First step of migration to explicit nulls

Author: noti0na1

compiler/src/dotty/tools/FatalError.scala

@@ -1,3 +1,5 @@
 package dotty.tools
 
+import scala.language.{unsafeNulls => _}
+
 case class FatalError(msg: String) extends Exception(msg)

compiler/src/dotty/tools/MainGenericRunner.scala

@@ -1,5 +1,6 @@
 package dotty.tools
 
+import scala.language.unsafeNulls
 
 import scala.annotation.tailrec
 import scala.io.Source

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

@@ -1,6 +1,8 @@
 package dotty.tools
 package dotc
 
+import scala.language.{unsafeNulls => _}
+
 import core.Contexts._
 import reporting.Reporter
 import io.AbstractFile
@@ -30,7 +32,7 @@ object Bench extends Driver:
       println(s"time elapsed: ${times(i)}ms")
       if ctx.settings.Xprompt.value then
         print("hit <return> to continue >")
-        System.in.read()
+        System.in.nn.read()
         println()
     reporter
 

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

@@ -1,6 +1,8 @@
 package dotty.tools
 package dotc
 
+import scala.language.{unsafeNulls => _}
+
 import core._
 import Contexts._
 import SymDenotations.ClassDenotation
@@ -14,6 +16,7 @@ import typer.Nullables
 import transform.SymUtils._
 import core.Decorators._
 import config.SourceVersion
+import scala.annotation.internal.sharable
 
 class CompilationUnit protected (val source: SourceFile) {
 
@@ -76,15 +79,25 @@ class CompilationUnit protected (val source: SourceFile) {
         suspendedAtInliningPhase = true
     throw CompilationUnit.SuspendException()
 
-  private var myAssignmentSpans: Map[Int, List[Span]] = null
+  private var myAssignmentSpans: Map[Int, List[Span]] | Null = null
 
   /** 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
    *  to these variables.
    */
   def assignmentSpans(using Context): Map[Int, List[Span]] =
     if myAssignmentSpans == null then myAssignmentSpans = Nullables.assignmentSpans
-    myAssignmentSpans
+    myAssignmentSpans.nn
+}
+
+@sharable object NoCompilationUnit extends CompilationUnit(NoSource) {
+
+  override def isJava: Boolean = false
+
+  override def suspend()(using Context): Nothing =
+    throw CompilationUnit.SuspendException()
+
+  override def assignmentSpans(using Context): Map[Int, List[Span]] = Map.empty
 }
 
 object CompilationUnit {
@@ -93,7 +106,8 @@ object CompilationUnit {
 
   /** Make a compilation unit for top class `clsd` with the contents of the `unpickled` tree */
   def apply(clsd: ClassDenotation, unpickled: Tree, forceTrees: Boolean)(using Context): CompilationUnit =
-    apply(new SourceFile(clsd.symbol.associatedFile, Array.empty[Char]), unpickled, forceTrees)
+    val file = clsd.symbol.associatedFile.nn
+    apply(new SourceFile(file, Array.empty[Char]), unpickled, forceTrees)
 
   /** Make a compilation unit, given picked bytes and unpickled tree */
   def apply(source: SourceFile, unpickled: Tree, forceTrees: Boolean)(using Context): CompilationUnit = {

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

@@ -1,6 +1,8 @@
 package dotty.tools
 package dotc
 
+import scala.language.{unsafeNulls => _}
+
 import core._
 import Contexts._
 import typer.{TyperPhase, RefChecks}
@@ -152,7 +154,8 @@ class Compiler {
 
   def reset()(using Context): Unit = {
     ctx.base.reset()
-    if (ctx.run != null) ctx.run.reset()
+    val run: Run | Null = ctx.run
+    if (run != null) run.reset()
   }
 
   def newRun(using Context): Run = {

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

@@ -1,5 +1,7 @@
 package dotty.tools.dotc
 
+import scala.language.{unsafeNulls => _}
+
 import java.nio.file.{Files, Paths}
 
 import dotty.tools.FatalError
@@ -32,15 +34,15 @@ class Driver {
 
   protected def emptyReporter: Reporter = new StoreReporter(null)
 
