Handle empty optionals correctly

Closes #78

8 files changed, 37 insertions, 9 deletions

diff --git a/dhall/src/binary.rs b/dhall/src/binary.rs
index 8a23e76..72704de 100644
--- a/dhall/src/binary.rs
+++ b/dhall/src/binary.rs
@@ -107,7 +107,7 @@ fn cbor_value_to_dhall(data: &cbor::Value) -> Result<ParsedExpr, DecodeError> {
             }
             [U64(5), t] => {
                 let t = cbor_value_to_dhall(&t)?;
-                EmptyOptionalLit(t)
+                OldOptionalLit(None, t)
             }
             [U64(5), Null, x] => {
                 let x = cbor_value_to_dhall(&x)?;
@@ -116,7 +116,7 @@ fn cbor_value_to_dhall(data: &cbor::Value) -> Result<ParsedExpr, DecodeError> {
             [U64(5), t, x] => {
                 let x = cbor_value_to_dhall(&x)?;
                 let t = cbor_value_to_dhall(&t)?;
-                Annot(rc(NEOptionalLit(x)), t)
+                OldOptionalLit(Some(x), t)
             }
             [U64(6), x, y] => {
                 let x = cbor_value_to_dhall(&x)?;
diff --git a/dhall/src/normalize.rs b/dhall/src/normalize.rs
index 716b7ee..58deb87 100644
--- a/dhall/src/normalize.rs
+++ b/dhall/src/normalize.rs
@@ -265,6 +265,8 @@ fn normalize_ref(expr: &Expr<X, Normalized<'static>>) -> Expr<X, X> {
         BoolIf(BoolLit(false), _, f) => DoneRef(f),
         // TODO: interpolation
         // TextLit(t) =>
+        OldOptionalLit(None, t) => Done(EmptyOptionalLit(t.roll())),
+        OldOptionalLit(Some(x), _) => Done(NEOptionalLit(x.roll())),
         BinOp(BoolAnd, BoolLit(x), BoolLit(y)) => Done(BoolLit(*x && *y)),
         BinOp(BoolOr, BoolLit(x), BoolLit(y)) => Done(BoolLit(*x || *y)),
         BinOp(BoolEQ, BoolLit(x), BoolLit(y)) => Done(BoolLit(x == y)),
diff --git a/dhall/src/tests.rs b/dhall/src/tests.rs
index f57f23f..ce24bfc 100644
--- a/dhall/src/tests.rs
+++ b/dhall/src/tests.rs
@@ -124,7 +124,7 @@ pub fn run_test(
             let expected = parse_file_str(&expected_file_path)?
                 .resolve()?
                 .skip_typecheck()
-                .skip_normalize();
+                .normalize();
 
             match feature {
                 Parser => unreachable!(),
diff --git a/dhall/src/typecheck.rs b/dhall/src/typecheck.rs
index b8f2d86..5162f4f 100644
--- a/dhall/src/typecheck.rs
+++ b/dhall/src/typecheck.rs
@@ -266,6 +266,9 @@ fn type_of_builtin<S>(b: Builtin) -> Expr<S, Normalized<'static>> {
             forall (nothing: optional) ->
             optional
         ),
+        OptionalNone => dhall::expr!(
+            forall (a: Type) -> Optional a
+        ),
         _ => panic!("Unimplemented typecheck case: {:?}", b),
     }
 }
@@ -544,6 +547,17 @@ fn type_last_layer(
             let t = x.get_type_move()?.into_normalized()?.into_expr();
             Ok(RetExpr(dhall::expr!(List t)))
         }
+        OldOptionalLit(None, t) => {
+            let t = t.into_expr();
+            let e = dhall::subexpr!(None t);
+            Ok(RetType(type_with(ctx, e)?.get_type()?.into_owned()))
+        }
+        OldOptionalLit(Some(x), t) => {
+            let x = x.into_expr();
+            let t = t.into_expr();
+            let e = dhall::subexpr!(Some x : Optional t);
+            Ok(RetType(type_with(ctx, e)?.get_type()?.into_owned()))
+        }
         EmptyOptionalLit(t) => {
             let t = t.normalize().into_type();
             ensure_simple_type!(
diff --git a/dhall_core/src/core.rs b/dhall_core/src/core.rs
index 7859c73..c0e04ed 100644
--- a/dhall_core/src/core.rs
+++ b/dhall_core/src/core.rs
@@ -174,6 +174,10 @@ pub enum ExprF<SubExpr, Label, Note, Embed> {
     EmptyListLit(SubExpr),
     ///  [x, y, z]
     NEListLit(Vec<SubExpr>),
+    /// Deprecated Optional literal form
+    ///  [] : Optional a
+    ///  [x] : Optional a
+    OldOptionalLit(Option<SubExpr>, SubExpr),
     ///  None t
     EmptyOptionalLit(SubExpr),
     ///  Some e
diff --git a/dhall_core/src/parser.rs b/dhall_core/src/parser.rs
index cea7cea..c4ae2e5 100644
--- a/dhall_core/src/parser.rs
+++ b/dhall_core/src/parser.rs
@@ -641,13 +641,13 @@ make_parser! {
             spanned(span, EmptyListLit(rc(t)))
         },
         [Optional(_), expression(t)] => {
-            spanned(span, EmptyOptionalLit(rc(t)))
+            spanned(span, OldOptionalLit(None, rc(t)))
         },
     ));
 
