process: add NODE_NO_WARNINGS environment variable

This commit adds support for a NODE_NO_WARNINGS environment
variable, which duplicates the functionality of the --no-warnings
command line flag.

Fixes: nodejs#10802
PR-URL: nodejs#10842
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
Reviewed-By: Italo A. Casas <me@italoacasas.com>

doc/api/cli.md

@@ -301,6 +301,13 @@ added: v0.11.15
 Data path for ICU (Intl object) data. Will extend linked-in data when compiled
 with small-icu support.
 
+### `NODE_NO_WARNINGS=1`
+<!-- YAML
+added: REPLACEME
+-->
+
+When set to `1`, process warnings are silenced.
+
 ### `NODE_PRESERVE_SYMLINKS=1`
 <!-- YAML
 added: v7.1.0

doc/node.1

@@ -207,6 +207,10 @@ errors are otherwise ignored.
 Data path for ICU (Intl object) data. Will extend linked-in data when compiled
 with small\-icu support.
 
+.TP
+.BR NODE_NO_WARNINGS =\fI1\fR
+When set to \fI1\fR, process warnings are silenced.
+
 .TP
 .BR NODE_PATH =\fIpath\fR[:\fI...\fR]
 \':\'\-separated list of directories prefixed to the module search path.

lib/internal/process/warning.js

@@ -5,7 +5,7 @@ const prefix = `(${process.release.name}:${process.pid}) `;
 exports.setup = setupProcessWarnings;
 
 function setupProcessWarnings() {
-  if (!process.noProcessWarnings) {
+  if (!process.noProcessWarnings && process.env.NODE_NO_WARNINGS !== '1') {
     process.on('warning', (warning) => {
       if (!(warning instanceof Error)) return;
       const isDeprecation = warning.name === 'DeprecationWarning';

test/parallel/test-env-var-no-warnings.js

@@ -0,0 +1,41 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const cp = require('child_process');
+
+if (process.argv[2] === 'child') {
+  process.emitWarning('foo');
+} else {
+  function test(env) {
+    const cmd = `${process.execPath} ${__filename} child`;
+
+    cp.exec(cmd, { env }, common.mustCall((err, stdout, stderr) => {
+      assert.strictEqual(err, null);
+      assert.strictEqual(stdout, '');
+
+      if (env.NODE_NO_WARNINGS === '1')
+        assert.strictEqual(stderr, '');
+      else
+        assert(/Warning: foo$/.test(stderr.trim()));
+    }));
+  }
+
+  test({});
+  test(process.env);
+  test({ NODE_NO_WARNINGS: undefined });
+  test({ NODE_NO_WARNINGS: null });
+  test({ NODE_NO_WARNINGS: 'foo' });
+  test({ NODE_NO_WARNINGS: true });
+  test({ NODE_NO_WARNINGS: false });
+  test({ NODE_NO_WARNINGS: {} });
+  test({ NODE_NO_WARNINGS: [] });
+  test({ NODE_NO_WARNINGS: function() {} });
+  test({ NODE_NO_WARNINGS: 0 });
+  test({ NODE_NO_WARNINGS: -1 });
+  test({ NODE_NO_WARNINGS: '0' });
+  test({ NODE_NO_WARNINGS: '01' });
+  test({ NODE_NO_WARNINGS: '2' });
+  // Don't test the number 1 because it will come through as a string in the
+  // the child process environment.
+  test({ NODE_NO_WARNINGS: '1' });
+}