Do not set the PREFIX environment variable (#13)

* Restore npm v6 behavior with INIT_CWD

This should always be set to the npm cwd, even if already in the env.

Fix: npm/cli#2578

* Do not set the PREFIX environment variable

Fix: npm/cli#2398

lib/set-envs.js

@@ -53,12 +53,6 @@ const setEnvs = (config) => {
     list: [cliConf, envConf],
   } = config
 
-  const { DESTDIR } = env
-  if (platform !== 'win32' && DESTDIR && globalPrefix.indexOf(DESTDIR) === 0)
-    env.PREFIX = globalPrefix.substr(DESTDIR.length)
-  else
-    env.PREFIX = globalPrefix
-
   env.INIT_CWD = process.cwd()
 
   // if the key is the default value,

test/set-envs.js

@@ -14,7 +14,6 @@ t.test('set envs that are not defaults and not already in env', t => {
     INIT_CWD: cwd,
     EDITOR: 'vim',
     HOME: undefined,
-    PREFIX: undefined,
     npm_execpath: require.main.filename,
     npm_node_execpath: execPath,
   }
@@ -56,7 +55,6 @@ t.test('set envs that are not defaults and not already in env, array style', t =
     INIT_CWD: cwd,
     EDITOR: 'vim',
     HOME: undefined,
-    PREFIX: undefined,
     npm_execpath: require.main.filename,
     npm_node_execpath: execPath,
   }
@@ -95,7 +93,6 @@ t.test('set envs that are not defaults and not already in env, boolean edition',
     INIT_CWD: cwd,
     EDITOR: 'vim',
     HOME: undefined,
-    PREFIX: undefined,
     npm_execpath: require.main.filename,
     npm_node_execpath: execPath,
   }
@@ -127,33 +124,6 @@ t.test('set envs that are not defaults and not already in env, boolean edition',
   t.end()
 })
 
-t.test('set PREFIX based on DESTDIR', t => {
-  // also, don't set editor
-  const d = { ...defaults, editor: null }
-  const envConf = Object.create(d)
-  const cliConf = Object.create(envConf)
-  const extras = {
-    NODE,
-    INIT_CWD: cwd,
-    HOME: undefined,
-    PREFIX: '/usr/local',
-    DESTDIR: '/some/dest',
-    npm_execpath: require.main.filename,
-    npm_node_execpath: execPath,
-  }
-  const env = { DESTDIR: '/some/dest' }
-  const config = {
-    list: [cliConf, envConf],
-    env,
-    defaults: d,
-    globalPrefix: '/some/dest/usr/local',
-    execPath,
-  }
-  setEnvs(config)
-  t.strictSame(env, { ...extras })
-  t.end()
-})
-
 t.test('dont set npm_execpath if require.main.filename is not set', t => {
   const { filename } = require.main
   t.teardown(() => require.main.filename = filename)