From 01d038c43dbe47c792823776fea0b906d1c33692 Mon Sep 17 00:00:00 2001
From: Som Snytt <som.snytt@gmail.com>
Date: Sat, 6 Dec 2025 23:52:48 -0800
Subject: [PATCH] Overcome Name comparison hurdles

---
 compiler/src/dotty/tools/dotc/core/NameOps.scala   | 12 ++++++++++--
 compiler/src/dotty/tools/dotc/typer/Checking.scala |  7 ++++---
 tests/neg/i19274.scala                             | 13 +++++++++++++
 tests/pos/i19274.scala                             | 13 +++++++++++++
 4 files changed, 40 insertions(+), 5 deletions(-)
 create mode 100644 tests/neg/i19274.scala
 create mode 100644 tests/pos/i19274.scala

diff --git a/compiler/src/dotty/tools/dotc/core/NameOps.scala b/compiler/src/dotty/tools/dotc/core/NameOps.scala
index f157da843f41..87f6371f552f 100644
--- a/compiler/src/dotty/tools/dotc/core/NameOps.scala
+++ b/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
diff --git a/compiler/src/dotty/tools/dotc/typer/Checking.scala b/compiler/src/dotty/tools/dotc/typer/Checking.scala
index d975e2341111..bf1a070f6106 100644
--- a/compiler/src/dotty/tools/dotc/typer/Checking.scala
+++ b/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
diff --git a/tests/neg/i19274.scala b/tests/neg/i19274.scala
new file mode 100644
index 000000000000..5cc745c62375
--- /dev/null
+++ b/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)
diff --git a/tests/pos/i19274.scala b/tests/pos/i19274.scala
new file mode 100644
index 000000000000..6b3fe27dfd5d
--- /dev/null
+++ 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)