use std;
use std::fmt::{self, Debug, Display};
use std::iter::FromIterator;
use proc_macro2::{
Delimiter, Group, Ident, LexError, Literal, Punct, Spacing, Span, TokenStream, TokenTree,
};
#[cfg(feature = "printing")]
use quote::ToTokens;
#[cfg(feature = "parsing")]
use buffer::Cursor;
#[cfg(all(procmacro2_semver_exempt, feature = "parsing"))]
use private;
use thread::ThreadBound;
/// 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.*
//
// TODO: change the parse module link to an intra rustdoc link, currently
// blocked on https://github.com/rust-lang/rust/issues/62830
pub struct Error {
// Span is implemented as an index into a thread-local interner to keep the
// size small. It is not safe to access from a different thread. We want
// errors to be Send and Sync to play nicely with the Failure crate, so pin
// the span we're given to its original thread and assume it is
// Span::call_site if accessed from any other thread.
start_span: ThreadBound<Span>,
end_span: ThreadBound<Span>,
message: String,
}
#[cfg(test)]
struct _Test
where
Error: Send + Sync;
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`]: crate::parse::ParseBuffer::error
///
/// # Example
///
/// ```edition2018
/// use syn::{Error, Ident, LitStr, Result, Token};
/// use syn::parse::ParseStream;
///
/// // 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)
/// }
/// ```
pub fn new<T: Display>(span: Span, message: T) -> Self {
Error {
start_span: ThreadBound::new(span),
end_span: ThreadBound::new(span),
message: message.to_string(),
}
}
/// Creates an error with the specified message spanning the given syntax
/// tree node.
///
/// Unlike the `Error::new` constructor, this constructor takes an argument
/// `tokens` which is a syntax tree node. This allows the resulting `Error`
/// to attempt to span all tokens inside of `tokens`. While you would
/// typically be able to use the `Spanned` trait with the above `Error::new`
/// constructor, implementation limitations today mean that
/// `Error::new_spanned` may provide a higher-quality error message on
/// stable Rust.
///
/// When in doubt it's recommended to stick to `Error::new` (or
/// `ParseStream::error`)!
#[cfg(feature = "printing")]
pub fn new_spanned<T: ToTokens, U: Display>(tokens: T, message: U) -> Self {
let mut iter = tokens.into_token_stream().into_iter();
let start = iter.next().map_or_else(Span::call_site, |t| t.span());
let end = iter.last().map_or(start, |t| t.span());
Error {
start_span: ThreadBound::new(start),
end_span: ThreadBound::new(end),
message: message.to_string(),
}
}
/// The source location of the error.
///
/// Spans are not thread-safe so this function returns `Span::call_site()`
/// if called from a different thread than the one on which the `Error` was
/// originally created.
pub fn span(&self) -> Span {
let start = match self.start_span.get() {
Some(span) => *span,
None => return Span::call_site(),
};
#[cfg(procmacro2_semver_exempt)]
{
let end = match self.end_span.get() {
Some(span) => *span,
None => return Span::call_site(),
};
start.join(end).unwrap_or(start)
}
#[cfg(not(procmacro2_semver_exempt))]
{
start
}
}
/// 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
pub fn to_compile_error(&self) -> TokenStream {
let start = self
.start_span
.get()
.cloned()
.unwrap_or_else(Span::call_site);
let end = self.end_span.get().cloned().unwrap_or_else(Span::call_site);
// compile_error!($message)
TokenStream::from_iter(vec![
TokenTree::Ident(Ident::new("compile_error", start)),
TokenTree::Punct({
let mut punct = Punct::new('!', Spacing::Alone);
punct.set_span(start);
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(end);
string
})])
});
group.set_span(end);
group
}),
])
}
}
#[cfg(feature = "parsing")]
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 {
#[cfg(procmacro2_semver_exempt)]
let span = private::open_span_of_group(cursor);
#[cfg(not(procmacro2_semver_exempt))]
let span = cursor.span();
Error::new(span, message)
}
}
impl Debug for Error {
fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
formatter.debug_tuple("Error").field(&self.message).finish()
}
}
impl Display for Error {
fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
formatter.write_str(&self.message)
}
}
impl Clone for Error {
fn clone(&self) -> Self {
let start = self
.start_span
.get()
.cloned()
.unwrap_or_else(Span::call_site);
let end = self.end_span.get().cloned().unwrap_or_else(Span::call_site);
Error {
start_span: ThreadBound::new(start),
end_span: ThreadBound::new(end),
message: self.message.clone(),
}
}
}
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))
}
}