Use compiletime.uninitialized in compiler (#18823)

Author: nicolasstucki

compiler/src/dotty/tools/backend/jvm/BCodeHelpers.scala

@@ -9,6 +9,7 @@ import scala.tools.asm
 import scala.tools.asm.AnnotationVisitor
 import scala.tools.asm.ClassWriter
 import scala.collection.mutable
+import scala.compiletime.uninitialized
 
 import dotty.tools.dotc.CompilationUnit
 import dotty.tools.dotc.ast.tpd
@@ -576,7 +577,7 @@ trait BCodeHelpers extends BCodeIdiomatic {
   /* builder of mirror classes */
   class JMirrorBuilder extends JCommonBuilder {
 
-    private var cunit: CompilationUnit = _
+    private var cunit: CompilationUnit = uninitialized
     def getCurrentCUnit(): CompilationUnit = cunit;
 
     /* Generate a mirror class for a top-level module. A mirror class is a class

compiler/src/dotty/tools/backend/jvm/GenBCode.scala

@@ -9,6 +9,7 @@ import Contexts._
 import Symbols._
 import dotty.tools.io._
 import scala.collection.mutable
+import scala.compiletime.uninitialized
 
 class GenBCode extends Phase { self =>
 
@@ -25,7 +26,7 @@ class GenBCode extends Phase { self =>
   private val entryPoints = new mutable.HashSet[String]()
   def registerEntryPoint(s: String): Unit = entryPoints += s
 
-  private var _backendInterface: DottyBackendInterface = _
+  private var _backendInterface: DottyBackendInterface = uninitialized
   def backendInterface(using ctx: Context): DottyBackendInterface = {
     if _backendInterface eq null then
       // Enforce usage of FreshContext so we would be able to modify compilation unit between runs
@@ -36,7 +37,7 @@ class GenBCode extends Phase { self =>
     _backendInterface
   }
 
-  private var _codeGen: CodeGen = _
+  private var _codeGen: CodeGen = uninitialized
   def codeGen(using Context): CodeGen = {
     if _codeGen eq null then
       val int = backendInterface
@@ -45,28 +46,28 @@ class GenBCode extends Phase { self =>
     _codeGen
   }
 
-  private var _bTypes: BTypesFromSymbols[DottyBackendInterface] = _
+  private var _bTypes: BTypesFromSymbols[DottyBackendInterface] = uninitialized
   def bTypes(using Context): BTypesFromSymbols[DottyBackendInterface] = {
     if _bTypes eq null then
       _bTypes = BTypesFromSymbols(backendInterface, frontendAccess)
     _bTypes
   }
 
-  private var _frontendAccess: PostProcessorFrontendAccess | Null = _
+  private var _frontendAccess: PostProcessorFrontendAccess | Null = uninitialized
   def frontendAccess(using Context): PostProcessorFrontendAccess = {
     if _frontendAccess eq null then
       _frontendAccess = PostProcessorFrontendAccess.Impl(backendInterface, entryPoints)
     _frontendAccess.nn
   }
 
-  private var _postProcessor: PostProcessor | Null = _
+  private var _postProcessor: PostProcessor | Null = uninitialized
   def postProcessor(using Context): PostProcessor = {
     if _postProcessor eq null then
       _postProcessor = new PostProcessor(frontendAccess, bTypes)
     _postProcessor.nn
   }
 
-  private var _generatedClassHandler: GeneratedClassHandler | Null = _
+  private var _generatedClassHandler: GeneratedClassHandler | Null = uninitialized
   def generatedClassHandler(using Context): GeneratedClassHandler = {
     if _generatedClassHandler eq null then
       _generatedClassHandler = GeneratedClassHandler(postProcessor)

compiler/src/dotty/tools/backend/jvm/GeneratedClassHandler.scala

@@ -15,6 +15,7 @@ import dotty.tools.dotc.core.Phases
 import dotty.tools.dotc.core.Decorators.em
 
 import scala.language.unsafeNulls
+import scala.compiletime.uninitialized
 
 /**
  * Interface to handle post-processing and classfile writing (see [[PostProcessor]]) of generated
@@ -185,7 +186,7 @@ final private class CompilationUnitInPostProcess(private var classes: List[Gener
   }
 
