Don't simplify lubs when unpickling Ifs

I was not able to find out why that's the case, but the original test
case with the import in the function body requires that if's are _not_
simplified by Unpickler. The interaction with lubs and unsafenulls seems
to be very tricky.

Anyway, we now have two versions of all test cases, with local as well as
globak unsafe nulls.

Author: odersky

compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala

@@ -1236,13 +1236,12 @@ class TreeUnpickler(reader: TastyReader,
               val expansion = exprReader.readTerm() // need bindings in scope, so needs to be read before
               Inlined(call, bindings, expansion)
             case IF =>
-              simplifyLub(
-                if (nextByte == INLINE) {
-                  readByte()
-                  InlineIf(readTerm(), readTerm(), readTerm())
-                }
-                else
-                  If(readTerm(), readTerm(), readTerm()))
+              if (nextByte == INLINE) {
+                readByte()
+                InlineIf(readTerm(), readTerm(), readTerm())
+              }
+              else
+                If(readTerm(), readTerm(), readTerm())
             case LAMBDA =>
               val meth = readTerm()
               val tpt = ifBefore(end)(readTpt(), EmptyTree)

tests/pos/i15097.scala

@@ -1,13 +1,30 @@
-import scala.language.unsafeNulls
-class C {
+class C:
   def g: String | Null = ???
 
   def f =
+    import scala.language.unsafeNulls
     try g catch case _ => ""
 
-  def f2 = if ??? then g else ""
+  def f2 =
+    import scala.language.unsafeNulls
+    if ??? then g else ""
 
-  def f3 = (??? : Boolean) match
+  def f3 =
+    (??? : Boolean) match
+    case true => g
+    case _ => ""
+
+class C2:
+  import scala.language.unsafeNulls
+  def g: String | Null = ???
+
+  def f =
+    try g catch case _ => ""
+
+  def f2 =
+    if ??? then g else ""
+
+  def f3 =
+    (??? : Boolean) match
     case true => g
     case _ => ""
-}