Make nested map ops in Decorators an extension

Also, add a nestedZipWithConserve method

Author: odersky

compiler/src/dotty/tools/dotc/ast/Desugar.scala

@@ -5,7 +5,7 @@ package ast
 import core._
 import util.Spans._, Types._, Contexts._, Constants._, Names._, NameOps._, Flags._
 import Symbols._, StdNames._, Trees._
-import Decorators._, transform.SymUtils._
+import Decorators.{given _}, transform.SymUtils._
 import NameKinds.{UniqueName, EvidenceParamName, DefaultGetterName}
 import typer.{FrontEnd, Namer}
 import util.{Property, SourceFile, SourcePosition}
@@ -501,16 +501,11 @@ object desugar {
 
     // Annotations are dropped from the constructor parameters but should be
     // preserved in all derived parameters.
-    val derivedTparams = {
-      val impliedTparamsIt = impliedTparams.iterator
-      constrTparams.map(tparam => derivedTypeParam(tparam)
-        .withAnnotations(impliedTparamsIt.next().mods.annotations))
-    }
-    val derivedVparamss = {
-      val constrVparamsIt = constrVparamss.iterator.flatten
-      constrVparamss.nestedMap(vparam => derivedTermParam(vparam)
-        .withAnnotations(constrVparamsIt.next().mods.annotations))
-    }
+    val derivedTparams =
+      constrTparams.zipWithConserve(impliedTparams)((tparam, impliedParam) =>
+        derivedTypeParam(tparam).withAnnotations(impliedParam.mods.annotations))
+    val derivedVparamss =
+      constrVparamss.nestedMap(vparam => derivedTermParam(vparam))
 
     val arity = constrVparamss.head.length
 

compiler/src/dotty/tools/dotc/ast/tpd.scala

@@ -9,7 +9,7 @@ import transform.TypeUtils._
 import core._
 import util.Spans._, Types._, Contexts._, Constants._, Names._, Flags._, NameOps._
 import Symbols._, StdNames._, Annotations._, Trees._, Symbols._
-import Decorators._, DenotTransformers._
+import Decorators.{given _}, DenotTransformers._
 import collection.{immutable, mutable}
 import util.{Property, SourceFile, NoSource}
 import NameKinds.{TempResultName, OuterSelectName}

compiler/src/dotty/tools/dotc/core/Decorators.scala

@@ -155,10 +155,13 @@ object Decorators {
     def & (ys: List[T]): List[T] = xs filter (ys contains _)
   }
 
-  implicit class ListOfListDecorator[T](val xss: List[List[T]]) extends AnyVal {
-    def nestedMap[U](f: T => U): List[List[U]] = xss map (_ map f)
-    def nestedMapconserve[U](f: T => U): List[List[U]] = xss mapconserve (_ mapconserve f)
-  }
+  extension ListOfListDecorator on [T, U](xss: List[List[T]]):
+    def nestedMap(f: T => U): List[List[U]] =
+      xss.map(_.map(f))
+    def nestedMapConserve(f: T => U): List[List[U]] =
+      xss.mapconserve(_.mapconserve(f))
+    def nestedZipWithConserve(yss: List[List[U]])(f: (T, U) => T): List[List[T]] =
+      xss.zipWithConserve(yss)((xs, ys) => xs.zipWithConserve(ys)(f))
 
   implicit class TextToString(val text: Text) extends AnyVal {
     def show(implicit ctx: Context): String = text.mkString(ctx.settings.pageWidth.value, ctx.settings.printLines.value)

compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala

@@ -23,7 +23,7 @@ import util.Spans._
 import util.SourceFile
 import ast.{TreeTypeMap, Trees, tpd, untpd}
 import Trees._
-import Decorators._
+import Decorators.{given _}
 import transform.SymUtils._
 
 import dotty.tools.tasty.{TastyBuffer, TastyReader}

compiler/src/dotty/tools/dotc/transform/FullParameterization.scala

@@ -5,7 +5,7 @@ import core._
 import Types._
 import Contexts._
 import Symbols._
-import Decorators._
+import Decorators.{given _}
 import TypeUtils._
 import StdNames.nme
 import NameOps._

compiler/src/dotty/tools/dotc/typer/Namer.scala

@@ -5,7 +5,8 @@ package typer
 import core._
 import ast._
 import Trees._, StdNames._, Scopes._, Denotations._, Comments._
-import Contexts._, Symbols._, Types._, SymDenotations._, Names._, NameOps._, Flags._, Decorators._
+import Contexts._, Symbols._, Types._, SymDenotations._, Names._, NameOps._, Flags._
+import Decorators.{given _}
 import NameKinds.DefaultGetterName
 import TypeApplications.TypeParamInfo
 import ast.desugar, ast.desugar._

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -19,7 +19,7 @@ import Names._
 import NameOps._
 import NameKinds._
 import Flags._
-import Decorators._
+import Decorators.{given _}
 import ErrorReporting._
 import Checking._
 import Inferencing._
@@ -1706,8 +1706,8 @@ class Typer extends Namer
     }
     val DefDef(name, tparams, vparamss, tpt, _) = ddef
     completeAnnotations(ddef, sym)
-    val tparams1 = tparams mapconserve (typed(_).asInstanceOf[TypeDef])
-    val vparamss1 = vparamss nestedMapconserve (typed(_).asInstanceOf[ValDef])
+    val tparams1 = tparams.mapconserve(typed(_).asInstanceOf[TypeDef])
+    val vparamss1 = vparamss.nestedMapConserve(typed(_).asInstanceOf[ValDef])
     vparamss1.foreach(checkNoForwardDependencies)
     if (sym.isOneOf(GivenOrImplicit)) checkImplicitConversionDefOK(sym)
     val tpt1 = checkSimpleKinded(typedType(tpt))