Fix #11654: create new symbol for stdlib patches

Author: liufengyun

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

@@ -5,12 +5,14 @@ package core
 import scala.annotation.{threadUnsafe => tu}
 import Types._, Contexts._, Symbols._, SymDenotations._, StdNames._, Names._, Phases._
 import Flags._, Scopes._, Decorators._, NameOps._, Periods._, NullOpsDecorator._
+import ast.tpd.Literal, Constants.Constant
 import unpickleScala2.Scala2Unpickler.ensureConstructor
 import scala.collection.mutable
 import collection.mutable
 import Denotations.SingleDenotation
 import util.{SimpleIdentityMap, SourceFile, NoSource}
 import typer.ImportInfo.RootRef
+import Annotations.Annotation
 
 import scala.annotation.tailrec
 
@@ -1108,6 +1110,9 @@ class Definitions {
    *  is read from a classfile.
    */
   def patchStdLibClass(denot: ClassDenotation)(using Context): Unit =
+    val annot = Annotation.deferredSymAndTree(defn.CompileTimeOnlyAnnot) {
+      Literal(Constant("The symbol can only be used at compile time in import statements"))
+    }
 
     def patch2(denot: ClassDenotation, patchCls: Symbol): Unit =
       val scope = denot.info.decls.openForMutations
@@ -1121,9 +1126,11 @@ class Definitions {
         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
+            val copy = patch.copy(owner = denot.symbol)
+            copy.denot = patch.denot.copySymDenotation(owner = denot.symbol)
+            copy.addAnnotation(annot)
+            scope.enter(copy)
+          if patch.isClass then
             patch2(scope.lookup(patch.name).asClass, patch)
 
     def patchWith(patchCls: Symbol) =