From c73a7f63c77077ff02f65ab18a4deab83c2f353d Mon Sep 17 00:00:00 2001
From: Solal Pirelli <solal.pirelli@gmail.com>
Date: Thu, 8 Jan 2026 09:49:58 +0100
Subject: [PATCH 01/12] Delete dead code

---
 .../src/dotty/tools/MainGenericCompiler.scala | 38 -------------------
 compiler/src/dotty/tools/package.scala        |  9 +----
 2 files changed, 1 insertion(+), 46 deletions(-)

diff --git a/compiler/src/dotty/tools/MainGenericCompiler.scala b/compiler/src/dotty/tools/MainGenericCompiler.scala
index 98b1b31f06a5..c43428dc0e7b 100644
--- a/compiler/src/dotty/tools/MainGenericCompiler.scala
+++ b/compiler/src/dotty/tools/MainGenericCompiler.scala
@@ -4,14 +4,7 @@ import scala.annotation.tailrec
 import scala.io.Source
 import scala.util.Try
 import java.io.File
-import java.lang.Thread
 import scala.annotation.internal.sharable
-import dotty.tools.dotc.util.ClasspathFromClassloader
-import dotty.tools.dotc.config.Properties.envOrNone
-import dotty.tools.io.Jar
-import java.nio.file.Paths
-import dotty.tools.dotc.config.CommandLineParser
-import dotty.tools.scripting.StringDriver
 
 enum CompileMode:
   case Guess
@@ -21,19 +14,14 @@ enum CompileMode:
   case Script
 
 case class CompileSettings(
-  verbose: Boolean = false,
   classPath: List[String] = List.empty,
   compileMode: CompileMode = CompileMode.Guess,
   exitCode: Int = 0,
-  javaArgs: List[String] = List.empty,
   javaProps: List[(String, String)] = List.empty,
   scalaArgs: List[String] = List.empty,
   residualArgs: List[String] = List.empty,
   scriptArgs: List[String] = List.empty,
   targetScript: String = "",
-  compiler: Boolean = false,
-  quiet: Boolean = false,
-  colors: Boolean = false,
 ) {
   def withCompileMode(em: CompileMode): CompileSettings = this.compileMode match
     case CompileMode.Guess =>
@@ -46,9 +34,6 @@ case class CompileSettings(
   def withScalaArgs(args: String*): CompileSettings =
     this.copy(scalaArgs = scalaArgs.appendedAll(args.toList.filter(_.nonEmpty)))
 
-  def withJavaArgs(args: String*): CompileSettings =
-    this.copy(javaArgs = javaArgs.appendedAll(args.toList.filter(_.nonEmpty)))
-
   def withJavaProps(args: (String, String)*): CompileSettings =
     this.copy(javaProps = javaProps.appendedAll(args.toList))
 
@@ -65,18 +50,6 @@ case class CompileSettings(
         println(s"not found $file")
         this.copy(exitCode = 2)
   end withTargetScript
-
-  def withCompiler: CompileSettings =
-    this.copy(compiler = true)
-
-  def withQuiet: CompileSettings =
-    this.copy(quiet = true)
-
-  def withColors: CompileSettings =
-    this.copy(colors = true)
-
-  def withNoColors: CompileSettings =
-    this.copy(colors = false)
 }
 
 object MainGenericCompiler {
@@ -97,7 +70,6 @@ object MainGenericCompiler {
     else
       (tail, cpEntries)
 
-  @sharable val javaOption = raw"""-J(.*)""".r
   @sharable val javaPropOption = raw"""-D(.+?)=(.?)""".r
   @tailrec
   def process(args: List[String], settings: CompileSettings): CompileSettings = args match
@@ -107,8 +79,6 @@ object MainGenericCompiler {
       process(Nil, settings.withResidualArgs(tail.toList*))
     case ("-v" | "-verbose" | "--verbose") :: tail =>
       process(tail, settings.withScalaArgs("-verbose"))
-    case ("-q" | "-quiet") :: tail =>
-      process(tail, settings.withQuiet)
     case "-script" :: targetScript :: tail =>
       process(Nil, settings
         .withCompileMode(CompileMode.Script)
@@ -121,12 +91,6 @@ object MainGenericCompiler {
       process(tail, settings.withCompileMode(CompileMode.Decompile))
     case "-print-tasty" :: tail =>
       process(tail, settings.withCompileMode(CompileMode.PrintTasty))
-    case "-colors" :: tail =>
-      process(tail, settings.withColors)
-    case "-no-colors" :: tail =>
-      process(tail, settings.withNoColors)
-    case "-with-compiler" :: tail =>
-      process(tail, settings.withCompiler)
     case ("-cp" | "-classpath" | "--class-path") :: cp :: tail =>
       val (tailargs, newEntries) = processClasspath(cp, tail)
       process(tailargs, settings.copy(classPath = settings.classPath ++ newEntries.filter(_.nonEmpty)))
@@ -136,8 +100,6 @@ object MainGenericCompiler {
       val tStopAtLvl="-XX:TieredStopAtLevel=1"
       println(s"ignoring deprecated -Oshort flag, please add `-J$addTC` and `-J$tStopAtLvl` flags manually")
       process(tail, settings)
-    case javaOption(stripped: String) :: tail =>
-      process(tail, settings.withJavaArgs(stripped))
     case javaPropOption(opt: String, value: String) :: tail =>
       process(tail, settings.withJavaProps(opt -> value))
     case arg :: tail =>
diff --git a/compiler/src/dotty/tools/package.scala b/compiler/src/dotty/tools/package.scala
index 0da6e66fd824..098e9d637cb3 100644
--- a/compiler/src/dotty/tools/package.scala
+++ b/compiler/src/dotty/tools/package.scala
@@ -29,14 +29,7 @@ package object tools {
 
   def unreachable(x: Any = "<< this case was declared unreachable >>"): Nothing =
     throw new MatchError(x)
-
-  transparent inline def assertShort(inline assertion: Boolean, inline message: Any = null): Unit =
-    if !assertion then
-      val msg = message
-      val e = if msg == null then AssertionError() else AssertionError("assertion failed: " + msg)
-      e.setStackTrace(Array())
-      throw e
-
+  
   // Ensure this object is already classloaded, since it's only actually used
   // when handling stack overflows and every operation (including class loading)
   // risks failing.

From bc581c44d454d0fc25f8129ef647a9e0c749ffed Mon Sep 17 00:00:00 2001
From: Solal Pirelli <solal.pirelli@gmail.com>
Date: Thu, 8 Jan 2026 10:01:27 +0100
Subject: [PATCH 02/12] Cleanup

---
 .../src/dotty/tools/MainGenericCompiler.scala | 57 +++++++------------
 .../tools/debug/ExpressionCompiler.scala      |  2 +-
 .../dotty/tools/debug/ExtractExpression.scala |  2 +-
 .../dotty/tools/debug/InsertExpression.scala  |  1 -
 .../tools/debug/ResolveReflectEval.scala      |  1 -
 .../dotty/tools/dotc/CompilationUnit.scala    |  1 -
 compiler/src/dotty/tools/dotc/Driver.scala    |  1 -
 compiler/src/dotty/tools/dotc/Resident.scala  |  2 +-
 .../src/dotty/tools/dotc/ast/Desugar.scala    |  4 +-
 compiler/src/dotty/tools/dotc/ast/Trees.scala |  4 +-
 .../src/dotty/tools/dotc/cc/Capability.scala  | 18 +++---
 compiler/src/dotty/tools/dotc/cc/Setup.scala  |  2 +-
 .../src/dotty/tools/dotc/cc/ccConfig.scala    |  2 +-
 .../dotty/tools/dotc/core/SymbolLoaders.scala |  3 +-
 .../dotc/core/tasty/TastyUnpickler.scala      |  1 -
 .../tools/dotc/coverage/Serializer.scala      |  2 +-
 .../tools/dotc/parsing/JavaParsers.scala      |  2 +-
 .../dotc/parsing/xml/SymbolicXMLBuilder.scala |  2 +-
 .../dotty/tools/dotc/plugins/Plugins.scala    |  4 +-
 .../tools/dotc/printing/Formatting.scala      |  2 -
 .../dotc/transform/UnrollDefinitions.scala    |  6 +-
 .../src/dotty/tools/dotc/typer/Typer.scala    |  2 +-
 .../src/dotty/tools/dotc/util/IntMap.scala    |  2 +-
 compiler/src/dotty/tools/package.scala        | 20 ++++---
 .../tools/scripting/ScriptingDriver.scala     |  6 +-
 compiler/src/dotty/tools/scripting/Util.scala |  4 +-
 26 files changed, 62 insertions(+), 91 deletions(-)

diff --git a/compiler/src/dotty/tools/MainGenericCompiler.scala b/compiler/src/dotty/tools/MainGenericCompiler.scala
index c43428dc0e7b..de4682ab4380 100644
--- a/compiler/src/dotty/tools/MainGenericCompiler.scala
+++ b/compiler/src/dotty/tools/MainGenericCompiler.scala
@@ -2,9 +2,8 @@ package dotty.tools
 
 import scala.annotation.tailrec
 import scala.io.Source
-import scala.util.Try
+import scala.util.{Try, Success, Failure}
 import java.io.File
-import scala.annotation.internal.sharable
 
 enum CompileMode:
   case Guess
@@ -44,9 +43,9 @@ case class CompileSettings(
     this.copy(scriptArgs = scriptArgs.appendedAll(args.toList.filter(_.nonEmpty)))
 
   def withTargetScript(file: String): CompileSettings =
-    Try(Source.fromFile(file)).toOption match
-      case Some(_) => this.copy(targetScript = file)
-      case None      =>
+    Try(Source.fromFile(file)) match
+      case Success(_) => this.copy(targetScript = file)
+      case Failure(_) =>
         println(s"not found $file")
         this.copy(exitCode = 2)
   end withTargetScript
@@ -54,29 +53,29 @@ case class CompileSettings(
 
 object MainGenericCompiler {
 
-  val classpathSeparator: String = File.pathSeparator
+  private val classpathSeparator: String = File.pathSeparator
+  private val javaPropOption = raw"""-D(.+?)=(.?)""".r
 
-  def processClasspath(cp: String, tail: List[String]): (List[String], List[String]) =
+  private def processClasspath(cp: String, tail: List[String]): (List[String], List[String]) =
     val cpEntries = cp.split(classpathSeparator).toList
     val singleEntryClasspath: Boolean = cpEntries.take(2).size == 1
-    val globdir: String = if singleEntryClasspath then cp.replaceAll("[\\\\/][^\\\\/]*$", "") else "" // slash/backslash agnostic
-    def validGlobbedJar(s: String): Boolean = s.startsWith(globdir) && ((s.toLowerCase.endsWith(".jar") || s.toLowerCase.endsWith(".zip")))
+    val globDir: String = if singleEntryClasspath then cp.replaceAll("[\\\\/][^\\\\/]*$", "") else "" // slash/backslash agnostic
+    def validGlobbedJar(s: String): Boolean = s.startsWith(globDir) && (s.toLowerCase.endsWith(".jar") || s.toLowerCase.endsWith(".zip"))
     if singleEntryClasspath && validGlobbedJar(cpEntries.head) then
       // reassemble globbed wildcard classpath
-      // globdir is wildcard directory for globbed jar files, reconstruct the intended classpath
-      val cpJars = tail.takeWhile( f => validGlobbedJar(f) )
+      // globDir is wildcard directory for globbed jar files, reconstruct the intended classpath
+      val cpJars = tail.takeWhile(validGlobbedJar)
       val remainingArgs = tail.drop(cpJars.size)
       (remainingArgs, cpEntries ++ cpJars)
     else
       (tail, cpEntries)
 
