From e3cdf3f386b6a682981e6bdf6ca6d215b0d0788d Mon Sep 17 00:00:00 2001
From: Nadrieril
Date: Thu, 25 Jun 2020 14:06:24 +0100
Subject: spec: not all ABNF parsers like empty rules

---
 dhall/src/syntax/text/dhall.abnf            | 20 ++++++----------
 dhall/src/syntax/text/dhall.pest.visibility |  8 ++-----
 dhall/src/syntax/text/parser.rs             | 37 ++++++++++-------------------
 3 files changed, 21 insertions(+), 44 deletions(-)

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

diff --git a/dhall/src/syntax/text/dhall.abnf b/dhall/src/syntax/text/dhall.abnf
index 05d76e6..362a436 100644
--- a/dhall/src/syntax/text/dhall.abnf
+++ b/dhall/src/syntax/text/dhall.abnf
@@ -896,11 +896,9 @@ primitive-expression =
 
 record-type-or-literal =
       empty-record-literal
-    / non-empty-record-type-or-literal
-    / empty-record-type
+    / [non-empty-record-type-or-literal]
 
 empty-record-literal = "="
-empty-record-type = ""
 
 non-empty-record-type-or-literal =
     (non-empty-record-type / non-empty-record-literal)
@@ -913,22 +911,18 @@ record-type-entry = any-label-or-some whsp ":" whsp1 expression
 non-empty-record-literal =
     record-literal-entry *(whsp "," whsp record-literal-entry)
 
+; If the `record-literal-normal-entry` is absent, that represents a punned
+; record entry, such as in `{ x }`, which is a short-hand for `{ x = x }`
 record-literal-entry =
-    any-label-or-some (record-literal-normal-entry / record-literal-punned-entry)
+    any-label-or-some [record-literal-normal-entry]
 
 record-literal-normal-entry =
     *(whsp "." whsp any-label-or-some) whsp "=" whsp expression
-record-literal-punned-entry = ""
-
 
+; If the `union-type-entry` is absent, that represents an empty union
+; alternative, such as in `< Heads | Tails >`
 union-type =
-      non-empty-union-type
-    / empty-union-type
-
-empty-union-type = ""
-
-non-empty-union-type =
-    union-type-entry *(whsp "|" whsp union-type-entry)
+    [union-type-entry *(whsp "|" whsp union-type-entry)]
 
 ; x : Natural
 ; x
diff --git a/dhall/src/syntax/text/dhall.pest.visibility b/dhall/src/syntax/text/dhall.pest.visibility
index b2114ce..2fee160 100644
--- a/dhall/src/syntax/text/dhall.pest.visibility
+++ b/dhall/src/syntax/text/dhall.pest.visibility
@@ -178,19 +178,15 @@ selector
 labels
 # type_selector
 primitive_expression
-# record_type_or_literal
+record_type_or_literal
 empty_record_literal
-empty_record_type
-non_empty_record_type_or_literal
+# non_empty_record_type_or_literal
 non_empty_record_type
 record_type_entry
 non_empty_record_literal
 record_literal_entry
-# record_literal_punned_entry
 # record_literal_normal_entry
 union_type
-empty_union_type
-# non_empty_union_type
 union_type_entry
 non_empty_list_literal
 # complete_expression
diff --git a/dhall/src/syntax/text/parser.rs b/dhall/src/syntax/text/parser.rs
index e870db3..1c51ca2 100644
--- a/dhall/src/syntax/text/parser.rs
+++ b/dhall/src/syntax/text/parser.rs
@@ -909,26 +909,19 @@ impl DhallParser {
         ))
     }
 
-    #[alias(record_type_or_literal)]
-    fn empty_record_literal(input: ParseInput) -> ParseResult<UnspannedExpr> {
-        Ok(RecordLit(Default::default()))
-    }
-
-    #[alias(record_type_or_literal)]
-    fn empty_record_type(input: ParseInput) -> ParseResult<UnspannedExpr> {
-        Ok(RecordType(Default::default()))
-    }
-
-    #[alias(record_type_or_literal)]
-    fn non_empty_record_type_or_literal(
-        input: ParseInput,
-    ) -> ParseResult<UnspannedExpr> {
+    fn record_type_or_literal(input: ParseInput) -> ParseResult<UnspannedExpr> {
         Ok(match_nodes!(input.children();
+            [empty_record_literal(_)] => RecordLit(Default::default()),
             [non_empty_record_type(map)] => RecordType(map),
             [non_empty_record_literal(map)] => RecordLit(map),
+            [] => RecordType(Default::default()),
         ))
     }
 
+    fn empty_record_literal(input: ParseInput) -> ParseResult<()> {
+        Ok(())
+    }
+
     fn non_empty_record_type(
         input: ParseInput,
     ) -> ParseResult<BTreeMap<Label, Expr>> {
@@ -997,8 +990,7 @@ impl DhallParser {
     }
 
     fn union_type(input: ParseInput) -> ParseResult<UnspannedExpr> {
-        let map = match_nodes!(input.children();
-            [empty_union_type(_)] => Default::default(),
+        Ok(match_nodes!(input.children();
             [union_type_entry(entries)..] => {
                 let mut map = BTreeMap::default();
                 for (l, t) in entries {
@@ -1015,14 +1007,9 @@ impl DhallParser {
                         }
                     }
                 }
-                map
+                UnionType(map)
             },
-        );
-        Ok(UnionType(map))
-    }
-
-    fn empty_union_type(_input: ParseInput) -> ParseResult<()> {
-        Ok(())
+        ))
     }
 
     fn union_type_entry(
@@ -1065,7 +1052,7 @@ pub fn parse_expr(input_str: &str) -> ParseResult<Expr> {
 }
 
 #[test]
-#[ignore]
+#[cfg_attr(windows, ignore)]
 // Check that the local copy of the grammar file is in sync with the one from dhall-lang.
 fn test_grammar_files_in_sync() {
     use std::process::Command;
@@ -1079,8 +1066,8 @@ fn test_grammar_files_in_sync() {
         .arg("--ignore-space-change")
         .arg("--color")
         .arg("--")
-        .arg(spec_abnf_path)
         .arg(local_abnf_path)
+        .arg(spec_abnf_path)
         .output()
         .expect("failed to run `git diff` command");
 
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