Overcome Name comparison hurdles

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

@@ -188,9 +188,17 @@ object NameOps {
       }
     }
 
-    /** Do two target names match? An empty target name matchws any other name. */
+    /** Do two target names match? An empty target name matches any other name.
+     *  Target names match if their simple names compare equal,
+     *  if they belong to the same term or type namespace,
+     *  and it's not the case that only one is a field name.
+     */
     def matchesTargetName(other: Name) =
-      name == other || name.isEmpty || other.isEmpty
+         name.isEmpty
+      || other.isEmpty
+      ||    name.isTermName == other.isTermName
+         && name.is(NameKinds.FieldName) == other.is(NameKinds.FieldName)
+         && name.toSimpleName == other.toSimpleName
 
     private def functionSuffixStart: Int =
       val first = name.firstPart

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

@@ -1350,11 +1350,12 @@ trait Checking {
 
   /** Check that class does not declare same symbol twice */
   def checkNoDoubleDeclaration(cls: Symbol)(using Context): Unit =
-    val seen = new mutable.HashMap[Name, List[Symbol]].withDefaultValue(Nil)
+    val seen = new mutable.HashMap[String, List[Symbol]].withDefaultValue(Nil)
     typr.println(i"check no double declarations $cls")
 
     def checkDecl(decl: Symbol): Unit =
-      for other <- seen(decl.name) if decl.name != nme.ERROR && !decl.isAbsent() && !other.isAbsent() do
+      val key = decl.name.toString
+      for other <- seen(key) if decl.name != nme.ERROR && !decl.isAbsent() && !other.isAbsent() do
         typr.println(i"conflict? $decl $other")
         def javaFieldMethodPair =
           decl.is(JavaDefined) && other.is(JavaDefined) &&
@@ -1371,7 +1372,7 @@ trait Checking {
           report.error(em"two or more overloaded variants of $decl have default arguments", decl.srcPos)
           decl.resetFlag(HasDefaultParams)
       if !excludeFromDoubleDeclCheck(decl) then
-        seen(decl.name) = decl :: seen(decl.name)
+        seen(key) ::= decl
 
     cls.info.decls.foreach(checkDecl)
     cls.info match

tests/neg/i19274.scala

@@ -0,0 +1,13 @@
+import annotation.*
+
+case class StaticBinding(v: String) {
+  private def copy$default$1(): String = ??? // error
+}
+
+case class DynamicBinding(v: String):
+  @targetName("copy$default$1")
+  private def dynamo(): String = ??? // TODO
+
+@main def Demo =
+  val b = StaticBinding("test")
+  println(b)

tests/pos/i19274.scala

@@ -0,0 +1,13 @@
+//> using options -Ycheck:mixin
+
+object Diagnostic:
+  trait OriginWarning(val origin: String):
+    self: Warning =>
+  object OriginWarning:
+    val NoOrigin = "..."
+
+  class LintWarning(msg: String, origin: String = OriginWarning.NoOrigin)
+  extends Warning(msg), OriginWarning(origin)
+
+  class Warning(msg: String) extends Diagnostic(msg)
+class Diagnostic(val msg: String)