-  @sharable val javaPropOption = raw"""-D(.+?)=(.?)""".r
   @tailrec
   def process(args: List[String], settings: CompileSettings): CompileSettings = args match
     case Nil =>
       settings
     case "--" :: tail =>
-      process(Nil, settings.withResidualArgs(tail.toList*))
+      settings.withResidualArgs(tail*)
     case ("-v" | "-verbose" | "--verbose") :: tail =>
       process(tail, settings.withScalaArgs("-verbose"))
     case "-script" :: targetScript :: tail =>
@@ -92,8 +91,8 @@ object MainGenericCompiler {
     case "-print-tasty" :: tail =>
       process(tail, settings.withCompileMode(CompileMode.PrintTasty))
     case ("-cp" | "-classpath" | "--class-path") :: cp :: tail =>
-      val (tailargs, newEntries) = processClasspath(cp, tail)
-      process(tailargs, settings.copy(classPath = settings.classPath ++ newEntries.filter(_.nonEmpty)))
+      val (tailArgs, newEntries) = processClasspath(cp, tail)
+      process(tailArgs, settings.copy(classPath = settings.classPath ++ newEntries.filter(_.nonEmpty)))
     case "-Oshort" :: tail =>
       // Nothing is to be done here. Request that the user adds the relevant flags manually.
       val addTC="-XX:+TieredCompilation"
@@ -110,40 +109,26 @@ object MainGenericCompiler {
     val settings = process(args.toList, CompileSettings())
     if settings.exitCode != 0 then System.exit(settings.exitCode)
 
-    def classpathSetting =
+    val classpathSetting =
       if settings.classPath.isEmpty then List()
       else List("-classpath", settings.classPath.mkString(classpathSeparator))
 
-    def reconstructedArgs() =
-      classpathSetting ++ settings.scalaArgs ++ settings.residualArgs
+    val properArgs = classpathSetting ++ settings.scalaArgs ++ settings.residualArgs
 
-    def addJavaProps(): Unit =
-      settings.javaProps.foreach { (k, v) => sys.props(k) = v }
+    settings.javaProps.foreach { (k, v) => sys.props(k) = v }
 
-    def run(settings: CompileSettings): Unit = settings.compileMode match
-      case CompileMode.Compile =>
-        addJavaProps()
-        val properArgs = reconstructedArgs()
+    settings.compileMode match
+      case CompileMode.Guess | CompileMode.Compile =>
         dotty.tools.dotc.Main.main(properArgs.toArray)
       case CompileMode.Decompile =>
-        addJavaProps()
-        val properArgs = reconstructedArgs()
         dotty.tools.dotc.decompiler.Main.main(properArgs.toArray)
       case CompileMode.PrintTasty =>
-        addJavaProps()
-        val properArgs = reconstructedArgs()
         dotty.tools.dotc.core.tasty.TastyPrinter.main(properArgs.toArray)
       case CompileMode.Script => // Naive copy from scalac bash script
-        addJavaProps()
-        val properArgs =
-          reconstructedArgs()
+        val fullArgs =
+          properArgs
           ++ List("-script", settings.targetScript)
           ++ settings.scriptArgs
         scripting.Main.main(properArgs.toArray)
-      case CompileMode.Guess =>
-        run(settings.withCompileMode(CompileMode.Compile))
-    end run
-
-    run(settings)
   end main
 }
diff --git a/compiler/src/dotty/tools/debug/ExpressionCompiler.scala b/compiler/src/dotty/tools/debug/ExpressionCompiler.scala
index 83c20b0f54a7..9931aa94270c 100644
--- a/compiler/src/dotty/tools/debug/ExpressionCompiler.scala
+++ b/compiler/src/dotty/tools/debug/ExpressionCompiler.scala
@@ -14,7 +14,7 @@ import dotty.tools.dotc.transform.ElimByName
   * To do so, it extends the Compiler with 3 phases:
   *  - InsertExpression: parses and inserts the expression in the original source tree
   *  - ExtractExpression: extract the typed expression and places it in the new expression class
-  *  - ResolveReflectEval: resolves local variables or inacessible members using reflection calls
+  *  - ResolveReflectEval: resolves local variables or inaccessible members using reflection calls
   */
 class ExpressionCompiler(config: ExpressionCompilerConfig) extends Compiler:
 
diff --git a/compiler/src/dotty/tools/debug/ExtractExpression.scala b/compiler/src/dotty/tools/debug/ExtractExpression.scala
index 151d75270c6e..68e35f7f17dc 100644
--- a/compiler/src/dotty/tools/debug/ExtractExpression.scala
+++ b/compiler/src/dotty/tools/debug/ExtractExpression.scala
@@ -18,7 +18,7 @@ import dotty.tools.dotc.util.SrcPos
 import scala.annotation.nowarn
 
 /**
-  * This phase extracts the typed expression from the source tree, transfoms it and places it
+  * This phase extracts the typed expression from the source tree, transforms it and places it
   * in the evaluate method of the Expression class.
   * 
   * Before:
diff --git a/compiler/src/dotty/tools/debug/InsertExpression.scala b/compiler/src/dotty/tools/debug/InsertExpression.scala
index 17d2d7f6ea92..520b2cb9080a 100644
--- a/compiler/src/dotty/tools/debug/InsertExpression.scala
+++ b/compiler/src/dotty/tools/debug/InsertExpression.scala
@@ -7,7 +7,6 @@ import dotty.tools.dotc.core.Names.*
 import dotty.tools.dotc.core.Phases.Phase
 import dotty.tools.dotc.parsing.Parsers
 import dotty.tools.dotc.report
-import dotty.tools.dotc.transform.MegaPhase.MiniPhase
 import dotty.tools.dotc.util.NoSourcePosition
 import dotty.tools.dotc.util.SourceFile
 import dotty.tools.dotc.util.SourcePosition
diff --git a/compiler/src/dotty/tools/debug/ResolveReflectEval.scala b/compiler/src/dotty/tools/debug/ResolveReflectEval.scala
index f79aa462fcb4..318fc4112e37 100644
--- a/compiler/src/dotty/tools/debug/ResolveReflectEval.scala
+++ b/compiler/src/dotty/tools/debug/ResolveReflectEval.scala
@@ -1,6 +1,5 @@
 package dotty.tools.debug
 
-import dotty.tools.dotc.core.SymUtils
 import dotty.tools.dotc.ast.tpd.*
 import dotty.tools.dotc.core.Constants.Constant
 import dotty.tools.dotc.core.Contexts.*
diff --git a/compiler/src/dotty/tools/dotc/CompilationUnit.scala b/compiler/src/dotty/tools/dotc/CompilationUnit.scala
index b627e149e5fb..33143a162169 100644
--- a/compiler/src/dotty/tools/dotc/CompilationUnit.scala
+++ b/compiler/src/dotty/tools/dotc/CompilationUnit.scala
@@ -14,7 +14,6 @@ import ast.Trees.{Import, Ident}
 import typer.Nullables
 import core.Decorators.*
 import config.{SourceVersion, Feature}
-import StdNames.nme
 import scala.annotation.internal.sharable
 import scala.util.control.NoStackTrace
 import transform.MacroAnnotations.isMacroAnnotation
diff --git a/compiler/src/dotty/tools/dotc/Driver.scala b/compiler/src/dotty/tools/dotc/Driver.scala
index f8daabf3ec5d..2a4feea9ed05 100644
--- a/compiler/src/dotty/tools/dotc/Driver.scala
+++ b/compiler/src/dotty/tools/dotc/Driver.scala
@@ -9,7 +9,6 @@ import dotty.tools.dotc.ast.Positioned
 import dotty.tools.io.{AbstractFile, FileExtension}
 import reporting.*
 import core.Decorators.*
-import config.Feature
 import util.chaining.*
 
 import scala.util.control.NonFatal
diff --git a/compiler/src/dotty/tools/dotc/Resident.scala b/compiler/src/dotty/tools/dotc/Resident.scala
index 5912825f712e..38343b2a568e 100644
--- a/compiler/src/dotty/tools/dotc/Resident.scala
+++ b/compiler/src/dotty/tools/dotc/Resident.scala
@@ -52,7 +52,7 @@ class Resident extends Driver {
             line = getLine()
           }
           if line.startsWith(quit) then ctx.reporter
-          else loop((line.split("\\s+")).asInstanceOf[Array[String]], nextCtx)
+          else loop(line.split("\\s+"), nextCtx)
         case None =>
           prevCtx.reporter
     }
diff --git a/compiler/src/dotty/tools/dotc/ast/Desugar.scala b/compiler/src/dotty/tools/dotc/ast/Desugar.scala
index 8a1ff74a0f13..5e5e1831f8e8 100644
--- a/compiler/src/dotty/tools/dotc/ast/Desugar.scala
+++ b/compiler/src/dotty/tools/dotc/ast/Desugar.scala
@@ -745,11 +745,11 @@ object desugar {
       if (originalVparamss.isEmpty) { // ensure parameter list is non-empty
         if (isCaseClass)
           report.error(CaseClassMissingParamList(cdef), namePos)
-        ListOfNil
+        List(Nil)
       }
       else if (isCaseClass && originalVparamss.head.exists(_.mods.isOneOf(GivenOrImplicit))) {
         report.error(CaseClassMissingNonImplicitParamList(cdef), namePos)
-        ListOfNil
+        List(Nil)
       }
       else originalVparamss.nestedMap(toMethParam(_, KeepAnnotations.All, keepDefault = true))
     val derivedTparams =
diff --git a/compiler/src/dotty/tools/dotc/ast/Trees.scala b/compiler/src/dotty/tools/dotc/ast/Trees.scala
index 56a58d358b15..50d7a8c643a3 100644
--- a/compiler/src/dotty/tools/dotc/ast/Trees.scala
+++ b/compiler/src/dotty/tools/dotc/ast/Trees.scala
@@ -1149,7 +1149,7 @@ object Trees {
 
   end WithLazyFields
 
-  // ----- Generic Tree Instances, inherited from `tpt` and `untpd`.
+  // ----- Generic Tree Instances, inherited from `tpd` and `untpd`.
 
   abstract class Instance[T <: Untyped] { inst =>
 
@@ -1259,7 +1259,7 @@ object Trees {
       protected def postProcess(tree: Tree, copied: untpd.Tree): copied.ThisTree[T]
       protected def postProcess(tree: Tree, copied: untpd.MemberDef): copied.ThisTree[T]
 
-      /** Soucre of the copied tree */
+      /** Source of the copied tree */
       protected def sourceFile(tree: Tree): SourceFile = tree.source
 
       protected def finalize(tree: Tree, copied: untpd.Tree): copied.ThisTree[T] =
diff --git a/compiler/src/dotty/tools/dotc/cc/Capability.scala b/compiler/src/dotty/tools/dotc/cc/Capability.scala
index 0c2fe68fee23..4dd6220a4709 100644
--- a/compiler/src/dotty/tools/dotc/cc/Capability.scala
+++ b/compiler/src/dotty/tools/dotc/cc/Capability.scala
@@ -5,21 +5,17 @@ package cc
 import core.*
 import Types.*, Symbols.*, Contexts.*, Decorators.*
 import util.{SimpleIdentitySet, EqHashMap}
-import util.common.alwaysTrue
-import scala.collection.mutable
-import CCState.*
 import Periods.{NoRunId, RunWidth}
 import compiletime.uninitialized
 import StdNames.nme
 import CaptureSet.{Refs, emptyRefs, VarState}
-import Annotations.Annotation
 import Flags.*
 import config.Printers.capt
 import annotation.constructorOnly
 import ast.tpd
 import printing.{Printer, Showable}
 import printing.Texts.Text
-import reporting.{Message, trace}
+import reporting.Message
 import NameOps.isImpureFunction
 import annotation.internal.sharable
 import collection.immutable
@@ -27,9 +23,9 @@ import collection.immutable
 /** Capabilities are members of capture sets. They partially overlap with types
  *  as shown in the trait hierarchy below.
  *
- *  Capability --+-- RootCapabilty -----+-- GlobalCap
- *               |                      +-- FreshCap
- *               |                      +-- ResultCap
+ *  Capability --+-- RootCapability -----+-- GlobalCap
+ *               |                       +-- FreshCap
+ *               |                       +-- ResultCap
  *               |
  *               +-- CoreCapability ----+-- ObjectCapability --+-- TermRef
  *               |                      |                      +-- ThisType
@@ -60,7 +56,7 @@ object Capabilities:
     nextRootId += 1
     def descr(using Context): String
 
-  /** The base trait of all capabilties represented as types */
+  /** The base trait of all capabilities represented as types */
   trait CoreCapability extends TypeProxy, Capability:
     override def toText(printer: Printer): Text = printer.toText(this)
 
@@ -140,7 +136,7 @@ object Capabilities:
     override def cached[C <: DerivedCapability](newRef: C): C = unsupported("cached")
     override def invalidateCaches() = ()
 
