literal.
/// // Returns the string literal.
/// fn parse_name(input: ParseStream) -> Result<LitStr> {
/// let name_token: Ident = input.parse()?;
/// if name_token != "name" {
/// // Trigger an error not on the current position of the stream,
/// // but on the position of the unexpected identifier.
/// return Err(Error::new(name_token.span(), "expected `name`"));
/// }
/// input.parse::<Token![=]>()?;
/// let s: LitStr = input.parse()?;
/// Ok(s)
/// }
/// #
/// # fn main() {}
/// ```
pub fn new<T: Display>(span: Span, message: T) -> Self {
Error {
span: span,
message: message.to_string(),
}
}
pub fn span(&self) -> Span {
self.span
}
/// Render the error as an invocation of [`compile_error!`].
///
/// The [`parse_macro_input!`] macro provides a convenient way to invoke
/// this method correctly in a procedural macro.
///
/// [`compile_error!`]: https://doc.rust-lang.org/std/macro.compile_error.html
/// [`parse_macro_input!`]: ../macro.parse_macro_input.html
pub fn to_compile_error(&self) -> TokenStream {
// compile_error!($message)
TokenStream::from_iter(vec![
TokenTree::Ident(Ident::new("compile_error", self.span)),
TokenTree::Punct({
let mut punct = Punct::new('!', Spacing::Alone);
punct.set_span(self.span);
punct
}),
TokenTree::Group({
let mut group = Group::new(Delimiter::Brace, {
TokenStream::from_iter(vec![TokenTree::Literal({
let mut string = Literal::string(&self.message);
string.set_span(self.span);
string
})])
});
group.set_span(self.span);
group
}),
])
}
}
pub fn new_at<T: Display>(scope: Span, cursor: Cursor, message: T) -> Error {
if cursor.eof() {
Error::new(scope, format!("unexpected end of input, {}", message))
} else {
Error::new(cursor.span(), message)
}
}
impl Display for Error {
fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
formatter.write_str(&self.message)
}
}
impl std::error::Error for Error {
fn description(&self) -> &str {
"parse error"
}
}
impl From<LexError> for Error {
fn from(err: LexError) -> Self {
Error::new(Span::call_site(), format!("{:?}", err))
}
}