Remove printing inefficiencies

Two major changes

 - Remove the recursive `show` when homogenizing Or-types.
   This one caused a combinatorial explosion when test-pickling
   Compiler.scala, because the phases list is an OrType of many
   element types.

 - Make `provided` by name in its text prefix.

Author: odersky

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

@@ -53,10 +53,7 @@ class PlainPrinter(_ctx: Context) extends Printer {
         case AndType(tp1, tp2) =>
           homogenize(tp1) & homogenize(tp2)
         case OrType(tp1, tp2) =>
-          if (tp1.show > tp2.show)
-            homogenize(tp1) | homogenize(tp2)
-          else
-            homogenize(tp2) | homogenize(tp1)
+          homogenize(tp1) | homogenize(tp2)
         case tp: SkolemType =>
           homogenize(tp.info)
         case tp: LazyRef =>
@@ -199,20 +196,20 @@ class PlainPrinter(_ctx: Context) extends Printer {
       case tp: TypeLambda =>
         changePrec(GlobalPrec) {
           "[" ~ paramsText(tp) ~ "]" ~ lambdaHash(tp) ~
-          (" => " provided !tp.resultType.isInstanceOf[MethodType]) ~
+          (Str(" => ") provided !tp.resultType.isInstanceOf[MethodType]) ~
           toTextGlobal(tp.resultType)
         }
       case AnnotatedType(tpe, annot) =>
         toTextLocal(tpe) ~ " " ~ toText(annot)
       case tp: TypeVar =>
         if (tp.isInstantiated)
-          toTextLocal(tp.instanceOpt) ~ ("^" provided ctx.settings.YprintDebug.value)
+          toTextLocal(tp.instanceOpt) ~ (Str("^") provided ctx.settings.YprintDebug.value)
         else {
           val constr = ctx.typerState.constraint
           val bounds =
             if (constr.contains(tp)) constr.fullBounds(tp.origin)(ctx.addMode(Mode.Printing))
             else TypeBounds.empty
-          if (bounds.isAlias) toText(bounds.lo) ~ ("^" provided ctx.settings.YprintDebug.value)
+          if (bounds.isAlias) toText(bounds.lo) ~ (Str("^") provided ctx.settings.YprintDebug.value)
           else if (ctx.settings.YshowVarBounds.value) "(" ~ toText(tp.origin) ~ "?" ~ toText(bounds) ~ ")"
           else toText(tp.origin)
         }
@@ -498,7 +495,7 @@ class PlainPrinter(_ctx: Context) extends Printer {
           else
             Text()
 
-        nodeName ~ "(" ~ elems ~ tpSuffix ~ ")" ~ (node.pos.toString provided ctx.settings.YprintPos.value)
+        nodeName ~ "(" ~ elems ~ tpSuffix ~ ")" ~ (Str(node.pos.toString) provided ctx.settings.YprintPos.value)
       case _ =>
         tree.fallbackToText(this)
     }
@@ -544,6 +541,7 @@ class PlainPrinter(_ctx: Context) extends Printer {
   def plain = this
 
   protected def keywordStr(text: String): String = coloredStr(text, SyntaxHighlighting.KeywordColor)
+  protected def keywordText(text: String): Text = coloredStr(text, SyntaxHighlighting.KeywordColor)
   protected def valDefText(text: Text): Text = coloredText(text, SyntaxHighlighting.ValDefColor)
   protected def typeText(text: Text): Text = coloredText(text, SyntaxHighlighting.TypeColor)
   protected def literalText(text: Text): Text = coloredText(text, SyntaxHighlighting.LiteralColor)

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

@@ -124,11 +124,11 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
             atPrec(InfixPrec) { argText(args.head) }
           else
             toTextTuple(args.init)
-        (keywordStr("implicit ") provided isImplicit) ~ argStr ~ " => " ~ argText(args.last)
+        (keywordText("implicit ") provided isImplicit) ~ argStr ~ " => " ~ argText(args.last)
       }
 
     def toTextDependentFunction(appType: MethodType): Text = {
-      ("implicit " provided appType.isImplicitMethod) ~
+      (keywordText("implicit ") provided appType.isImplicitMethod) ~
       "(" ~ paramsText(appType) ~ ") => " ~ toText(appType.resultType)
     }
 
@@ -185,7 +185,7 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
         withoutPos(super.toText(tp))
       case tp: SelectionProto =>
         return "?{ " ~ toText(tp.name) ~
-           (" " provided !tp.name.toSimpleName.last.isLetterOrDigit) ~
+           (Str(" ") provided !tp.name.toSimpleName.last.isLetterOrDigit) ~
            ": " ~ toText(tp.memberProto) ~ " }"
       case tp: ViewProto =>
         return toText(tp.argType) ~ " ?=>? " ~ toText(tp.resultType)
@@ -271,7 +271,7 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
       if (homogenizedView && mods.flags.isTypeFlags) flagMask &~= Implicit // drop implicit from classes
       val flags = mods.flags & flagMask
       val flagsText = if (flags.isEmpty) "" else keywordStr((mods.flags & flagMask).toString)
-      Text(mods.annotations.map(annotText), " ") ~~ flagsText ~~ (kw provided !suppressKw)
+      Text(mods.annotations.map(annotText), " ") ~~ flagsText ~~ (Str(kw) provided !suppressKw)
     }
 
     def varianceText(mods: untpd.Modifiers) =
@@ -342,7 +342,7 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
 
       val bodyText = "{" ~~ selfText ~~ toTextGlobal(primaryConstrs ::: body, "\n") ~ "}"
 
-      prefix ~ (keywordStr(" extends") provided !ofNew) ~~ parentsText ~~ bodyText
+      prefix ~ (keywordText(" extends") provided !ofNew) ~~ parentsText ~~ bodyText
     }
 
     def toTextPackageId(pid: Tree): Text =
@@ -411,7 +411,7 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
         blockText(stats :+ expr)
       case If(cond, thenp, elsep) =>
         changePrec(GlobalPrec) {
-          keywordStr("if ") ~ toText(cond) ~ (keywordStr(" then") provided !cond.isInstanceOf[Parens]) ~~ toText(thenp) ~ optText(elsep)(keywordStr(" else ") ~ _)
+          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) ~

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

@@ -146,8 +146,6 @@ object Texts {
     def over (that: Text) =
       if (this.isVertical) Vertical(that :: this.relems)
       else Vertical(that :: this :: Nil)
-
-    def provided(pred: Boolean) = if (pred) this else Str("")
   }
 
   object Text {
@@ -169,6 +167,10 @@ object Texts {
 
     /** The given texts `xs`, each on a separate line */
     def lines(xs: Traversable[Text]) = Vertical(xs.toList.reverse)
+
+    implicit class textDeco(text: => Text) {
+      def provided(cond: Boolean): Text = if (cond) text else Str("")
+    }
   }
 
   case class Str(s: String, lineRange: LineRange = EmptyLineRange) extends Text {