Store Spans at every node when parsing

2 files changed, 51 insertions, 17 deletions

diff --git a/dhall_syntax/src/core/expr.rs b/dhall_syntax/src/core/expr.rs
index 2cb23c9..455e42a 100644
--- a/dhall_syntax/src/core/expr.rs
+++ b/dhall_syntax/src/core/expr.rs
@@ -37,6 +37,16 @@ impl Span {
             end: sp.end(),
         }
     }
+    /// Takes the union of the two spans. Assumes that the spans come from the same input.
+    /// This will also capture any input between the spans.
+    pub fn union(&self, other: &Span) -> Self {
+        use std::cmp::{max, min};
+        Span {
+            input: self.input.clone(),
+            start: min(self.start, other.start),
+            end: max(self.start, other.start),
+        }
+    }
 }
 
 /// Double with bitwise equality
@@ -324,8 +334,11 @@ impl<E> Expr<E> {
     pub fn as_mut(&mut self) -> &mut RawExpr<E> {
         &mut self.0.as_mut().0
     }
+    pub fn span(&self) -> Option<&Span> {
+        self.0.as_ref().1.as_ref()
+    }
 
-    pub fn new(x: RawExpr<E>, n: Span) -> Self {
+    pub(crate) fn new(x: RawExpr<E>, n: Span) -> Self {
         Expr(Box::new((x, Some(n))))
     }
 
@@ -387,9 +400,6 @@ pub fn rc<E>(x: RawExpr<E>) -> Expr<E> {
 pub(crate) fn spanned<E>(span: Span, x: RawExpr<E>) -> Expr<E> {
     Expr::new(x, span)
 }
-pub(crate) fn unspanned<E>(x: RawExpr<E>) -> Expr<E> {
-    Expr::from_expr_no_span(x)
-}
 
 /// Add an isize to an usize
 /// Panics on over/underflow
diff --git a/dhall_syntax/src/parser.rs b/dhall_syntax/src/parser.rs
index 3f961e8..4cce5ed 100644
--- a/dhall_syntax/src/parser.rs
+++ b/dhall_syntax/src/parser.rs
@@ -783,7 +783,12 @@ impl Parsers {
             [let_binding(bindings).., expression(final_expr)] => {
                 bindings.rev().fold(
                     final_expr,
-                    |acc, x| unspanned(Let(x.0, x.1, x.2, acc))
+                    |acc, x| {
+                        spanned(
+                            acc.span().unwrap().union(&x.3),
+                            Let(x.0, x.1, x.2, acc)
+                        )
+                    }
                 )
             },
             [forall(()), label(l), expression(typ),
@@ -811,12 +816,12 @@ impl Parsers {
 
     fn let_binding<E: Clone>(
         input: ParseInput<Rule>,
-    ) -> ParseResult<(Label, Option<Expr<E>>, Expr<E>)> {
+    ) -> ParseResult<(Label, Option<Expr<E>>, Expr<E>, Span)> {
         Ok(parse_children!(input;
             [label(name), expression(annot), expression(expr)] =>
-                (name, Some(annot), expr),
+                (name, Some(annot), expr, input.as_span()),
             [label(name), expression(expr)] =>
-                (name, None, expr),
+                (name, None, expr, input.as_span()),
         ))
     }
 
@@ -847,7 +852,10 @@ impl Parsers {
             r => Err(input.error(format!("Rule {:?} isn't an operator", r)))?,
         };
 
-        Ok(unspanned(BinOp(op, l, r)))
+        Ok(spanned(
+            l.span().unwrap().union(r.span().unwrap()),
+            BinOp(op, l, r),
+        ))
     }
 
     fn Some_(_input: ParseInput<Rule>) -> ParseResult<()> {
@@ -861,7 +869,15 @@ impl Parsers {
         Ok(parse_children!(input;
             [expression(e)] => e,
             [expression(first), expression(rest)..] => {
-                rest.fold(first, |acc, e| unspanned(App(acc, e)))
+                rest.fold(
+                    first,
+                    |acc, e| {
+                        spanned(
+                            acc.span().unwrap().union(e.span().unwrap()),
+                            App(acc, e)
+                        )
+                    }
+                )
             },
         ))
     }
@@ -892,20 +908,28 @@ impl Parsers {
         Ok(parse_children!(input;
             [expression(e)] => e,
             [expression(first), selector(rest)..] => {
-                rest.fold(first, |acc, e| unspanned(match e {
-                    Either::Left(l) => Field(acc, l),
-                    Either::Right(ls) => Projection(acc, ls),
-                }))
+                rest.fold(
+                    first,
+                    |acc, e| {
+                        spanned(
+                            acc.span().unwrap().union(&e.1),
+                            match e.0 {
+                                Either::Left(l) => Field(acc, l),
+                                Either::Right(ls) => Projection(acc, ls),
+                            }
+                        )
+                    }
+                )
             },
         ))
     }
 
     fn selector(
         input: ParseInput<Rule>,
-    ) -> ParseResult<Either<Label, DupTreeSet<Label>>> {
+    ) -> ParseResult<(Either<Label, DupTreeSet<Label>>, Span)> {
         Ok(parse_children!(input;
-            [label(l)] => Either::Left(l),
-            [labels(ls)] => Either::Right(ls),
+            [label(l)] => (Either::Left(l), input.as_span()),
+            [labels(ls)] => (Either::Right(ls), input.as_span()),
             // [expression(_e)] => unimplemented!("selection by expression"), // TODO
         ))
     }