-  /** The class of "fresh" roots. These do subsume other capabilties in scope.
+  /** The class of "fresh" roots. These do subsume other capabilities in scope.
    *  They track with hidden sets which other capabilities were subsumed.
    *  Hidden sets are inspected by separation checking.
    *  @param owner   the owner of the context in which the FreshCap was created
@@ -198,7 +194,7 @@ object Capabilities:
         case _ => true
 
     /** Classify this FreshCap as `cls`, provided `isClassified` is still false.
-     *  @param  freeze  Deterermines future `isClassified` state.
+     *  @param  freeze  Determines future `isClassified` state.
      */
     def adoptClassifier(cls: ClassSymbol, freeze: Boolean)(using Context): Unit =
       if !isClassified then
diff --git a/compiler/src/dotty/tools/dotc/cc/Setup.scala b/compiler/src/dotty/tools/dotc/cc/Setup.scala
index 7e5050b758fc..3204504c0650 100644
--- a/compiler/src/dotty/tools/dotc/cc/Setup.scala
+++ b/compiler/src/dotty/tools/dotc/cc/Setup.scala
@@ -87,7 +87,7 @@ object Setup:
 end Setup
 import Setup.*
 
-/** Phase that sets up everthing for capture checking.
+/** Phase that sets up everything for capture checking.
  *
  *  A tree traverser that prepares a compilation unit to be capture checked.
  *  It does the following:
diff --git a/compiler/src/dotty/tools/dotc/cc/ccConfig.scala b/compiler/src/dotty/tools/dotc/cc/ccConfig.scala
index e7d07f4f91eb..120b0cee82b8 100644
--- a/compiler/src/dotty/tools/dotc/cc/ccConfig.scala
+++ b/compiler/src/dotty/tools/dotc/cc/ccConfig.scala
@@ -7,7 +7,7 @@ import config.{Feature, SourceVersion}
 
 object ccConfig:
 
-  /** If enabled, cache capture sets of infos capabilties */
+  /** If enabled, cache capture sets of infos capabilities */
   inline val cacheCaptureSetOfInfo = false
 
   /** If this and `preTypeClosureResults` are both enabled, disable `preTypeClosureResults`
diff --git a/compiler/src/dotty/tools/dotc/core/SymbolLoaders.scala b/compiler/src/dotty/tools/dotc/core/SymbolLoaders.scala
index c3337959cef6..3a639963659d 100644
--- a/compiler/src/dotty/tools/dotc/core/SymbolLoaders.scala
+++ b/compiler/src/dotty/tools/dotc/core/SymbolLoaders.scala
@@ -25,8 +25,7 @@ import ast.desugar
 
 import parsing.JavaParsers.OutlineJavaParser
 import parsing.Parsers.OutlineParser
-import dotty.tools.tasty.{TastyHeaderUnpickler, UnpickleException, UnpicklerConfig, TastyVersion}
-import dotty.tools.dotc.core.tasty.TastyUnpickler
+import dotty.tools.tasty.UnpickleException
 import dotty.tools.tasty.besteffort.BestEffortTastyHeaderUnpickler
 
 object SymbolLoaders {
diff --git a/compiler/src/dotty/tools/dotc/core/tasty/TastyUnpickler.scala b/compiler/src/dotty/tools/dotc/core/tasty/TastyUnpickler.scala
index 6ce27b8b77af..61a10491d8cc 100644
--- a/compiler/src/dotty/tools/dotc/core/tasty/TastyUnpickler.scala
+++ b/compiler/src/dotty/tools/dotc/core/tasty/TastyUnpickler.scala
@@ -13,7 +13,6 @@ import scala.collection.mutable
 import Names.{TermName, termName, EmptyTermName}
 import NameKinds.*
 import dotty.tools.tasty.TastyHeader
-import dotty.tools.tasty.TastyBuffer.Addr
 
 case class CommonTastyHeader(
   uuid: UUID,
diff --git a/compiler/src/dotty/tools/dotc/coverage/Serializer.scala b/compiler/src/dotty/tools/dotc/coverage/Serializer.scala
index 21d3a83cb3a0..84392991aef3 100644
--- a/compiler/src/dotty/tools/dotc/coverage/Serializer.scala
+++ b/compiler/src/dotty/tools/dotc/coverage/Serializer.scala
@@ -142,7 +142,7 @@ object Serializer:
 
     val linesWithoutHeader = lines.dropWhile(_.startsWith("#"))
     val coverage = Coverage()
-    while !linesWithoutHeader.isEmpty do
+    while linesWithoutHeader.nonEmpty do
       val oneStatementLines = linesWithoutHeader.takeWhile(_ != "\f")
       coverage.addStatement(toStatement(oneStatementLines))
     end while
diff --git a/compiler/src/dotty/tools/dotc/parsing/JavaParsers.scala b/compiler/src/dotty/tools/dotc/parsing/JavaParsers.scala
index c15e6c93bf90..7112402945f2 100644
--- a/compiler/src/dotty/tools/dotc/parsing/JavaParsers.scala
+++ b/compiler/src/dotty/tools/dotc/parsing/JavaParsers.scala
@@ -1014,7 +1014,7 @@ object JavaParsers {
       val predefs = List(
         DefDef(
           nme.values,
-          ListOfNil,
+          List(Nil),
           arrayOf(enumType),
           unimplementedExpr).withMods(Modifiers(Flags.JavaDefined | Flags.JavaStatic | Flags.Method)),
         DefDef(
diff --git a/compiler/src/dotty/tools/dotc/parsing/xml/SymbolicXMLBuilder.scala b/compiler/src/dotty/tools/dotc/parsing/xml/SymbolicXMLBuilder.scala
index aa8532b1d969..79162c47b887 100644
--- a/compiler/src/dotty/tools/dotc/parsing/xml/SymbolicXMLBuilder.scala
+++ b/compiler/src/dotty/tools/dotc/parsing/xml/SymbolicXMLBuilder.scala
@@ -163,7 +163,7 @@ class SymbolicXMLBuilder(parser: Parser, preserveWS: Boolean)(using Context) {
 
   /** could optimize if args.length == 0, args.length == 1 AND args(0) is <: Node. */
   def makeXMLseq(span: Span, args: collection.Seq[Tree]): Block = {
-    val buffer = ValDef(_buf, TypeTree(), New(_scala_xml_NodeBuffer, ListOfNil))
+    val buffer = ValDef(_buf, TypeTree(), New(_scala_xml_NodeBuffer, List(Nil)))
     val applies = args filterNot isEmptyText map (t => Apply(Select(Ident(_buf), _plus), List(t)))
 
     atSpan(span)(new XMLBlock(buffer :: applies.toList, Ident(_buf)) )
diff --git a/compiler/src/dotty/tools/dotc/plugins/Plugins.scala b/compiler/src/dotty/tools/dotc/plugins/Plugins.scala
index 6c162184f816..04d12a670f2b 100644
--- a/compiler/src/dotty/tools/dotc/plugins/Plugins.scala
+++ b/compiler/src/dotty/tools/dotc/plugins/Plugins.scala
@@ -4,14 +4,12 @@ package plugins
 import core.*
 import Contexts.*
 import Decorators.em
-import config.{ PathResolver, Feature }
+import config.PathResolver
 import dotty.tools.io.*
 import Phases.*
 import config.Printers.plugins.{ println => debug }
 import config.Properties
 
-import scala.compiletime.uninitialized
-
 /** Support for run-time loading of compiler plugins.
  *
  *  @author Lex Spoon
diff --git a/compiler/src/dotty/tools/dotc/printing/Formatting.scala b/compiler/src/dotty/tools/dotc/printing/Formatting.scala
index daf4e70ad25a..1a8e61c32aeb 100644
--- a/compiler/src/dotty/tools/dotc/printing/Formatting.scala
+++ b/compiler/src/dotty/tools/dotc/printing/Formatting.scala
@@ -2,8 +2,6 @@ package dotty.tools
 package dotc
 package printing
 
-import scala.collection.mutable
-
 import core.*
 import Texts.*, Types.*, Flags.*, Symbols.*, Contexts.*
 import Decorators.*
diff --git a/compiler/src/dotty/tools/dotc/transform/UnrollDefinitions.scala b/compiler/src/dotty/tools/dotc/transform/UnrollDefinitions.scala
index bf9e20e68930..7c5c260402b9 100644
--- a/compiler/src/dotty/tools/dotc/transform/UnrollDefinitions.scala
+++ b/compiler/src/dotty/tools/dotc/transform/UnrollDefinitions.scala
@@ -5,7 +5,6 @@ import ast.tpd
 import ast.Trees.*
 import core.*
 import Flags.*
-import Decorators.*
 import Contexts.*
 import Symbols.*
 import Constants.Constant
@@ -14,15 +13,12 @@ import DenotTransformers.IdentityDenotTransformer
 import Names.*
 import dotty.tools.dotc.core.NameKinds.DefaultGetterName
 
-import dotty.tools.dotc.core.Types.{MethodType, NamedType, PolyType, Type, NoPrefix, NoType}
+import dotty.tools.dotc.core.Types.{NoPrefix, NoType}
 
 import dotty.tools.dotc.printing.Formatting.hl
 
-import scala.collection.mutable
-import scala.util.boundary, boundary.break
 import dotty.tools.dotc.core.StdNames.nme
 import dotty.tools.unreachable
-import dotty.tools.dotc.util.Spans.Span
 
 /**Implementation of SIP-61.
  * Runs when `@unroll` annotations are found in a compilation unit, installing new definitions
diff --git a/compiler/src/dotty/tools/dotc/typer/Typer.scala b/compiler/src/dotty/tools/dotc/typer/Typer.scala
index dfa667573405..daf056eabe95 100644
--- a/compiler/src/dotty/tools/dotc/typer/Typer.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Typer.scala
@@ -4387,7 +4387,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
         alts.filter(_.info.isParameterless) match
         case alt :: Nil => readaptSimplified(tree.withType(alt))
         case _ =>
-          altDenots.find(_.info.paramInfoss == ListOfNil) match
+          altDenots.find(_.info.paramInfoss == List(Nil)) match
           case Some(alt) => readaptSimplified(tree.withType(altRef(alt)))
           case _ => error
 
diff --git a/compiler/src/dotty/tools/dotc/util/IntMap.scala b/compiler/src/dotty/tools/dotc/util/IntMap.scala
index 1d04567e99c7..896dd42c1e81 100644
--- a/compiler/src/dotty/tools/dotc/util/IntMap.scala
+++ b/compiler/src/dotty/tools/dotc/util/IntMap.scala
@@ -2,7 +2,7 @@ package dotty.tools.dotc.util
 
 import scala.compiletime.uninitialized
 
-/** A dense map from some `Key` type to `Int. Dense means: All keys and values
+/** A dense map from some `Key` type to `Int`. Dense means: All keys and values
  *  are stored in arrays from 0 up to the size of the map. Keys and values
  *  can be obtained by index using `key(index)` and `value(index)`. Values
  *  can also be stored using `setValue(index, value)`.
diff --git a/compiler/src/dotty/tools/package.scala b/compiler/src/dotty/tools/package.scala
index 098e9d637cb3..bf1aad806c9c 100644
--- a/compiler/src/dotty/tools/package.scala
+++ b/compiler/src/dotty/tools/package.scala
@@ -2,12 +2,14 @@ package dotty
 
 package object tools {
 
-  val ListOfNil: List[Nil.type] = Nil :: Nil
-
   /** Throws an `UnsupportedOperationException` with the given method name. */
   def unsupported(methodName: String): Nothing =
     throw new UnsupportedOperationException(methodName)
 
+  /** Throws a `MatchError` with the given argument, or a default "unreachable" message. */
+  def unreachable(x: Any = "<< this case was declared unreachable >>"): Nothing =
+    throw new MatchError(x)
+
   /** Forward-ported from the explicit-nulls branch. */
   extension [T](x: T | Null)
     /** Should be used when we know from the context that `x` is not null.
@@ -15,21 +17,23 @@ package object tools {
      *  occurrences of uncheckedNN.
      */
     transparent inline def uncheckedNN: T = x.asInstanceOf[T]
-
   end extension
 
