Revert "Wrap unsafeNull members in flexible types during unpickling"

This reverts commit c335b18.

Author: olhotak

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

@@ -55,7 +55,7 @@ object JavaNullInterop {
    */
   def nullifyMember(sym: Symbol, tp: Type, isEnumValueDef: Boolean)(using Context): Type = trace(i"nullifyMember ${sym}, ${tp}"){
     assert(ctx.explicitNulls)
-    // assert(sym.is(JavaDefined), "can only nullify java-defined members")
+    assert(sym.is(JavaDefined), "can only nullify java-defined members")
 
     // Some special cases when nullifying the type
     if isEnumValueDef || sym.name == nme.TYPE_ then

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

@@ -981,12 +981,6 @@ class TreeUnpickler(reader: TastyReader,
           sym.info = tpt.tpe
           ValDef(tpt)
       }
-
-      // If explicit nulls is enabled, and the source file did not have explicit
-      // nulls enabled, nullify the member to allow for compatibility.
-      if (ctx.explicitNulls && !explicitNulls) then
-        sym.info = JavaNullInterop.nullifyMember(sym, sym.info, sym.is(Enum))
-
       goto(end)
       setSpan(start, tree)
 

compiler/test/dotty/tools/dotc/CompilationTests.scala

@@ -217,18 +217,8 @@ class CompilationTests {
       compileFilesInDir("tests/explicit-nulls/pos", explicitNullsOptions),
       compileFilesInDir("tests/explicit-nulls/flexible-types-common", explicitNullsOptions),
       compileFilesInDir("tests/explicit-nulls/unsafe-common", explicitNullsOptions and "-language:unsafeNulls" and "-Yno-flexible-types"),
-    ).checkCompile()
-
-    locally {
-      val tests = List(
-        compileFile("tests/explicit-nulls/flexible-unpickle/Unsafe_1.scala", explicitNullsOptions without "-Yexplicit-nulls"),
-        compileFile("tests/explicit-nulls/flexible-unpickle/Flexible_2.scala", explicitNullsOptions.withClasspath(
-          defaultOutputDir + testGroup + "/Unsafe_1/flexible-unpickle/Unsafe_1")),
-      ).map(_.keepOutput.checkCompile())
-
-      tests.foreach(_.delete())
-    }
-  }
+    )
+  }.checkCompile()
 
   @Test def explicitNullsWarn: Unit = {
     implicit val testGroup: TestGroup = TestGroup("explicitNullsWarn")