use Uninitialized instead of Null for relevant vars in dotty

Author: olhotak

compiler/src/dotty/tools/dotc/CompilationUnit.scala

@@ -71,7 +71,7 @@ class CompilationUnit protected (val source: SourceFile) {
         suspendedAtInliningPhase = true
     throw CompilationUnit.SuspendException()
 
-  private var myAssignmentSpans: Map[Int, List[Span]] | Null = null
+  private var myAssignmentSpans: Map[Int, List[Span]] | Uninitialized = initiallyNull
 
   /** A map from (name-) offsets of all local variables in this compilation unit
    *  that can be tracked for being not null to the list of spans of assignments

compiler/src/dotty/tools/dotc/ast/Positioned.scala

@@ -160,7 +160,7 @@ abstract class Positioned(implicit @constructorOnly src: SourceFile) extends Src
    */
   def checkPos(nonOverlapping: Boolean)(using Context): Unit = try {
     import untpd._
-    var lastPositioned: Positioned | Null = null
+    var lastPositioned: Positioned | Uninitialized = initiallyNull
     var lastSpan = NoSpan
     def check(p: Any): Unit = p match {
       case p: Positioned =>
@@ -234,7 +234,7 @@ abstract class Positioned(implicit @constructorOnly src: SourceFile) extends Src
 
 object Positioned {
   @sharable private var debugId = Int.MinValue
-  @sharable private var ids: java.util.WeakHashMap[Positioned, Int] | Null = null
+  @sharable private var ids: java.util.WeakHashMap[Positioned, Int] | Uninitialized = initiallyNull
   @sharable private var nextId: Int = 0
 
   def init(using Context): Unit =

compiler/src/dotty/tools/dotc/ast/Trees.scala

@@ -294,7 +294,7 @@ object Trees {
   trait DefTree[-T >: Untyped] extends DenotingTree[T] {
     type ThisTree[-T >: Untyped] <: DefTree[T]
 
-    private var myMods: untpd.Modifiers | Null = _
+    private var myMods: untpd.Modifiers | Uninitialized = _
 
     private[dotc] def rawMods: untpd.Modifiers =
       if (myMods == null) untpd.EmptyModifiers else myMods.uncheckedNN

compiler/src/dotty/tools/dotc/ast/tpd.scala

@@ -1256,7 +1256,7 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
   trait TreeProvider {
     protected def computeRootTrees(using Context): List[Tree]
 
-    private var myTrees: List[Tree] | Null = _
+    private var myTrees: List[Tree] | Uninitialized = _
 
     /** Get trees defined by this provider. Cache them if -Yretain-trees is set. */
     def rootTrees(using Context): List[Tree] =

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

@@ -1,12 +1,13 @@
-package dotty.tools.dotc
+package dotty.tools
+package dotc
 package core
 
 import Contexts._
 import config.Printers.{default, typr}
 
 trait ConstraintRunInfo { self: Run =>
   private var maxSize = 0
-  private var maxConstraint: Constraint | Null = _
+  private var maxConstraint: Constraint | Uninitialized = _
   def recordConstraintSize(c: Constraint, size: Int): Unit =
     if (size > maxSize) {
       maxSize = size

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

@@ -308,7 +308,7 @@ object Contexts {
     def getFile(name: String): AbstractFile = getFile(name.toTermName)
 
 
-    private var related: SimpleIdentityMap[Phase | SourceFile, Context] | Null = null
+    private var related: SimpleIdentityMap[Phase | SourceFile, Context] | Uninitialized = initiallyNull
 
     private def lookup(key: Phase | SourceFile): Context | Null =
       util.Stats.record("Context.related.lookup")
@@ -853,7 +853,7 @@ object Contexts {
     val initialCtx: Context = new InitialContext(this, settings)
 
     /** The platform, initialized by `initPlatform()`. */
-    private var _platform: Platform | Null = _
+    private var _platform: Platform | Uninitialized = _
 
     /** The platform */
     def platform: Platform = {
@@ -911,8 +911,8 @@ object Contexts {
     /** A table for hash consing unique named types */
     private[core] val uniqueNamedTypes: NamedTypeUniques = NamedTypeUniques()
 
-    var emptyTypeBounds: TypeBounds | Null = null
-    var emptyWildcardBounds: WildcardType | Null = null
+    var emptyTypeBounds: TypeBounds | Uninitialized = initiallyNull
+    var emptyWildcardBounds: WildcardType | Uninitialized = initiallyNull
 
     /** Number of findMember calls on stack */
     private[core] var findMemberCount: Int = 0
@@ -1006,7 +1006,7 @@ object Contexts {
     // Test that access is single threaded
 
     /** The thread on which `checkSingleThreaded was invoked last */
-    @sharable private var thread: Thread | Null = null
+    @sharable private var thread: Thread | Uninitialized = initiallyNull
 
     /** Check that we are on the same thread as before */
     def checkSingleThreaded(): Unit =