-  object resultWrapper {
+  /**
+   * Infrastructure to shorten method calls by not requiring a lambda.
+   * Instead of `def f(x: ... => ...)` that must be called as, e.g.,  `f(x => x + 1)`,
+   * write `def f(x: WrappedResult[...] ?=> ...)`, use that parameter by creating a `WrappedResult`,
+   * and call `f(result + 1)`.
+   */
+  private object resultWrapper {
     opaque type WrappedResult[T] = T
     private[tools] def unwrap[T](x: WrappedResult[T]): T = x
     private[tools] def wrap[T](x: T): WrappedResult[T] = x
   }
   type WrappedResult[T] = resultWrapper.WrappedResult[T]
-  def WrappedResult[T](x: T) = resultWrapper.wrap(x)
+  def WrappedResult[T](x: T): WrappedResult[T] = resultWrapper.wrap(x)
   def result[T](using x: WrappedResult[T]): T = resultWrapper.unwrap(x)
 
-  def unreachable(x: Any = "<< this case was declared unreachable >>"): Nothing =
-    throw new MatchError(x)
-  
   // Ensure this object is already classloaded, since it's only actually used
   // when handling stack overflows and every operation (including class loading)
   // risks failing.
diff --git a/compiler/src/dotty/tools/scripting/ScriptingDriver.scala b/compiler/src/dotty/tools/scripting/ScriptingDriver.scala
index e4c357494ff1..3750d0fdff9f 100755
--- a/compiler/src/dotty/tools/scripting/ScriptingDriver.scala
+++ b/compiler/src/dotty/tools/scripting/ScriptingDriver.scala
@@ -27,9 +27,9 @@ class ScriptingDriver(compilerArgs: Array[String], scriptFile: File, scriptArgs:
             val classpathEntries: Seq[Path] = ClassPath.expandPath(classpath, expandStar=true).map { Paths.get(_) }
             detectMainClassAndMethod(outDir, classpathEntries, scriptFile.toString) match
               case Right((mainClass, mainMethod)) =>
-                val invokeMain: Boolean = Option(pack).map { func =>
-                    func(outDir, classpathEntries, mainClass)
-                  }.getOrElse(true)
+                val invokeMain: Boolean = Option(pack).forall { func =>
+                  func(outDir, classpathEntries, mainClass)
+                }
                 if invokeMain then mainMethod.invoke(null, scriptArgs)
                 None
               case Left(ex) => Some(ex)
diff --git a/compiler/src/dotty/tools/scripting/Util.scala b/compiler/src/dotty/tools/scripting/Util.scala
index 5ce71aa7c130..b31e252c568a 100755
--- a/compiler/src/dotty/tools/scripting/Util.scala
+++ b/compiler/src/dotty/tools/scripting/Util.scala
@@ -1,8 +1,8 @@
 package dotty.tools.scripting
 
-import java.nio.file.{ Path }
+import java.nio.file.Path
 import java.io.File
-import java.net.{ URLClassLoader }
+import java.net.URLClassLoader
 import java.lang.reflect.{ Modifier, Method }
 
 object Util:

From 82aa1b1fdcdc19bceaa112872f2f1eee67d9a3e9 Mon Sep 17 00:00:00 2001
From: Solal Pirelli <solal.pirelli@gmail.com>
Date: Thu, 8 Jan 2026 11:21:43 +0100
Subject: [PATCH 03/12] Remove file disabled for 11+ years

---
 .../tools/dotc/ast/CheckTrees.scala.disabled  | 258 ------------------
 1 file changed, 258 deletions(-)
 delete mode 100644 compiler/src/dotty/tools/dotc/ast/CheckTrees.scala.disabled

diff --git a/compiler/src/dotty/tools/dotc/ast/CheckTrees.scala.disabled b/compiler/src/dotty/tools/dotc/ast/CheckTrees.scala.disabled
deleted file mode 100644
index 08d409772331..000000000000
--- a/compiler/src/dotty/tools/dotc/ast/CheckTrees.scala.disabled
+++ /dev/null
@@ -1,258 +0,0 @@
-package dotty.tools
-package dotc
-package ast
-
-import core.*
-import util.Spans.*, Types.*, Contexts.*, Constants.*, Names.*, Flags.*
-import SymDenotations.*, Symbols.*, StdNames.*, Annotations.*, Trees.*
-
-// TODO: revise, integrate in a checking phase.
-object CheckTrees {
-
-  import tpd.*
-
-  def check(p: Boolean, msg: => String = "")(using Context): Unit = assert(p, msg)
-
-  def checkTypeArg(arg: Tree, bounds: TypeBounds)(using Context): Unit = {
-    check(arg.isValueType)
-    check(bounds contains arg.tpe)
-  }
-
-  def escapingRefs(block: Block)(using Context): collection.Set[NamedType] = {
-    var hoisted: Set[Symbol] = Set()
-    lazy val locals = ctx.typeAssigner.localSyms(block.stats).toSet
-    def isLocal(sym: Symbol): Boolean =
-      (locals contains sym) && !isHoistableClass(sym)
-    def isHoistableClass(sym: Symbol) =
-      sym.isClass && {
-        (hoisted contains sym) || {
-          hoisted += sym
-          !classLeaks(sym.asClass)
-        }
-      }
-    def leakingTypes(tp: Type): collection.Set[NamedType] =
-      tp namedPartsWith (tp => isLocal(tp.symbol))
-    def typeLeaks(tp: Type): Boolean = leakingTypes(tp).nonEmpty
-    def classLeaks(sym: ClassSymbol): Boolean =
-      (ctx.owner is Method) || // can't hoist classes out of method bodies
-      (sym.info.parents exists typeLeaks) ||
-      (sym.decls.toList exists (t => typeLeaks(t.info)))
-    leakingTypes(block.tpe)
-  }
-
-  def checkType(tree: Tree)(using Context): Unit = tree match {
-    case Ident(name) =>
-    case Select(qualifier, name) =>
-      check(qualifier.isValue)
-      check(qualifier.tpe =:= tree.tpe.normalizedPrefix)
-      val denot = qualifier.tpe.member(name)
-      check(denot.exists)
-      check(denot.hasAltWith(_.symbol == tree.symbol))
-    case This(cls) =>
-    case Super(qual, mixin) =>
-      check(qual.isValue)
-      val cls = qual.tpe.typeSymbol
-      check(cls.isClass)
-    case Apply(fn, args) =>
-      def checkArg(arg: Tree, name: Name, formal: Type): Unit = {
-        arg match {
-          case NamedArg(argName, _) =>
-            check(argName == name)
-          case _ =>
-            check(arg.isValue)
-        }
-        check(arg.tpe <:< formal)
-      }
-      val MethodType(paramNames, paramTypes) = fn.tpe.widen // checked already at construction
-      args.lazyZip(paramNames).lazyZip(paramTypes) foreach checkArg
-    case TypeApply(fn, args) =>
-      val pt @ PolyType(_) = fn.tpe.widen // checked already at construction
-      args.lazyZip(pt.instantiateBounds(args map (_.tpe))) foreach checkTypeArg
-    case Literal(const: Constant) =>
-    case New(tpt) =>
-      check(tpt.isValueType)
-      val cls = tpt.tpe.typeSymbol
-      check(cls.isClass)
-      check(!(cls is AbstractOrTrait))
-    case Pair(left, right) =>
-      check(left.isValue)
-      check(right.isValue)
-    case Typed(expr, tpt) =>
-      check(tpt.isValueType)
-      expr.tpe.widen match {
-        case tp: MethodType =>
-          val cls = tpt.tpe.typeSymbol
-          check(cls.isClass)
-          check((cls is Trait) ||
-                cls.primaryConstructor.info.paramTypess.flatten.isEmpty)
-          val absMembers = tpt.tpe.abstractTermMembers
-          check(absMembers.size == 1)
-          check(tp <:< absMembers.head.info)
-        case _ =>
-          check(expr.isValueOrPattern)
-          check(expr.tpe <:< tpt.tpe.translateParameterized(defn.RepeatedParamClass, defn.SeqClass))
-      }
-    case NamedArg(name, arg) =>
-    case Assign(lhs, rhs) =>
-      check(lhs.isValue); check(rhs.isValue)
-      lhs.tpe match {
-        case ltpe: TermRef =>
-          check(ltpe.symbol is Mutable)
-        case _ =>
-          check(false)
-      }
-      check(rhs.tpe <:< lhs.tpe.widen)
-    case tree @ Block(stats, expr) =>
-      check(expr.isValue)
-      check(escapingRefs(tree).isEmpty)
-    case If(cond, thenp, elsep) =>
-      check(cond.isValue); check(thenp.isValue); check(elsep.isValue)
-      check(cond.tpe isRef defn.BooleanClass)
-    case Closure(env, meth, target) =>
-   	  meth.tpe.widen match {
-   	    case mt @ MethodType(_, paramTypes) =>
-   	      if (target.isEmpty) {
-   	        check(env.length < paramTypes.length)
-   	        for ((arg, formal) <- env zip paramTypes)
-   	          check(arg.tpe <:< formal)
-   	      }
-   	      else
-   	        // env is stored in class, not method
-   	        target.tpe match {
-   	          case SAMType(targetMeth) =>
-   	            check(mt <:< targetMeth.info)
-   	        }
-   	  }
-    case Match(selector, cases) =>
-      check(selector.isValue)
-      // are any checks that relate selector and patterns desirable?
-    case CaseDef(pat, guard, body) =>
-      check(pat.isValueOrPattern); check(guard.isValue); check(body.isValue)
-      check(guard.tpe.derivesFrom(defn.BooleanClass))
-    case Return(expr, from) =>
-      check(expr.isValue); check(from.isTerm)
-      check(from.tpe.termSymbol.isRealMethod)
-    case Try(block, handler, finalizer) =>
-      check(block.isTerm)
-      check(finalizer.isTerm)
-      check(handler.isTerm)
-      check(handler.tpe derivesFrom defn.FunctionClass(1))
-      check(handler.tpe.baseArgInfos(defn.FunctionClass(1)).head <:< defn.ThrowableType)
-    case Throw(expr) =>
-      check(expr.isValue)
-      check(expr.tpe.derivesFrom(defn.ThrowableClass))
-    case SeqLiteral(elems) =>
-      val elemtp = tree.tpe.elemType
-      for (elem <- elems) {
-        check(elem.isValue)
-        check(elem.tpe <:< elemtp)
-      }
-    case TypeTree(original) =>
-      if (!original.isEmpty) {
-        check(original.isValueType)
-        check(original.tpe == tree.tpe)
-      }
-    case SingletonTypeTree(ref) =>
-      check(ref.isValue)
-      check(ref.symbol.isStable)
-    case SelectFromTypeTree(qualifier, name) =>
-      check(qualifier.isValueType)
-      check(qualifier.tpe =:= tree.tpe.normalizedPrefix)
-      val denot = qualifier.tpe.member(name)
-      check(denot.exists)
-      check(denot.symbol == tree.symbol)
-    case AndTypeTree(left, right) =>
-      check(left.isValueType); check(right.isValueType)
-    case OrTypeTree(left, right) =>
-      check(left.isValueType); check(right.isValueType)
-    case RefinedTypeTree(tpt, refinements) =>
-      check(tpt.isValueType)
-      def checkRefinements(forbidden: Set[Symbol], rs: List[Tree]): Unit = rs match {
-        case r :: rs1 =>
-          val rsym = r.symbol
-          check(rsym.isTerm || rsym.isAbstractOrAliasType)
-          if (rsym.isAbstractType) check(tpt.tpe.member(rsym.name).exists)
-          check(rsym.info forallParts {
-            case nt: NamedType => !(forbidden contains nt.symbol)
-            case _ => true
-          })
-          checkRefinements(forbidden - rsym, rs1)
-        case nil =>
-      }
-      checkRefinements(ctx.typeAssigner.localSyms(refinements).toSet, refinements)
-    case AppliedTypeTree(tpt, args) =>
-      check(tpt.isValueType)
-      val tparams = tpt.tpe.typeParams
-      check(sameLength(tparams, args))
-      args.lazyZip(tparams map (_.info.bounds)) foreach checkTypeArg
-    case TypeBoundsTree(lo, hi) =>
-      check(lo.isValueType); check(hi.isValueType)
-      check(lo.tpe <:< hi.tpe)
-    case Bind(sym, body) =>
-      check(body.isValueOrPattern)
-      check(!(tree.symbol is Method))
-      body match {
-        case Ident(nme.WILDCARD) =>
-        case _ => check(body.tpe.widen =:= tree.symbol.info)
-      }
-    case Alternative(alts) =>
-      for (alt <- alts) check(alt.isValueOrPattern)
-    case UnApply(fun, implicits, args) => // todo: review
-      check(fun.isTerm)
-      for (arg <- args) check(arg.isValueOrPattern)
-      val funtpe @ MethodType(_, _) = fun.tpe.widen
-      fun.symbol.name match { // check arg arity
-        case nme.unapplySeq =>
-          // args need to be wrapped in (...: _*)
-          check(args.length == 1)
-          check(args.head.isInstanceOf[SeqLiteral])
-        case nme.unapply =>
-          val rtp = funtpe.resultType
-          if (rtp isRef defn.BooleanClass)
-            check(args.isEmpty)
-          else {
-            check(rtp isRef defn.OptionClass)
-            val normArgs = rtp.argTypesHi match {
-              case optionArg :: Nil =>
-                optionArg.argTypesHi match {
-                  case Nil =>
-                    optionArg :: Nil
-                  case tupleArgs if defn.isTupleNType(optionArg) =>
-                    tupleArgs
-                }
-              case _ =>
-                check(false)
-                Nil
-            }
-            check(sameLength(normArgs, args))
-          }
-      }
-    case ValDef(mods, name, tpt, rhs) =>
-      check(!(tree.symbol is Method))
-      if (!rhs.isEmpty) {
-        check(rhs.isValue)
-        check(rhs.tpe <:< tpt.tpe)
-      }
-    case DefDef(mods, name, tparams, vparamss, tpt, rhs) =>
-      check(tree.symbol is Method)
-      if (!rhs.isEmpty) {
-        check(rhs.isValue)
-        check(rhs.tpe <:< tpt.tpe)
-      }
-    case TypeDef(mods, name, tpt) =>
-      check(tpt.isInstanceOf[Template] || tpt.tpe.isInstanceOf[TypeBounds])
-    case Template(constr, parents, selfType, body) =>
-    case Import(expr, selectors) =>
-      check(expr.isValue)
-      check(expr.tpe.termSymbol.isStable)
-    case PackageDef(pid, stats) =>
-      check(pid.isTerm)
-      check(pid.symbol is Package)
-    case Annotated(annot, arg) =>
-      check(annot.isInstantiation)
-      check(annot.symbol.owner.isSubClass(defn.AnnotationClass))
-      check(arg.isValueType || arg.isValue)
-    case EmptyTree =>
-  }
-}
-

