Drop scala shadowing and DottyPredef

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

@@ -75,8 +75,6 @@ class Driver {
     inContext(ictx) {
       if !ctx.settings.YdropComments.value || ctx.mode.is(Mode.ReadComments) then
         ictx.setProperty(ContextDoc, new ContextDocstrings)
-      if Feature.enabledBySetting(nme.Scala2Compat) then
-        report.warning("-language:Scala2Compat will go away; use -source 3.0-migration instead")
       val fileNames = CompilerCommand.checkUsage(summary, sourcesRequired)
       fromTastySetup(fileNames, ctx)
     }

compiler/src/dotty/tools/dotc/config/Feature.scala

@@ -82,8 +82,7 @@ object Feature:
       case Some(v) => v
       case none => sourceVersionSetting
 
-  def migrateTo3(using Context): Boolean =
-    sourceVersion == `3.0-migration` || enabledBySetting(nme.Scala2Compat)
+  def migrateTo3(using Context): Boolean = sourceVersion == `3.0-migration`
 
   /** If current source migrates to `version`, issue given warning message
    *  and return `true`, otherwise return `false`.

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

@@ -9,7 +9,7 @@ import unpickleScala2.Scala2Unpickler.ensureConstructor
 import scala.collection.mutable
 import collection.mutable
 import Denotations.SingleDenotation
-import util.SimpleIdentityMap
+import util.{SimpleIdentityMap, SourceFile, NoSource}
 import typer.ImportInfo.RootRef
 
 import scala.annotation.tailrec
@@ -252,6 +252,7 @@ class Definitions {
    *  or classes with the same name. But their binary artifacts are
    *  in `scalaShadowing` so they don't clash with the same-named `scala`
    *  members at runtime.
+   *  It is used only for non-bootstrapped code
    */
   @tu lazy val ScalaShadowingPackage: TermSymbol = requiredPackage(nme.scalaShadowing)
 
@@ -481,12 +482,12 @@ class Definitions {
     newPermanentSymbol(ScalaPackageClass, tpnme.IMPLICITkw, EmptyFlags, TypeBounds.empty).entered
   def ImplicitScrutineeTypeRef: TypeRef = ImplicitScrutineeTypeSym.typeRef
 
-
   @tu lazy val ScalaPredefModule: Symbol = requiredModule("scala.Predef")
     @tu lazy val Predef_conforms : Symbol = ScalaPredefModule.requiredMethod(nme.conforms_)
     @tu lazy val Predef_classOf  : Symbol = ScalaPredefModule.requiredMethod(nme.classOf)
     @tu lazy val Predef_identity : Symbol = ScalaPredefModule.requiredMethod(nme.identity)
     @tu lazy val Predef_undefined: Symbol = ScalaPredefModule.requiredMethod(nme.???)
+  @tu lazy val ScalaPredefModuleClass: ClassSymbol = ScalaPredefModule.moduleClass.asClass
 
   @tu lazy val SubTypeClass: ClassSymbol = requiredClass("scala.<:<")
   @tu lazy val SubType_refl: Symbol = SubTypeClass.companionModule.requiredMethod(nme.refl)
@@ -510,7 +511,7 @@ class Definitions {
   // will return "null" when called recursively, see #1856.
   def DottyPredefModule: Symbol = {
     if (myDottyPredefModule == null) {
-      myDottyPredefModule = requiredModule("dotty.DottyPredef")
+      myDottyPredefModule = getModuleIfDefined("dotty.DottyPredef")
       assert(myDottyPredefModule != null)
     }
     myDottyPredefModule
@@ -782,6 +783,7 @@ class Definitions {
   @tu lazy val Mirror_SingletonProxyClass: ClassSymbol = requiredClass("scala.deriving.Mirror.SingletonProxy")
 
   @tu lazy val LanguageModule: Symbol = requiredModule("scala.language")
+  @tu lazy val LanguageModuleClass: Symbol = LanguageModule.moduleClass.asClass
   @tu lazy val LanguageExperimentalModule: Symbol = requiredModule("scala.language.experimental")
   @tu lazy val NonLocalReturnControlClass: ClassSymbol = requiredClass("scala.runtime.NonLocalReturnControl")
   @tu lazy val SelectableClass: ClassSymbol = requiredClass("scala.Selectable")
@@ -1101,6 +1103,65 @@ class Definitions {
       || sym.owner == CompiletimeOpsPackageObjectString.moduleClass && compiletimePackageStringTypes.contains(sym.name)
     )
 
