Dollars in idents

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

@@ -34,6 +34,7 @@ enum MigrationVersion(val warnFrom: SourceVersion, val errorFrom: SourceVersion)
   case GivenSyntax extends MigrationVersion(future, future)
   case ImplicitParamsWithoutUsing extends MigrationVersion(`3.7`, future)
   case Scala2Implicits extends MigrationVersion(future, future)
+  case IdentifierDollars extends MigrationVersion(`3.8`, `3.9`)
 
   require(warnFrom.ordinal <= errorFrom.ordinal)
 

compiler/src/dotty/tools/dotc/core/classfile/ClassfileTastyUUIDParser.scala

@@ -104,6 +104,6 @@ class ClassfileTastyUUIDParser(classfile: AbstractFile)(ictx: Context) {
   class ConstantPool(using in: DataReader) extends ClassfileParser.AbstractConstantPool {
     def getClassOrArrayType(index: Int)(using ctx: Context, in: DataReader): Type = throw new UnsupportedOperationException
     def getClassSymbol(index: Int)(using ctx: Context, in: DataReader): Symbol = throw new UnsupportedOperationException
-    def getType(index: Int, isVarargs: Boolean)(using x$3: Context, x$4: DataReader): Type = throw new UnsupportedOperationException
+    def getType(index: Int, isVarargs: Boolean)(using Context, DataReader): Type = throw new UnsupportedOperationException
   }
 }

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -1286,9 +1286,7 @@ object Parsers {
       if (isIdent) {
         val name = in.name
         if name == nme.CONSTRUCTOR || name == nme.STATIC_CONSTRUCTOR then
-          report.error(
-            em"""Illegal backquoted identifier: `<init>` and `<clinit>` are forbidden""",
-            in.sourcePos())
+          report.error(IllegalIdentifier(name), in.sourcePos())
         in.nextToken()
         name
       }
@@ -1297,6 +1295,19 @@ object Parsers {
         nme.ERROR
       }
 
+    /** An ident that is checked to be clean for a definition. */
+    def defName(): TermName =
+      val checkable = in.token != BACKQUOTED_IDENT
+      val start = in.sourcePos()
+      ident().tap: name =>
+        if checkable && name.toSimpleName.contains('$') then
+          report.errorOrMigrationWarning(IllegalIdentifier(name), start, MigrationVersion.IdentifierDollars)
+
+    extension (nameTree: NameTree) def checkName: nameTree.type =
+      if !isBackquoted(nameTree) && nameTree.name.toSimpleName.contains('$') then
+        report.errorOrMigrationWarning(IllegalIdentifier(nameTree.name), nameTree.srcPos, MigrationVersion.IdentifierDollars)
+      nameTree
+
     /** Accept identifier and return Ident with its name as a term name. */
     def termIdent(): Ident =
       makeIdent(in.token, in.offset, ident())
@@ -1309,7 +1320,7 @@ object Parsers {
       val tree = Ident(name)
       if (tok == BACKQUOTED_IDENT) tree.pushAttachment(Backquoted, ())
 
-      // Make sure that even trees with parsing errors have a offset that is within the offset
+      // Make sure that even trees with parsing errors have an offset that is within the offset
       val errorOffset = offset min (in.lastOffset - 1)
       if (tree.name == nme.ERROR && tree.span == NoSpan) tree.withSpan(Span(errorOffset, errorOffset))
       else atSpan(offset)(tree)
@@ -1379,7 +1390,7 @@ object Parsers {
 
     /** QualId ::= id {`.' id}
     */
-    def qualId(): Tree = dotSelectors(termIdent())
+    def qualId(): Tree = dotSelectors(termIdent().checkName)
 
     /** SimpleLiteral     ::=  [‘-’] integerLiteral
      *                      |  [‘-’] floatingPointLiteral
@@ -3414,6 +3425,9 @@ object Parsers {
           p = atSpan(startOffset(t), in.offset) { TypeApply(p, typeArgs(namedOK = false, wildOK = false)) }
         if (in.token == LPAREN)
           p = atSpan(startOffset(t), in.offset) { Apply(p, argumentPatterns()) }
+        p match
+        case nt: NameTree if isVarPattern(nt) => checkName(nt)
+        case _ =>
         p
 