From 2489cb18162d37f58429fcf2e920da4ece680743 Mon Sep 17 00:00:00 2001
From: Solal Pirelli <solal.pirelli@gmail.com>
Date: Thu, 8 Jan 2026 11:48:20 +0100
Subject: [PATCH 04/12] Remove class not used in 7+ years

---
 compiler/src/dotty/tools/dotc/util/DotClass.scala | 8 --------
 1 file changed, 8 deletions(-)
 delete mode 100644 compiler/src/dotty/tools/dotc/util/DotClass.scala

diff --git a/compiler/src/dotty/tools/dotc/util/DotClass.scala b/compiler/src/dotty/tools/dotc/util/DotClass.scala
deleted file mode 100644
index f9e7e97a219d..000000000000
--- a/compiler/src/dotty/tools/dotc/util/DotClass.scala
+++ /dev/null
@@ -1,8 +0,0 @@
-package dotty.tools.dotc.util
-
-/** Adds standard functionality to a class.
- *  For now: Just the `unsupported` method.
- */
-class DotClass {
-
-}

From 08f38f1c4a9554805b7ac93604dc6b69114b584d Mon Sep 17 00:00:00 2001
From: Solal Pirelli <solal.pirelli@gmail.com>
Date: Thu, 8 Jan 2026 11:55:21 +0100
Subject: [PATCH 05/12] Remove 10+ year old near empty worksheet

---
 compiler/src/dotty/tools/dotc/util/kwords.sc | 18 ------------------
 1 file changed, 18 deletions(-)
 delete mode 100644 compiler/src/dotty/tools/dotc/util/kwords.sc

diff --git a/compiler/src/dotty/tools/dotc/util/kwords.sc b/compiler/src/dotty/tools/dotc/util/kwords.sc
deleted file mode 100644
index 377be9dbcb65..000000000000
--- a/compiler/src/dotty/tools/dotc/util/kwords.sc
+++ /dev/null
@@ -1,18 +0,0 @@
-package dotty.tools.dotc.util
-
-import dotty.tools.dotc.parsing.*
-import Scanners.*
-import Tokens.*
-
-object kwords {
-  println("Welcome to the Scala worksheet")       //> Welcome to the Scala worksheet
-  keywords.toList.map(tokenString)                //> res0: List[String] = List(if, for, else, this, null, new, with, super, case,
-                                                  //|  case class, case object, val, abstract, final, private, protected, override
-                                                  //| , implicit, var, def, type, extends, true, false, object, class, import, pac
-                                                  //| kage, yield, do, trait, sealed, throw, try, catch, finally, while, return, m
-                                                  //| atch, lazy, then, forSome, _, :, =, <-, =>, ';', ';', <:, >:, #, @, <%)
-  keywords.toList.filter(kw => tokenString(kw) == null)
-                                                  //> res1: List[Int] = List()
-  canStartStatTokens3 contains CASE               //> res2: Boolean = false
-
-}
\ No newline at end of file

From 4f08f737fc45481f0323356ecc36d5e30c1bc28d Mon Sep 17 00:00:00 2001
From: Solal Pirelli <solal.pirelli@gmail.com>
Date: Thu, 8 Jan 2026 15:22:37 +0100
Subject: [PATCH 06/12] More cleanup, remove one dependency of utils on
 non-utils

---
 .../tools/debug/ExpressionCompiler.scala      |  1 -
 .../debug/ExpressionCompilerBridge.scala      |  4 ----
 .../debug/ExpressionCompilerConfig.scala      |  6 +----
 .../dotty/tools/debug/ExpressionStore.scala   |  4 ----
 .../dotty/tools/debug/ExtractExpression.scala |  8 ++-----
 .../src/dotty/tools/dotc/typer/Typer.scala    | 10 ++++----
 .../tools/dotc/util/CommentParsing.scala      | 24 +++++++++----------
 .../src/dotty/tools/dotc/util/LRUCache.scala  |  4 ++--
 .../src/dotty/tools/dotc/util/LinearMap.scala |  2 +-
 .../src/dotty/tools/dotc/util/LinearSet.scala |  2 +-
 .../dotty/tools/dotc/util/Signatures.scala    |  3 +--
 .../tools/dotc/util/SimpleIdentityMap.scala   |  2 +-
 .../tools/dotc/util/SimpleIdentitySet.scala   |  3 +--
 .../dotty/tools/dotc/util/SourceFile.scala    |  3 +--
 .../src/dotty/tools/dotc/util/Spans.scala     |  2 +-
 .../src/dotty/tools/dotc/util/Stats.scala     |  2 +-
 .../src/dotty/tools/dotc/util/common.scala    |  3 ---
 .../dotty/tools/dotc/util/concurrent.scala    |  3 ++-
 18 files changed, 31 insertions(+), 55 deletions(-)

diff --git a/compiler/src/dotty/tools/debug/ExpressionCompiler.scala b/compiler/src/dotty/tools/debug/ExpressionCompiler.scala
index 9931aa94270c..cb9c96b43a77 100644
--- a/compiler/src/dotty/tools/debug/ExpressionCompiler.scala
+++ b/compiler/src/dotty/tools/debug/ExpressionCompiler.scala
@@ -1,7 +1,6 @@
 package dotty.tools.debug
 
 import dotty.tools.dotc.Compiler
-import dotty.tools.dotc.core.Contexts.Context
 import dotty.tools.dotc.core.Phases.Phase
 import dotty.tools.dotc.transform.ElimByName
 
diff --git a/compiler/src/dotty/tools/debug/ExpressionCompilerBridge.scala b/compiler/src/dotty/tools/debug/ExpressionCompilerBridge.scala
index 3ffbdc860abe..c596c6d4a1e0 100644
--- a/compiler/src/dotty/tools/debug/ExpressionCompilerBridge.scala
+++ b/compiler/src/dotty/tools/debug/ExpressionCompilerBridge.scala
@@ -1,11 +1,7 @@
 package dotty.tools.debug
 
 import java.nio.file.Path
-import java.util.function.Consumer
-import java.{util => ju}
-import scala.jdk.CollectionConverters.*
 import scala.util.control.NonFatal
-import dotty.tools.dotc.reporting.StoreReporter
 import dotty.tools.dotc.core.Contexts.Context
 import dotty.tools.dotc.Driver
 
diff --git a/compiler/src/dotty/tools/debug/ExpressionCompilerConfig.scala b/compiler/src/dotty/tools/debug/ExpressionCompilerConfig.scala
index 895489143f9e..81bd66f0ea8b 100644
--- a/compiler/src/dotty/tools/debug/ExpressionCompilerConfig.scala
+++ b/compiler/src/dotty/tools/debug/ExpressionCompilerConfig.scala
@@ -1,12 +1,8 @@
 package dotty.tools.debug
 
-import dotty.tools.dotc.ast.tpd.*
 import dotty.tools.dotc.core.Symbols.*
-import dotty.tools.dotc.core.Types.*
 import dotty.tools.dotc.core.Names.*
-import dotty.tools.dotc.core.Flags.*
 import dotty.tools.dotc.core.Contexts.*
-import dotty.tools.dotc.core.SymUtils
 
 import java.{util => ju}
 import ju.function.Consumer
@@ -37,7 +33,7 @@ class ExpressionCompilerConfig private[debug] (
   def withLocalVariables(localVariables: ju.Set[String]): ExpressionCompilerConfig = copy(localVariables = localVariables)
   def withErrorReporter(errorReporter: Consumer[String]): ExpressionCompilerConfig = copy(errorReporter = errorReporter)
 
-  private[debug] val expressionTermName: TermName = termName(outputClassName.toLowerCase.toString)
+  private[debug] val expressionTermName: TermName = termName(outputClassName.toLowerCase)
   private[debug] val expressionClassName: TypeName = typeName(outputClassName)
 
   private[debug] def expressionClass(using Context): ClassSymbol =
diff --git a/compiler/src/dotty/tools/debug/ExpressionStore.scala b/compiler/src/dotty/tools/debug/ExpressionStore.scala
index 3151c43b9a7a..8018d7ca306d 100644
--- a/compiler/src/dotty/tools/debug/ExpressionStore.scala
+++ b/compiler/src/dotty/tools/debug/ExpressionStore.scala
@@ -1,12 +1,8 @@
 package dotty.tools.debug
 
-import dotty.tools.dotc.ast.tpd.*
 import dotty.tools.dotc.core.Symbols.*
-import dotty.tools.dotc.core.Types.*
-import dotty.tools.dotc.core.Names.*
 import dotty.tools.dotc.core.Flags.*
 import dotty.tools.dotc.core.Contexts.*
-import dotty.tools.dotc.core.SymUtils
 
 private class ExpressionStore:
   var symbol: TermSymbol | Null = null
diff --git a/compiler/src/dotty/tools/debug/ExtractExpression.scala b/compiler/src/dotty/tools/debug/ExtractExpression.scala
index 68e35f7f17dc..d87875d9018a 100644
--- a/compiler/src/dotty/tools/debug/ExtractExpression.scala
+++ b/compiler/src/dotty/tools/debug/ExtractExpression.scala
@@ -1,6 +1,5 @@
 package dotty.tools.debug
 
-import dotty.tools.dotc.core.SymUtils
 import dotty.tools.dotc.ast.tpd.*
 import dotty.tools.dotc.core.Constants.Constant
 import dotty.tools.dotc.core.Contexts.*
@@ -14,9 +13,6 @@ import dotty.tools.dotc.core.SymDenotations.SymDenotation
 import dotty.tools.dotc.transform.MacroTransform
 import dotty.tools.dotc.core.Phases.*
 import dotty.tools.dotc.report
-import dotty.tools.dotc.util.SrcPos
-import scala.annotation.nowarn
-
 /**
   * This phase extracts the typed expression from the source tree, transforms it and places it
   * in the evaluate method of the Expression class.
@@ -110,7 +106,7 @@ private class ExtractExpression(
         case tree: (Ident | Select | This) if isStaticObject(tree.symbol) =>
           getStaticObject(tree)(tree.symbol.moduleClass)
 
