repl: fix error message printing

The REPL implementation would strip away the first and last character of a formatted error message if it ended with `]` (but with the obviously missing check for a starting `]`), leading to things like `Uncaught rror: foo[a` being printed for input like `Error: foo[a]`. Refs: #22436
nodejs · addaleax · Apr 12, 2021 · Apr 12, 2021 · Apr 12, 2021 · a4824874fb8e3f3802ebd2f7bbf5885d18f0f7e6
commit a4824874fb8e3f3802ebd2f7bbf5885d18f0f7e6
diff --git a/lib/repl.js b/lib/repl.js
@@ -651,7 +651,7 @@ function REPLServer(prompt,
         errStack = self.writer(e);
 
         // Remove one line error braces to keep the old style in place.
-        if (errStack[errStack.length - 1] === ']') {
+        if (errStack[0] === '[' && errStack[errStack.length - 1] === ']') {
           errStack = StringPrototypeSlice(errStack, 1, -1);
         }
       }

diff --git a/test/parallel/test-repl-pretty-stack-custom-writer.js b/test/parallel/test-repl-pretty-stack-custom-writer.js
@@ -0,0 +1,23 @@
+'use strict';
+require('../common');
+const { PassThrough } = require('stream');
+const assert = require('assert');
+const repl = require('repl');
+
+{
+  const input = new PassThrough();
+  const output = new PassThrough();
+
+  const r = repl.start({
+    prompt: '',
+    input,
+    output,
+    writer: String,
+    terminal: false,
+    useColors: false
+  });
+
+  r.write(`throw new Error("foo[a]")\n`);
+  r.close();
+  assert.strictEqual(output.read().toString(), 'Uncaught Error: foo[a]\n');
+}