Handle blocked port

.npmrc

@@ -1 +1,2 @@
 registry=https://registry.npmjs.org
+package-lock=false

lib/_inspect.js

@@ -42,6 +42,13 @@ const [ InspectClient, createRepl ] =
 
 const debuglog = util.debuglog('inspect');
 
+class StartupError extends Error {
+  constructor(message) {
+    super(message);
+    this.name = 'StartupError';
+  }
+}
+
 function portIsFree(host, port, timeout = 2000) {
   if (port === 0) return Promise.resolve();  // Binding to a random port.
 
@@ -51,7 +58,7 @@ function portIsFree(host, port, timeout = 2000) {
   return new Promise((resolve, reject) => {
     setTimeout(() => {
       didTimeOut = true;
-      reject(new Error(
+      reject(new StartupError(
         `Timeout (${timeout}) waiting for ${host}:${port} to be free`));
     }, timeout);
 
@@ -346,10 +353,14 @@ function startInspect(argv = process.argv.slice(2),
   stdin.resume();
 
   function handleUnexpectedError(e) {
-    console.error('There was an internal error in node-inspect. ' +
-                  'Please report this bug.');
-    console.error(e.message);
-    console.error(e.stack);
+    if (!(e instanceof StartupError)) {
+      console.error('There was an internal error in node-inspect. ' +
+                    'Please report this bug.');
+      console.error(e.message);
+      console.error(e.stack);
+    } else {
+      console.error(e.message);
+    }
     if (inspector.child) inspector.child.kill();
     process.exit(1);
   }

test/cli/invalid-args.test.js

@@ -1,4 +1,7 @@
 'use strict';
+const Path = require('path');
+const { createServer } = require('net');
+
 const { test } = require('tap');
 
 const startCLI = require('./start-cli');
@@ -23,3 +26,29 @@ test('launch w/ invalid host:port', (t) => {
       t.equal(code, 1, 'exits with non-zero exit code');
     });
 });
+
+test('launch w/ unavailable port', async (t) => {
+  const blocker = createServer(socket => socket.end());
+  const port = await new Promise((resolve, reject) => {
+    blocker.on('error', reject);
+    blocker.listen(0, '127.0.0.1', () => resolve(blocker.address().port));
+  });
+
+  try {
+    const script = Path.join('examples', 'three-lines.js');
+    const cli = startCLI([`--port=${port}`, script]);
+    const code = await cli.quit();
+
+    t.notMatch(
+      cli.output,
+      'report this bug',
+      'Omits message about reporting this as a bug');
+    t.match(
+      cli.output,
+      `waiting for 127.0.0.1:${port} to be free`,
+      'Tells the user that the port wasn\'t available');
+    t.equal(code, 1, 'exits with non-zero exit code');
+  } finally {
+    blocker.close();
+  }
+});