Fix handling of baseType of (A & Double) | Null

Author: dwijnand

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

@@ -369,7 +369,7 @@ object TypeOps:
       }
 
       // Step 3: Intersect base classes of both sides
-      val commonBaseClasses = tp.mapReduceOr(_.baseClasses)(intersect)
+      val commonBaseClasses = tp.mapReduceAndOr(_.baseClasses)(intersect)
       val doms = dominators(commonBaseClasses, Nil)
       def baseTp(cls: ClassSymbol): Type =
         tp.baseType(cls).mapReduceOr(identity)(mergeRefinedOrApplied)

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

@@ -478,6 +478,11 @@ object Types {
       case _ => f(this)
     }
 
+    final def mapReduceAndOr[T](f: Type => T)(g: (T, T) => T)(using Context): T = stripTypeVar match {
+      case tp: AndOrType => g(tp.tp1.mapReduceAndOr(f)(g), tp.tp2.mapReduceAndOr(f)(g))
+      case _ => f(this)
+    }
+
 // ----- Associated symbols ----------------------------------------------
 
     /** The type symbol associated with the type */

tests/pos/i16236.scala

@@ -0,0 +1,9 @@
+trait A
+
+def consume[T](t: T): Unit = ()
+
+def fails(p: (Double & A) | Null): Unit = consume(p) // was: assertion failed: <notype> & A
+
+def switchedOrder(p: (A & Double) | Null): Unit = consume(p) // ok
+def nonPrimitive(p: (String & A) | Null): Unit = consume(p) // ok
+def notNull(p: (Double & A)): Unit = consume(p) // ok