Harden orDominator

Fixes #13435

Author: odersky

compiler/src/dotty/tools/dotc/core/TypeOps.scala

@@ -349,7 +349,7 @@ object TypeOps:
       val doms = dominators(commonBaseClasses, Nil)
       def baseTp(cls: ClassSymbol): Type =
         tp.baseType(cls).mapReduceOr(identity)(mergeRefinedOrApplied)
-      doms.map(baseTp).reduceLeft(AndType.apply)
+      doms.map(baseTp).filter(_.exists).reduceLeft(AndType.apply)
     }
 
     tp match {

tests/neg/i13435.check

@@ -0,0 +1,32 @@
+class sym (Axis, Int) | ShapeTuple
+class sym Int *: EmptyTuple.type | (EmptyTuple.type | (Axis, Int) *: EmptyTuple.type)
+approx or Int *: EmptyTuple.type | (EmptyTuple.type | (Axis, Int) *: EmptyTuple.type)///trait Tuple/// Tuple
+approx or (Axis, Int) | ShapeTuple///trait Product2, trait Serializable, class *:/// <notype>, Serializable, (Axis | (Axis, Int)) *: (Int *: EmptyTuple.type | (EmptyTuple.type | (Axis, Int)
+   
+*: EmptyTuple.type))
+class sym Tuple1[(Axis, Int)] | ((Axis, Int), (Axis, Int))
+class sym EmptyTuple.type | (Axis, Int) *: EmptyTuple.type
+approx or EmptyTuple | (Axis, Int) *: EmptyTuple.type///trait Tuple/// Tuple
+approx or Tuple1[(Axis, Int)] | ((Axis, Int), (Axis, Int))///trait Serializable, class *:/// Serializable, (Axis, Int) *: (EmptyTuple.type | (Axis, Int) *: EmptyTuple.type)
+-- [E029] Pattern Match Exhaustivity Warning: i13435.scala:7:2 -----------------
+7 |  s match
+  |  ^
+  |  match may not be exhaustive.
+  |
+  |  It would fail on pattern case: (_), ((_, _), (_, _))
+
+longer explanation available when compiling with `-explain`
+class sym (Axis, Int) | ShapeTuple
+class sym Tuple1[(Axis, Int)] | ((Axis, Int), (Axis, Int))
+class sym (Axis, Int) | ShapeTuple
+class sym Int *: EmptyTuple.type | (EmptyTuple.type | (Axis, Int) *: EmptyTuple.type)
+approx or Int *: EmptyTuple.type | (EmptyTuple.type | (Axis, Int) *: EmptyTuple.type)///trait Tuple/// Tuple
+approx or (Axis, Int) | ShapeTuple///trait Product2, trait Serializable, class *:/// <notype>, Serializable, (Axis | (Axis, Int)) *: (Int *: EmptyTuple.type | (EmptyTuple.type | (Axis, Int)
+   
+*: EmptyTuple.type))
+-- Error: i13435.scala:8:10 ----------------------------------------------------
+8 |    case (dim: Axis, size: Int) => dim // error
+  |          ^^^^^^^^^
+  |          trait Singleton cannot be used in runtime type tests
+1 warning found
+1 error found

tests/neg/i13435.scala

@@ -0,0 +1,8 @@
+type Axis = String&Singleton
+type ShapeTuple = Tuple1[(Axis, Int)]|Tuple2[(Axis, Int), (Axis, Int)]
+type Shape = (Axis, Int) |ShapeTuple
+
+
+def mkSchema(s: Shape) =
+  s match
+    case (dim: Axis, size: Int) => dim // error