feat: show proxy environment variables in npm config list

Fixes #4170

pm config list now displays proxy-related environment variables
(HTTP_PROXY, HTTPS_PROXY, NO_PROXY and their lowercase equivalents)
when they are set. This helps users understand what proxy settings
are being used by npm.

The environment variables are shown in a separate '; environment-related config'
section before the system information (node version, npm version, etc.).

Author: Max Black

lib/commands/config.js

@@ -4,7 +4,7 @@ const { spawn } = require('node:child_process')
 const { EOL } = require('node:os')
 const localeCompare = require('@isaacs/string-locale-compare')('en')
 const pkgJson = require('@npmcli/package-json')
-const { defaults, definitions, nerfDarts } = require('@npmcli/config/lib/definitions')
+const { defaults, definitions, nerfDarts, proxyEnv } = require('@npmcli/config/lib/definitions')
 const { log, output } = require('proc-log')
 const BaseCommand = require('../base-cmd.js')
 const { redact } = require('@npmcli/redact')
@@ -350,6 +350,21 @@ ${defData}
     }
 
     if (!long) {
+      const envVars = []
+
+      // Show proxy-related environment variables if they're set
+      for (const envVar of proxyEnv) {
+        if (process.env[envVar]) {
+          envVars.push(`; ${envVar} = ${JSON.stringify(process.env[envVar])}`)
+        }
+      }
+
+      if (envVars.length > 0) {
+        msg.push('; environment-related config', '')
+        msg.push(...envVars)
+        msg.push('')
+      }
+
       msg.push(
         `; node bin location = ${process.execPath}`,
         `; node version = ${process.version}`,

test/lib/commands/config.js

@@ -101,6 +101,49 @@ t.test('config list', async t => {
   t.matchSnapshot(output, 'output matches snapshot')
 })
 
+t.test('config list with proxy environment variables', async t => {
+  const originalHTTP = process.env.HTTP_PROXY
+  const originalHTTPS = process.env.HTTPS_PROXY
+  const originalNO = process.env.NO_PROXY
+
+  t.teardown(() => {
+    if (originalHTTP !== undefined) {
+      process.env.HTTP_PROXY = originalHTTP
+    } else {
+      delete process.env.HTTP_PROXY
+    }
+    if (originalHTTPS !== undefined) {
+      process.env.HTTPS_PROXY = originalHTTPS
+    } else {
+      delete process.env.HTTPS_PROXY
+    }
+    if (originalNO !== undefined) {
+      process.env.NO_PROXY = originalNO
+    } else {
+      delete process.env.NO_PROXY
+    }
+  })
+
+  process.env.HTTP_PROXY = 'http://proxy.example.com:8080'
+  process.env.HTTPS_PROXY = 'https://secure-proxy.example.com:8443'
+  process.env.NO_PROXY = 'localhost,127.0.0.1'
+
+  const { npm, joinedOutput } = await loadMockNpm(t, {
+    prefixDir: {
+      '.npmrc': 'test=value',
+    },
+  })
+
+  await npm.exec('config', ['list'])
+
+  const output = joinedOutput()
+
+  t.match(output, 'HTTP_PROXY = "http://proxy.example.com:8080"')
+  t.match(output, 'HTTPS_PROXY = "https://secure-proxy.example.com:8443"')
+  t.match(output, 'NO_PROXY = "localhost,127.0.0.1"')
+  t.match(output, 'environment-related config')
+})
+
 t.test('config list --long', async t => {
   const { npm, joinedOutput } = await loadMockNpm(t, {
     prefixDir: {

workspaces/config/lib/definitions/index.js

@@ -71,10 +71,22 @@ const nerfDarts = [
   'username', // Does not have a config
 ]
 
+// Environment variables that can affect npm's behavior but are not npm configs
+// These are shown in `npm config list` to help users understand their environment
+const proxyEnv = [
+  'HTTP_PROXY',
+  'HTTPS_PROXY',
+  'NO_PROXY',
+  'http_proxy',
+  'https_proxy',
+  'no_proxy',
+]
+
 module.exports = {
   defaults: definitionProps.defaults,
   definitions,
   flatten,
   nerfDarts,
+  proxyEnv,
   shorthands,
 }