-  protected def doCompile(compiler: Compiler,  files: List[AbstractFile])(using Context): Reporter =
+  protected def doCompile(compiler: Compiler, files: List[AbstractFile])(using Context): Reporter =
     if files.nonEmpty then
       try
         val run = compiler.newRun
         run.compile(files)
         finish(compiler, run)
       catch
         case ex: FatalError =>
-          report.error(ex.getMessage) // signals that we should fail compilation.
+          report.error(ex.getMessage.nn) // signals that we should fail compilation.
         case ex: TypeError =>
           println(s"${ex.toMessage} while compiling ${files.map(_.path).mkString(", ")}")
           throw ex
@@ -115,7 +117,7 @@ class Driver {
         .distinct
       val ctx1 = ctx.fresh
       val fullClassPath =
-        (newEntries :+ ctx.settings.classpath.value).mkString(java.io.File.pathSeparator)
+        (newEntries :+ ctx.settings.classpath.value).mkString(java.io.File.pathSeparator.nn)
       ctx1.setSetting(ctx1.settings.classpath, fullClassPath)
     else ctx
 
@@ -138,8 +140,8 @@ class Driver {
    *                    process. No callbacks will be executed if this is `null`.
    *  @return
    */
-  final def process(args: Array[String], simple: interfaces.SimpleReporter,
-    callback: interfaces.CompilerCallback): interfaces.ReporterResult = {
+  final def process(args: Array[String], simple: interfaces.SimpleReporter | Null,
+    callback: interfaces.CompilerCallback | Null): interfaces.ReporterResult = {
     val reporter = if (simple == null) null else Reporter.fromSimpleReporter(simple)
     process(args, reporter, callback)
   }
@@ -157,8 +159,8 @@ class Driver {
    *  @return           The `Reporter` used. Use `Reporter#hasErrors` to check
    *                    if compilation succeeded.
    */
-  final def process(args: Array[String], reporter: Reporter = null,
-    callback: interfaces.CompilerCallback = null): Reporter = {
+  final def process(args: Array[String], reporter: Reporter | Null = null,
+    callback: interfaces.CompilerCallback | Null = null): Reporter = {
     val compileCtx = initCtx.fresh
     if (reporter != null)
       compileCtx.setReporter(reporter)
@@ -176,7 +178,7 @@ class Driver {
    *  with sbt.
    */
   final def process(args: Array[String]): Reporter =
-    process(args, null: Reporter, null: interfaces.CompilerCallback)
+    process(args, null: Reporter | Null, null: interfaces.CompilerCallback | Null)
 
   /** Entry point to the compiler using a custom `Context`.
    *

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

@@ -1,5 +1,7 @@
 package dotty.tools
 package dotc
 
+import scala.language.{unsafeNulls => _}
+
 /** Main class of the `dotc` batch compiler. */
 object Main extends Driver

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

@@ -1,5 +1,7 @@
 package dotty.tools.dotc
 
+import scala.language.{unsafeNulls => _}
+
 import dotty.tools.FatalError
 
 class MissingCoreLibraryException(rootPackage: String) extends FatalError(

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

@@ -1,6 +1,8 @@
 package dotty.tools
 package dotc
 
+import scala.language.{unsafeNulls => _}
+
 import core.Contexts._
 import reporting.Reporter
 import java.io.EOFException
@@ -52,7 +54,9 @@ class Resident extends Driver {
             line = getLine()
           }
           if (line.startsWith(quit)) ctx.reporter
-          else loop(line split "\\s+", nextCtx)
+          else
+            // split returns non-nullable values
+            loop((line split "\\s+").asInstanceOf[Array[String]], nextCtx)
         case None =>
           prevCtx.reporter
     }

