Add support for dotted field syntax

2 files changed, 14 insertions, 2 deletions

diff --git a/dhall/src/syntax/ast/span.rs b/dhall/src/syntax/ast/span.rs
index 6d017f6..7c004c5 100644
--- a/dhall/src/syntax/ast/span.rs
+++ b/dhall/src/syntax/ast/span.rs
@@ -18,8 +18,9 @@ pub(crate) struct ParsedSpan {
 pub(crate) enum Span {
     /// A location in the source text
     Parsed(ParsedSpan),
-    /// Desugaring of duplicate fields
+    /// Desugarings
     DuplicateRecordFieldsSugar,
+    DottedFieldSugar,
     /// For expressions obtained from decoding binary
     Decoded,
     /// For expressions constructed during normalization/typecheck
diff --git a/dhall/src/syntax/text/parser.rs b/dhall/src/syntax/text/parser.rs
index f74794b..ba64a75 100644
--- a/dhall/src/syntax/text/parser.rs
+++ b/dhall/src/syntax/text/parser.rs
@@ -915,7 +915,18 @@ impl DhallParser {
 
     fn record_literal_entry(input: ParseInput) -> ParseResult<(Label, Expr)> {
         Ok(match_nodes!(input.into_children();
-            [label(name), expression(expr)] => (name, expr)
+            [label(name), expression(expr)] => (name, expr),
+            [label(first_name), label(names).., expression(expr)] => {
+                // Desugar dotted field syntax into nested records
+                let expr = names.rev().fold(expr, |e, l| {
+                    let map = Some((l, e)).into_iter().collect();
+                    Expr::new(
+                        RecordLit(map),
+                        Span::DottedFieldSugar,
+                    )
+                });
+                (first_name, expr)
+            },
         ))
     }