From 8110651ccf498bcf3f0cd55f3b1730d9972cf254 Mon Sep 17 00:00:00 2001
From: Nadrieril
Date: Fri, 22 Mar 2019 18:12:13 +0100
Subject: Handle quoted labels

---
 dhall/tests/parser.rs     |  2 +-
 dhall_core/src/label.rs   |  7 -------
 dhall_core/src/parser.rs  |  7 ++++++-
 dhall_core/src/printer.rs | 15 +++++++++++++++
 dhall_parser/build.rs     |  2 +-
 5 files changed, 23 insertions(+), 10 deletions(-)

diff --git a/dhall/tests/parser.rs b/dhall/tests/parser.rs
index 637341d..e73e78c 100644
--- a/dhall/tests/parser.rs
+++ b/dhall/tests/parser.rs
@@ -45,7 +45,7 @@ parser_success!(spec_parser_success_operators, "operators");
 // parser_success!(spec_parser_success_parenthesizeUsing, "parenthesizeUsing");
 parser_success!(spec_parser_success_pathTermination, "pathTermination");
 parser_success!(spec_parser_success_paths, "paths");
-// parser_success!(spec_parser_success_quotedLabel, "quotedLabel");
+parser_success!(spec_parser_success_quotedLabel, "quotedLabel");
 parser_success!(spec_parser_success_quotedPaths, "quotedPaths");
 parser_success!(spec_parser_success_record, "record");
 parser_success!(spec_parser_success_reservedPrefix, "reservedPrefix");
diff --git a/dhall_core/src/label.rs b/dhall_core/src/label.rs
index 3633b93..8b371af 100644
--- a/dhall_core/src/label.rs
+++ b/dhall_core/src/label.rs
@@ -1,4 +1,3 @@
-use std::fmt::{self, Display};
 use std::rc::Rc;
 
 // The type for labels throughout the AST
@@ -25,12 +24,6 @@ impl From<Label> for String {
     }
 }
 
-impl Display for Label {
-    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
-        self.0.as_ref().fmt(f)
-    }
-}
-
 impl Label {
     pub fn from_str(s: &str) -> Label {
         Label(s.into())
diff --git a/dhall_core/src/parser.rs b/dhall_core/src/parser.rs
index 165b393..8908c78 100644
--- a/dhall_core/src/parser.rs
+++ b/dhall_core/src/parser.rs
@@ -257,7 +257,12 @@ fn can_be_shortcutted(rule: Rule) -> bool {
 make_parser! {
     rule!(EOI<()>; raw_pair!(_) => ());
 
-    rule!(label_raw<Label>; captured_str!(s) => Label::from(s.trim().to_owned()));
+    rule!(simple_label<Label>; captured_str!(s) => Label::from(s.trim().to_owned()));
+    rule!(quoted_label<Label>; captured_str!(s) => Label::from(s.trim().to_owned()));
+    rule!(label_raw<Label>; children!(
+        [simple_label(l)] => l,
+        [quoted_label(l)] => l,
+    ));
 
     rule!(double_quote_literal<ParsedText>; children!(
         [double_quote_chunk(chunks..)] => {
diff --git a/dhall_core/src/printer.rs b/dhall_core/src/printer.rs
index 7b108d5..508c1c8 100644
--- a/dhall_core/src/printer.rs
+++ b/dhall_core/src/printer.rs
@@ -285,6 +285,21 @@ impl Display for Const {
     }
 }
 
+impl Display for Label {
+    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
+        let s = String::from(self.clone());
+        let is_keyword = |s| match s {
+            "let" | "in" | "if" | "then" | "else" => true,
+            _ => false,
+        };
+        if s.chars().all(|c| c.is_ascii_alphanumeric()) && !is_keyword(&s) {
+            write!(f, "{}", s)
+        } else {
+            write!(f, "`{}`", s)
+        }
+    }
+}
+
 impl Display for Import {
     fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
         use std::path::PathBuf;
diff --git a/dhall_parser/build.rs b/dhall_parser/build.rs
index a07c7e0..fc398ff 100644
--- a/dhall_parser/build.rs
+++ b/dhall_parser/build.rs
@@ -35,7 +35,7 @@ fn main() -> std::io::Result<()> {
     writeln!(&mut file)?;
     writeln!(
         &mut file,
-        "simple_label = _{{
+        "simple_label = {{
               keyword_raw ~ simple_label_next_char+
             | !keyword_raw ~ simple_label_first_char ~ simple_label_next_char*
     }}"
-- 
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