Simplify type bounds.

I started out looking to limit the noise from empty type
bounds, i.e. the endless repetition of

  class A[T >: _root_.scala.Nothing <: _root_.scala.Any]

This led me to be reminded of all the unnecessary and
in fact damaging overreaches which are performed during parsing.
Why should a type parameter for which no bounds are
specified be immediately encoded with this giant tree:

  TypeBounds(
    Select(Select(Ident(nme.ROOTPKG), tpnme.scala_), tpnme.Nothing),
    Select(Select(Ident(nme.ROOTPKG), tpnme.scala_), tpnme.Any)
  )

...which must then be manually recognized as empty type bounds?
Truly, this is madness.

 - It deftly eliminates the possibility of recognizing
   whether the user wrote "class A[T]" or "class A[T >: Nothing]"
   or "class A[T <: Any]" or specified both bounds. The fact
   that these work out the same internally does not imply the
   information should be exterminated even before parsing completes.
 - It burdens everyone who must recognize type bounds trees,
   such as this author
 - It is far less efficient than the obvious encoding
 - It offers literally no advantage whatsoever

Encode empty type bounds as

  TypeBounds(EmptyTree, EmptyTree)

What could be simpler.

1 files changed, 2 insertions, 6 deletions

diff --git a/test/files/run/analyzerPlugins.check b/test/files/run/analyzerPlugins.check
index 297bd36bae..641fbfff6b 100644
--- a/test/files/run/analyzerPlugins.check
+++ b/test/files/run/analyzerPlugins.check
@@ -25,13 +25,13 @@ pluginsPt(?, Trees$Assign) [7]
 pluginsPt(?, Trees$Block) [4]
 pluginsPt(?, Trees$ClassDef) [2]
 pluginsPt(?, Trees$DefDef) [14]
-pluginsPt(?, Trees$Ident) [51]
+pluginsPt(?, Trees$Ident) [50]
 pluginsPt(?, Trees$If) [2]
 pluginsPt(?, Trees$Literal) [16]
 pluginsPt(?, Trees$New) [5]
 pluginsPt(?, Trees$PackageDef) [1]
 pluginsPt(?, Trees$Return) [1]
-pluginsPt(?, Trees$Select) [52]
+pluginsPt(?, Trees$Select) [48]
 pluginsPt(?, Trees$Super) [2]
 pluginsPt(?, Trees$This) [20]
 pluginsPt(?, Trees$TypeApply) [4]
@@ -112,7 +112,6 @@ pluginsTyped(<notype>, Trees$DefDef) [14]
 pluginsTyped(<notype>, Trees$PackageDef) [1]
 pluginsTyped(<notype>, Trees$TypeDef) [1]
 pluginsTyped(<notype>, Trees$ValDef) [21]
-pluginsTyped(<root>, Trees$Ident) [1]
 pluginsTyped(=> Boolean @testAnn, Trees$Select) [1]
 pluginsTyped(=> Double, Trees$Select) [4]
 pluginsTyped(=> Int, Trees$Select) [5]
@@ -151,7 +150,6 @@ pluginsTyped(List[Any], Trees$Apply) [1]
 pluginsTyped(List[Any], Trees$Select) [1]
 pluginsTyped(List[Any], Trees$TypeTree) [3]
 pluginsTyped(Nothing, Trees$Return) [1]
-pluginsTyped(Nothing, Trees$Select) [2]
 pluginsTyped(Object, Trees$Apply) [1]
 pluginsTyped(String @testAnn, Trees$Ident) [1]
 pluginsTyped(String @testAnn, Trees$Select) [1]
@@ -185,8 +183,6 @@ pluginsTyped(scala.annotation.TypeConstraint, Trees$TypeTree) [2]
 pluginsTyped(scala.collection.immutable.List.type, Trees$Select) [2]
 pluginsTyped(scala.collection.immutable.StringOps, Trees$ApplyImplicitView) [2]
 pluginsTyped(scala.collection.mutable.WrappedArray[Any], Trees$Apply) [1]
-pluginsTyped(scala.type, Trees$Ident) [1]
-pluginsTyped(scala.type, Trees$Select) [1]
 pluginsTyped(str.type, Trees$Ident) [3]
 pluginsTyped(testAnn, Trees$Apply) [5]
 pluginsTyped(testAnn, Trees$Ident) [5]