Revert <: Product requierment in pattern matching

The change in question broke the following pattern, commonly used in name based pattern matching:

```scala
object ProdEmpty {
  def _1: Int = ???
  def _2: String = ???
  def isEmpty = true
  def get = this
}
```

This type define both `_1` and `get` + `isEmpty` (but is not <: Product). After #1938, `ProdEmpty` became eligibles for both product and name based pattern. Because "in case of ambiguities, *Product Pattern* is preferred over *Name Based Pattern*", isEmpty wouldn't be used, breaking the scalac semantics.

1 files changed, 3 insertions, 1 deletions

diff --git a/compiler/src/dotty/tools/dotc/core/Definitions.scala b/compiler/src/dotty/tools/dotc/core/Definitions.scala
index a97589d73..eee6ba785 100644
--- a/compiler/src/dotty/tools/dotc/core/Definitions.scala
+++ b/compiler/src/dotty/tools/dotc/core/Definitions.scala
@@ -10,7 +10,6 @@ import scala.collection.{ mutable, immutable }
 import PartialFunction._
 import collection.mutable
 import util.common.alwaysZero
-import typer.Applications
 
 object Definitions {
 
@@ -846,6 +845,9 @@ class Definitions {
     TupleType(elems.size).appliedTo(elems)
   }
 
+  def isProductSubType(tp: Type)(implicit ctx: Context) =
+    tp.derivesFrom(ProductType.symbol)
+
   /** Is `tp` (an alias) of either a scala.FunctionN or a scala.ImplicitFunctionN? */
   def isFunctionType(tp: Type)(implicit ctx: Context) = {
     val arity = functionArity(tp)