-        // non static this or outer this
+        // non-static this or outer this
         case tree: This if !tree.symbol.is(Package) =>
           thisOrOuterValue(tree)(tree.symbol.enclosingClass.asClass)
 
@@ -362,7 +358,7 @@ private class ExtractExpression(
 
   private def isLocalToExpression(symbol: Symbol)(using Context): Boolean =
     val evaluateMethod = config.evaluateMethod
-    symbol.ownersIterator.exists(_ == evaluateMethod)
+    symbol.ownersIterator.contains(evaluateMethod)
 
 private object ExtractExpression:
   val name: String = "extractExpression"
diff --git a/compiler/src/dotty/tools/dotc/typer/Typer.scala b/compiler/src/dotty/tools/dotc/typer/Typer.scala
index daf056eabe95..56d01edd2ecb 100644
--- a/compiler/src/dotty/tools/dotc/typer/Typer.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Typer.scala
@@ -31,10 +31,8 @@ import EtaExpansion.etaExpand
 import TypeComparer.CompareResult
 import inlines.{Inlines, PrepareInlineable}
 import util.Spans.*
-import util.chaining.*
-import util.common.*
 import util.{Property, SimpleIdentityMap, SrcPos}
-import Applications.{tupleComponentTypes, wrapDefs, defaultArgument}
+import Applications.{wrapDefs, defaultArgument}
 
 import collection.mutable
 import Implicits.*
@@ -48,13 +46,11 @@ import reporting.*
 import Nullables.*
 import NullOpsDecorator.*
 import cc.{CheckCaptures, isRetainsLike}
-import config.Config
 import config.MigrationVersion
 import transform.CheckUnused.OriginalName
 
 import scala.annotation.{unchecked as _, *}
 import dotty.tools.dotc.util.chaining.*
-import dotty.tools.dotc.ast.untpd.Mod
 
 object Typer {
 
@@ -110,7 +106,6 @@ object Typer {
    */
   private[typer] val HiddenSearchFailure = new Property.Key[List[SearchFailure]]
 
-
   /** An attachment on a Typed node. Indicates that the Typed node was synthetically
    *  inserted by the Typer phase. We might want to remove it for the purpose of inlining,
    *  but only if it was not manually inserted by the user.
@@ -126,6 +121,9 @@ object Typer {
     case _ => false
   }
 
+  /** Hoisted out for performance */
+  private val alwaysWildcardType: Any => WildcardType.type = Function.const(WildcardType)
+
   /** Add `fail` to the list of search failures attached to `tree` */
   def rememberSearchFailure(tree: tpd.Tree, fail: SearchFailure) =
     tree.putAttachment(HiddenSearchFailure,
diff --git a/compiler/src/dotty/tools/dotc/util/CommentParsing.scala b/compiler/src/dotty/tools/dotc/util/CommentParsing.scala
index 56c72457d02a..99f8df5f349f 100644
--- a/compiler/src/dotty/tools/dotc/util/CommentParsing.scala
+++ b/compiler/src/dotty/tools/dotc/util/CommentParsing.scala
@@ -19,8 +19,8 @@ import scala.collection.mutable
 object CommentParsing {
   import Chars.*
 
-  /** Returns index of string `str` following `start` skipping longest
-   *  sequence of whitespace characters characters (but no newlines)
+  /** Returns index of string `str` following `start` skipping
+   *  sequence of whitespace characters (but no newlines)
    */
   def skipWhitespace(str: String, start: Int): Int =
     if (start < str.length && isWhitespace(str.charAt(start))) skipWhitespace(str, start + 1)
@@ -41,7 +41,7 @@ object CommentParsing {
     else start
 
 
-  /** Returns index of string `str` after `start` skipping longest
+  /** Returns index of string `str` after `start` skipping
    *  sequence of space and tab characters, possibly also containing
    *  a single `*` character or the `/``**` sequence.
    *  @pre  start == str.length || str(start) == `\n`
@@ -50,8 +50,8 @@ object CommentParsing {
     if (start == str.length) start
     else {
       val idx = skipWhitespace(str, start + 1)
-      if (idx < str.length && (str.charAt(idx)) == '*') skipWhitespace(str, idx + 1)
-      else if (idx + 2 < str.length && (str.charAt(idx)) == '/' && (str.charAt(idx + 1)) == '*' && (str.charAt(idx + 2)) == '*')
+      if (idx < str.length && str.charAt(idx) == '*') skipWhitespace(str, idx + 1)
+      else if (idx + 2 < str.length && str.charAt(idx) == '/' && str.charAt(idx + 1) == '*' && str.charAt(idx + 2) == '*')
         skipWhitespace(str, idx + 3)
       else idx
     }
@@ -59,8 +59,8 @@ object CommentParsing {
   /** Skips to next occurrence of `\n` or to the position after the `/``**` sequence following index `start`.
    */
   def skipToEol(str: String, start: Int): Int =
-    if (start + 2 < str.length && (str.charAt(start)) == '/' && (str.charAt(start + 1)) == '*' && (str.charAt(start + 2)) == '*') start + 3
-    else if (start < str.length && (str.charAt(start)) != '\n') skipToEol(str, start + 1)
+    if (start + 2 < str.length && str.charAt(start) == '/' && str.charAt(start + 1) == '*' && str.charAt(start + 2) == '*') start + 3
+    else if (start < str.length && str.charAt(start) != '\n') skipToEol(str, start + 1)
     else start
 
   /** Returns first index following `start` and starting a line (i.e. after skipLineLead) or starting the comment
@@ -81,7 +81,7 @@ object CommentParsing {
     else idx :: findAll(str, idx)(p)
   }
 
-  /** Produces a string index, which is a list of `sections`, i.e
+  /** Produces a string index, which is a list of `sections`, i.e.,
    *  pairs of start/end positions of all tagged sections in the string.
    *  Every section starts with an at sign and extends to the next at sign,
    *  or to the end of the comment string, but excluding the final two
@@ -103,7 +103,7 @@ object CommentParsing {
   }
 
   /**
-   * Merge sections following an usecase into the usecase comment, so they
+   * Merge sections following a usecase into the usecase comment, so they
    * can override the parent symbol's sections
    */
   def mergeUsecaseSections(str: String, idxs: List[Int]): List[Int] =
@@ -163,7 +163,7 @@ object CommentParsing {
 
   /** Extracts variable name from a string, stripping any pair of surrounding braces */
   def variableName(str: String): String =
-    if (str.length >= 2 && (str.charAt(0)) == '{' && (str.charAt(str.length - 1)) == '}')
+    if (str.length >= 2 && str.charAt(0) == '{' && str.charAt(str.length - 1) == '}')
       str.substring(1, str.length - 1)
     else
       str
@@ -172,10 +172,10 @@ object CommentParsing {
    */
   def skipVariable(str: String, start: Int): Int = {
     var idx = start
-    if (idx < str.length && (str.charAt(idx)) == '{') {
+    if (idx < str.length && str.charAt(idx) == '{') {
       while ({
         idx += 1
-        idx < str.length && (str.charAt(idx)) != '}'
+        idx < str.length && str.charAt(idx) != '}'
       })
       ()
       if (idx < str.length) idx + 1 else start
diff --git a/compiler/src/dotty/tools/dotc/util/LRUCache.scala b/compiler/src/dotty/tools/dotc/util/LRUCache.scala
index 4abe8962ae5b..82345f700aff 100644
--- a/compiler/src/dotty/tools/dotc/util/LRUCache.scala
+++ b/compiler/src/dotty/tools/dotc/util/LRUCache.scala
@@ -1,8 +1,8 @@
 package dotty.tools.dotc.util
 
 
-import reflect.ClassTag
-import annotation.tailrec
+import scala.reflect.ClassTag
+import scala.annotation.tailrec
 
 /** A least-recently-used cache for Key -> Value computations
  *  It currently keeps the last 8 associations, but this can be
diff --git a/compiler/src/dotty/tools/dotc/util/LinearMap.scala b/compiler/src/dotty/tools/dotc/util/LinearMap.scala
index 28a5daaefdba..a8e2f558c602 100644
--- a/compiler/src/dotty/tools/dotc/util/LinearMap.scala
+++ b/compiler/src/dotty/tools/dotc/util/LinearMap.scala
@@ -1,6 +1,6 @@
 package dotty.tools.dotc.util
 
-import collection.immutable
+import scala.collection.immutable
 
 /** A linear map is a map where after an `updated` the previous map
  *  value cannot be used anymore. The map is implemented as an immutable
diff --git a/compiler/src/dotty/tools/dotc/util/LinearSet.scala b/compiler/src/dotty/tools/dotc/util/LinearSet.scala
index d057c4ebeda9..52834f03bc42 100644
--- a/compiler/src/dotty/tools/dotc/util/LinearSet.scala
+++ b/compiler/src/dotty/tools/dotc/util/LinearSet.scala
@@ -1,6 +1,6 @@
 package dotty.tools.dotc.util
 
-import collection.immutable
+import scala.collection.immutable
 
 /** A linear set is a set where after a `+` the previous set value cannot be
  *  used anymore. The set is implemented as an immutable set for sizes <= 4
diff --git a/compiler/src/dotty/tools/dotc/util/Signatures.scala b/compiler/src/dotty/tools/dotc/util/Signatures.scala
index 8bf720e388ea..09f14b6ebb9c 100644
--- a/compiler/src/dotty/tools/dotc/util/Signatures.scala
+++ b/compiler/src/dotty/tools/dotc/util/Signatures.scala
@@ -6,7 +6,6 @@ import dotty.tools.dotc.ast.Positioned
 import dotty.tools.dotc.ast.untpd
 import dotty.tools.dotc.core.NameOps.*
 import dotty.tools.dotc.core.StdNames.nme
-import dotty.tools.dotc.core.Symbols.defn
 
 import ast.Trees.*
 import ast.tpd
@@ -16,7 +15,7 @@ import core.Flags
 import core.Names.*
 import core.NameKinds
 import core.Types.*
-import core.Symbols.{NoSymbol, isLocalToBlock}
+import core.Symbols.isLocalToBlock
 import interactive.Interactive
 import util.Spans.Span
 import reporting.*
diff --git a/compiler/src/dotty/tools/dotc/util/SimpleIdentityMap.scala b/compiler/src/dotty/tools/dotc/util/SimpleIdentityMap.scala
index 2f202bc05921..0d945536864c 100644
--- a/compiler/src/dotty/tools/dotc/util/SimpleIdentityMap.scala
+++ b/compiler/src/dotty/tools/dotc/util/SimpleIdentityMap.scala
@@ -1,6 +1,6 @@
 package dotty.tools.dotc.util
 
-import collection.mutable.ListBuffer
+import scala.collection.mutable.ListBuffer
 
 /** A simple linked map with `eq` as the key comparison, optimized for small maps.
  *  It has linear complexity for `apply`, `updated`, and `remove`.
diff --git a/compiler/src/dotty/tools/dotc/util/SimpleIdentitySet.scala b/compiler/src/dotty/tools/dotc/util/SimpleIdentitySet.scala
index 1d8dc484c989..32fffbb3911d 100644
--- a/compiler/src/dotty/tools/dotc/util/SimpleIdentitySet.scala
+++ b/compiler/src/dotty/tools/dotc/util/SimpleIdentitySet.scala
@@ -1,7 +1,6 @@
 package dotty.tools.dotc.util
 
