Migrating the main compiler to explicit nulls

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/backend/jvm/AsmUtils.scala

@@ -2,6 +2,8 @@ package dotty.tools
 package backend
 package jvm
 
+import scala.language.unsafeNulls
+
 import scala.tools.asm.tree.{AbstractInsnNode}
 import java.io.PrintWriter
 import scala.tools.asm.util.{TraceClassVisitor, TraceMethodVisitor, Textifier}

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

@@ -2,6 +2,8 @@ package dotty.tools
 package backend
 package jvm
 
+import scala.language.unsafeNulls
+
 import dotty.tools.dotc.core.Flags._
 import dotty.tools.dotc.core.Symbols._
 import dotty.tools.dotc.report

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

@@ -2,6 +2,8 @@ package dotty.tools
 package backend
 package jvm
 
+import scala.language.unsafeNulls
+
 import scala.annotation.switch
 import scala.collection.mutable.SortedMap
 

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

@@ -2,6 +2,8 @@ package dotty.tools
 package backend
 package jvm
 
+import scala.language.unsafeNulls
+
 import scala.annotation.threadUnsafe
 import scala.tools.asm
 import scala.tools.asm.AnnotationVisitor

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

@@ -2,6 +2,8 @@ package dotty.tools
 package backend
 package jvm
 
+import scala.language.unsafeNulls
+
 import scala.tools.asm
 import scala.annotation.switch
 import Primitives.{NE, EQ, TestOp, ArithmeticOp}

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

@@ -2,10 +2,11 @@ package dotty.tools
 package backend
 package jvm
 
+import scala.language.unsafeNulls
+
 import scala.collection.{ mutable, immutable }
 
 import scala.tools.asm
-
 import dotty.tools.dotc.ast.tpd
 import dotty.tools.dotc.ast.TreeTypeMap
 import dotty.tools.dotc.CompilationUnit

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

@@ -2,6 +2,8 @@ package dotty.tools
 package backend
 package jvm
 
+import scala.language.unsafeNulls
+
 import scala.collection.immutable
 import scala.tools.asm
 

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

@@ -2,6 +2,8 @@ package dotty.tools
 package backend
 package jvm
 
+import scala.language.unsafeNulls
+
 import scala.tools.asm
 
 /**

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

@@ -2,6 +2,8 @@ package dotty.tools
 package backend
 package jvm
 
+import scala.language.unsafeNulls
+
 import java.io.{ DataOutputStream, FileOutputStream, IOException, File as JFile }
 import java.nio.channels.ClosedByInterruptException
 import dotty.tools.io._

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

@@ -1,5 +1,7 @@
 package dotty.tools.backend.jvm
 
+import scala.language.unsafeNulls
+
 import dotty.tools.dotc.ast.tpd
 import dotty.tools.dotc.core.Flags._
 import dotty.tools.dotc.transform.SymUtils._

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

@@ -1,5 +1,7 @@
 package dotty.tools.backend.jvm
 
+import scala.language.unsafeNulls
+
 import dotty.tools.dotc.CompilationUnit
 import dotty.tools.dotc.ast.Trees.{PackageDef, ValDef}
 import dotty.tools.dotc.ast.tpd
@@ -73,7 +75,7 @@ class GenBCode extends Phase {
     try super.runOn(units)
     finally outputDir match {
       case jar: JarArchive =>
-        if (ctx.run.suspendedUnits.nonEmpty)
+        if (ctx.run.nn.suspendedUnits.nonEmpty)
           // If we close the jar the next run will not be able to write on the jar.
           // But if we do not close it we cannot use it as part of the macro classpath of the suspended files.
           report.error("Can not suspend and output to a jar at the same time. See suspension with -Xprint-suspension.")

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

@@ -1,14 +1,13 @@
 package dotty.tools.backend.sjs
 
-import scala.annotation.switch
+import scala.language.unsafeNulls
 
+import scala.annotation.switch
 import scala.collection.mutable
 
 import dotty.tools.FatalError
-
 import dotty.tools.dotc.CompilationUnit
 import dotty.tools.dotc.ast.tpd
-
 import dotty.tools.dotc.core._
 import Contexts._
 import Decorators._

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

@@ -1,8 +1,10 @@
 package dotty.tools.backend.sjs
 
-import dotty.tools.dotc.core._
+import scala.language.unsafeNulls
 
 import scala.annotation.threadUnsafe
+
+import dotty.tools.dotc.core._
 import Types._
 import Contexts._
 import Symbols._

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

@@ -1,5 +1,7 @@
 package dotty.tools.backend.sjs
 
+import scala.language.unsafeNulls
+
 import scala.collection.mutable
 
 import dotty.tools.dotc.core._

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

@@ -1,7 +1,8 @@
 package dotty.tools.backend.sjs
 
-import scala.annotation.tailrec
+import scala.language.unsafeNulls
 
+import scala.annotation.tailrec
 import scala.collection.mutable
 
 import dotty.tools.dotc.core._

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

@@ -1,5 +1,7 @@
 package dotty.tools.backend.sjs
 
+import scala.language.unsafeNulls
+
 import java.net.{URI, URISyntaxException}
 
 import dotty.tools.dotc.core._

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

@@ -30,7 +30,7 @@ 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

@@ -13,6 +13,7 @@ import typer.Nullables
 import transform.SymUtils._
 import core.Decorators._
 import config.SourceVersion
+import scala.annotation.internal.sharable
 
 class CompilationUnit protected (val source: SourceFile) {
 
@@ -70,20 +71,30 @@ class CompilationUnit protected (val source: SourceFile) {
       if (ctx.settings.XprintSuspension.value)
         report.echo(i"suspended: $this")
       suspended = true
-      ctx.run.suspendedUnits += this
+      ctx.run.nn.suspendedUnits += this
       if ctx.phase == Phases.inliningPhase then
         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 {
@@ -92,7 +103,8 @@ 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

@@ -152,7 +152,8 @@ class Compiler {
 
   def reset()(using Context): Unit = {
     ctx.base.reset()
-    if (ctx.run != null) ctx.run.reset()
+    val run = ctx.run
+    if (run != null) run.reset()
   }
 
   def newRun(using Context): Run = {

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

@@ -28,15 +28,15 @@ 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
@@ -111,7 +111,7 @@ 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
 
@@ -134,8 +134,8 @@ 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)
   }
@@ -153,8 +153,8 @@ 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)
@@ -172,7 +172,7 @@ 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/Resident.scala

@@ -51,8 +51,8 @@ class Resident extends Driver {
             nextCtx = rootCtx
             line = getLine()
           }
-          if (line.startsWith(quit)) ctx.reporter
-          else loop(line split "\\s+", nextCtx)
+          if line.startsWith(quit) then ctx.reporter
+          else loop((line split "\\s+").asInstanceOf[Array[String]], nextCtx)
         case None =>
           prevCtx.reporter
     }

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

@@ -58,8 +58,8 @@ 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
@@ -73,7 +73,7 @@ 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
 
@@ -170,7 +170,7 @@ 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.nonEmpty then report.echo(i"exception occurred while compiling $units%, %")
         else report.echo(s"exception occurred while compiling ${files.map(_.name).mkString(", ")}")
         throw ex
 
@@ -309,7 +309,7 @@ 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)
@@ -332,8 +332,8 @@ 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
@@ -366,9 +366,9 @@ 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)
 }