fix 14823: handle unions in companion path

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

@@ -9,6 +9,8 @@ import Contexts._
 import Symbols._
 import Names.Name
 
+import dotty.tools.dotc.core.Decorators.*
+
 object TypeUtils {
   /** A decorator that provides methods on types
    *  that are needed in the transformer pipeline.
@@ -84,11 +86,16 @@ object TypeUtils {
     /** The TermRef referring to the companion of the underlying class reference
      *  of this type, while keeping the same prefix.
      */
-    def companionRef(using Context): TermRef = self match {
+    def mirrorCompanionRef(using Context): TermRef = self match {
+      case OrType(tp1, tp2) =>
+        val r1 = tp1.mirrorCompanionRef
+        val r2 = tp2.mirrorCompanionRef
+        assert(r1.symbol == r2.symbol, em"mirrorCompanionRef mismatch for $self: $r1, $r2 did not have the same symbol")
+        r1
       case self @ TypeRef(prefix, _) if self.symbol.isClass =>
         prefix.select(self.symbol.companionModule).asInstanceOf[TermRef]
       case self: TypeProxy =>
-        self.underlying.companionRef
+        self.underlying.mirrorCompanionRef
     }
 
     /** Is this type a methodic type that takes implicit parameters (both old and new) at some point? */

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

@@ -249,7 +249,7 @@ class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
 
   /** A path referencing the companion of class type `clsType` */
   private def companionPath(clsType: Type, span: Span)(using Context) =
-    val ref = pathFor(clsType.companionRef)
+    val ref = pathFor(clsType.mirrorCompanionRef)
     assert(ref.symbol.is(Module) && (clsType.classSymbol.is(ModuleClass) || (ref.symbol.companionClass == clsType.classSymbol)))
     ref.withSpan(span)
 
@@ -275,6 +275,35 @@ class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
     monoMap(mirroredType.resultType)
 
   private def productMirror(mirroredType: Type, formal: Type, span: Span)(using Context): Tree =
+
+    /** do all parts match the class symbol? */
+    def acceptable(tp: Type, cls: Symbol): Boolean = tp match
+      case tp: TypeProxy    => acceptable(tp.underlying, cls)
+      case OrType(tp1, tp2) => acceptable(tp1, cls) && acceptable(tp2, cls)
+      case _                => tp.classSymbol eq cls
+
+    def makeProductMirror(cls: Symbol): Tree =
+      val accessors = cls.caseAccessors.filterNot(_.isAllOf(PrivateLocal))
+      val elemLabels = accessors.map(acc => ConstantType(Constant(acc.name.toString)))
+      val nestedPairs = TypeOps.nestedPairs(accessors.map(mirroredType.resultType.memberInfo(_).widenExpr))
+      val (monoType, elemsType) = mirroredType match
+        case mirroredType: HKTypeLambda =>
+          (mkMirroredMonoType(mirroredType), mirroredType.derivedLambdaType(resType = nestedPairs))
+        case _ =>
+          (mirroredType, nestedPairs)
+      val elemsLabels = TypeOps.nestedPairs(elemLabels)
+      checkRefinement(formal, tpnme.MirroredElemTypes, elemsType, span)
+      checkRefinement(formal, tpnme.MirroredElemLabels, elemsLabels, span)
+      val mirrorType =
+        mirrorCore(defn.Mirror_ProductClass, monoType, mirroredType, cls.name, formal)
+          .refinedWith(tpnme.MirroredElemTypes, TypeAlias(elemsType))
+          .refinedWith(tpnme.MirroredElemLabels, TypeAlias(elemsLabels))
+      val mirrorRef =
+        if (cls.is(Scala2x) || cls.linkedClass.is(Case)) anonymousMirror(monoType, ExtendsProductMirror, span)
+        else companionPath(mirroredType, span)
+      mirrorRef.cast(mirrorType)
+    end makeProductMirror
+
     mirroredType match
       case AndType(tp1, tp2) =>
         productMirror(tp1, formal, span).orElse(productMirror(tp2, formal, span))
@@ -289,28 +318,10 @@ class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
           else
             val mirrorType = mirrorCore(defn.Mirror_SingletonClass, mirroredType, mirroredType, module.name, formal)
             modulePath.cast(mirrorType)
-        else if mirroredType.classSymbol.isGenericProduct then
+        else
           val cls = mirroredType.classSymbol
-          val accessors = cls.caseAccessors.filterNot(_.isAllOf(PrivateLocal))
-          val elemLabels = accessors.map(acc => ConstantType(Constant(acc.name.toString)))
-          val nestedPairs = TypeOps.nestedPairs(accessors.map(mirroredType.resultType.memberInfo(_).widenExpr))
-          val (monoType, elemsType) = mirroredType match
-            case mirroredType: HKTypeLambda =>
-              (mkMirroredMonoType(mirroredType), mirroredType.derivedLambdaType(resType = nestedPairs))
-            case _ =>
-              (mirroredType, nestedPairs)
-          val elemsLabels = TypeOps.nestedPairs(elemLabels)
-          checkRefinement(formal, tpnme.MirroredElemTypes, elemsType, span)
-          checkRefinement(formal, tpnme.MirroredElemLabels, elemsLabels, span)
-          val mirrorType =
-            mirrorCore(defn.Mirror_ProductClass, monoType, mirroredType, cls.name, formal)
-              .refinedWith(tpnme.MirroredElemTypes, TypeAlias(elemsType))
-              .refinedWith(tpnme.MirroredElemLabels, TypeAlias(elemsLabels))
-          val mirrorRef =
-            if (cls.is(Scala2x) || cls.linkedClass.is(Case)) anonymousMirror(monoType, ExtendsProductMirror, span)
-            else companionPath(mirroredType, span)
-          mirrorRef.cast(mirrorType)
-        else EmptyTree
+          if acceptable(mirroredType, cls) && cls.isGenericProduct then makeProductMirror(cls)
+          else EmptyTree
   end productMirror
 
   private def sumMirror(mirroredType: Type, formal: Type, span: Span)(using Context): Tree =

tests/neg/i14823.check

@@ -0,0 +1,4 @@
+-- Error: tests/neg/i14823.scala:8:50 ----------------------------------------------------------------------------------
+8 |val baz = summon[Mirror.Of[SubA[Int] | SubB[Int]]] // error
+  |                                                  ^
+  |no given instance of type deriving.Mirror.Of[SubA[Int] | SubB[Int]] was found for parameter x of method summon in object Predef

tests/neg/i14823.scala

@@ -0,0 +1,12 @@
+import deriving.Mirror
+
+case class Cov[+T]()
+
+class SubA[+T]() extends Cov[T]
+class SubB[+T]() extends Cov[T]
+
+val baz = summon[Mirror.Of[SubA[Int] | SubB[Int]]] // error
+//        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+//        this should fail because:
+//        1) SubA and SubB are not individually product types
+//        2) SubA and SubB are different classes

tests/pos/i14823.scala

@@ -0,0 +1,18 @@
+import deriving.Mirror
+
+object MirrorK1:
+  type Of[F[_]] = Mirror { type MirroredType[A] = F[A] }
+
+sealed trait Box[T]
+object Box
+
+case class Child[T]() extends Box[T]
+
+sealed abstract class Foo[T]
+object Foo {
+  case class A[T]() extends Foo[T]
+}
+
+val foo = summon[Mirror.Of[Box[Int] | Box[Int]]]
+val bar = summon[MirrorK1.Of[[X] =>> Box[Int] | Box[Int]]]
+def baz = summon[deriving.Mirror.Of[Foo[String] | Foo[String]]]