-
-import collection.mutable
+import scala.collection.mutable
 
 /** A simple linked set with `eq` as the comparison, optimized for small sets.
  *  It has linear complexity for `contains`, `+`, and `-`.
diff --git a/compiler/src/dotty/tools/dotc/util/SourceFile.scala b/compiler/src/dotty/tools/dotc/util/SourceFile.scala
index 8800743c4f1c..0b002cd29fa5 100644
--- a/compiler/src/dotty/tools/dotc/util/SourceFile.scala
+++ b/compiler/src/dotty/tools/dotc/util/SourceFile.scala
@@ -20,9 +20,8 @@ import dotty.tools.dotc.util.chaining.*
 import java.io.File.separator
 import java.net.URI
 import java.nio.charset.StandardCharsets
-import java.nio.file.{FileSystemException, NoSuchFileException, Paths}
+import java.nio.file.{FileSystemException, Paths}
 import java.util.Optional
-import java.util.concurrent.atomic.AtomicInteger
 import java.util.regex.Pattern
 
 object ScriptSourceFile {
diff --git a/compiler/src/dotty/tools/dotc/util/Spans.scala b/compiler/src/dotty/tools/dotc/util/Spans.scala
index 33346ad6da17..4d9137efb837 100644
--- a/compiler/src/dotty/tools/dotc/util/Spans.scala
+++ b/compiler/src/dotty/tools/dotc/util/Spans.scala
@@ -1,7 +1,7 @@
 package dotty.tools.dotc
 package util
 
-import language.implicitConversions
+import scala.language.implicitConversions
 
 /** The offsets part of a full position, consisting of 2 or 3 entries:
  *    - start:  the start offset of the span, in characters from start of file
diff --git a/compiler/src/dotty/tools/dotc/util/Stats.scala b/compiler/src/dotty/tools/dotc/util/Stats.scala
index 2f4e3bd9cb4f..66308158d1f7 100644
--- a/compiler/src/dotty/tools/dotc/util/Stats.scala
+++ b/compiler/src/dotty/tools/dotc/util/Stats.scala
@@ -5,7 +5,7 @@ package util
 import scala.annotation.internal.sharable
 
 import core.Contexts.*
-import collection.mutable
+import scala.collection.mutable
 
 @sharable object Stats {
 
diff --git a/compiler/src/dotty/tools/dotc/util/common.scala b/compiler/src/dotty/tools/dotc/util/common.scala
index 85ce9a29f2df..8d0d7289c45b 100644
--- a/compiler/src/dotty/tools/dotc/util/common.scala
+++ b/compiler/src/dotty/tools/dotc/util/common.scala
@@ -1,13 +1,10 @@
 package dotty.tools.dotc
 package util
 
-import core.Types.WildcardType
-
 /** Common values hoisted out for performance */
 object common {
 
   val alwaysTrue: Any => Boolean = Function.const(true)
   val alwaysFalse: Any => Boolean = Function.const(false)
   val alwaysZero: Any => Int = Function.const(0)
-  val alwaysWildcardType: Any => WildcardType.type = Function.const(WildcardType)
 }
diff --git a/compiler/src/dotty/tools/dotc/util/concurrent.scala b/compiler/src/dotty/tools/dotc/util/concurrent.scala
index 2710aae6c9b0..cd83948ba58a 100644
--- a/compiler/src/dotty/tools/dotc/util/concurrent.scala
+++ b/compiler/src/dotty/tools/dotc/util/concurrent.scala
@@ -1,5 +1,6 @@
 package dotty.tools.dotc.util
-import scala.util.{Try, Failure, Success}
+
+import scala.util.{Try, Failure}
 import scala.collection.mutable.ArrayBuffer
 
 object concurrent:

From 6f553c5ed7b72ed9a472b1ded49676d667e04426 Mon Sep 17 00:00:00 2001
From: Solal Pirelli <solal.pirelli@gmail.com>
Date: Thu, 8 Jan 2026 15:31:54 +0100
Subject: [PATCH 07/12] Remove more dead imports including the only
 'semanticdb' use outside Compiler

---
 .../tools/dotc/transform/CheckShadowing.scala | 20 -------------------
 1 file changed, 20 deletions(-)

diff --git a/compiler/src/dotty/tools/dotc/transform/CheckShadowing.scala b/compiler/src/dotty/tools/dotc/transform/CheckShadowing.scala
index fe7ed64e3c82..64edbb8a70ff 100644
--- a/compiler/src/dotty/tools/dotc/transform/CheckShadowing.scala
+++ b/compiler/src/dotty/tools/dotc/transform/CheckShadowing.scala
@@ -1,37 +1,17 @@
 package dotty.tools.dotc.transform
 
 import dotty.tools.dotc.ast.tpd
-import dotty.tools.dotc.ast.Trees.EmptyTree
-import dotty.tools.dotc.transform.MegaPhase
 import dotty.tools.dotc.transform.MegaPhase.MiniPhase
 import dotty.tools.dotc.report
 import dotty.tools.dotc.core.Contexts.*
 import dotty.tools.dotc.core.Flags.*
 import dotty.tools.dotc.util.{Property, SrcPos}
-import dotty.tools.dotc.core.Symbols.ClassSymbol
 import dotty.tools.dotc.core.Names.Name
 import dotty.tools.dotc.core.Symbols.Symbol
-import dotty.tools.dotc.core.Flags.EmptyFlags
 import dotty.tools.dotc.ast.tpd.TreeTraverser
-import dotty.tools.dotc.core.Types.watchList
-import dotty.tools.dotc.core.Types.NoType
-import dotty.tools.dotc.core.Types.Type
-import dotty.tools.dotc.core.Types
-import dotty.tools.dotc.semanticdb.TypeOps
-import dotty.tools.dotc.core.Symbols.{NoSymbol, isParamOrAccessor}
-import scala.collection.mutable
-import dotty.tools.dotc.core.Scopes.Scope
-import scala.collection.immutable.HashMap
 import dotty.tools.dotc.core.Symbols
-import dotty.tools.dotc.typer.ImportInfo
-import dotty.tools.dotc.ast.untpd.ImportSelector
-import dotty.tools.dotc.core.StdNames.nme
-import dotty.tools.dotc.ast.untpd
 import dotty.tools.dotc.core.Denotations.SingleDenotation
 import dotty.tools.dotc.ast.Trees.Ident
-import dotty.tools.dotc.core.Names.TypeName
-import dotty.tools.dotc.core.Names.TermName
-import dotty.tools.dotc.core.Mode.Type
 import dotty.tools.dotc.core.Names.SimpleName
 
 class CheckShadowing extends MiniPhase:

From 291cc053b3f6c5f5ddf5fdb6bf671e7c805b7af7 Mon Sep 17 00:00:00 2001
From: Solal Pirelli <solal.pirelli@gmail.com>
Date: Thu, 8 Jan 2026 15:49:44 +0100
Subject: [PATCH 08/12] Restore ListOfNil

---
 compiler/src/dotty/tools/dotc/ast/Desugar.scala               | 4 ++--
 compiler/src/dotty/tools/dotc/parsing/JavaParsers.scala       | 2 +-
 .../src/dotty/tools/dotc/parsing/xml/SymbolicXMLBuilder.scala | 2 +-
 compiler/src/dotty/tools/dotc/typer/Typer.scala               | 2 +-
 compiler/src/dotty/tools/package.scala                        | 3 +++
 5 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/compiler/src/dotty/tools/dotc/ast/Desugar.scala b/compiler/src/dotty/tools/dotc/ast/Desugar.scala
index 5e5e1831f8e8..8a1ff74a0f13 100644
--- a/compiler/src/dotty/tools/dotc/ast/Desugar.scala
+++ b/compiler/src/dotty/tools/dotc/ast/Desugar.scala
@@ -745,11 +745,11 @@ object desugar {
       if (originalVparamss.isEmpty) { // ensure parameter list is non-empty
         if (isCaseClass)
           report.error(CaseClassMissingParamList(cdef), namePos)
-        List(Nil)
+        ListOfNil
       }
       else if (isCaseClass && originalVparamss.head.exists(_.mods.isOneOf(GivenOrImplicit))) {
         report.error(CaseClassMissingNonImplicitParamList(cdef), namePos)
-        List(Nil)
+        ListOfNil
       }
       else originalVparamss.nestedMap(toMethParam(_, KeepAnnotations.All, keepDefault = true))
     val derivedTparams =
diff --git a/compiler/src/dotty/tools/dotc/parsing/JavaParsers.scala b/compiler/src/dotty/tools/dotc/parsing/JavaParsers.scala
index 7112402945f2..061516698d68 100644
--- a/compiler/src/dotty/tools/dotc/parsing/JavaParsers.scala
+++ b/compiler/src/dotty/tools/dotc/parsing/JavaParsers.scala
@@ -886,7 +886,7 @@ object JavaParsers {
 
       val accessors =
         (for (name, (tpt, annots)) <- fieldsByName yield
-          DefDef(name, List(Nil), adaptVarargsType(tpt), unimplementedExpr)
+          DefDef(name, ListOfNil, adaptVarargsType(tpt), unimplementedExpr)
             .withMods(Modifiers(Flags.JavaDefined | Flags.Method | Flags.Synthetic))
         ).toList
 
diff --git a/compiler/src/dotty/tools/dotc/parsing/xml/SymbolicXMLBuilder.scala b/compiler/src/dotty/tools/dotc/parsing/xml/SymbolicXMLBuilder.scala
index 79162c47b887..aa8532b1d969 100644
--- a/compiler/src/dotty/tools/dotc/parsing/xml/SymbolicXMLBuilder.scala
+++ b/compiler/src/dotty/tools/dotc/parsing/xml/SymbolicXMLBuilder.scala
@@ -163,7 +163,7 @@ class SymbolicXMLBuilder(parser: Parser, preserveWS: Boolean)(using Context) {
 
   /** could optimize if args.length == 0, args.length == 1 AND args(0) is <: Node. */
   def makeXMLseq(span: Span, args: collection.Seq[Tree]): Block = {
-    val buffer = ValDef(_buf, TypeTree(), New(_scala_xml_NodeBuffer, List(Nil)))
+    val buffer = ValDef(_buf, TypeTree(), New(_scala_xml_NodeBuffer, ListOfNil))
     val applies = args filterNot isEmptyText map (t => Apply(Select(Ident(_buf), _plus), List(t)))
 
     atSpan(span)(new XMLBlock(buffer :: applies.toList, Ident(_buf)) )
diff --git a/compiler/src/dotty/tools/dotc/typer/Typer.scala b/compiler/src/dotty/tools/dotc/typer/Typer.scala
index 56d01edd2ecb..651169bcce21 100644
--- a/compiler/src/dotty/tools/dotc/typer/Typer.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Typer.scala
@@ -4385,7 +4385,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
         alts.filter(_.info.isParameterless) match
         case alt :: Nil => readaptSimplified(tree.withType(alt))
         case _ =>
-          altDenots.find(_.info.paramInfoss == List(Nil)) match
+          altDenots.find(_.info.paramInfoss == ListOfNil) match
           case Some(alt) => readaptSimplified(tree.withType(altRef(alt)))
           case _ => error
 
diff --git a/compiler/src/dotty/tools/package.scala b/compiler/src/dotty/tools/package.scala
index bf1aad806c9c..475befce3807 100644
--- a/compiler/src/dotty/tools/package.scala
+++ b/compiler/src/dotty/tools/package.scala
@@ -2,6 +2,9 @@ package dotty
 
 package object tools {
 
+  /** Cached single-element list of Nil. (Whether this helps performance has not been tested) */
+  val ListOfNil: List[Nil.type] = Nil :: Nil
+
   /** Throws an `UnsupportedOperationException` with the given method name. */
   def unsupported(methodName: String): Nothing =
     throw new UnsupportedOperationException(methodName)

From fa339f67029180c58398376c2d0274408724a513 Mon Sep 17 00:00:00 2001
From: Solal Pirelli <solal.pirelli@gmail.com>
Date: Fri, 9 Jan 2026 11:04:26 +0100
Subject: [PATCH 09/12] PR feedback

