From 2cb647a1af179662832fb978b90f0b1df6e3dc18 Mon Sep 17 00:00:00 2001
From: Nadrieril
Date: Thu, 25 Jun 2020 13:55:49 +0100
Subject: spec: allow quoted labels to be empty

---
 dhall/src/syntax/text/dhall.abnf | 2 +-
 dhall/src/syntax/text/printer.rs | 4 +++-
 2 files changed, 4 insertions(+), 2 deletions(-)

(limited to 'dhall/src/syntax/text')

diff --git a/dhall/src/syntax/text/dhall.abnf b/dhall/src/syntax/text/dhall.abnf
index 861f7b3..05d76e6 100644
--- a/dhall/src/syntax/text/dhall.abnf
+++ b/dhall/src/syntax/text/dhall.abnf
@@ -206,7 +206,7 @@ quoted-label-char =
         ; %x60 = '`'
     / %x61-7E
 
-quoted-label = 1*quoted-label-char
+quoted-label = *quoted-label-char
 
 ; NOTE: Dhall does not support Unicode labels, mainly to minimize the potential
 ; for code obfuscation
diff --git a/dhall/src/syntax/text/printer.rs b/dhall/src/syntax/text/printer.rs
index ccba385..8815d69 100644
--- a/dhall/src/syntax/text/printer.rs
+++ b/dhall/src/syntax/text/printer.rs
@@ -154,7 +154,9 @@ fn fmt_label(label: &Label, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
         | "True" | "False" | "Some" => true,
         _ => Builtin::parse(&s).is_some(),
     };
-    if !is_reserved && s.chars().all(|c| c.is_ascii_alphanumeric()) {
+    if s.is_empty() {
+        write!(f, "``")
+    } else if !is_reserved && s.chars().all(|c| c.is_ascii_alphanumeric()) {
         write!(f, "{}", s)
     } else {
         write!(f, "`{}`", s)
-- 
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