Fix joins and join approximations of capturing types

Author: odersky

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

@@ -2090,8 +2090,8 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
     if (tp1 eq tp2) tp1
     else if (!tp1.exists) tp1
     else if (!tp2.exists) tp2
-    else if tp1.isAny && !tp2.isLambdaSub || tp1.isAnyKind || isBottom(tp2) then tp1
-    else if tp2.isAny && !tp1.isLambdaSub || tp2.isAnyKind || isBottom(tp1) then tp2
+    else if tp1.isAny && !tp2.isLambdaSub && tp2.noCaptures || tp1.isAnyKind || isBottom(tp2) then tp1
+    else if tp2.isAny && !tp1.isLambdaSub && tp1.noCaptures || tp2.isAnyKind || isBottom(tp1) then tp2
     else
       def mergedLub(tp1: Type, tp2: Type): Type = {
         tp1.atoms match

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

@@ -266,15 +266,23 @@ object TypeOps:
         case _ => false
       }
 
-      // Step 1: Get RecTypes and ErrorTypes out of the way,
+      // Step 1: Get RecTypes and ErrorTypes and CapturingTypes out of the way,
       tp1 match {
-        case tp1: RecType => return tp1.rebind(approximateOr(tp1.parent, tp2))
-        case err: ErrorType => return err
+        case tp1: RecType =>
+          return tp1.rebind(approximateOr(tp1.parent, tp2))
+        case tp1: CapturingType =>
+          return tp1.derivedCapturingType(approximateOr(tp1.parent, tp2), tp1.ref)
+        case err: ErrorType =>
+          return err
         case _ =>
       }
       tp2 match {
-        case tp2: RecType => return tp2.rebind(approximateOr(tp1, tp2.parent))
-        case err: ErrorType => return err
+        case tp2: RecType =>
+          return tp2.rebind(approximateOr(tp1, tp2.parent))
+        case tp2: CapturingType =>
+          return tp2.derivedCapturingType(approximateOr(tp1, tp2.parent), tp2.ref)
+        case err: ErrorType =>
+          return err
         case _ =>
       }