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

@@ -1,6 +1,8 @@
 package dotty.tools
 package dotc
 
+import scala.language.{unsafeNulls => _}
+
 import core._
 import Contexts._
 import Periods._
@@ -59,8 +61,8 @@ class Run(comp: Compiler, ictx: Context) extends ImplicitRunInfo with Constraint
 
   private var compiling = false
 
-  private var myUnits: List[CompilationUnit] = _
-  private var myUnitsCached: List[CompilationUnit] = _
+  private var myUnits: List[CompilationUnit] = Nil
+  private var myUnitsCached: List[CompilationUnit] = Nil
   private var myFiles: Set[AbstractFile] = _
 
   // `@nowarn` annotations by source file, populated during typer
@@ -74,7 +76,7 @@ class Run(comp: Compiler, ictx: Context) extends ImplicitRunInfo with Constraint
     // When the REPL creates a new run (ReplDriver.compile), parsing is already done in the old context, with the
     // previous Run. Parser warnings were suspended in the old run and need to be copied over so they are not lost.
     // Same as scala/scala/commit/79ca1408c7.
-    def initSuspendedMessages(oldRun: Run) = if oldRun != null then
+    def initSuspendedMessages(oldRun: Run | Null) = if oldRun != null then
       mySuspendedMessages.clear()
       mySuspendedMessages ++= oldRun.mySuspendedMessages
 
@@ -171,7 +173,7 @@ class Run(comp: Compiler, ictx: Context) extends ImplicitRunInfo with Constraint
       compileSources(sources)
     catch
       case NonFatal(ex) =>
-        if units != null then report.echo(i"exception occurred while compiling $units%, %")
+        if units != Nil then report.echo(i"exception occurred while compiling $units%, %")
         else report.echo(s"exception occurred while compiling ${files.map(_.name).mkString(", ")}")
         throw ex
 
@@ -310,7 +312,7 @@ class Run(comp: Compiler, ictx: Context) extends ImplicitRunInfo with Constraint
       val uuid = java.util.UUID.randomUUID().toString
       val ext = if (isJava) ".java" else ".scala"
       val virtualFile = new VirtualFile(s"compileFromString-$uuid.$ext")
-      val writer = new BufferedWriter(new OutputStreamWriter(virtualFile.output, StandardCharsets.UTF_8.name)) // buffering is still advised by javadoc
+      val writer = new BufferedWriter(new OutputStreamWriter(virtualFile.output, StandardCharsets.UTF_8.nn.name)) // buffering is still advised by javadoc
       writer.write(source)
       writer.close()
       new SourceFile(virtualFile, Codec.UTF8)
@@ -333,8 +335,8 @@ class Run(comp: Compiler, ictx: Context) extends ImplicitRunInfo with Constraint
     super[ImplicitRunInfo].reset()
     super[ConstraintRunInfo].reset()
     myCtx = null
-    myUnits = null
-    myUnitsCached = null
+    myUnits = Nil
+    myUnitsCached = Nil
   }
 
   /** Produces the following contexts, from outermost to innermost
@@ -367,9 +369,9 @@ class Run(comp: Compiler, ictx: Context) extends ImplicitRunInfo with Constraint
     start.setRun(this: @unchecked)
   }
 
-  private var myCtx = rootContext(using ictx)
+  private var myCtx: Context | Null = rootContext(using ictx)
 
   /** The context created for this run */
-  given runContext[Dummy_so_its_a_def]: Context = myCtx
+  given runContext[Dummy_so_its_a_def]: Context = myCtx.nn
   assert(runContext.runId <= Periods.MaxPossibleRunId)
 }

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

@@ -1,5 +1,7 @@
 package dotty.tools.dotc
 
+import scala.language.{unsafeNulls => _}
+
 import config.Properties._
 import config.CompilerCommand
 