     rule!(non_empty_optional<ParsedExpr<'a>> as expression; span; children!(
         [expression(x), Optional(_), expression(t)] => {
-            spanned(span, Annot(rc(NEOptionalLit(rc(x))), rc(t)))
+            spanned(span, OldOptionalLit(Option::Some(rc(x)), rc(t)))
         }
     ));
 
@@ -747,10 +747,6 @@ make_parser! {
 
     rule!(application_expression<ParsedExpr<'a>> as expression; span; children!(
         [expression(e)] => e,
-        [expression(Builtin(crate::Builtin::OptionalNone)),
-                expression(e), expression(rest)..] => {
-            spanned(span, app(EmptyOptionalLit(rc(e)), rest.map(rc).collect()))
-        },
         [Some(()), expression(e), expression(rest)..] => {
             spanned(span, app(NEOptionalLit(rc(e)), rest.map(rc).collect()))
         },
diff --git a/dhall_core/src/printer.rs b/dhall_core/src/printer.rs
index e53c1ec..bb094de 100644
--- a/dhall_core/src/printer.rs
+++ b/dhall_core/src/printer.rs
@@ -32,6 +32,12 @@ impl<SE: Display + Clone, N, E: Display> Display for ExprF<SE, Label, N, E> {
             NEListLit(es) => {
                 fmt_list("[", ", ", "]", es, f, Display::fmt)?;
             }
+            OldOptionalLit(None, t) => {
+                write!(f, "[] : Optional {}", t)?;
+            }
+            OldOptionalLit(Some(x), t) => {
+                write!(f, "[{}] : Optional {}", x, t)?;
+            }
             EmptyOptionalLit(t) => {
                 write!(f, "None {}", t)?;
             }
@@ -149,6 +155,7 @@ impl<S: Clone, A: Display + Clone> Expr<S, A> {
             | Let(_, _, _, _)
             | EmptyListLit(_)
             | NEListLit(_)
+            | OldOptionalLit(_, _)
             | EmptyOptionalLit(_)
             | NEOptionalLit(_)
             | Merge(_, _, _)
@@ -189,6 +196,7 @@ impl<S: Clone, A: Display + Clone> Expr<S, A> {
                 b.phase(PrintPhase::BinOp(op)),
             ),
             EmptyListLit(t) => EmptyListLit(t.phase(Import)),
+            OldOptionalLit(x, t) => OldOptionalLit(x, t.phase(Import)),
             EmptyOptionalLit(t) => EmptyOptionalLit(t.phase(Import)),
             NEOptionalLit(e) => NEOptionalLit(e.phase(Import)),
             ExprF::App(a, args) => ExprF::App(
diff --git a/dhall_core/src/visitor.rs b/dhall_core/src/visitor.rs
index b0424ac..3b06f8b 100644
--- a/dhall_core/src/visitor.rs
+++ b/dhall_core/src/visitor.rs
@@ -148,6 +148,10 @@ where
             ),
             EmptyListLit(t) => EmptyListLit(v.visit_subexpr(t)?),
             NEListLit(es) => NEListLit(vec(es, |e| v.visit_subexpr(e))?),
+            OldOptionalLit(x, t) => OldOptionalLit(
+                opt(x, |e| v.visit_subexpr(e))?,
+                v.visit_subexpr(t)?,
+            ),
             EmptyOptionalLit(t) => EmptyOptionalLit(v.visit_subexpr(t)?),
             NEOptionalLit(e) => NEOptionalLit(v.visit_subexpr(e)?),
             RecordType(kts) => RecordType(btmap(kts, v)?),