Add -XprintUser and pretty print lambdas with it

Enable flag by default for the decompiler

Author: nicolasstucki

compiler/src/dotty/tools/dotc/config/ScalaSettings.scala

@@ -60,6 +60,7 @@ class ScalaSettings extends Settings.SettingGroup {
   val XprintTypes = BooleanSetting("-Xprint-types", "Print tree types (debugging option).")
   val XprintDiff = BooleanSetting("-Xprint-diff", "Print changed parts of the tree since last print.")
   val XprintDiffDel = BooleanSetting("-Xprint-diff-del", "Print chaged parts of the tree since last print including deleted parts.")
+  val XprintUser = BooleanSetting("-Xprint-user", "Print the program using user friendly abstractions.")
   val Xprompt = BooleanSetting("-Xprompt", "Display a prompt after each error (debugging option).")
   val XmainClass = StringSetting("-Xmain-class", "path", "Class for manifest's Main-Class entry (only useful with -d <jar>)", "")
   val XnoValueClasses = BooleanSetting("-Xno-value-classes", "Do not use value classes. Helps debugging.")

compiler/src/dotty/tools/dotc/decompiler/Main.scala

@@ -16,6 +16,6 @@ object Main extends dotc.Driver {
   override def setup(args0: Array[String], rootCtx: Context): (List[String], Context) = {
     var args = args0.filter(a => a != "-decompile")
     args = if (args.contains("-from-tasty")) args else "-from-tasty" +: args
-    super.setup(args, rootCtx)
+    super.setup("-Xprint-user" +: args, rootCtx)
   }
 }

compiler/src/dotty/tools/dotc/printing/RefinedPrinter.scala

@@ -421,8 +421,8 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
           keywordStr("if ") ~ toText(cond) ~ (keywordText(" then") provided !cond.isInstanceOf[Parens]) ~~ toText(thenp) ~ optText(elsep)(keywordStr(" else ") ~ _)
         }
       case Closure(env, ref, target) =>
-        "closure(" ~ (toTextGlobal(env, ", ") ~ " | " provided env.nonEmpty) ~
-        toTextGlobal(ref) ~ (":" ~ toText(target) provided !target.isEmpty) ~ ")"
+        ("closure(" ~ (toTextGlobal(env, ", ") ~ " | " provided env.nonEmpty) ~
+        toTextGlobal(ref) ~ (":" ~ toText(target) provided !target.isEmpty) ~ ")").provided(!ctx.settings.XprintUser.value)
       case Match(sel, cases) =>
         if (sel.isEmpty) blockText(cases)
         else changePrec(GlobalPrec) { toText(sel) ~ keywordStr(" match ") ~ blockText(cases) }
@@ -486,10 +486,11 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
         }
       case tree @ DefDef(name, tparams, vparamss, tpt, _) =>
         dclTextOr {
-          val prefix = modText(tree.mods, keywordStr("def")) ~~ valDefText(nameIdText(tree))
+          val printLambda = tree.symbol.isAnonymousFunction && ctx.settings.XprintUser.value
+          val prefix = modText(tree.mods, keywordStr("def")) ~~ valDefText(nameIdText(tree)) provided (!printLambda)
           withEnclosingDef(tree) {
-            addVparamssText(prefix ~ tparamsText(tparams), vparamss) ~ optAscription(tpt) ~
-            optText(tree.rhs)(" = " ~ _)
+            addVparamssText(prefix ~ tparamsText(tparams), vparamss) ~ optAscription(tpt).provided(!printLambda) ~
+            optText(tree.rhs)((if (printLambda) " => " else " = ") ~ _)
           }
         }
       case tree @ TypeDef(name, rhs) =>