From 51c147053e831ad922753b8a4296cde67fa51dd2 Mon Sep 17 00:00:00 2001
From: Amin Yahyaabadi <aminyahyaabadi74@gmail.com>
Date: Sat, 15 May 2021 17:06:32 -0500
Subject: [PATCH] feat: error out if an empty string is in the `extras` array

This prevents never-ending loops in the parser
---
 cli/src/generate/parse_grammar.rs | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/cli/src/generate/parse_grammar.rs b/cli/src/generate/parse_grammar.rs
index 5ae03f3f..fe863276 100644
--- a/cli/src/generate/parse_grammar.rs
+++ b/cli/src/generate/parse_grammar.rs
@@ -120,7 +120,22 @@ pub(crate) fn parse_grammar(input: &str) -> Result<InputGrammar> {
         precedence_orderings.push(ordering);
     }
 
-    let extra_symbols = grammar_json.extras.into_iter().map(parse_rule).collect();
+    let extra_symbols = grammar_json
+        .extras
+        .into_iter()
+        .try_fold(Vec::new(), |mut acc, item| {
+            let rule = parse_rule(item);
+            if let Rule::String(ref value) = rule {
+                if value.is_empty() {
+                    return Err(anyhow!(
+                        "Rules in the `extras` array must not contain empty strings"
+                    ));
+                }
+            }
+            acc.push(rule);
+            Ok(acc)
+        })?;
+
     let external_tokens = grammar_json.externals.into_iter().map(parse_rule).collect();
 
     Ok(InputGrammar {