More refined treatement of pattern type variables

Previously all lower case names were treated as variables
in patterns. But that made code like

    x: cls

crash the compiler if `cls` was a class. Also, it owuld preventing
this idiom unless one wrote

    x: `cls`

We now do it like scalac and treat lower case names as variables
only in arguments of types.

1 files changed, 6 insertions, 0 deletions

diff --git a/src/dotty/tools/dotc/ast/Desugar.scala b/src/dotty/tools/dotc/ast/Desugar.scala
index 6c914c934..327b39897 100644
--- a/src/dotty/tools/dotc/ast/Desugar.scala
+++ b/src/dotty/tools/dotc/ast/Desugar.scala
@@ -517,6 +517,12 @@ object desugar {
       }
   }
 
+  /** Expand variable identifier x to x @ _ */
+  def patternVar(tree: Tree)(implicit ctx: Context) = {
+    val Ident(name) = tree
+    Bind(name, Ident(nme.WILDCARD)).withPos(tree.pos)
+  }
+
   def defTree(tree: Tree)(implicit ctx: Context): Tree = tree match {
     case tree: ValDef => valDef(tree)
     case tree: TypeDef => if (tree.isClassDef) classDef(tree) else typeDef(tree)