buffer: runtime deprecation of calling Buffer without new

PR-URL: #8169
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Stephen Belanger <admin@stephenbelanger.com>
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/buffer.js

@@ -64,7 +64,17 @@ function alignPool() {
  * much breakage at this time. It's not likely that the Buffer constructors
  * would ever actually be removed.
  **/
+var newBufferWarned = false;
 function Buffer(arg, encodingOrOffset, length) {
+  if (!new.target && !newBufferWarned) {
+    newBufferWarned = true;
+    process.emitWarning(
+      'Using Buffer without `new` will soon stop working. ' +
+      'Use `new Buffer()`, or preferably ' +
+      '`Buffer.from()`, `Buffer.allocUnsafe()` or `Buffer.alloc()` instead.',
+      'DeprecationWarning'
+    );
+  }
   // Common case.
   if (typeof arg === 'number') {
     if (typeof encodingOrOffset === 'string') {

test/parallel/test-buffer-deprecated.js

@@ -0,0 +1,17 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+
+const expected =
+  'Using Buffer without `new` will soon stop working. ' +
+  'Use `new Buffer()`, or preferably ' +
+  '`Buffer.from()`, `Buffer.allocUnsafe()` or `Buffer.alloc()` instead.';
+
+process.on('warning', common.mustCall((warning) => {
+  assert.strictEqual(warning.name, 'DeprecationWarning');
+  assert.strictEqual(warning.message, expected,
+                     `unexpected error message: "${warning.message}"`);
+}, 1));
+
+Buffer(1);
+Buffer(1);