fix: throw an explicit error when there is nothing to repeat

Author: Y

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");
+  });
+});

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()));