repl: fix disruptive autocomplete without inspector

Fix an issue where the autocomplete wrongly autocompletes
a value from a correct value to an undefined value when node
is built without an inspector by disabling the preview view

fixes: nodejs#40635

lib/internal/repl/utils.js

@@ -141,7 +141,7 @@ function isRecoverableError(e, code) {
 
 function setupPreview(repl, contextSymbol, bufferSymbol, active) {
   // Simple terminals can't handle previews.
-  if (process.env.TERM === 'dumb' || !active) {
+  if (process.env.TERM === 'dumb' || !active || !process.features.inspector) {
     return { showPreview() {}, clearPreview() {} };
   }
 

test/parallel/test-repl-preview-without-inspector.js

@@ -0,0 +1,161 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const { REPLServer } = require('repl');
+const { Stream } = require('stream');
+
+if (process.features.inspector)
+  common.skip('test is for node compiled with --without-inspector only');
+
+// Ignore terminal settings. This is so the test can be run intact if TERM=dumb.
+process.env.TERM = '';
+const PROMPT = 'repl > ';
+
+class REPLStream extends Stream {
+  readable = true;
+  writable = true;
+
+  constructor() {
+    super();
+    this.lines = [''];
+  }
+  run(data) {
+    for (const entry of data) {
+      this.emit('data', entry);
+    }
+    this.emit('data', '\n');
+  }
+  write(chunk) {
+    const chunkLines = chunk.toString('utf8').split('\n');
+    this.lines[this.lines.length - 1] += chunkLines[0];
+    if (chunkLines.length > 1) {
+      this.lines.push(...chunkLines.slice(1));
+    }
+    this.emit('line');
+    return true;
+  }
+  wait() {
+    this.lines = [''];
+    return new Promise((resolve, reject) => {
+      const onError = (err) => {
+        this.removeListener('line', onLine);
+        reject(err);
+      };
+      const onLine = () => {
+        if (this.lines[this.lines.length - 1].includes(PROMPT)) {
+          this.removeListener('error', onError);
+          this.removeListener('line', onLine);
+          resolve(this.lines);
+        }
+      };
+      this.once('error', onError);
+      this.on('line', onLine);
+    });
+  }
+  pause() { }
+  resume() { }
+}
+
+function runAndWait(cmds, repl) {
+  const promise = repl.inputStream.wait();
+  for (const cmd of cmds) {
+    repl.inputStream.run(cmd);
+  }
+  return promise;
+}
+
+const repl = REPLServer({
+  prompt: PROMPT,
+  stream: new REPLStream(),
+  ignoreUndefined: true,
+  useColors: true,
+  terminal: true,
+});
+
+repl.inputStream.run([
+  'function foo(x) { return x; }',
+  'function koo() { console.log("abc"); }',
+  'a = undefined;',
+  'const r = 5;',
+]);
+
+const testCases = [{
+  input: 'foo',
+  preview: [
+    'foo\r',
+    '\x1B[36m[Function: foo]\x1B[39m',
+  ]
+}, {
+  input: 'r',
+  preview: [
+    'r\r',
+    '\x1B[33m5\x1B[39m',
+  ]
+}, {
+  input: 'koo',
+  preview: [
+    'koo\r',
+    '\x1B[36m[Function: koo]\x1B[39m',
+  ]
+}, {
+  input: 'a',
+  preview: ['a\r'] // No "undefined" preview.
+}, {
+  input: " { b: 1 }['b'] === 1",
+  preview: [
+    " { b: 1 }['b'] === 1\r",
+    '\x1B[33mtrue\x1B[39m',
+  ]
+}, {
+  input: "{ b: 1 }['b'] === 1;",
+  preview: [
+    "{ b: 1 }['b'] === 1;\r",
+    '\x1B[33mfalse\x1B[39m',
+  ]
+}, {
+  input: '{ a: true }',
+  preview: [
+    '{ a: true }\r',
+    '{ a: \x1B[33mtrue\x1B[39m }',
+  ]
+}, {
+  input: '{ a: true };',
+  preview: [
+    '{ a: true };\r',
+    '\x1B[33mtrue\x1B[39m',
+  ]
+}, {
+  input: ' \t { a: true};',
+  preview: [
+    '  { a: true};\r',
+    '\x1B[33mtrue\x1B[39m',
+  ]
+}, {
+  input: '1n + 2n',
+  preview: [
+    '1n + 2n\r',
+    '\x1B[33m3n\x1B[39m',
+  ]
+}, {
+  input: '{};1',
+  preview: [
+    '{};1\r',
+    '\x1B[33m1\x1B[39m',
+  ],
+}];
+
+async function runTest() {
+  for (const { input, preview } of testCases) {
+    const toBeRun = input.split('\n');
+    let lines = await runAndWait(toBeRun, repl);
+    // Remove error messages. That allows the code to run in different
+    // engines.
+    // eslint-disable-next-line no-control-regex
+    lines = lines.map((line) => line.replace(/Error: .+?\x1B/, ''));
+    assert.strictEqual(lines.pop(), '\x1B[1G\x1B[0Jrepl > \x1B[8G');
+    assert.deepStrictEqual(lines, preview);
+  }
+}
+
+runTest();