Add ast parsing

Signed-off-by: Marcel Müller <neikos@neikos.email>

src/lib.rs

@@ -5,8 +5,9 @@ use displaydoc::Display;
 use serde::Serialize;
 use thiserror::Error;
 
-pub mod parser;
+pub mod ast;
 pub mod eval;
+pub mod parser;
 
 #[derive(Debug, Error, Display)]
 pub enum TempleError {
@@ -79,6 +80,63 @@ impl Context {
     }
 }
 
+#[derive(Debug, Clone)]
+pub struct SourceSpan {
+    pub range: std::ops::Range<usize>,
+}
+
+// This is just like the standard .resume_after(), except we only resume on Cut errors.
+fn resume_after_cut<Input, Output, Error, ParseNext, ParseRecover>(
+    mut parser: ParseNext,
+    mut recover: ParseRecover,
+) -> impl winnow::Parser<Input, Option<Output>, Error>
+where
+    Input: winnow::stream::Stream + winnow::stream::Recover<Error>,
+    Error: winnow::error::ParserError<Input> + winnow::error::FromRecoverableError<Input, Error>,
+    ParseNext: winnow::Parser<Input, Output, Error>,
+    ParseRecover: winnow::Parser<Input, (), Error>,
+{
+    winnow::combinator::trace("resume_after_cut", move |input: &mut Input| {
+        resume_after_cut_inner(&mut parser, &mut recover, input)
+    })
+}
+
+fn resume_after_cut_inner<P, R, I, O, E>(
+    parser: &mut P,
+    recover: &mut R,
+    i: &mut I,
+) -> winnow::Result<Option<O>, E>
+where
+    P: winnow::Parser<I, O, E>,
+    R: winnow::Parser<I, (), E>,
+    I: winnow::stream::Stream,
+    I: winnow::stream::Recover<E>,
+    E: winnow::error::ParserError<I> + winnow::error::FromRecoverableError<I, E>,
+{
+    let token_start = i.checkpoint();
+    let mut err = match parser.parse_next(i) {
+        Ok(o) => {
+            return Ok(Some(o));
+        }
+        Err(e) if e.is_incomplete() || e.is_backtrack() => {
+            return Err(e);
+        }
+        Err(err) => err,
+    };
+    let err_start = i.checkpoint();
+    if recover.parse_next(i).is_ok() {
+        if let Err(err_) = i.record_err(&token_start, &err_start, err) {
+            err = err_;
+        } else {
+            return Ok(None);
+        }
+    }
+
+    i.reset(&err_start);
+    err = E::from_recoverable_error(&token_start, &err_start, i, err);
+    Err(err)
+}
+
 #[cfg(test)]
 mod tests {
     use crate::Context;