From d4ca9c94e7ee4ec0d5e008e976f71cd4c6a898b8 Mon Sep 17 00:00:00 2001
From: Y <yves@sutoiku.com>
Date: Fri, 26 Feb 2021 05:36:09 -0500
Subject: [PATCH] fix: throw an explicit error when there is nothing to repeat

---
 assembly/__tests__/regex.spec.ts | 8 ++++++++
 assembly/parser/parser.ts        | 4 ++++
 2 files changed, 12 insertions(+)

diff --git a/assembly/__tests__/regex.spec.ts b/assembly/__tests__/regex.spec.ts
index 691caed..e239556 100644
--- a/assembly/__tests__/regex.spec.ts
+++ b/assembly/__tests__/regex.spec.ts
@@ -155,3 +155,11 @@ describe("use cases", () => {
     expect(match.matches[3]).toBe("com");
   });
 });
+
+describe("error cases", () => {
+  it("throws an explicit error when there is nothing to repeat", () => {
+    expect(() => {
+      let foo = new RegExp("*m", ""); // eslint-disable-line no-invalid-regexp
+    }).toThrow("Invalid regular expression: Nothing to repeat");
+  });
+});
diff --git a/assembly/parser/parser.ts b/assembly/parser/parser.ts
index dad0242..e13aa94 100644
--- a/assembly/parser/parser.ts
+++ b/assembly/parser/parser.ts
@@ -251,6 +251,10 @@ export class Parser {
           nodes.push(this.parseCharacter());
         }
       } else if (isQuantifier(token)) {
+        if (nodes.length === 0) {
+          throw new Error("Invalid regular expression: Nothing to repeat");
+        }
+
         const expression = nodes.pop();
         const quantifier = this.eatToken();
         nodes.push(new RepetitionNode(expression, quantifier, this.isGreedy()));