util: emit deprecation code only once

If another function has already emitted the deprecation warning with the
same code as the warning that is about to be emitted, do not emit the
warning.

This is a breaking change. Previously, different functions could emit
the same deprecation warning multiple times. This was a known bug rather
than a feature, but this change is being treated as a breaking change
out of caution. Identical deprecation warnings should not be emitted.

PR-URL: https://github.com/nodejs/node/pull/16393
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

1 files changed, 57 insertions, 0 deletions

diff --git a/test/parallel/test-util-deprecate.js b/test/parallel/test-util-deprecate.js
new file mode 100644
index 0000000000..1b4a5e7662
--- /dev/null
+++ b/test/parallel/test-util-deprecate.js
@@ -0,0 +1,57 @@
+'use strict';
+
+require('../common');
+
+// Tests basic functionality of util.deprecate().
+
+const assert = require('assert');
+const util = require('util');
+
+const expectedWarnings = new Map();
+
+// Emits deprecation only once if same function is called.
+{
+  const msg = 'fhqwhgads';
+  const fn = util.deprecate(() => {}, msg);
+  expectedWarnings.set(msg, { code: undefined, count: 1 });
+  fn();
+  fn();
+}
+
+// Emits deprecation twice for different functions.
+{
+  const msg = 'sterrance';
+  const fn1 = util.deprecate(() => {}, msg);
+  const fn2 = util.deprecate(() => {}, msg);
+  expectedWarnings.set(msg, { code: undefined, count: 2 });
+  fn1();
+  fn2();
+}
+
+// Emits deprecation only once if optional code is the same, even for different
+// functions.
+{
+  const msg = 'cannonmouth';
+  const code = 'deprecatesque';
+  const fn1 = util.deprecate(() => {}, msg, code);
+  const fn2 = util.deprecate(() => {}, msg, code);
+  expectedWarnings.set(msg, { code, count: 1 });
+  fn1();
+  fn2();
+  fn1();
+  fn2();
+}
+
+process.on('warning', (warning) => {
+  assert.strictEqual(warning.name, 'DeprecationWarning');
+  assert.ok(expectedWarnings.has(warning.message));
+  const expected = expectedWarnings.get(warning.message);
+  assert.strictEqual(warning.code, expected.code);
+  expected.count = expected.count - 1;
+  if (expected.count === 0)
+    expectedWarnings.delete(warning.message);
+});
+
+process.on('exit', () => {
+  assert.deepStrictEqual(expectedWarnings, new Map());
+});