Fix new problem uncovered by AndType fix

Fixes a new problem exhibited in the ZIO 1 code base that got uncovered
by the previous fix to AndTypes.

Author: odersky

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

@@ -926,10 +926,13 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
       then
         isSubType(base, tp2, if (tp1.isRef(cls2)) approx else approx.addLow)
         && recordGadtUsageIf { MatchType.thatReducesUsingGadt(tp1) }
-        || base.isInstanceOf[OrType] && fourthTry
-          // if base is a disjunction, this might have come from a tp1 type that
+        || base.isInstanceOf[AndOrType] && fourthTry
+          // If base is a disjunction, this might have come from a tp1 type that
           // expands to a match type. In this case, we should try to reduce the type
           // and compare the redux. This is done in fourthTry
+          // If base is a conjunction, it could be that one of the original
+          // branches of the AndType tp1 conforms to tp2, but its base type does
+          // not. So we need to also fall back to fourthTry. Test case is i18226a.scala.
       else fourthTry
     end tryBaseType
 

tests/neg-custom-args/allow-deep-subtypes/i5877.scala

@@ -20,7 +20,7 @@ object Main {
 
     def testHasThisType(): Unit = {
       def testSelf[PThis <: HasThisType[_ <: PThis]](that: HasThisType[PThis]): Unit = {
-        val thatSelf = that.self() // error: recursion limit exceeded
+        val thatSelf = that.self()
         // that.self().type <: that.This
         assert(implicitly[thatSelf.type <:< that.This] != null)
       }

tests/pos/i18226a.scala

@@ -0,0 +1,19 @@
+class Has[A]
+trait Foo
+
+class TestAspect[+LowerR, -UpperR]
+
+class Spec[-R] {
+  def foo[R1 <: R](aspect: TestAspect[R1, R1]): Unit = {}
+}
+
+class SuiteBuilder[R <: Has[_]] {
+  def toSpec(
+    spec: Spec[R & Has[Foo]],
+    aspect: TestAspect[
+      R & Has[Foo],
+      R & Has[Foo]
+    ]
+  ) =
+    spec.foo(aspect)
+}