Make the cached mirror methods invisible

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

@@ -348,7 +348,7 @@ import transform.SymUtils._
       val finalAddendum =
         if addendum.nonEmpty then prefixEnumClause(addendum)
         else closest match
-          case (d, sym) :: _ =>
+          case (d, sym) :: _ if sym.name != name =>
             val siteName = site match
               case site: NamedType => site.name.show
               case site => i"$site"
@@ -357,7 +357,7 @@ import transform.SymUtils._
               if sym.is(ModuleClass) then s"${sym.name.show}.type"
               else sym.name.show
             s" - did you mean $siteName.$showName?$enumClause"
-          case Nil => prefixEnumClause("")
+          case _ => prefixEnumClause("")
 
       ex"$selected $name is not a member of ${site.widen}$finalAddendum"
     }

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

@@ -547,8 +547,10 @@ class SyntheticMembers(thisPhase: DenotTransformer) {
         declaredParents = oldClassInfo.declaredParents :+ parent)
       clazz.copySymDenotation(info = newClassInfo).installAfter(thisPhase)
     }
-    def addMethod(name: TermName, info: Type, cls: Symbol, body: (Symbol, Tree) => Context ?=> Tree): Unit = {
-      val meth = newSymbol(clazz, name, Synthetic | Method, info, coord = clazz.coord)
+    def addMethod(
+        name: TermName, info: Type, cls: Symbol,
+        body: (Symbol, Tree) => Context ?=> Tree): Unit = {
+      val meth = newSymbol(clazz, name, Synthetic | Method | Invisible, info, coord = clazz.coord)
       if (!existingDef(meth, clazz).exists) {
         meth.enteredAfter(thisPhase)
         newBody = newBody :+
@@ -561,23 +563,23 @@ class SyntheticMembers(thisPhase: DenotTransformer) {
       if (existing.exists && !existing.is(Deferred)) existing
       else {
         val monoType =
-          newSymbol(clazz, tpnme.MirroredMonoType, Synthetic, TypeAlias(linked.reachableRawTypeRef), coord = clazz.coord)
+          newSymbol(clazz, tpnme.MirroredMonoType, Synthetic | Invisible, TypeAlias(linked.reachableRawTypeRef), coord = clazz.coord)
         newBody = newBody :+ TypeDef(monoType).withSpan(ctx.owner.span.focus)
         monoType.enteredAfter(thisPhase)
       }
     }
     def makeSingletonMirror() =
       addParent(defn.Mirror_SingletonClass.typeRef)
-    def makeProductMirror(cls: Symbol) = {
+
+    def makeProductMirror(cls: Symbol) =
       addParent(defn.Mirror_ProductClass.typeRef)
       addMethod(nme.fromProduct, MethodType(defn.ProductClass.typeRef :: Nil, monoType.typeRef), cls,
         fromProductBody(_, _).ensureConforms(monoType.typeRef))  // t4758.scala or i3381.scala are examples where a cast is needed
-    }
-    def makeSumMirror(cls: Symbol) = {
+
+    def makeSumMirror(cls: Symbol) =
       addParent(defn.Mirror_SumClass.typeRef)
       addMethod(nme.ordinal, MethodType(monoType.typeRef :: Nil, defn.IntType), cls,
         ordinalBody(_, _))
-    }
 
     if (clazz.is(Module)) {
       if (clazz.is(Case)) makeSingletonMirror()

tests/neg/i13815.check

@@ -0,0 +1,16 @@
+
+-- [E008] Not Found Error: tests/neg/i13815/Test_2.scala:1:14 ----------------------------------------------------------
+1 |val box = Box.fromProduct((1, "a"))  // error
+  |          ^^^^^^^^^^^^^^^
+  |          value fromProduct is not a member of object Box
+-- [E007] Type Mismatch Error: tests/neg/i13815/Test_2.scala:2:46 ------------------------------------------------------
+2 |val circleOrdinal = Shape.ordinal(Shape.Circle(r = 23)) // error
+  |                                  ^^^^^^^^^^^^^^^^^^^^
+  |                                  Found:    Shape.Circle
+  |                                  Required: Shape.MirroredMonoType
+
+longer explanation available when compiling with `-explain`
+-- [E008] Not Found Error: tests/neg/i13815/Test_2.scala:3:13 ----------------------------------------------------------
+3 |type T = Box.MirroredMonoType // error
+  |         ^^^^^^^^^^^^^^^^^^^^
+  |         type MirroredMonoType is not a member of object Box

tests/neg/i13815/Box_1.scala

@@ -0,0 +1 @@
+case class Box(i: Int, s: String)

tests/neg/i13815/Shape_1.scala

@@ -0,0 +1,5 @@
+sealed trait Shape
+
+object Shape:
+  case class Circle(r: Int) extends Shape
+  case class Square(width: Int) extends Shape

tests/neg/i13815/Test_2.scala

@@ -0,0 +1,3 @@
+val box = Box.fromProduct((1, "a"))  // error
+val circleOrdinal = Shape.ordinal(Shape.Circle(r = 23)) // error
+type T = Box.MirroredMonoType // error