+  // ----- Scala-2 library patches --------------------------------------
+
+  /** The `scala.runtime.stdLibPacthes` package contains objects
+   *  that contain defnitions that get added as members to standard library
+   *  objects with the same name.
+   */
+  @tu lazy val StdLibPatchesPackage: TermSymbol = requiredPackage("scala.runtime.stdLibPatches")
+  @tu private lazy val ScalaPredefModuleClassPatch: Symbol = getModuleIfDefined("scala.runtime.stdLibPatches.Predef").moduleClass
+  @tu private lazy val LanguageModuleClassPatch: Symbol = getModuleIfDefined("scala.runtime.stdLibPatches.language").moduleClass
+
+  /** If `sym` is a patched library class, the source file of its patch class,
+   *  otherwise `NoSource`
+   */
+  def patchSource(sym: Symbol)(using Context): SourceFile =
+    if sym == ScalaPredefModuleClass then ScalaPredefModuleClassPatch.source
+    else if sym == LanguageModuleClass then LanguageModuleClassPatch.source
+    else NoSource
+
+  /** A finalizer that patches standard library classes.
+   *  It copies all non-private, non-synthetic definitions from `patchCls`
+   *  to `denot` while changing their owners to `denot`. Before that it deletes
+   *  any definitions of `denot` that have the same name as one of the copied
+   *  definitions.
+   *
+   *  If an object is present in both the original class and the patch class,
+   *  it is not overwritten. Instead its members are copied recursively.
+   *
+   *  To avpid running into cycles on bootstrap, patching happens only if `patchCls`
+   *  is read from a classfile.
+   */
+  def patchStdLibClass(denot: ClassDenotation)(using Context): Unit =
+
+    def patch2(denot: ClassDenotation, patchCls: Symbol): Unit =
+      val scope = denot.info.decls.openForMutations
+      def recurse(patch: Symbol) = patch.is(Module) && scope.lookup(patch.name).exists
+      if patchCls.exists then
+        val patches = patchCls.info.decls.filter(patch =>
+          !patch.isConstructor && !patch.isOneOf(PrivateOrSynthetic))
+        for patch <- patches if !recurse(patch) do
+          val e = scope.lookupEntry(patch.name)
+          if e != null then scope.unlink(e)
+        for patch <- patches do
+          patch.ensureCompleted()
+          if !recurse(patch) then
+            patch.denot = patch.denot.copySymDenotation(owner = denot.symbol)
+            scope.enter(patch)
+          else if patch.isClass then
+            patch2(scope.lookup(patch.name).asClass, patch)
+
+    def patchWith(patchCls: Symbol) =
+      denot.sourceModule.info = denot.typeRef // we run into a cyclic reference when patching if this line is omitted
+      patch2(denot, patchCls)
+
+    if denot.name == tpnme.Predef.moduleClassName && denot.symbol == ScalaPredefModuleClass then
+      patchWith(ScalaPredefModuleClassPatch)
+    else if denot.name == tpnme.language.moduleClassName && denot.symbol == LanguageModuleClass then
+      patchWith(LanguageModuleClassPatch)
+  end patchStdLibClass
+
   // ----- Symbol sets ---------------------------------------------------
 
   @tu lazy val AbstractFunctionType: Array[TypeRef] = mkArityArray("scala.runtime.AbstractFunction", MaxImplementedFunctionArity, 0)

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

@@ -386,7 +386,6 @@ object StdNames {
     val Ref: N                  = "Ref"
     val RootPackage: N          = "RootPackage"
     val RootClass: N            = "RootClass"
-    val Scala2Compat: N         = "Scala2Compat"
     val Select: N               = "Select"
     val Shape: N                = "Shape"
     val StringContext: N        = "StringContext"

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

@@ -428,23 +428,21 @@ object Symbols {
     private var mySource: SourceFile = NoSource
 
     final def sourceOfClass(using Context): SourceFile = {
-      if (!mySource.exists && !denot.is(Package))
+      if !mySource.exists && !denot.is(Package) then
         // this allows sources to be added in annotations after `sourceOfClass` is first called
-        mySource = {
-          val file = associatedFile
-          if (file != null && file.extension != "class") ctx.getSource(file)
-          else {
-            def sourceFromTopLevel(using Context) =
-              denot.topLevelClass.unforcedAnnotation(defn.SourceFileAnnot) match {
-                case Some(sourceAnnot) => sourceAnnot.argumentConstant(0) match {
+        val file = associatedFile
+        if file != null && file.extension != "class" then
+          mySource = ctx.getSource(file)
+        else
+          mySource = defn.patchSource(this)
+          if !mySource.exists then
+            mySource = atPhaseNoLater(flattenPhase) {
+              denot.topLevelClass.unforcedAnnotation(defn.SourceFileAnnot) match
+                case Some(sourceAnnot) => sourceAnnot.argumentConstant(0) match
                   case Some(Constant(path: String)) => ctx.getSource(path)
                   case none => NoSource
-                }
                 case none => NoSource
-              }
-            atPhaseNoLater(flattenPhase)(sourceFromTopLevel)
-          }
-        }
+            }
       mySource
     }
 