     /** Patterns          ::=  Pattern [`,' Pattern]
@@ -3773,7 +3787,7 @@ object Parsers {
           mods |= Param
         }
         atSpan(start, nameStart) {
-          val name = ident()
+          val name = defName()
           acceptColon()
           if (in.token == ARROW && paramOwner.isClass && !mods.is(Local))
             syntaxError(VarValParametersMayNotBeCallByName(name, mods.is(Mutable)))
@@ -4103,6 +4117,7 @@ object Parsers {
         case IdPattern(id, t) :: Nil if t.isEmpty =>
           val vdef = ValDef(id.name.asTermName, tpt, rhs)
           if (isBackquoted(id)) vdef.pushAttachment(Backquoted, ())
+          else checkName(id)
           finalizeDef(vdef, mods, start)
         case _ =>
           def isAllIds = lhs.forall {
@@ -4158,7 +4173,7 @@ object Parsers {
       }
       else {
         val mods1 = addFlag(mods, Method)
-        val ident = termIdent()
+        val ident = termIdent().checkName
         var name = ident.name.asTermName
         val paramss =
           if sourceVersion.enablesClauseInterleaving then
@@ -4229,7 +4244,7 @@ object Parsers {
 
       newLinesOpt()
       atSpan(start, nameStart) {
-        val nameIdent = typeIdent()
+        val nameIdent = typeIdent().checkName
         val isCapDef = gobbleHat()
         val tname = nameIdent.name.asTypeName
         val tparams = typeParamClauseOpt(ParamOwner.Hk)
@@ -4321,7 +4336,7 @@ object Parsers {
     /** ClassDef ::= id ClassConstr TemplateOpt
      */
     def classDef(start: Offset, mods: Modifiers): TypeDef = atSpan(start, nameStart) {
-      classDefRest(start, mods, ident().toTypeName)
+      classDefRest(start, mods, defName().toTypeName)
     }
 
     def classDefRest(start: Offset, mods: Modifiers, name: TypeName): TypeDef =
@@ -4346,7 +4361,7 @@ object Parsers {
     /** ObjectDef       ::= id TemplateOpt
      */
     def objectDef(start: Offset, mods: Modifiers): ModuleDef = atSpan(start, nameStart) {
-      val name = ident()
+      val name = defName()
       val templ = templateOpt(emptyConstructor)
       finalizeDef(ModuleDef(name, templ), mods, start)
     }
@@ -4366,7 +4381,7 @@ object Parsers {
      */
     def enumDef(start: Offset, mods: Modifiers): TypeDef = atSpan(start, nameStart) {
       val mods1 = checkAccessOnly(mods, "")
-      val modulName = ident()
+      val modulName = defName()
       val clsName = modulName.toTypeName
       val constr = classConstr(ParamOwner.Class)
       val templ = template(constr, isEnum = true)
@@ -4380,10 +4395,10 @@ object Parsers {
       accept(CASE)
 
       atSpan(start, nameStart) {
-        val id = termIdent()
+        val id = termIdent().checkName
         if (in.token == COMMA) {
           in.nextToken()
-          val ids = commaSeparated(() => termIdent())
+          val ids = commaSeparated(() => termIdent().checkName)
           if ctx.settings.Whas.enumCommentDiscard then
             in.getDocComment(start).foreach: comm =>
               warning(

compiler/src/dotty/tools/dotc/reporting/ErrorMessageID.scala

@@ -236,6 +236,7 @@ enum ErrorMessageID(val isActive: Boolean = true) extends java.lang.Enum[ErrorMe
   case DefaultShadowsGivenID // errorNumber: 220
   case RecurseWithDefaultID // errorNumber: 221
   case EncodedPackageNameID // errorNumber: 222
+  case IllegalIdentifierID // errorNumber: 223
 
   def errorNumber = ordinal - 1
 

compiler/src/dotty/tools/dotc/reporting/messages.scala

@@ -3749,3 +3749,21 @@ final class EncodedPackageName(name: Name)(using Context) extends SyntaxMsg(Enco
        |or `myfile-test.scala` can produce encoded names for the generated package objects.
        |
        |In this case, the name `$name` is encoded as `${name.encode}`."""
+
+final class IllegalIdentifier(name: Name)(using Context) extends SyntaxMsg(IllegalIdentifierID):
+  override protected def msg(using Context): String =
+    name match
+    case nme.CONSTRUCTOR | nme.STATIC_CONSTRUCTOR =>
+      "Illegal backquoted identifier: `<init>` and `<clinit>` are forbidden"
+    case _ =>
+      i"The identifier `$name` should not contain `$$`, which is reserved for internal compiler use."
+  override protected def explain(using Context): String =
+    name match
+    case nme.CONSTRUCTOR | nme.STATIC_CONSTRUCTOR =>
+      "Names can include unusual characters when enclosed in backquotes, but `<init>` and `<clinit>` are reserved."
+    case _ =>
+      i"""User identifiers may be encoded with embedded `$$`, and other compiler artifacts
+         |may rely on using `$$` with specific meanings.
+         |
+         |The prohibition against explicit `$$` may be ignored by enclosing the identifier in backquotes
+         |at the definition site."""

