From 559197b1ba7aed4853f074269b35d2eed14c1c51 Mon Sep 17 00:00:00 2001
From: Anna Henningsen <anna@addaleax.net>
Date: Tue, 8 Sep 2020 20:36:33 +0200
Subject: [PATCH] doc,test: specify and test CLI option precedence rules

Refs: https://github.com/nodejs/node/pull/35098#issuecomment-689051526
---
 doc/api/cli.md                               |  6 ++++++
 test/parallel/test-cli-options-precedence.js | 22 ++++++++++++++++++++
 2 files changed, 28 insertions(+)
 create mode 100644 test/parallel/test-cli-options-precedence.js

diff --git a/doc/api/cli.md b/doc/api/cli.md
index 260f48093129e2..5900ffd5ccbe4f 100644
--- a/doc/api/cli.md
+++ b/doc/api/cli.md
@@ -34,6 +34,11 @@ dashes (`-`) or underscores (`_`).
 
 For example, `--pending-deprecation` is equivalent to `--pending_deprecation`.
 
+If an option that takes a single value, for example `--max-http-header-size`,
+is passed more than once, then the last passed value will be used. Options
+from the command line take precedence over options passed through the
+[`NODE_OPTIONS`][] environment variable.
+
 ### `-`
 <!-- YAML
 added: v8.0.0
@@ -1588,6 +1593,7 @@ $ node --max-old-space-size=1536 index.js
 [`Atomics.wait()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Atomics/wait
 [`Buffer`]: buffer.html#buffer_class_buffer
 [`SlowBuffer`]: buffer.html#buffer_class_slowbuffer
+[`NODE_OPTIONS`]: #cli_node_options_options
 [`process.setUncaughtExceptionCaptureCallback()`]: process.html#process_process_setuncaughtexceptioncapturecallback_fn
 [`tls.DEFAULT_MAX_VERSION`]: tls.html#tls_tls_default_max_version
 [`tls.DEFAULT_MIN_VERSION`]: tls.html#tls_tls_default_min_version
diff --git a/test/parallel/test-cli-options-precedence.js b/test/parallel/test-cli-options-precedence.js
new file mode 100644
index 00000000000000..f76c12043e29cd
--- /dev/null
+++ b/test/parallel/test-cli-options-precedence.js
@@ -0,0 +1,22 @@
+'use strict';
+require('../common');
+const assert = require('assert');
+const { spawnSync } = require('child_process');
+
+// The last option on the command line takes precedence:
+assert.strictEqual(spawnSync(process.execPath, [
+  '--max-http-header-size=1234',
+  '--max-http-header-size=5678',
+  '-p', 'http.maxHeaderSize'
+], {
+  encoding: 'utf8'
+}).stdout.trim(), '5678');
+
+// The command line takes precedence over NODE_OPTIONS:
+assert.strictEqual(spawnSync(process.execPath, [
+  '--max-http-header-size=5678',
+  '-p', 'http.maxHeaderSize'
+], {
+  encoding: 'utf8',
+  env: { ...process.env, NODE_OPTIONS: '--max-http-header-size=1234' }
+}).stdout.trim(), '5678');