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

@@ -2,6 +2,8 @@ package dotty.tools
 package dotc
 package ast
 
+import scala.language.{unsafeNulls => _}
+
 import core._
 import util.Spans._, Types._, Contexts._, Constants._, Names._, NameOps._, Flags._
 import Symbols._, StdNames._, Trees._, Phases._, ContextOps._
@@ -1298,7 +1300,7 @@ object desugar {
     val ts = tree.trees
     val arity = ts.length
     assert(arity <= Definitions.MaxTupleArity)
-    def tupleTypeRef = defn.TupleType(arity)
+    def tupleTypeRef = defn.TupleType(arity).nn
     if (arity == 0)
       if (ctx.mode is Mode.Type) TypeTree(defn.UnitType) else unitLiteral
     else if (ctx.mode is Mode.Type) AppliedTypeTree(ref(tupleTypeRef), ts)
@@ -1361,7 +1363,7 @@ object desugar {
    *      def $anonfun(params) = body
    *      Closure($anonfun)
    */
-  def makeClosure(params: List[ValDef], body: Tree, tpt: Tree = null, isContextual: Boolean, span: Span)(using Context): Block =
+  def makeClosure(params: List[ValDef], body: Tree, tpt: Tree | Null = null, isContextual: Boolean, span: Span)(using Context): Block =
     Block(
       DefDef(nme.ANON_FUN, params :: Nil, if (tpt == null) TypeTree() else tpt, body)
         .withSpan(span)

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

@@ -2,6 +2,8 @@ package dotty.tools
 package dotc
 package ast
 
+import scala.language.{unsafeNulls => _}
+
 import core._
 import util.Spans._, Types._, Contexts._, Constants._, Names._, NameOps._, Flags._
 import Symbols._, StdNames._, Trees._

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

@@ -1,6 +1,8 @@
 package dotty.tools.dotc
 package ast
 
+import scala.language.{unsafeNulls => _}
+
 import core._
 import Symbols._, Types._, Contexts._, Decorators._, util.Spans._, Flags._, Constants._
 import StdNames.nme

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

@@ -1,6 +1,8 @@
 package dotty.tools.dotc
 package ast
 
+import scala.language.{unsafeNulls => _}
+
 import core.Contexts._
 import core.Decorators._
 import util.Spans._

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

@@ -2,6 +2,8 @@ package dotty.tools
 package dotc
 package ast
 
+import scala.language.{unsafeNulls => _}
+
 import util.Spans._
 import util.{SourceFile, NoSource, SourcePosition, SrcPos}
 import core.Contexts._
@@ -29,13 +31,13 @@ abstract class Positioned(implicit @constructorOnly src: SourceFile) extends Src
    *  is set, -1 otherwise.
    */
   def uniqueId: Int =
-    if ids != null && ids.containsKey(this) then ids.get(this) else -1
+    if ids != null && ids.nn.containsKey(this) then ids.nn.get(this).nn else -1
 
   private def allocateId() =
     if ids != null then
       val ownId = nextId
       nextId += 1
-      ids.put(this, ownId)
+      ids.nn.put(this, ownId)
       if ownId == debugId then
         println(s"Debug tree (id=$debugId) creation \n$this\n")
         Thread.dumpStack()
@@ -163,7 +165,7 @@ abstract class Positioned(implicit @constructorOnly src: SourceFile) extends Src
    */
   def checkPos(nonOverlapping: Boolean)(using Context): Unit = try {
     import untpd._
-    var lastPositioned: Positioned = null
+    var lastPositioned: Positioned | Null = null
     var lastSpan = NoSpan
     def check(p: Any): Unit = p match {
       case p: Positioned =>
@@ -184,7 +186,7 @@ abstract class Positioned(implicit @constructorOnly src: SourceFile) extends Src
             case _: XMLBlock =>
               // FIXME: Trees generated by the XML parser do not satisfy `checkPos`
             case _: WildcardFunction
-            if lastPositioned.isInstanceOf[ValDef] && !p.isInstanceOf[ValDef] =>
+            if lastPositioned != null && lastPositioned.isInstanceOf[ValDef] && !p.isInstanceOf[ValDef] =>
               // ignore transition from last wildcard parameter to body
             case _ =>
               assert(!lastSpan.exists || !p.span.exists || lastSpan.end <= p.span.start,
@@ -237,7 +239,7 @@ 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
+  @sharable private var ids: java.util.WeakHashMap[Positioned, Int] | Null = null
   @sharable private var nextId: Int = 0
 
   def init(using Context): Unit =