library/src/scala/collection/immutable/List.scala

@@ -652,7 +652,7 @@ final case class :: [+A](override val head: A, private[scala] var next: List[A @
   override def tail: List[A] = next
 
   @publicInBinary
-  private[::] def next$access$1 = next
+  private[::] def `next$access$1` = next
 
 }
 

presentation-compiler/test/dotty/tools/pc/tests/CompilerCachingSuite.scala

@@ -30,7 +30,7 @@ class CompilerCachingSuite extends BasePCSuite:
       case pc: ScalaPresentationCompiler =>
         val compilations = pc.compilerAccess.withNonInterruptableCompiler(-1, EmptyCancelToken) { driver =>
           driver.compiler().currentCtx.runId
-        }(emptyQueryContext).get(timeout.length, timeout.unit)
+        }(using emptyQueryContext).get(timeout.length, timeout.unit)
         assertEquals(expected, compilations, s"Expected $expected compilations but got $compilations")
       case _ => throw IllegalStateException("Presentation compiler should always be of type of ScalaPresentationCompiler")
 
@@ -39,7 +39,7 @@ class CompilerCachingSuite extends BasePCSuite:
       case pc: ScalaPresentationCompiler =>
         pc.compilerAccess.withNonInterruptableCompiler(null, EmptyCancelToken) { driver =>
           driver.compiler().currentCtx
-        }(emptyQueryContext).get(timeout.length, timeout.unit)
+        }(using emptyQueryContext).get(timeout.length, timeout.unit)
       case _ => throw IllegalStateException("Presentation compiler should always be of type of ScalaPresentationCompiler")
 
   private def emptyQueryContext = PcQueryContext(None, () => "")(using EmptyReportContext())
@@ -133,7 +133,7 @@ class CompilerCachingSuite extends BasePCSuite:
     checkCompilationCount(6)
 
 
-  private val testFunctions: List[OffsetParams => CompletableFuture[_]] = List(
+  private val testFunctions: List[OffsetParams => CompletableFuture[?]] = List(
     presentationCompiler.complete(_),
     presentationCompiler.convertToNamedArguments(_, Collections.emptyList()),
     presentationCompiler.autoImports("a", _, false),

repl/test-resources/type-printer/source-compatible

@@ -7,7 +7,7 @@ val m:
       def i_=(x$1: Int): Unit; type N = Int; val l: List[Int];
       def p[T](t: T): String
   } = Bag()
-scala> type t = Bag { val f: Int; def g: Int; def h(i: Int): Int; val i: Int; def i_=(x$1: Int): Unit; type N = Int; val l: List[Int]; val s: String @unchecked }
+scala> type t = Bag { val f: Int; def g: Int; def h(i: Int): Int; val i: Int; def i_=(`x$1`: Int): Unit; type N = Int; val l: List[Int]; val s: String @unchecked }
 // defined alias type t
    =
     Bag{

scaladoc/src/dotty/tools/scaladoc/site/LoadedTemplate.scala

@@ -11,7 +11,7 @@ import scala.jdk.CollectionConverters._
 
 case class LazyEntry(getKey: String, value: () => String) extends JMapEntry[String, Object]:
   lazy val getValue: Object = value()
-  def setValue(x$0: Object): Object = ???
+  def setValue(`x$0`: Object): Object = ???
 
 case class LoadedTemplate(
   templateFile: TemplateFile,

tests/init/pos/i10549a.scala

@@ -2,6 +2,6 @@ class Wrap {
   class E
   object E {
     final val A = new E {}
-    val $values = Array(A)
+    val `$values` = Array(A)
   }
 }

tests/init/pos/i9664.scala

@@ -2,7 +2,7 @@ object Wrap1 {
   class E
   object E {
     final val A = E()
-    val $values = Array(A)
+    val `$values` = Array(A)
   }
 }
 object Wrap2 {

tests/init/warn/java1.scala

@@ -5,7 +5,7 @@ class A extends Spliterator.OfDouble:
   def characteristics() = 10
   def estimateSize() = 10
   def trySplit() = ???
-  def tryAdvance(x$0: java.util.function.DoubleConsumer): Boolean = false
+  def tryAdvance(`x$0`: java.util.function.DoubleConsumer): Boolean = false
 
   val m = n + 1
   val n = 10     // warn

tests/neg/i15381.scala

@@ -1,6 +1,6 @@
 //> using options -Vprint:parser
 
-case class $[A](value: A)
+case class `$`[A](value: A)
 
 def g: Int = $        // error