Capture absence of span in Span itself

3 files changed, 20 insertions, 25 deletions

diff --git a/dhall_syntax/src/core/expr.rs b/dhall_syntax/src/core/expr.rs
index 70ce1dc..750b58b 100644
--- a/dhall_syntax/src/core/expr.rs
+++ b/dhall_syntax/src/core/expr.rs
@@ -1,4 +1,3 @@
-
 use crate::map::{DupTreeMap, DupTreeSet};
 use crate::visitor::{self, ExprFMutVisitor, ExprFVisitor};
 use crate::*;
@@ -143,7 +142,7 @@ pub enum Builtin {
 
 // Each node carries an annotation.
 #[derive(Debug, Clone)]
-pub struct Expr<Embed>(Box<(RawExpr<Embed>, Option<Span>)>);
+pub struct Expr<Embed>(Box<(RawExpr<Embed>, Span)>);
 
 pub type RawExpr<Embed> = ExprF<Expr<Embed>, Embed>;
 
@@ -299,16 +298,12 @@ 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> {
+    pub fn span(&self) -> Span {
         self.0.as_ref().1.clone()
     }
 
-    pub(crate) fn new(x: RawExpr<E>, n: Span) -> Self {
-        Expr(Box::new((x, Some(n))))
-    }
-
-    pub fn from_expr_no_span(x: RawExpr<E>) -> Self {
-        Expr(Box::new((x, None)))
+    pub fn new(x: RawExpr<E>, n: Span) -> Self {
+        Expr(Box::new((x, n)))
     }
 
     pub fn rewrap<E2>(&self, x: RawExpr<E2>) -> Expr<E2> {
@@ -353,11 +348,6 @@ impl<E> Expr<E> {
     }
 }
 
-// Should probably rename this
-pub fn rc<E>(x: RawExpr<E>) -> Expr<E> {
-    Expr::from_expr_no_span(x)
-}
-
 /// Add an isize to an usize
 /// Panics on over/underflow
 fn add_ui(u: usize, i: isize) -> Option<usize> {
diff --git a/dhall_syntax/src/core/span.rs b/dhall_syntax/src/core/span.rs
index f0eb89a..fc8de6e 100644
--- a/dhall_syntax/src/core/span.rs
+++ b/dhall_syntax/src/core/span.rs
@@ -14,10 +14,14 @@ pub struct ParsedSpan {
     end: usize,
 }
 
-/// A location in the source text
 #[derive(Debug, Clone)]
 pub enum Span {
+    /// A location in the source text
     Parsed(ParsedSpan),
+    /// For expressions obtained from decoding binary
+    Decoded,
+    /// For expressions constructed during normalization/typecheck
+    Artificial,
 }
 
 impl Span {
@@ -28,17 +32,22 @@ 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};
         use Span::*;
         match (self, other) {
-            (Parsed(x), Parsed(y)) => Span::Parsed(ParsedSpan {
+            (Parsed(x), Parsed(y)) => Parsed(ParsedSpan {
                 input: x.input.clone(),
                 start: min(x.start, y.start),
                 end: max(x.end, y.end),
             }),
+            _ => panic!(
+                "Tried to union incompatible spans: {:?} and {:?}",
+                self, other
+            ),
         }
     }
 }
diff --git a/dhall_syntax/src/parser.rs b/dhall_syntax/src/parser.rs
index 83f62ee..eaded50 100644
--- a/dhall_syntax/src/parser.rs
+++ b/dhall_syntax/src/parser.rs
@@ -650,7 +650,7 @@ impl DhallParser {
                     final_expr,
                     |acc, x| {
                         spanned_union(
-                            acc.span().unwrap(),
+                            acc.span(),
                             x.3,
                             Let(x.0, x.1, x.2, acc)
                         )
@@ -717,11 +717,7 @@ impl DhallParser {
             r => Err(op.error(format!("Rule {:?} isn't an operator", r)))?,
         };
 
-        Ok(spanned_union(
-            l.span().unwrap(),
-            r.span().unwrap(),
-            BinOp(op, l, r),
-        ))
+        Ok(spanned_union(l.span(), r.span(), BinOp(op, l, r)))
     }
 
     fn Some_(_input: ParseInput) -> ParseResult<()> {
@@ -739,8 +735,8 @@ impl DhallParser {
                     first,
                     |acc, e| {
                         spanned_union(
-                            acc.span().unwrap(),
-                            e.span().unwrap(),
+                            acc.span(),
+                            e.span(),
                             App(acc, e)
                         )
                     }
@@ -778,7 +774,7 @@ impl DhallParser {
                     first,
                     |acc, e| {
                         spanned_union(
-                            acc.span().unwrap(),
+                            acc.span(),
                             e.1,
                             match e.0 {
                                 Either::Left(l) => Field(acc, l),