Fix REPL bug with previous line carryover

src/repl.ts

@@ -208,13 +208,23 @@ export function createRepl(options: CreateReplOptions = {}) {
     context: Context;
   }) {
     const { code, enableTopLevelAwait, context } = options;
-    return appendCompileAndEvalInput({
+    const result = appendCompileAndEvalInput({
       service: service!,
       state,
       input: code,
       enableTopLevelAwait,
       context,
     });
+    // A semicolon is added to make sure that the code doesn't interact with the next line,
+    // for example to prevent `2\n+ 2` from producing 4.
+    // This is safe since the output will not change since we can only get here with successful inputs,
+    // and adding a semicolon to the end of a successful input won't ever change the output.
+    // We check to make sure the previous line ends in a newline just in case, even though it should
+    // always be the case.
+    if (/\n$/.test(state.input)) {
+      state.input = state.input.slice(0, state.input.length - 1) + ';\n';
+    }
+    return result;
   }
 
   function nodeEval(