Merge syn-error-experiment
diff --git a/src/next/parse.rs b/src/next/parse.rs
new file mode 100644
index 0000000..447b8e1
--- /dev/null
+++ b/src/next/parse.rs
@@ -0,0 +1,135 @@
+//! Parsing interface for parsing a token stream into a syntax tree node.
+
+use std::cell::Cell;
+use std::fmt::Display;
+use std::marker::PhantomData;
+use std::mem;
+use std::ops::Deref;
+
+use buffer::Cursor;
+use proc_macro2::{Ident, Span};
+
+use super::error;
+
+pub use super::error::{Error, Result};
+pub use super::lookahead::{Lookahead1, Peek};
+
+/// Parsing interface implemented by all types that can be parsed in a default
+/// way from a token stream.
+pub trait Parse: Sized {
+ fn parse(input: ParseStream) -> Result<Self>;
+}
+
+/// Input to a Syn parser function.
+pub type ParseStream<'a> = &'a ParseBuffer<'a>;
+
+/// Cursor position within a buffered token stream.
+#[derive(Clone)]
+pub struct ParseBuffer<'a> {
+ scope: Span,
+ cell: Cell<Cursor<'static>>,
+ marker: PhantomData<Cursor<'a>>,
+}
+
+// Not public API.
+#[doc(hidden)]
+#[derive(Copy, Clone)]
+pub struct StepCursor<'c, 'a> {
+ scope: Span,
+ cursor: Cursor<'c>,
+ marker: PhantomData<fn(Cursor<'c>) -> Cursor<'a>>,
+}
+
+impl<'c, 'a> Deref for StepCursor<'c, 'a> {
+ type Target = Cursor<'c>;
+
+ fn deref(&self) -> &Self::Target {
+ &self.cursor
+ }
+}
+
+impl<'c, 'a> StepCursor<'c, 'a> {
+ // Not public API.
+ #[doc(hidden)]
+ pub fn advance(self, other: Cursor<'c>) -> Cursor<'a> {
+ unsafe { mem::transmute::<Cursor<'c>, Cursor<'a>>(other) }
+ }
+
+ // Not public API.
+ #[doc(hidden)]
+ pub fn error<T: Display>(self, message: T) -> Error {
+ error::new_at(self.scope, self.cursor, message)
+ }
+}
+
+impl<'a> ParseBuffer<'a> {
+ // Not public API.
+ #[doc(hidden)]
+ pub fn new(scope: Span, cursor: Cursor<'a>) -> Self {
+ let extend = unsafe { mem::transmute::<Cursor<'a>, Cursor<'static>>(cursor) };
+ ParseBuffer {
+ scope: scope,
+ cell: Cell::new(extend),
+ marker: PhantomData,
+ }
+ }
+
+ pub fn cursor(&self) -> Cursor<'a> {
+ self.cell.get()
+ }
+
+ pub fn is_empty(&self) -> bool {
+ self.cursor().eof()
+ }
+
+ pub fn lookahead1(&self) -> Lookahead1<'a> {
+ Lookahead1::new(self.scope, self.cursor())
+ }
+
+ pub fn parse<T: Parse>(&self) -> Result<T> {
+ T::parse(self)
+ }
+
+ // Not public API.
+ #[doc(hidden)]
+ pub fn step_cursor<F, R>(&self, function: F) -> Result<R>
+ where
+ F: for<'c> FnOnce(StepCursor<'c, 'a>) -> Result<(R, Cursor<'c>)>,
+ {
+ match function(StepCursor {
+ scope: self.scope,
+ cursor: self.cell.get(),
+ marker: PhantomData,
+ }) {
+ Ok((ret, cursor)) => {
+ self.cell.set(cursor);
+ Ok(ret)
+ }
+ Err(err) => Err(err),
+ }
+ }
+}
+
+impl Parse for Ident {
+ fn parse(input: ParseStream) -> Result<Self> {
+ input.step_cursor(|cursor| {
+ if let Some((ident, rest)) = cursor.ident() {
+ Ok((ident, rest))
+ } else {
+ Err(cursor.error("expected identifier"))
+ }
+ })
+ }
+}
+
+// In reality the impl would be for Punctuated.
+impl<T: Parse> Parse for Vec<T> {
+ fn parse(input: ParseStream) -> Result<Self> {
+ let mut vec = Vec::new();
+ while !input.is_empty() {
+ let t = input.parse::<T>()?;
+ vec.push(t);
+ }
+ Ok(vec)
+ }
+}