---
 compiler/src/dotty/tools/debug/ExtractExpression.scala  | 2 +-
 compiler/src/dotty/tools/dotc/cc/Capability.scala       | 6 +++++-
 compiler/src/dotty/tools/dotc/parsing/JavaParsers.scala | 2 +-
 3 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/compiler/src/dotty/tools/debug/ExtractExpression.scala b/compiler/src/dotty/tools/debug/ExtractExpression.scala
index d87875d9018a..71e7091b8ebf 100644
--- a/compiler/src/dotty/tools/debug/ExtractExpression.scala
+++ b/compiler/src/dotty/tools/debug/ExtractExpression.scala
@@ -358,7 +358,7 @@ private class ExtractExpression(
 
   private def isLocalToExpression(symbol: Symbol)(using Context): Boolean =
     val evaluateMethod = config.evaluateMethod
-    symbol.ownersIterator.contains(evaluateMethod)
+    symbol.ownersIterator.exists(_ == evaluateMethod)
 
 private object ExtractExpression:
   val name: String = "extractExpression"
diff --git a/compiler/src/dotty/tools/dotc/cc/Capability.scala b/compiler/src/dotty/tools/dotc/cc/Capability.scala
index 4dd6220a4709..f45c6d579ebb 100644
--- a/compiler/src/dotty/tools/dotc/cc/Capability.scala
+++ b/compiler/src/dotty/tools/dotc/cc/Capability.scala
@@ -5,17 +5,21 @@ package cc
 import core.*
 import Types.*, Symbols.*, Contexts.*, Decorators.*
 import util.{SimpleIdentitySet, EqHashMap}
+import util.common.alwaysTrue
+import scala.collection.mutable
+import CCState.*
 import Periods.{NoRunId, RunWidth}
 import compiletime.uninitialized
 import StdNames.nme
 import CaptureSet.{Refs, emptyRefs, VarState}
+import Annotations.Annotation
 import Flags.*
 import config.Printers.capt
 import annotation.constructorOnly
 import ast.tpd
 import printing.{Printer, Showable}
 import printing.Texts.Text
-import reporting.Message
+import reporting.{Message, trace}
 import NameOps.isImpureFunction
 import annotation.internal.sharable
 import collection.immutable
diff --git a/compiler/src/dotty/tools/dotc/parsing/JavaParsers.scala b/compiler/src/dotty/tools/dotc/parsing/JavaParsers.scala
index 061516698d68..52fa946f9305 100644
--- a/compiler/src/dotty/tools/dotc/parsing/JavaParsers.scala
+++ b/compiler/src/dotty/tools/dotc/parsing/JavaParsers.scala
@@ -1014,7 +1014,7 @@ object JavaParsers {
       val predefs = List(
         DefDef(
           nme.values,
-          List(Nil),
+          ListOfNil,
           arrayOf(enumType),
           unimplementedExpr).withMods(Modifiers(Flags.JavaDefined | Flags.JavaStatic | Flags.Method)),
         DefDef(

From 13956b960a9ccb2bbc7c6886566dd64817bd0bc2 Mon Sep 17 00:00:00 2001
From: Solal Pirelli <solal.pirelli@gmail.com>
Date: Fri, 9 Jan 2026 11:07:22 +0100
Subject: [PATCH 10/12] PR feedback

---
 compiler/src/dotty/tools/dotc/transform/UnrollDefinitions.scala | 1 +
 compiler/src/dotty/tools/dotc/typer/Typer.scala                 | 1 +
 2 files changed, 2 insertions(+)

diff --git a/compiler/src/dotty/tools/dotc/transform/UnrollDefinitions.scala b/compiler/src/dotty/tools/dotc/transform/UnrollDefinitions.scala
index 7c5c260402b9..4aa598d1aa3f 100644
--- a/compiler/src/dotty/tools/dotc/transform/UnrollDefinitions.scala
+++ b/compiler/src/dotty/tools/dotc/transform/UnrollDefinitions.scala
@@ -5,6 +5,7 @@ import ast.tpd
 import ast.Trees.*
 import core.*
 import Flags.*
+import Decorators.*
 import Contexts.*
 import Symbols.*
 import Constants.Constant
diff --git a/compiler/src/dotty/tools/dotc/typer/Typer.scala b/compiler/src/dotty/tools/dotc/typer/Typer.scala
index 651169bcce21..27be413dbd84 100644
--- a/compiler/src/dotty/tools/dotc/typer/Typer.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Typer.scala
@@ -31,6 +31,7 @@ import EtaExpansion.etaExpand
 import TypeComparer.CompareResult
 import inlines.{Inlines, PrepareInlineable}
 import util.Spans.*
+import util.chaining.*
 import util.{Property, SimpleIdentityMap, SrcPos}
 import Applications.{wrapDefs, defaultArgument}
 

From ac15a3888598322dfdb8657ed145d49921971561 Mon Sep 17 00:00:00 2001
From: Solal Pirelli <solal.pirelli@gmail.com>
Date: Tue, 13 Jan 2026 15:45:42 +0100
Subject: [PATCH 11/12] PR feedback

---
 compiler/src/dotty/tools/dotc/util/LinearMap.scala         | 2 +-
 compiler/src/dotty/tools/dotc/util/LinearSet.scala         | 2 +-
 compiler/src/dotty/tools/dotc/util/SimpleIdentityMap.scala | 2 +-
 compiler/src/dotty/tools/dotc/util/SimpleIdentitySet.scala | 2 +-
 compiler/src/dotty/tools/dotc/util/Spans.scala             | 2 +-
 compiler/src/dotty/tools/dotc/util/Stats.scala             | 2 +-
 6 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/compiler/src/dotty/tools/dotc/util/LinearMap.scala b/compiler/src/dotty/tools/dotc/util/LinearMap.scala
index a8e2f558c602..28a5daaefdba 100644
--- a/compiler/src/dotty/tools/dotc/util/LinearMap.scala
+++ b/compiler/src/dotty/tools/dotc/util/LinearMap.scala
@@ -1,6 +1,6 @@
 package dotty.tools.dotc.util
 
-import scala.collection.immutable
+import collection.immutable
 
 /** A linear map is a map where after an `updated` the previous map
  *  value cannot be used anymore. The map is implemented as an immutable
diff --git a/compiler/src/dotty/tools/dotc/util/LinearSet.scala b/compiler/src/dotty/tools/dotc/util/LinearSet.scala
index 52834f03bc42..d057c4ebeda9 100644
--- a/compiler/src/dotty/tools/dotc/util/LinearSet.scala
+++ b/compiler/src/dotty/tools/dotc/util/LinearSet.scala
@@ -1,6 +1,6 @@
 package dotty.tools.dotc.util
 
-import scala.collection.immutable
+import collection.immutable
 
 /** A linear set is a set where after a `+` the previous set value cannot be
  *  used anymore. The set is implemented as an immutable set for sizes <= 4
diff --git a/compiler/src/dotty/tools/dotc/util/SimpleIdentityMap.scala b/compiler/src/dotty/tools/dotc/util/SimpleIdentityMap.scala
index 0d945536864c..2f202bc05921 100644
--- a/compiler/src/dotty/tools/dotc/util/SimpleIdentityMap.scala
+++ b/compiler/src/dotty/tools/dotc/util/SimpleIdentityMap.scala
@@ -1,6 +1,6 @@
 package dotty.tools.dotc.util
 
-import scala.collection.mutable.ListBuffer
+import collection.mutable.ListBuffer
 
 /** A simple linked map with `eq` as the key comparison, optimized for small maps.
  *  It has linear complexity for `apply`, `updated`, and `remove`.
diff --git a/compiler/src/dotty/tools/dotc/util/SimpleIdentitySet.scala b/compiler/src/dotty/tools/dotc/util/SimpleIdentitySet.scala
index 32fffbb3911d..654681b2edef 100644
--- a/compiler/src/dotty/tools/dotc/util/SimpleIdentitySet.scala
+++ b/compiler/src/dotty/tools/dotc/util/SimpleIdentitySet.scala
@@ -1,6 +1,6 @@
 package dotty.tools.dotc.util
 
-import scala.collection.mutable
+import collection.mutable
 
 /** A simple linked set with `eq` as the comparison, optimized for small sets.
  *  It has linear complexity for `contains`, `+`, and `-`.
diff --git a/compiler/src/dotty/tools/dotc/util/Spans.scala b/compiler/src/dotty/tools/dotc/util/Spans.scala
index 4d9137efb837..33346ad6da17 100644
--- a/compiler/src/dotty/tools/dotc/util/Spans.scala
+++ b/compiler/src/dotty/tools/dotc/util/Spans.scala
@@ -1,7 +1,7 @@
 package dotty.tools.dotc
 package util
 
-import scala.language.implicitConversions
+import language.implicitConversions
 
 /** The offsets part of a full position, consisting of 2 or 3 entries:
  *    - start:  the start offset of the span, in characters from start of file
diff --git a/compiler/src/dotty/tools/dotc/util/Stats.scala b/compiler/src/dotty/tools/dotc/util/Stats.scala
index 66308158d1f7..2f4e3bd9cb4f 100644
--- a/compiler/src/dotty/tools/dotc/util/Stats.scala
+++ b/compiler/src/dotty/tools/dotc/util/Stats.scala
@@ -5,7 +5,7 @@ package util
 import scala.annotation.internal.sharable
 
 import core.Contexts.*
-import scala.collection.mutable
+import collection.mutable
 
 @sharable object Stats {
 

From 0eca63186e6555205335cd78d57a4b7f4ff082ae Mon Sep 17 00:00:00 2001
From: Solal Pirelli <solal.pirelli@gmail.com>
Date: Mon, 19 Jan 2026 14:08:03 +0100
Subject: [PATCH 12/12] Offline feedback

---
 compiler/src/dotty/tools/debug/ExpressionCompilerConfig.scala | 4 ++++
 compiler/src/dotty/tools/debug/ExpressionStore.scala          | 4 ++++
 compiler/src/dotty/tools/dotc/typer/Typer.scala               | 1 +
 compiler/src/dotty/tools/dotc/util/LRUCache.scala             | 4 ++--
 4 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/compiler/src/dotty/tools/debug/ExpressionCompilerConfig.scala b/compiler/src/dotty/tools/debug/ExpressionCompilerConfig.scala
index 81bd66f0ea8b..0a464299899f 100644
--- a/compiler/src/dotty/tools/debug/ExpressionCompilerConfig.scala
+++ b/compiler/src/dotty/tools/debug/ExpressionCompilerConfig.scala
@@ -1,8 +1,12 @@
 package dotty.tools.debug
 
+import dotty.tools.dotc.ast.tpd.*
 import dotty.tools.dotc.core.Symbols.*
+import dotty.tools.dotc.core.Types.*
 import dotty.tools.dotc.core.Names.*
+import dotty.tools.dotc.core.Flags.*
 import dotty.tools.dotc.core.Contexts.*
+import dotty.tools.dotc.core.SymUtils
 
 import java.{util => ju}
 import ju.function.Consumer
diff --git a/compiler/src/dotty/tools/debug/ExpressionStore.scala b/compiler/src/dotty/tools/debug/ExpressionStore.scala
index 8018d7ca306d..3151c43b9a7a 100644
--- a/compiler/src/dotty/tools/debug/ExpressionStore.scala
+++ b/compiler/src/dotty/tools/debug/ExpressionStore.scala
@@ -1,8 +1,12 @@
 package dotty.tools.debug
 
+import dotty.tools.dotc.ast.tpd.*
 import dotty.tools.dotc.core.Symbols.*
+import dotty.tools.dotc.core.Types.*
+import dotty.tools.dotc.core.Names.*
 import dotty.tools.dotc.core.Flags.*
 import dotty.tools.dotc.core.Contexts.*
+import dotty.tools.dotc.core.SymUtils
 
 private class ExpressionStore:
   var symbol: TermSymbol | Null = null
diff --git a/compiler/src/dotty/tools/dotc/typer/Typer.scala b/compiler/src/dotty/tools/dotc/typer/Typer.scala
index 27be413dbd84..29be088643c6 100644
--- a/compiler/src/dotty/tools/dotc/typer/Typer.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Typer.scala
@@ -32,6 +32,7 @@ import TypeComparer.CompareResult
 import inlines.{Inlines, PrepareInlineable}
 import util.Spans.*
 import util.chaining.*
+import util.common.*
 import util.{Property, SimpleIdentityMap, SrcPos}
 import Applications.{wrapDefs, defaultArgument}
 
diff --git a/compiler/src/dotty/tools/dotc/util/LRUCache.scala b/compiler/src/dotty/tools/dotc/util/LRUCache.scala
index 82345f700aff..4abe8962ae5b 100644
--- a/compiler/src/dotty/tools/dotc/util/LRUCache.scala
+++ b/compiler/src/dotty/tools/dotc/util/LRUCache.scala
@@ -1,8 +1,8 @@
 package dotty.tools.dotc.util
 
 
-import scala.reflect.ClassTag
-import scala.annotation.tailrec
+import reflect.ClassTag
+import annotation.tailrec
 
 /** A least-recently-used cache for Key -> Value computations
  *  It currently keeps the last 8 associations, but this can be