Use JGit in the build instead of shell and bat scripts

Author: allanrenucci

project/VersionUtil.scala

@@ -1,18 +1,43 @@
-import scala.sys.process.Process
+import org.eclipse.jgit.storage.file.FileRepositoryBuilder
+import org.eclipse.jgit.lib.{Constants, ObjectId, Ref, Repository}
+import org.eclipse.jgit.revwalk.{RevCommit, RevWalk}
+
+import java.text.SimpleDateFormat
+import java.util.Date
 
 object VersionUtil {
-  def executeScript(scriptName: String) = {
-    val cmd =
-      if (System.getProperty("os.name").toLowerCase.contains("windows"))
-        s"cmd.exe /c project\\scripts\\build\\$scriptName.bat -p"
-      else s"project/scripts/build/$scriptName"
-    Process(cmd).lineStream.head.trim
+
+  // Adapted from sbt-git
+  private class JGit(repo: Repository) {
+    def headCommit: ObjectId =
+      repo.exactRef(Constants.HEAD).getObjectId
+
+    def headCommitSha: String = headCommit.name
+
+    def headCommitDate: Date = {
+      val walk = new RevWalk(repo)
+      val commit = walk.parseCommit(headCommit)
+      val seconds = commit.getCommitTime.toLong
+      val millis = seconds * 1000L
+      new Date(millis)
+    }
+  }
+
+  private lazy val git = {
+    val repo = new FileRepositoryBuilder()
+      .setMustExist(true)
+      .findGitDir()
+      .build()
+    new JGit(repo)
   }
 
   /** Seven letters of the SHA hash is considered enough to uniquely identify a
    *  commit, albeit extremely large projects - such as the Linux kernel - need
    *  more letters to stay unique
    */
-  def gitHash = executeScript("get-scala-commit-sha").substring(0, 7)
-  def commitDate = executeScript("get-scala-commit-date")
+  def gitHash: String = git.headCommitSha.substring(0, 7)
+  def commitDate: String = {
+    val format = new SimpleDateFormat("yyyyMMdd")
+    format.format(git.headCommitDate)
+  }
 }

project/build.sbt

@@ -0,0 +1,2 @@
+// Used by VersionUtil to get gitHash and commitDate
+libraryDependencies += "org.eclipse.jgit" % "org.eclipse.jgit" % "4.11.0.201803080745-r"