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

@@ -350,6 +350,22 @@ ${defData}
     }
 
     if (!long) {
+      const envVars = []
+
+      // Show proxy-related environment variables if they're set
+      const proxyEnvVars = ['HTTP_PROXY', 'HTTPS_PROXY', 'NO_PROXY', 'http_proxy', 'https_proxy', 'no_proxy']
+      for (const envVar of proxyEnvVars) {
+        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: {