Adding GitAlg.diff

Author: Devon Stewart

modules/core/src/main/scala/org/scalasteward/core/git/FileGitAlg.scala

@@ -138,6 +138,9 @@ final class FileGitAlg[F[_]](config: GitCfg)(implicit
   override def version: F[String] =
     workspaceAlg.rootDir.flatMap(git("--version")).map(_.mkString.trim)
 
+  override def diff(repo: File, branch: Branch): F[List[String]] =
+    git("diff", branch.name)(repo)
+
   private def git(args: String*)(repo: File): F[List[String]] =
     processAlg.exec(Nel.of("git", args: _*), repo, "GIT_ASKPASS" -> config.gitAskPass.pathAsString)
 

modules/core/src/main/scala/org/scalasteward/core/git/GenGitAlg.scala

@@ -69,6 +69,8 @@ trait GenGitAlg[F[_], Repo] {
 
   def version: F[String]
 
+  def diff(repo: Repo, branch: Branch): F[List[String]]
+
   final def commitAllIfDirty(repo: Repo, message: String, messages: String*)(implicit
       F: Monad[F]
   ): F[Option[Commit]] =
@@ -142,6 +144,9 @@ trait GenGitAlg[F[_], Repo] {
 
       override def version: F[String] =
         self.version
+
+      override def diff(repo: A, branch: Branch): F[List[String]] =
+        f(repo).flatMap(self.diff(_, branch))
     }
   }
 }