Fixes #6626. Refrain from calling asSimpleName method on DerivedName

Author: ashwinbhaskar

compiler/src/dotty/tools/dotc/transform/GenericSignatures.scala

@@ -6,7 +6,7 @@ import core.Annotations.Annotation
 import core.Contexts.Context
 import core.Definitions
 import core.Flags._
-import core.Names.Name
+import core.Names.{DerivedName, Name, SimpleName, TypeName}
 import core.Symbols._
 import core.TypeApplications.TypeParamInfo
 import core.TypeErasure.erasure
@@ -17,6 +17,8 @@ import SymUtils._
 import TypeUtils._
 import java.lang.StringBuilder
 
+import scala.annotation.tailrec
+
 /** Helper object to generate generic java signatures, as defined in
  *  the Java Virtual Machine Specification, §4.3.4
  */
@@ -161,7 +163,14 @@ object GenericSignatures {
 
             // TODO revisit this. Does it align with javac for code that can be expressed in both languages?
             val delimiter = if (builder.charAt(builder.length() - 1) == '>') '.' else '$'
-            builder.append(delimiter).append(sanitizeName(sym.name.asSimpleName))
+
+            @tailrec def appendIfNotDerivedName(name: Name): Unit = name match {
+              case _: DerivedName => //do nothing
+              case typeName: TypeName => appendIfNotDerivedName(typeName.toTermName)
+              case _  => builder.append(delimiter).append(sanitizeName(name.asSimpleName))
+            }
+
+            appendIfNotDerivedName(sym.name)
           }
           else fullNameInSig(sym)
         }