@@ -880,6 +878,13 @@ object Symbols {
     staticRef(name).requiredSymbol("object", name)(_.is(Module)).asTerm
   }
 
+  /** Get module symbol if the module is either defined in current compilation run
+   *  or present on classpath. Returns NoSymbol otherwise.
+   */
+  def getModuleIfDefined(path: PreName)(using Context): Symbol =
+    staticRef(path.toTermName, generateStubs = false)
+      .disambiguate(_.is(Module)).symbol
+
   def requiredModuleRef(path: PreName)(using Context): TermRef = requiredModule(path).termRef
 
   def requiredMethod(path: PreName)(using Context): TermSymbol = {

compiler/src/dotty/tools/dotc/core/tasty/TreePickler.scala

@@ -764,7 +764,9 @@ class TreePickler(pickler: TastyPickler) {
 
   def pickle(trees: List[Tree])(using Context): Unit = {
     trees.foreach(tree => if (!tree.isEmpty) pickleTree(tree))
-    def missing = forwardSymRefs.keysIterator.map(sym => sym.showLocated + "(line " + sym.srcPos.line + ")").toList
+    def missing = forwardSymRefs.keysIterator
+      .map(sym => i"${sym.showLocated} (line ${sym.srcPos.line}) #${sym.id}")
+      .toList
     assert(forwardSymRefs.isEmpty, i"unresolved symbols: $missing%, % when pickling ${ctx.source}")
   }
 

compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala

@@ -940,6 +940,7 @@ class TreeUnpickler(reader: TastyReader,
         val stats = rdr.readIndexedStats(localDummy, end)
         tparams ++ vparams ++ stats
       })
+      defn.patchStdLibClass(cls)
       setSpan(start,
         untpd.Template(constr, mappedParents, Nil, self, lazyStats)
           .withType(localDummy.termRef))

compiler/src/dotty/tools/dotc/core/unpickleScala2/Scala2Unpickler.scala

@@ -111,6 +111,7 @@ object Scala2Unpickler {
 
     denot.info = tempInfo.finalized(normalizedParents)
     denot.ensureTypeParamsInCorrectOrder()
+    defn.patchStdLibClass(denot)
   }
 }
 

compiler/src/dotty/tools/dotc/transform/TreeChecker.scala

@@ -446,9 +446,9 @@ class TreeChecker extends Phase with SymTransformer {
       val symbolsNotDefined = decls -- defined - constr.symbol
 
       assert(symbolsNotDefined.isEmpty,
-          i" $cls tree does not define members: ${symbolsNotDefined.toList}%, %\n" +
-          i"expected: ${decls.toList}%, %\n" +
-          i"defined: ${defined}%, %")
+        i" $cls tree does not define members: ${symbolsNotDefined.toList}%, %\n" +
+        i"expected: ${decls.toList}%, %\n" +
+        i"defined: ${defined}%, %")
 
       super.typedClassDef(cdef, cls)
     }
@@ -540,6 +540,12 @@ class TreeChecker extends Phase with SymTransformer {
       super.typedWhileDo(tree)
     }
 
+    override def typedPackageDef(tree: untpd.PackageDef)(using Context): Tree =
+      if tree.symbol == defn.StdLibPatchesPackage then
+        promote(tree) // don't check stdlib patches, since their symbols were highjacked by stdlib classes
+      else
+        super.typedPackageDef(tree)
+
     override def ensureNoLocalRefs(tree: Tree, pt: Type, localSyms: => List[Symbol])(using Context): Tree =
       tree
 

compiler/src/dotty/tools/dotc/typer/Namer.scala

@@ -1199,6 +1199,7 @@ class Namer { typer: Typer =>
       cls.setNoInitsFlags(parentsKind(parents), untpd.bodyKind(rest))
       if (cls.isNoInitsClass) cls.primaryConstructor.setFlag(StableRealizable)
       processExports(using localCtx)
+      defn.patchStdLibClass(denot.asClass)
     }
   }
 

library/src-bootstrapped/dotty/DottyPredef.scala

@@ -0,0 +1,3 @@
+package dotty
+
+object DottyPredef

library/src-bootstrapped/scalaShadowing/D_u_m_m_y.scala

@@ -0,0 +1,3 @@
+package scalaShadowing
+
+class D_u_m_m_y

library/src/scalaShadowing/language.scala → library/src-non-bootstrapped/scalaShadowing/language.scala

