CLI: add --mode diff-ref, deprecate --diff-branch

scalafmt-cli/src/main/scala/org/scalafmt/cli/CliArgParser.scala

@@ -123,12 +123,6 @@ object CliArgParser {
         .text(
           "test for mis-formatted code only, exits with status 1 on first failure."
         )
-      opt[Unit]("diff")
-        .action((_, c) => c.copy(mode = Option(DiffFiles("master"))))
-        .text(
-          s"""Format files listed in `git diff` against master.
-            |Deprecated: use --mode diff instead""".stripMargin
-        )
       opt[FileFetchMode]("mode")
         .action((m, c) => c.copy(mode = Option(m)))
         .text(
@@ -137,10 +131,17 @@ object CliArgParser {
             |${FileFetchMode.help}
             |""".stripMargin
         )
+      opt[Unit]("diff")
+        .action((_, c) => c.copy(mode = Option(DiffFiles("master"))))
+        .text(
+          s"""Format files listed in `git diff` against master.
+            |Deprecated: use --mode diff instead""".stripMargin
+        )
       opt[String]("diff-branch")
         .action((branch, c) => c.copy(mode = Option(DiffFiles(branch))))
         .text(
-          "If set, only format edited files in git diff against provided branch. Has no effect if mode set to `changed`."
+          s"""Format files listed in `git diff` against given git ref.
+            |Deprecated: use --mode diff-ref=<ref> instead""".stripMargin
         )
       opt[Unit]("build-info")
         .action((_, _) => { println(buildInfo); sys.exit })

scalafmt-cli/src/main/scala/org/scalafmt/cli/FileFetchMode.scala

@@ -10,24 +10,31 @@ sealed trait FileFetchMode {
 
 object FileFetchMode {
 
-  private val available: Map[String, FileFetchMode] = Map(
+  private val diffRefPrefix = "diff-ref="
+  private val availableModes = Seq(
     "diff" -> DiffFiles("master"),
     "changed" -> ChangedFiles,
     "any" -> RecursiveSearch,
     "anygit" -> GitFiles
   )
+  private val availableModesMap: Map[String, FileFetchMode] =
+    availableModes.toMap
 
-  def help = available
-    .map { case (k, v) => s"$k: ${v.desc}" }
-    .mkString("   ", "\n   ", "")
+  def help: String =
+    (("diff-ref=xxx", DiffFiles("xxx")) +: availableModes)
+      .map { case (k, v) => s"$k: ${v.desc}" }
+      .mkString("   ", "\n   ", "")
 
   /** The read instance is practically is not exhaustive due to the
     * RecursiveSearch and GitFiles are the fallback used in the absence of other
     * options
     */
   implicit val read: Read[FileFetchMode] = Read.reads { x =>
-    available
-      .getOrElse(x, throw new IllegalArgumentException(s"unknown mode: $x"))
+    if (x.startsWith(diffRefPrefix))
+      DiffFiles(x.substring(diffRefPrefix.length).trim)
+    else
+      availableModesMap
+        .getOrElse(x, throw new IllegalArgumentException(s"unknown mode: $x"))
   }
 
 }
@@ -49,7 +56,8 @@ case object GitFiles extends FileFetchMode {
   * When this is set, files passed via the cli are ignored.
   */
 final case class DiffFiles(branch: String) extends FileFetchMode {
-  def desc: String = s"format files listed in `git diff` against $branch"
+  def desc: String =
+    s"format files listed in `git diff` against gitref `$branch`"
 }
 
 /** A call to `git status --porcelain`