   /** the main async task submitted onto the scheduler */
-  var task: Future[Unit] = _
+  var task: Future[Unit] = uninitialized
 
   val bufferedReporting = new PostProcessorFrontendAccess.BufferingBackendReporting()
 }

compiler/src/dotty/tools/backend/sjs/JSDefinitions.scala

@@ -12,6 +12,7 @@ import Symbols._
 import StdNames._
 
 import dotty.tools.dotc.config.SJSPlatform
+import scala.compiletime.uninitialized
 
 object JSDefinitions {
   /** The Scala.js-specific definitions for the current context. */
@@ -249,7 +250,7 @@ final class JSDefinitions()(using Context) {
     @threadUnsafe lazy val Selectable_reflectiveSelectableFromLangReflectiveCallsR = SelectableModule.requiredMethodRef("reflectiveSelectableFromLangReflectiveCalls")
     def Selectable_reflectiveSelectableFromLangReflectiveCalls(using Context) = Selectable_reflectiveSelectableFromLangReflectiveCallsR.symbol
 
-  private var allRefClassesCache: Set[Symbol] = _
+  private var allRefClassesCache: Set[Symbol] = uninitialized
   def allRefClasses(using Context): Set[Symbol] = {
     if (allRefClassesCache == null) {
       val baseNames = List("Object", "Boolean", "Character", "Byte", "Short",

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

@@ -6,6 +6,7 @@ import reporting.Reporter
 import io.AbstractFile
 
 import scala.annotation.internal.sharable
+import scala.compiletime.uninitialized
 
 /** A main class for running compiler benchmarks. Can instantiate a given
  *  number of compilers and run each (sequentially) a given number of times
@@ -17,7 +18,7 @@ object Bench extends Driver:
   @sharable private var numCompilers = 1
   @sharable private var waitAfter = -1
   @sharable private var curCompiler = 0
-  @sharable private var times: Array[Int] = _
+  @sharable private var times: Array[Int] = uninitialized
 
   override def doCompile(compiler: Compiler, files: List[AbstractFile])(using Context): Reporter =
     var reporter: Reporter = emptyReporter

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

@@ -65,7 +65,7 @@ class Run(comp: Compiler, ictx: Context) extends ImplicitRunInfo with Constraint
 
   private var myUnits: List[CompilationUnit] = Nil
   private var myUnitsCached: List[CompilationUnit] = Nil
-  private var myFiles: Set[AbstractFile] = _
+  private var myFiles: Set[AbstractFile] = uninitialized
 
   // `@nowarn` annotations by source file, populated during typer
   private val mySuppressions: mutable.LinkedHashMap[SourceFile, mutable.ListBuffer[Suppression]] = mutable.LinkedHashMap.empty
@@ -511,7 +511,7 @@ object Run {
     var currentCompletedSubtraversalCount: Int = 0 // completed subphases in the current phase
     var seenPhaseCount: Int = 0 // how many phases we've seen so far
 
-    private var currPhase: Phase = uninitialized  // initialized by enterPhase
+    private var currPhase: Phase = uninitialized      // initialized by enterPhase
     private var subPhases: SubPhases = uninitialized  // initialized by enterPhase
     private var currPhaseName: String = uninitialized // initialized by enterPhase
     private var nextPhaseName: String = uninitialized // initialized by enterPhase

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

@@ -13,12 +13,14 @@ import ast.Trees.mods
 import annotation.constructorOnly
 import annotation.internal.sharable
 
+import scala.compiletime.uninitialized
+
 /** A base class for things that have positions (currently: modifiers and trees)
  */
 abstract class Positioned(implicit @constructorOnly src: SourceFile) extends SrcPos, Product, Cloneable {
   import Positioned.{ids, nextId, debugId}
 
-  private var mySpan: Span = _
+  private var mySpan: Span = uninitialized
 
   private var mySource: SourceFile = src
 

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

@@ -18,6 +18,7 @@ import typer.ConstFold
 
 import scala.annotation.tailrec
 import scala.collection.mutable.ListBuffer
+import scala.compiletime.uninitialized
 
 /** Some creators for typed trees */
 object tpd extends Trees.Instance[Type] with TypedTreeInfo {
@@ -1309,7 +1310,7 @@ 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] | Null = 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

@@ -3,10 +3,11 @@ package core
 
 import Contexts._
 import config.Printers.{default, typr}
+import scala.compiletime.uninitialized
 
 trait ConstraintRunInfo { self: Run =>
   private var maxSize = 0
-  private var maxConstraint: Constraint | Null = _
+  private var maxConstraint: Constraint | Null = uninitialized
   def recordConstraintSize(c: Constraint, size: Int): Unit =
     if (size > maxSize) {
       maxSize = size

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

@@ -558,7 +558,7 @@ object Contexts {
     private var _owner: Symbol = uninitialized
     final def owner: Symbol = _owner
 
-    private var _tree: Tree[?]= _
+    private var _tree: Tree[?] = uninitialized
     final def tree: Tree[?] = _tree
 
     private var _scope: Scope = uninitialized