Check types for overriding conditions.

Closes #241 -- that took a while!

1 files changed, 15 insertions, 5 deletions

diff --git a/src/dotty/tools/dotc/typer/RefChecks.scala b/src/dotty/tools/dotc/typer/RefChecks.scala
index 44d5ee576..4bd02b356 100644
--- a/src/dotty/tools/dotc/typer/RefChecks.scala
+++ b/src/dotty/tools/dotc/typer/RefChecks.scala
@@ -172,8 +172,8 @@ object RefChecks {
       val sym1 = sym.underlyingSymbol
       def info = self.memberInfo(sym1)
       i"${if (showLocation) sym1.showLocated else sym1}${
-        if (sym1.isAliasType) i", which equals $info"
-        else if (sym1.isAbstractType) i" with bounds $info"
+        if (sym1.isAliasType) i", which equals ${info.bounds.hi}"
+        else if (sym1.isAbstractType) i" with bounds$info"
         else if (sym1.is(Module)) ""
         else if (sym1.isTerm) i" of type $info"
         else ""
@@ -229,6 +229,18 @@ object RefChecks {
           (if (otherAccess == "") "public" else "at least " + otherAccess))
       }
 
+      def compatibleTypes =
+        if (member.isType) { // intersection of bounds to refined types must be nonempty
+          member.is(BaseTypeArg) ||
+          (memberTp <:< otherTp) || {
+            val jointBounds = (memberTp.bounds & otherTp.bounds).bounds
+            jointBounds.lo <:< jointBounds.hi
+          }
+        }
+        else
+          isDefaultGetter(member.name) || // default getters are not checked for compatibility
+          memberTp.overrides(otherTp)
+
       //Console.println(infoString(member) + " overrides " + infoString(other) + " in " + clazz);//DEBUG
 
       // return if we already checked this combination elsewhere
@@ -321,9 +333,7 @@ object RefChecks {
         overrideError("cannot be used here - term macros cannot override abstract methods")
       } else if (other.is(Macro) && !member.is(Macro)) { // (1.10)
         overrideError("cannot be used here - only term macros can override term macros")
-      } else if (member.isTerm && !isDefaultGetter(member.name) && !(memberTp overrides otherTp)) {
-        // types don't need to have their bounds in an overriding relationship
-        // since we automatically form their intersection when selecting.
+      } else if (!compatibleTypes) {
         overrideError("has incompatible type" + err.whyNoMatchStr(memberTp, otherTp))
       } else {
         checkOverrideDeprecated()