Update Span to include line and col information

pest::Span and pest::Position both carry a ref to the input text, while
we carry an Rc<String> so we don't have to supply the lifetime
everywhere we use Spans (which is everywhere). They also calculate line
information on-the-fly, while we cache it.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

src/syn/parser.rs

@@ -66,8 +66,8 @@ fn parse_atom(source: &Rc<String>, pair: Pair<Rule>) -> Result<SpAtom> {
     };
     let span = Span {
         source: Rc::clone(source),
-        start: pair_span.start(),
+        start: pair_span.start_pos().into(),
-        end: pair_span.end(),
+        end: pair_span.end_pos().into(),
     };
     Ok(SpAtom::new(span, atom))
 }
@@ -85,8 +85,8 @@ fn parse_expr(source: &Rc<String>, pair: Pair<Rule>) -> Result<SpExpr> {
     };
     let span = Span {
         source: Rc::clone(source),
-        start: pair_span.start(),
+        start: pair_span.start_pos().into(),
-        end: pair_span.end(),
+        end: pair_span.end_pos().into(),
     };
     Ok(SpExpr::new(span, expr))
 }
@@ -100,8 +100,8 @@ fn parse_stmt(source: &Rc<String>, pair: Pair<Rule>) -> Result<SpStmt> {
     };
     let span = Span {
         source: Rc::clone(&source),
-        start: pair_span.start(),
+        start: pair_span.start_pos().into(),
-        end: pair_span.end(),
+        end: pair_span.end_pos().into(),
     };
     Ok(SpStmt::new(span, stmt))
 }

src/syn/span.rs

@@ -3,12 +3,28 @@
 use std::fmt::{self, Debug};
 use std::rc::Rc;
 
+#[derive(Debug, Default, Clone, PartialEq, Eq)]
+pub struct Pos {
+    /// The byte index of this position.
+    pub source: usize,
+    pub line: usize,
+    pub col: usize,
+}
+
+impl From<pest::Position<'_>> for Pos {
+    fn from(other: pest::Position) -> Self {
+        let (line, col) = other.line_col();
+        let source = other.pos();
+        Pos { source, line, col }
+    }
+}
+
 #[cfg_attr(not(test), derive(PartialEq))]
 #[derive(Debug, Default, Clone, Eq)]
 pub struct Span {
     pub source: Rc<String>,
-    pub start: usize,
+    pub start: Pos,
-    pub end: usize,
+    pub end: Pos,
 }
 
 #[cfg(test)]