Workaround to allow usage within git worktrees. fixes #110

src/main/scala/com/typesafe/sbt/SbtGit.scala

@@ -2,7 +2,7 @@ package com.typesafe.sbt
 
 import sbt._
 import Keys._
-import git.{ConsoleGitRunner, DefaultReadableGit, GitRunner, JGitRunner, ReadableGit}
+import git.{ConsoleGitReadableOnly, ConsoleGitRunner, DefaultReadableGit, GitRunner, JGitRunner, ReadableGit}
 import sys.process.Process
 
 /** This plugin has all the basic 'git' functionality for other plugins. */
@@ -40,6 +40,9 @@ object SbtGit {
 
     // The remote repository we're using.
     val gitRemoteRepo = SettingKey[String]("git-remote-repo", "The remote git repository associated with this project")
+
+    // Git worktree workaround
+    val useConsoleForROGit = SettingKey[Boolean]("console-ro-runner", "Whether to shell out to git for ro ops in the current build.")
   }
 
   object GitCommand {
@@ -110,7 +113,8 @@ object SbtGit {
   // Build settings.
   import GitKeys._
   def buildSettings = Seq(
-    gitReader := new DefaultReadableGit(baseDirectory.value),
+    useConsoleForROGit := false,
+    gitReader := new DefaultReadableGit(baseDirectory.value, if (useConsoleForROGit.value) Some(new ConsoleGitReadableOnly(ConsoleGitRunner, file("."), ConsoleLogger())) else None),
     gitRunner := ConsoleGitRunner,
     gitHeadCommit := gitReader.value.withGit(_.headCommitSha),
     gitHeadMessage := gitReader.value.withGit(_.headCommitMessage),
@@ -153,6 +157,9 @@ object SbtGit {
   /** A Predefined setting to use JGit runner for git. */
   def useJGit: Setting[_] = gitRunner in ThisBuild := JGitRunner
 
+  /** Setting to use console git for readable ops, to allow working with git worktrees */
+  def useReadableConsoleGit: Setting[_] = useConsoleForROGit in ThisBuild := true
+
   /** Adapts the project prompt to show the current project name *and* the current git branch. */
   def showCurrentGitBranch: Setting[_] =
     shellPrompt := GitCommand.prompt

src/main/scala/com/typesafe/sbt/git/ConsoleGitReadableOnly.scala

@@ -0,0 +1,27 @@
+package com.typesafe.sbt.git
+
+import scala.util.Try
+
+import sbt.{File, Logger}
+
+class ConsoleGitReadableOnly(git: GitRunner, cwd: File, log: Logger) extends GitReadonlyInterface {
+  def branch: String = git("rev-parse", "--abbrev-ref", "HEAD")(cwd, log)
+
+  def headCommitSha: Option[String] = Try(git("rev-parse", "HEAD")(cwd, log)).toOption
+
+  def headCommitDate: Option[String] = Try(git("log", """--pretty="%cI"""", "-n", "1")(cwd, log)).toOption
+
+  def currentTags: Seq[String] = git("tag", "--points-at", "HEAD")(cwd, log).split("\\s+")
+
+  def describedVersion: Option[String] = git("describe", "--tags")(cwd, log).split("\\s+").headOption
+
+  def hasUncommittedChanges: Boolean = git("status")(cwd, log).contains("nothing to commit, working tree clean")
+
+  def branches: Seq[String] = git("branch", "--list")(cwd, log).split("\\s+")
+
+  def remoteBranches: Seq[String] = git("branch", "-l", "--remotes")(cwd, log).split("\\s+")
+
+  def remoteOrigin: String = git("ls-remote", "--get-url", "origin")(cwd, log)
+
+  def headCommitMessage: Option[String] = Try(git("log", "--pretty=%s\n\n%b", "-n", "1")(cwd, log)).toOption
+}

src/main/scala/com/typesafe/sbt/git/ReadableGit.scala

@@ -31,11 +31,13 @@ trait GitReadonlyInterface {
 }
 
 
-/** Our default readable git uses JGit instead of a process-forking and reading, for speed/safety. */
-final class DefaultReadableGit(base: sbt.File) extends ReadableGit {
+/** Our default readable git uses JGit instead of a process-forking and reading, for speed/safety. However, we allow
+  * overriding, since JGit doesn't currently work with git worktrees
+  * */
+final class DefaultReadableGit(base: sbt.File, gitOverride: Option[GitReadonlyInterface]) extends ReadableGit {
   // TODO - Should we cache git, or just create on each request?
   // For now, let's cache.
-  private[this] val git = JGit(base)
+  private[this] val git = gitOverride getOrElse JGit(base)
   /** Use the git read-only interface. */
   def withGit[A](f: GitReadonlyInterface => A): A =
     // JGit has concurrency issues so we synchronize access to it.