Also propagate language imports into block expressions

Author: odersky

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

@@ -1059,7 +1059,7 @@ class TreeUnpickler(reader: TastyReader,
       else
         Nil
 
-    def readIndexedStats(exprOwner: Symbol, end: Addr)(using Context): List[Tree] =
+    def readIndexedStats[T](exprOwner: Symbol, end: Addr, k: (List[Tree], Context) => T = sameTrees)(using Context): T =
       val buf = new mutable.ListBuffer[Tree]
       var curCtx = ctx
       while currentAddr.index < end.index do
@@ -1069,13 +1069,15 @@ class TreeUnpickler(reader: TastyReader,
           case stat: Import => curCtx = ctx.importContext(stat, stat.symbol)
           case _ =>
       assert(currentAddr.index == end.index)
-      buf.toList
+      k(buf.toList, curCtx)
 
-    def readStats(exprOwner: Symbol, end: Addr)(using Context): List[Tree] = {
+    def readStats[T](exprOwner: Symbol, end: Addr, k: (List[Tree], Context) => T = sameTrees)(using Context): T = {
       fork.indexStats(end)
-      readIndexedStats(exprOwner, end)
+      readIndexedStats(exprOwner, end, k)
     }
 
+    private def sameTrees(xs: List[Tree], ctx: Context) = xs
+
     def readIndexedParams[T <: MemberDef](tag: Int)(using Context): List[T] =
       collectWhile(nextByte == tag) { readIndexedDef().asInstanceOf[T] }
 
@@ -1183,9 +1185,8 @@ class TreeUnpickler(reader: TastyReader,
             case BLOCK =>
               val exprReader = fork
               skipTree()
-              val stats = readStats(ctx.owner, end)
-              val expr = exprReader.readTerm()
-              Block(stats, expr)
+              readStats(ctx.owner, end,
+                (stats, ctx) => Block(stats, exprReader.readTerm()(using ctx)))
             case INLINED =>
               val exprReader = fork
               skipTree()

tests/explicit-nulls/pos-special/i14947.scala

@@ -1,7 +1,14 @@
+class B:
+  def g: String | Null = ???
+
+  def f =
+    import scala.language.unsafeNulls
+    if ??? then "" else g
+
 import scala.language.unsafeNulls
 class C {
   def g: String | Null = ???
 
   def f =
     if ??? then "" else g
-}
+}