Which returns first result

Summary:
This fixes a problem on windows where `where.exe` can return multiple lines if the command is found multiple times on the `PATH`. This is especially painful since the recommended `npm install -g flow-bin` creates two `flow` binaries on by default so the entire flow support is broken, as mentioned in #321.

Also added tests.
Closes #712

Reviewed By: nmote

Differential Revision: D3892797

Pulled By: zsol

fbshipit-source-id: 9de5a425f2f113525677e3dcae7ec3e1ec294bd3

pkg/commons-node/spec/which-spec.js

@@ -0,0 +1,86 @@
+'use babel';
+/* @flow */
+
+/*
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the license found in the LICENSE file in
+ * the root directory of this source tree.
+ */
+
+import which from '../which';
+
+describe('which', () => {
+  let checkOutput: JasmineSpy;
+  let checkOutputReturn: {stdout: string} = (null: any);
+
+  beforeEach(() => {
+    checkOutputReturn = {stdout: ''};
+    checkOutput = spyOn(require('../process'), 'checkOutput').andCallFake(() =>
+      checkOutputReturn,
+    );
+  });
+
+  afterEach(() => {
+    jasmine.unspy(require('../process'), 'checkOutput');
+  });
+
+  describe('on windows', () => {
+    const real_platform: string = process.platform;
+    const eol = '\r\n';
+    const os = require('os');
+    const real_eol = os.EOL;
+    beforeEach(() => {
+      Object.defineProperty(process, 'platform', {value: 'win32'});
+      os.EOL = eol;
+    });
+    afterEach(() => {
+      Object.defineProperty(process, 'platform', {value: real_platform});
+      os.EOL = real_eol;
+    });
+
+    it('calls where on Windows', () => {
+      const param: string = '';
+      which(param);
+      expect(checkOutput).toHaveBeenCalledWith('where', [param]);
+    });
+
+    it('returns the first match', () => {
+      waitsForPromise(async () => {
+        checkOutputReturn.stdout = 'hello' + os.EOL + 'hello.exe' + os.EOL;
+        const ret = await which('bla');
+        expect(ret).toEqual('hello');
+      });
+    });
+  });
+
+  describe('on linux', () => {
+    const real_platform: string = process.platform;
+    const eol = '\n';
+    const os = require('os');
+    const real_eol = os.EOL;
+    beforeEach(() => {
+      Object.defineProperty(process, 'platform', {value: 'linux'});
+      os.EOL = eol;
+    });
+    afterEach(() => {
+      Object.defineProperty(process, 'platform', {value: real_platform});
+      os.EOL = real_eol;
+    });
+
+    it('calls which', () => {
+      const param: string = '';
+      which(param);
+      expect(checkOutput).toHaveBeenCalledWith('which', [param]);
+    });
+
+    it('returns the first match', () => {
+      waitsForPromise(async () => {
+        checkOutputReturn.stdout = 'hello' + os.EOL + '/bin/hello' + os.EOL;
+        const ret = await which('bla');
+        expect(ret).toEqual('hello');
+      });
+    });
+  });
+});

pkg/commons-node/which.js

@@ -10,6 +10,7 @@
  */
 
 import {checkOutput} from './process';
+import os from 'os';
 
 /**
  * Provides a cross-platform way to check whether a binary is available.
@@ -21,7 +22,7 @@ export default async function which(command: string): Promise<?string> {
   const whichCommand = process.platform === 'win32' ? 'where' : 'which';
   try {
     const result = await checkOutput(whichCommand, [command]);
-    return result.stdout.trim();
+    return result.stdout.split(os.EOL)[0];
   } catch (e) {
     return null;
   }