From 67df3a69238ef159df63340a40dc3d0cd88c6992 Mon Sep 17 00:00:00 2001
From: ammkrn <ammkrn@tuta.io>
Date: Sat, 19 Jun 2021 11:29:31 -0500
Subject: [PATCH] More specific error for leading pipes

---
 lib/ungrammar/Cargo.toml    | 2 +-
 lib/ungrammar/src/parser.rs | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/lib/ungrammar/Cargo.toml b/lib/ungrammar/Cargo.toml
index 56dbc825fa..18c9dffecf 100644
--- a/lib/ungrammar/Cargo.toml
+++ b/lib/ungrammar/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "ungrammar"
 description = "A DSL for describing concrete syntax trees"
-version = "1.14.0"
+version = "1.14.1"
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/matklad/ungrammar"
 authors = ["Aleksey Kladov <aleksey.kladov@gmail.com>"]
diff --git a/lib/ungrammar/src/parser.rs b/lib/ungrammar/src/parser.rs
index bd067f22a5..a4ce9c1202 100644
--- a/lib/ungrammar/src/parser.rs
+++ b/lib/ungrammar/src/parser.rs
@@ -109,6 +109,14 @@ fn node(p: &mut Parser) -> Result<()> {
 }
 
 fn rule(p: &mut Parser) -> Result<Rule> {
+    if let Some(lexer::Token { kind: TokenKind::Pipe, loc }) = p.peek() {
+        bail!(
+            *loc,
+            "The first element in a sequence of productions or alternatives \
+            must not have a leading pipe (`|`)"
+        );
+    }
+
     let lhs = seq_rule(p)?;
     let mut alt = vec![lhs];
     while let Some(token) = p.peek() {