Fix #9252: Refine test for conflicting package objects

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

@@ -289,6 +289,13 @@ class Namer { typer: Typer =>
       val preExisting = owner.unforcedDecls.lookup(name)
       if (preExisting.isDefinedInCurrentRun || preExisting.lastKnownDenotation.is(Package))
           && (!preExisting.lastKnownDenotation.is(Private) || preExisting.owner.is(Package))
+          && (!preExisting.lastKnownDenotation.isPackageObject
+              || preExisting.associatedFile != ctx.source.file)
+              // isDefinedInCurrentRun does not work correctly for package objects, because
+              // package objects are updated to the new run earlier than normal classes, everytime
+              // some member of the enclosing package is accessed. Therefore, we use another
+              // test: conflict if package objects have the same name but come from different
+              // sources. See i9252.
       then conflict(preExisting)
 
     def pkgObjs(pkg: Symbol) =

tests/pos-macros/i9252/Clazz.scala

@@ -0,0 +1,3 @@
+class Clazz {
+  def foo = Macro.expand()
+}

tests/pos-macros/i9252/Macro.scala

@@ -0,0 +1,4 @@
+object Macro {
+  inline def expand(): Unit = ${impl}
+  def impl(using scala.quoted.QuoteContext) = '{???}
+}

tests/pos-macros/i9252/toplevel.scala

@@ -0,0 +1 @@
+def fct: Unit = Macro.expand()