@@ -225,9 +225,6 @@ object language {
     object genericNumberLiterals
   }
 
-  /** Where imported, a backwards compatibility mode for Scala2 is enabled */
-  object Scala2Compat
-
   /** Where imported, auto-tupling is disabled */
   object noAutoTupling
 

library/src/scala/runtime/stdLibPatches/Predef.scala

@@ -0,0 +1,47 @@
+package scala.runtime.stdLibPatches
+
+object Predef:
+  import compiletime.summonFrom
+
+  inline def assert(inline assertion: Boolean, inline message: => Any): Unit =
+    if !assertion then scala.runtime.Scala3RunTime.assertFailed(message)
+
+  inline def assert(inline assertion: Boolean): Unit =
+    if !assertion then scala.runtime.Scala3RunTime.assertFailed()
+
+  /**
+   * Retrieve the single value of a type with a unique inhabitant.
+   *
+   * @example {{{
+   * object Foo
+   * val foo = valueOf[Foo.type]
+   * // foo is Foo.type = Foo
+   *
+   * val bar = valueOf[23]
+   * // bar is 23.type = 23
+   * }}}
+   * @group utilities
+   */
+  inline def valueOf[T]: T = summonFrom {
+    case ev: ValueOf[T] => ev.value
+  }
+
+  /** Summon a given value of type `T`. Usually, the argument is not passed explicitly.
+   *
+   *  @tparam T the type of the value to be summoned
+   *  @return the given value typed as the provided type parameter
+   */
+  inline def summon[T](using x: T): x.type = x
+
+  // Extension methods for working with explicit nulls
+
+  /** Strips away the nullability from a value.
+   *  e.g.
+   *    val s1: String|Null = "hello"
+   *    val s: String = s1.nn
+   *
+   *  Note that `.nn` performs a checked cast, so if invoked on a null value it'll throw an NPE.
+   */
+  extension [T](x: T | Null) inline def nn: x.type & T =
+    scala.runtime.Scala3RunTime.nn(x)
+end Predef

library/src/scala/runtime/stdLibPatches/language.scala

@@ -0,0 +1,60 @@
+package scala.runtime.stdLibPatches
+
+/** Scala 3 additions and replacements to the `scala.language` object.
+ */
+object language:
+
+  /** The experimental object contains features that have been recently added but have not
+   *  been thoroughly tested in production yet.
+   *
+   *  Experimental features '''may undergo API changes''' in future releases, so production
+   *  code should not rely on them.
+   *
+   *  Programmers are encouraged to try out experimental features and
+   *  [[http://issues.scala-lang.org report any bugs or API inconsistencies]]
+   *  they encounter so they can be improved in future releases.
+   *
+   *  @group experimental
+   */
+  object experimental:
+
+    /** Experimental support for richer dependent types */
+    object dependent
+
+    /** Experimental support for named type arguments */
+    object namedTypeArguments
+
+    /** Experimental support for generic number literals */
+    object genericNumberLiterals
+  end experimental
+
+  /** Where imported, auto-tupling is disabled */
+  object noAutoTupling
+
+  /** Where imported, loose equality using eqAny is disabled */
+  object strictEquality
+
+  /** Where imported, ad hoc extensions of non-open classes in other
+   *  compilation units are allowed.
+   *
+   *  '''Why control the feature?''' Ad-hoc extensions should usually be avoided
+   *  since they typically cannot rely on an "internal" contract between a class
+   *  and its extensions. Only open classes need to specify such a contract.
+   *  Ad-hoc extensions might break for future versions of the extended class,
+   *  since the extended class is free to change its implementation without
+   *  being constrained by an internal contract.
+   *
+   *  '''Why allow it?''' An ad-hoc extension can sometimes be necessary,
+   *  for instance when mocking a class in a testing framework, or to work
+   *  around a bug or missing feature in the original class. Nevertheless,
+   *  such extensions should be limited in scope and clearly documented.
+   *  That's why the language import is required for them.
+   */
+  object adhocExtensions
+
+  /** Source version */
+  object `3.0-migration`
+  object `3.0`
+  object `3.1-migration`
+  object `3.1`
+end language