fix(git): support git packed refs --all mode (#77)

* test: git-pack-refs vs gitHead

also, let's have gitHead tests for both refs-packed and non-packed modes

re #76 (git packed refs --all mode not supported)

* Fall back to .git/packed-refs if .git/<ref> does not exist

* refactor: minor

read-json.js

@@ -339,10 +339,26 @@ function githead_ (file, data, dir, head, cb) {
     data.gitHead = head.trim()
     return cb(null, data)
   }
-  var headFile = head.replace(/^ref: /, '').trim()
-  headFile = path.resolve(dir, '.git', headFile)
+  var headRef = head.replace(/^ref: /, '').trim()
+  var headFile = path.resolve(dir, '.git', headRef)
   fs.readFile(headFile, 'utf8', function (er, head) {
-    if (er || !head) return cb(null, data)
+    if (er || !head) {
+      var packFile = path.resolve(dir, '.git/packed-refs')
+      return fs.readFile(packFile, 'utf8', function (er, refs) {
+        if (er || !refs) {
+          return cb(null, data)
+        }
+        refs = refs.split('\n')
+        for (var i = 0; i < refs.length; i++) {
+          var match = refs[i].match(/^([0-9a-f]{40}) (.+)$/)
+          if (match && match[2].trim() === headRef) {
+            data.gitHead = match[1]
+            break
+          }
+        }
+        return cb(null, data)
+      })
+    }
     head = head.replace(/^ref: /, '').trim()
     data.gitHead = head
     return cb(null, data)

test/gitHead.js

@@ -0,0 +1,64 @@
+var childProcess = require('child_process')
+var fs = require('fs')
+var path = require('path')
+
+var tap = require('tap')
+
+var readJson = require('../')
+
+var isGit
+try {
+  fs.readFileSync(path.resolve(__dirname, '../.git/HEAD'))
+  isGit = true
+} catch (e) {
+  isGit = false
+}
+
+if (isGit) {
+  tap.test('gitHead tests', function (t) {
+    t.plan(3)
+
+    const repoProjectName = 'read-package-json'
+    const repo = 'https://github.com/npm/' + repoProjectName + '.git'
+    var repoDirs = []
+
+    t.test('detached case', function (tt) {
+      var p = path.resolve(__dirname, '..', 'package.json')
+      readJson(p, function (er, data) {
+        if (er) throw er
+        tt.ok(data)
+        tt.similar(data.gitHead, /^[a-f0-9]{40}$/)
+        tt.end()
+      })
+    })
+
+    function testGitRepo (kind, extraRepoCommand, t) {
+      var repoDirName = repoProjectName + '-' + kind
+      var cmd = `cd ${__dirname} && git clone ${repo} ${repoDirName} && cd ${repoDirName}`
+      if (extraRepoCommand) cmd += ` && ${extraRepoCommand}`
+      childProcess.execSync(cmd)
+      repoDirs.push(repoDirName)
+      var p = path.resolve(__dirname, repoDirName, 'package.json')
+      readJson(p, function (er, data) {
+        if (er) throw er
+        t.ok(data)
+        t.similar(data.gitHead, /^[a-f0-9]{40}$/)
+        t.end()
+      })
+    }
+
+    t.test('basic case', function (tt) {
+      testGitRepo('basic', '', tt)
+    })
+
+    t.test('git-pack-refs vs gitHead', function (tt) {
+      testGitRepo('git-pack-refs', 'git pack-refs --all', tt)
+    })
+
+    t.tearDown(function () {
+      repoDirs.forEach(function (d) {
+        childProcess.execSync(`rm -rf ${path.resolve(__dirname, d)}`)
+      })
+    })
+  })
+}