fix: always run hooks as CommonJS

Add a `package.json` to `…/.git/hooks/` to force hooks to run as CommonJS, not
modules.

Fixes ghooks-org#394.

lib/install.js

@@ -1,7 +1,10 @@
 const fs = require('fs')
 const resolve = require('path').resolve
 const findup = require('findup')
-const template = require('./hook.template')
+const packageTemplate = require('./package.template')
+const hookTemplate = require('./hook.template')
+
+const JSON_INDENTATION = 2
 
 const hooks = [
   'applypatch-msg',
@@ -27,12 +30,17 @@ function installHooks() {
   const gitRoot = findGitRoot()
   if (gitRoot) {
     const hooksDir = resolve(gitRoot, 'hooks')
-    hooks.forEach(install.bind(null, hooksDir))
+    installHooksIntoDir(hooksDir)
   } else {
     warnAboutGit()
   }
 }
 
+function installHooksIntoDir(dir) {
+  installPackageJSON(dir)
+  hooks.forEach(install.bind(null, dir))
+}
+
 function findGitRoot() {
   try {
     return getGitRoot()
@@ -74,6 +82,13 @@ function warnAboutGit() {
   )
 }
 
+function installPackageJSON(dir) {
+  ensureDirExists(dir)
+  const file = resolve(dir, 'package.json')
+  needsBackup(file) && backup(file)
+  fs.writeFileSync(file, JSON.stringify(packageTemplate.content, null, JSON_INDENTATION))
+}
+
 function install(dir, hook) {
   ensureDirExists(dir)
   const file = resolve(dir, hook)
@@ -90,15 +105,15 @@ function needsBackup(file) {
 }
 
 function generatedByGHooks(file) {
-  return !!fs.readFileSync(file, 'UTF-8').match(template.generatedMessage)
+  return !!fs.readFileSync(file, 'UTF-8').match(hookTemplate.generatedMessage)
 }
 
 function backup(file) {
   fs.renameSync(file, `${file}.bkp`)
 }
 
 function createExecutableHook(file) {
-  fs.writeFileSync(file, template.content)
+  fs.writeFileSync(file, hookTemplate.content)
   fs.chmodSync(file, '755')
 }
 

lib/package.template.js

@@ -0,0 +1,7 @@
+exports.generatedMessage = 'Generated by ghooks. Do not edit this file.'
+exports.content = {
+  type: 'commonjs',
+  "//": [
+    exports.generatedMessage
+  ]
+}

test/install.test.js

@@ -17,6 +17,16 @@ describe('install', function describeInstall() {
     expect(fs.existsSync('.git/hooks')).to.be.true
   })
 
+  it('creates a package.json', () => {
+    fsStub({'.git/hooks': {}})
+    install()
+
+    const hooks = fs.readdirSync('.git/hooks')
+    const packageContent = require('../lib/package.template').content
+    expect(hooks).to.include('package.json')
+    expect(fs.readFileSync('.git/hooks/package.json', 'UTF-8')).to.equal(packageContent)
+  })
+
   it('creates hook files', () => {
     fsStub({'.git/hooks': {}})
     install()
@@ -49,6 +59,38 @@ describe('install', function describeInstall() {
     expectHook('post-rewrite', '.git/hooks/post-rewrite', '755')
   })
 
+  describe('backs up an existing package.json', () => {
+
+    const existingGHookPackage = '// Generated by ghooks. Do not edit this file.'
+    const existingUserPackage = '# existing content'
+
+    it('does not keep a copy of an existing GHook package.json', () => {
+      fsStub({'.git/hooks': {
+        'package.json': existingGHookPackage,
+      }})
+
+      install()
+      const files = fs.readdirSync('.git/hooks')
+
+      expect(files).to.not.include('package.json.bkp')
+      expect(files).to.include('package.json')
+    })
+
+    it('backs up an existing user package.json', () => {
+      fsStub({'.git/hooks': {
+        'package.json': existingUserPackage,
+      }})
+
+      install()
+      const files = fs.readdirSync('.git/hooks')
+
+      expect(files).to.include('package.json.bkp')
+      expect(files).to.include('package.json')
+      expect(fs.readFileSync('.git/hooks/package.json.bkp', 'UTF-8')).to.equal(existingUserPackage)
+    })
+
+  })
+
   describe('backing up existing hooks', () => {
 
     const existingGHook = '// Generated by ghooks. Do not edit this file.'