Disallow dollars in names in safe mode

compiler/src/dotty/tools/dotc/cc/SafeRefs.scala

@@ -7,14 +7,16 @@ import Symbols.*
 import Annotations.*
 import util.Spans.NoSpan
 import util.SrcPos
-import Contexts.Context
+import Contexts.{Context, ctx}
 import Constants.Constant
 import Decorators.*
 import ast.tpd.*
 import SymDenotations.*
 import Flags.*
 import Types.*
 import config.Feature
+import NameOps.isReplWrapperName
+import Names.Name
 import typer.ProtoTypes.SelectionProto
 
 /** Check whether references from safe mode should be allowed */
@@ -160,4 +162,8 @@ object SafeRefs {
       case _ =>
     if Feature.safeEnabled then
       tree.tpe.foreachPart(checkAnnotatedType(_))
+
+  /** Allow name in safe mode even though it contains `$` characters */
+  def allow(name: Name)(using Context): Boolean =
+    name.isReplWrapperName && ctx.mode.is(Mode.Interactive)
 }

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

@@ -21,6 +21,7 @@ import config.Feature.{migrateTo3, sourceVersion}
 import config.SourceVersion.{`3.0`, `3.0-migration`}
 import config.MigrationVersion
 import reporting.{NoProfile, Profile, Message}
+import cc.SafeRefs
 
 import java.util.Objects
 import dotty.tools.dotc.reporting.Message.rewriteNotice
@@ -150,6 +151,8 @@ object Scanners {
     def finishNamedToken(idtoken: Token, target: TokenData): Unit =
       target.name = termName(litBuf.chars, 0, litBuf.length)
       litBuf.clear()
+      if target.name.contains('$') && Feature.safeEnabled && !SafeRefs.allow(name) then
+        report.error(em"Identifier may not contain '$$' in safe mode", sourcePos())
       target.token = idtoken
       if idtoken == IDENTIFIER then
         val converted = toToken(target.name)

tests/neg/unsafe-dollar-in-name-2.check

@@ -0,0 +1,8 @@
+-- Error: tests/neg/unsafe-dollar-in-name-2.scala:3:7 ------------------------------------------------------------------
+3 |object Foo$ // error
+  |       ^
+  |       Identifier may not contain '$' in safe mode
+-- Error: tests/neg/unsafe-dollar-in-name-2.scala:5:6 ------------------------------------------------------------------
+5 |class `Bar$` // error
+  |      ^
+  |      Identifier may not contain '$' in safe mode

tests/neg/unsafe-dollar-in-name-2.scala

@@ -0,0 +1,5 @@
+//> using options -language:experimental.safe
+
+object Foo$ // error
+
+class `Bar$` // error

tests/neg/unsafe-dollar-in-name.check

@@ -0,0 +1,8 @@
+-- Error: tests/neg/unsafe-dollar-in-name.scala:3:7 --------------------------------------------------------------------
+3 |object Foo$ // error
+  |       ^
+  |       Identifier may not contain '$' in safe mode
+-- Error: tests/neg/unsafe-dollar-in-name.scala:5:6 --------------------------------------------------------------------
+5 |class `Bar$` // error
+  |      ^
+  |      Identifier may not contain '$' in safe mode

tests/neg/unsafe-dollar-in-name.scala

@@ -0,0 +1,5 @@
+import language.experimental.safe
+
+object Foo$ // error
+
+class `Bar$` // error