Check that non-abstract classes have realizable bounds.

2 files changed, 22 insertions, 10 deletions

diff --git a/src/dotty/tools/dotc/core/TypeOps.scala b/src/dotty/tools/dotc/core/TypeOps.scala
index 882ab9f10..227dbb90f 100644
--- a/src/dotty/tools/dotc/core/TypeOps.scala
+++ b/src/dotty/tools/dotc/core/TypeOps.scala
@@ -449,16 +449,21 @@ trait TypeOps { this: Context => // TODO: Make standalone object.
         case _ => false
       }
       if (!isConcrete(tp)) NotConcrete
-      else {
-        def hasBadBounds(mbr: SingleDenotation) = {
-          val bounds = mbr.info.bounds
-          !(bounds.lo <:< bounds.hi)
-        }
-        tp.nonClassTypeMembers.find(hasBadBounds) match {
-          case Some(mbr) => new HasProblemBounds(mbr)
-          case _ => Realizable
-        }
-      }
+      else boundsRealizability(tp)
+  }
+
+  /** `Realizable` is `tp` has good bounds, a `HasProblemBounds` instance
+   *  pointing to a bad bounds member otherwise.
+   */
+  def boundsRealizability(tp: Type)(implicit ctx: Context) = {
+    def hasBadBounds(mbr: SingleDenotation) = {
+      val bounds = mbr.info.bounds
+      !(bounds.lo <:< bounds.hi)
+    }
+    tp.nonClassTypeMembers.find(hasBadBounds) match {
+      case Some(mbr) => new HasProblemBounds(mbr)
+      case _ => Realizable
+    }
   }
 
   private def enterArgBinding(formal: Symbol, info: Type, cls: ClassSymbol, decls: Scope) = {
diff --git a/src/dotty/tools/dotc/typer/Checking.scala b/src/dotty/tools/dotc/typer/Checking.scala
index ca7c5c5ab..7e90d755b 100644
--- a/src/dotty/tools/dotc/typer/Checking.scala
+++ b/src/dotty/tools/dotc/typer/Checking.scala
@@ -330,6 +330,13 @@ trait Checking {
     }
   }
 
+  /** Check that all type members of `tp` have realizable bounds */
+  def checkRealizableBounds(tp: Type, pos: Position)(implicit ctx: Context): Unit = {
+    val rstatus = ctx.boundsRealizability(tp)
+    if (rstatus ne TypeOps.Realizable)
+      ctx.error(i"$tp cannot be instantiated since it${rstatus.msg}", pos)
+  }
+
  /**  Check that `tp` is a class type with a stable prefix. Also, if `traitReq` is
    *  true check that `tp` is a trait.
    *  Stability checking is disabled in phases after RefChecks.