Allow token replacement of .npmrc configuration with env vars (#1207)

* test IGNORE ME

* Update npm-registry to inject env vars into npm configuration the same way npm does

* Add type annotation to config object iteration

* Update envReplace function

* Move env-replace function to a separate util module. Add unit tests

* Correct the env-replace tests

* Updates per @kittens' comments

.editorconfig

@@ -9,3 +9,4 @@ end_of_line = lf
 [*.{js,json}]
 indent_style = space
 indent_size = 2
+

__tests__/util/env-replace.js

@@ -0,0 +1,32 @@
+/* @flow */
+import envReplace from '../../src/util/env-replace';
+import assert from 'assert';
+
+describe('environment variable replacement', () => {
+  it('will replace a token that exists in the environment', () => {
+    let result = envReplace('test ${a} replacement', {a: 'token'});
+    assert(result === 'test token replacement', `result: ${result}`);
+
+    result = envReplace('${a} replacement', {a: 'token'});
+    assert(result === 'token replacement', `result: ${result}`);
+
+    result = envReplace('${a}', {a: 'token'});
+    assert(result === 'token', `result: ${result}`);
+  });
+
+  it('will not replace a token that does not exist in the environment', () => {
+    let thrown = false;
+    try {
+      envReplace('${a} replacement', {b: 'token'});
+    } catch (err) {
+      thrown = true;
+      assert(err.message === 'Failed to replace env in config: ${a}', `error message: ${err.message}`);
+    }
+    assert(thrown);
+  });
+
+  it('will not replace a token when a the token-replacement mechanism is prefixed a backslash literal', () => {
+    const result = envReplace('\\${a} replacement', {a: 'token'});
+    assert(result === '\\${a} replacement', `result: ${result}`);
+  });
+});

src/registries/npm-registry.js

@@ -6,6 +6,7 @@ import type Config from '../config.js';
 import type {ConfigRegistries} from './index.js';
 import * as fs from '../util/fs.js';
 import NpmResolver from '../resolvers/registries/npm-resolver.js';
+import envReplace from '../util/env-replace.js';
 import Registry from './base-registry.js';
 import {addSuffix, removePrefix} from '../util/misc';
 
@@ -121,6 +122,9 @@ export default class NpmRegistry extends Registry {
 
     for (const [, loc, file] of await this.getPossibleConfigLocations('.npmrc')) {
       const config = Registry.normalizeConfig(ini.parse(file));
+      for (const key: string in config) {
+        config[key] = envReplace(config[key]);
+      }
 
       // normalize offline mirror path relative to the current npmrc
       const offlineLoc = config['yarn-offline-mirror'];

src/util/env-replace.js

@@ -0,0 +1,18 @@
+/* @flow */
+const ENV_EXPR = /(\\*)\$\{([^}]+)\}/g;
+
+export default function envReplace(value: string, env: {[key: string]: ?string} = process.env): string {
+  if (typeof value !== 'string' || !value) {
+    return value;
+  }
+
+  return value.replace(ENV_EXPR, (match: string, esc: string, envVarName: string) => {
+    if (esc.length && esc.length % 2) {
+      return match;
+    }
+    if (undefined === env[envVarName]) {
+      throw new Error('Failed to replace env in config: ' + match);
+    }
+    return env[envVarName] || '';
+  });
+}