Add explicit nulls tasty attribute to CompilationUnit

Author: nicolasstucki

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

@@ -9,10 +9,12 @@ import dotty.tools.tasty.TastyVersion
   *                       the class containing this symbol was generated,
   *                       null if not applicable.
   * @param tastyVersion   The TASTy version (major, minor, experimental)
+  * @param tastyExplicitNulls  Was this compilation unit compiled with explicit nulls?
   */
 class CompilationUnitInfo(
   val associatedFile: AbstractFile,
   val tastyVersion: Option[TastyVersion],
+  val tastyExplicitNulls: Boolean
 ) {
 
   override def toString(): String =
@@ -22,4 +24,8 @@ class CompilationUnitInfo(
 object CompilationUnitInfo:
   def apply(assocFile: AbstractFile | Null): CompilationUnitInfo | Null =
     if assocFile == null then null
-    else new CompilationUnitInfo(assocFile, tastyVersion = None) // TODO use current TASTy version
+    else new CompilationUnitInfo(
+      assocFile,
+      tastyVersion = None,
+      tastyExplicitNulls = false
+    )

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

@@ -424,9 +424,11 @@ class TastyLoader(val tastyFile: AbstractFile) extends SymbolLoader {
 
   def compilationUnitInfo: CompilationUnitInfo | Null =
     val tastyHeader = unpickler.unpickler.header
+    val attributes = unpickler.tastyAttributes
     new CompilationUnitInfo(
       tastyFile,
       tastyVersion = Some(tastyHeader.version),
+      tastyExplicitNulls = attributes.explicitNulls,
     )
 
   def description(using Context): String = "TASTy file " + tastyFile.toString

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

@@ -56,6 +56,9 @@ class DottyUnpickler(bytes: Array[Byte], mode: UnpickleMode = UnpickleMode.TopLe
   private val attributeUnpicklerOpt = unpickler.unpickle(new AttributesSectionUnpickler)
   private val treeUnpickler = unpickler.unpickle(treeSectionUnpickler(posUnpicklerOpt, commentUnpicklerOpt, attributeUnpicklerOpt)).get
 
+  def tastyAttributes: Attributes =
+    attributeUnpicklerOpt.map(_.attributes).getOrElse(Attributes(false, false))
+
   /** Enter all toplevel classes and objects into their scopes
    *  @param roots          a set of SymDenotations that should be overwritten by unpickling
    */