Do not print extends Object whlie decompiling

Author: nicolasstucki

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

@@ -1,6 +1,6 @@
 package dotty.tools.dotc.printing
 
-import dotty.tools.dotc.ast.Trees.{Closure, DefDef, Untyped, ValDef}
+import dotty.tools.dotc.ast.Trees._
 import dotty.tools.dotc.ast.untpd.{PackageDef, Template, TypeDef}
 import dotty.tools.dotc.ast.{Trees, untpd}
 import dotty.tools.dotc.printing.Texts._
@@ -49,6 +49,12 @@ class DecompilerPrinter(_ctx: Context) extends RefinedPrinter(_ctx) {
     decl ~~ typeText(nameIdText(tree)) ~ withEnclosingDef(tree) { toTextTemplate(impl) } ~ ""
   }
 
+  override protected def toTextTemplate(impl: Template, ofNew: Boolean = false): Text = {
+    val Template(constr, parents, self, preBody) = impl
+    val impl1 = Template(constr, parents.filterNot(_.symbol.maybeOwner == defn.ObjectClass), self, preBody)
+    super.toTextTemplate(impl1, ofNew)
+  }
+
   override protected def defDefToText[T >: Untyped](tree: DefDef[T]): Text = {
     import untpd.{modsDeco => _, _}
     dclTextOr(tree) {

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

@@ -654,7 +654,7 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
 
     val bodyText = "{" ~~ selfText ~~ toTextGlobal(primaryConstrs ::: body, "\n") ~ "}"
 
-    prefix ~ (keywordText(" extends") provided !ofNew) ~~ parentsText ~~ bodyText
+    prefix ~ (keywordText(" extends") provided (!ofNew && parents.nonEmpty)) ~~ parentsText ~~ bodyText
   }
 
   protected def templateText(tree: TypeDef, impl: Template): Text = {

tests/pos/lambda.decompiled

@@ -2,7 +2,7 @@
 out/posTestFromTasty/pos/lambda/foo/Foo.class
 --------------------------------------------------------------------------------
 package foo {
-  class Foo() extends Object() {
+  class Foo() {
     val a: Int => Int =
       {
         (x: Int) => x.*(x)

tests/pos/methodTypes.decompiled

@@ -1,7 +1,7 @@
 ================================================================================
 out/posTestFromTasty/pos/methodTypes/Foo.class
 --------------------------------------------------------------------------------
-class Foo() extends Object() {
+class Foo() {
   val x: Int = 1
   def y: Int = 2
   def z(): Int = 3

tests/pos/simpleCaseObject.decompiled

@@ -2,9 +2,7 @@
 out/posTestFromTasty/pos/simpleCaseObject/foo/Foo.class
 --------------------------------------------------------------------------------
 package foo {
-  case object Foo() extends Object() with _root_.scala.Product {
-    this: foo.Foo.type =>
-
+  case object Foo() extends _root_.scala.Product { this: foo.Foo.type =>
     override def hashCode(): Int = 1045991777
     override def toString(): String = "Foo"
     override def canEqual(that: Any): Boolean = that.isInstanceOf[foo.Foo]

tests/pos/simpleClass-2.decompiled

@@ -9,6 +9,6 @@ package foo {
 out/posTestFromTasty/pos/simpleClass-2/foo/B.class
 --------------------------------------------------------------------------------
 package foo {
-  class B() extends Object() {}
+  class B() {}
 }
 --------------------------------------------------------------------------------

tests/pos/simpleClass.decompiled

@@ -2,7 +2,7 @@
 out/posTestFromTasty/pos/simpleClass/foo/A.class
 --------------------------------------------------------------------------------
 package foo {
-  class A() extends Object() {}
+  class A() {}
 }
 --------------------------------------------------------------------------------
 ================================================================================

tests/pos/simpleDoWhile.decompiled

@@ -1,7 +1,7 @@
 ================================================================================
 out/posTestFromTasty/pos/simpleDoWhile/Foo.class
 --------------------------------------------------------------------------------
-class Foo() extends Object() {
+class Foo() {
   def foo: Unit =
     {
       var i: Int = 1

tests/pos/simpleWhile.decompiled

@@ -1,7 +1,7 @@
 ================================================================================
 out/posTestFromTasty/pos/simpleWhile/Foo.class
 --------------------------------------------------------------------------------
-class Foo() extends Object() {
+class Foo() {
   def foo: Unit =
     {
       var i: Int = 1

tests/run/puzzle.decompiled

@@ -1,7 +1,7 @@
 ================================================================================
 out/runTestFromTasty/run/puzzle/Test.class
 --------------------------------------------------------------------------------
-object Test() extends Object() { this: Test.type =>
+object Test() { this: Test.type =>
   def main(args: Array[String]): Unit =
     {
       println(if false then 5.0 else 53.0)