Fix #3364: Name clash in class and its companion object

Author: allanrenucci

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

@@ -1808,7 +1808,7 @@ object messages {
   case class ClassAndCompanionNameClash(cls: Symbol, other: Symbol)(implicit ctx: Context)
     extends Message(ClassAndCompanionNameClashID) {
     val kind = "Naming"
-    val msg = hl"Name clash: both ${cls.owner} and its companion object defines ${cls.name}"
+    val msg = hl"Name clash: both ${cls.owner} and its companion object defines ${cls.name.stripModuleClassSuffix}"
     val explanation = {
       val kind = if (cls.owner.is(Flags.Trait)) "trait" else "class"
 

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

@@ -112,10 +112,15 @@ object RefChecks {
    *  a class or module with same name
    */
   private def checkCompanionNameClashes(cls: Symbol)(implicit ctx: Context): Unit =
-    if (!(cls.owner is ModuleClass)) {
-      val other = cls.owner.linkedClass.info.decl(cls.name).symbol
-      if (other.isClass)
+    if (!cls.owner.is(ModuleClass)) {
+      def clashes(sym: Symbol) =
+        sym.isClass &&
+        sym.name.stripModuleClassSuffix == cls.name.stripModuleClassSuffix        
+
+      val others = cls.owner.linkedClass.info.decls.filter(clashes)
+      others.foreach { other =>
         ctx.error(ClassAndCompanionNameClash(cls, other), cls.pos)
+      }
     }
 
   // Override checking ------------------------------------------------------------

tests/neg/i3364.scala

@@ -0,0 +1,15 @@
+object Test {
+  object Foo
+}
+
+class Test {
+  class Foo  // error: name clash
+}
+
+object Test2 {
+  class Foo
+}
+
+class Test2 {
+  object Foo // error: name clash
+}