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

@@ -163,7 +163,7 @@ object Names {
     override def asTermName: TermName = this
 
     @sharable // because it is only modified in the synchronized block of toTypeName.
-    private var myTypeName: TypeName | Null = null
+    private var myTypeName: TypeName | Uninitialized = initiallyNull
       // Note: no @volatile needed since type names are immutable and therefore safely published
 
     override def toTypeName: TypeName =
@@ -225,10 +225,10 @@ object Names {
     }
 
     @sharable // because it's just a cache for performance
-    private var myMangledString: String | Null = null
+    private var myMangledString: String | Uninitialized = initiallyNull
 
     @sharable // because it's just a cache for performance
-    private var myMangled: Name | Null = null
+    private var myMangled: Name | Uninitialized = initiallyNull
 
     protected[Names] def mangle: ThisName
 
@@ -259,7 +259,7 @@ object Names {
 
     protected def computeToString: String
 
-    @sharable private var myToString: String | Null = null
+    @sharable private var myToString: String | Uninitialized = initiallyNull
 
     override def toString: String =
       if myToString == null then myToString = computeToString

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

@@ -565,7 +565,7 @@ class OrderingConstraint(private val boundsMap: ParamBounds,
         i += 1
     }
 
-  private var myUninstVars: mutable.ArrayBuffer[TypeVar] | Null = _
+  private var myUninstVars: mutable.ArrayBuffer[TypeVar] | Uninitialized = _
 
   /** The uninstantiated typevars of this constraint */
   def uninstVars: collection.Seq[TypeVar] = {

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

@@ -213,14 +213,14 @@ object Scopes {
 
     /** the hash table
      */
-    private var hashTable: Array[ScopeEntry | Null] | Null = null
+    private var hashTable: Array[ScopeEntry | Null] | Uninitialized = initiallyNull
 
     /** a cache for all elements, to be used by symbol iterator.
      */
-    private var elemsCache: List[Symbol] | Null = null
+    private var elemsCache: List[Symbol] | Uninitialized = initiallyNull
 
     /** The synthesizer to be used, or `null` if no synthesis is done on this scope */
-    private var synthesize: SymbolSynthesizer | Null = null
+    private var synthesize: SymbolSynthesizer | Uninitialized = initiallyNull
 
     /** Use specified synthesize for this scope */
     def useSynthesizer(s: SymbolSynthesizer): Unit = synthesize = s

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

@@ -495,7 +495,7 @@ object SymDenotations {
     /** `fullName` where `.' is the separator character */
     def fullName(using Context): Name = fullNameSeparated(QualifiedName)
 
-    private var myTargetName: Name | Null = null
+    private var myTargetName: Name | Uninitialized = initiallyNull
 
     private def computeTargetName(targetNameAnnot: Option[Annotation])(using Context): Name =
       targetNameAnnot match
@@ -1701,15 +1701,15 @@ object SymDenotations {
 
     // ----- caches -------------------------------------------------------
 
-    private var myTypeParams: List[TypeSymbol] | Null = null
+    private var myTypeParams: List[TypeSymbol] | Uninitialized = initiallyNull
     private var fullNameCache: SimpleIdentityMap[QualifiedNameKind, Name] = SimpleIdentityMap.empty
 
-    private var myMemberCache: EqHashMap[Name, PreDenotation] | Null = null
+    private var myMemberCache: EqHashMap[Name, PreDenotation] | Uninitialized = initiallyNull
     private var myMemberCachePeriod: Period = Nowhere
 
     /** A cache from types T to baseType(T, C) */
     type BaseTypeMap = EqHashMap[CachedType, Type]
-    private var myBaseTypeCache: BaseTypeMap | Null = null
+    private var myBaseTypeCache: BaseTypeMap | Uninitialized = initiallyNull
     private var myBaseTypeCachePeriod: Period = Nowhere
 
     private var baseDataCache: BaseData = BaseData.None
@@ -1838,7 +1838,7 @@ object SymDenotations {
 
    // ------ class-specific operations -----------------------------------
 
-    private var myThisType: Type | Null = null
+    private var myThisType: Type | Uninitialized = initiallyNull
 
     /** The this-type depends on the kind of class:
      *  - for a package class `p`:  ThisType(TypeRef(Noprefix, p))
@@ -1856,7 +1856,7 @@ object SymDenotations {
       ThisType.raw(TypeRef(pre, cls))
     }
 
-    private var myTypeRef: TypeRef | Null = null
+    private var myTypeRef: TypeRef | Uninitialized = initiallyNull
 
     override def typeRef(using Context): TypeRef = {
       if (myTypeRef == null) myTypeRef = super.typeRef
@@ -2628,8 +2628,8 @@ object SymDenotations {
     def apply(module: TermSymbol, modcls: ClassSymbol): LazyType = this
 
     private var myDecls: Scope = EmptyScope
-    private var mySourceModule: Symbol | Null = null
-    private var myModuleClass: Symbol | Null = null
+    private var mySourceModule: Symbol | Uninitialized = initiallyNull
+    private var myModuleClass: Symbol | Uninitialized = initiallyNull
     private var mySourceModuleFn: Context ?=> Symbol = LazyType.NoSymbolFn
     private var myModuleClassFn: Context ?=> Symbol = LazyType.NoSymbolFn