Search for type tests when matching abstract applied type

Fixes #13433

Author: nicolasstucki

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

@@ -50,7 +50,7 @@ class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
     (formal, span) => formal.argInfos match {
       case arg1 :: arg2 :: Nil if !defn.isBottomClass(arg2.typeSymbol) =>
         val tp1 = fullyDefinedType(arg1, "TypeTest argument", span)
-        val tp2 = fullyDefinedType(arg2, "TypeTest argument", span)
+        val tp2 = fullyDefinedType(arg2, "TypeTest argument", span).normalized
         val sym2 = tp2.typeSymbol
         if tp1 <:< tp2 then
           // optimization when we know the typetest will always succeed

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

@@ -888,28 +888,32 @@ class Typer extends Namer
    *  exists, rewrite to `tt(e)`.
    *  @pre We are in pattern-matching mode (Mode.Pattern)
    */
-  def tryWithTypeTest(tree: Typed, pt: Type)(using Context): Tree = tree.tpt.tpe.dealias match {
-    case tref: TypeRef if !tref.symbol.isClass && !ctx.isAfterTyper && !(tref =:= pt) =>
-      def withTag(tpe: Type): Option[Tree] = {
-        require(ctx.mode.is(Mode.Pattern))
-        withoutMode(Mode.Pattern)(
-          inferImplicit(tpe, EmptyTree, tree.tpt.span)
-        ) match
-          case SearchSuccess(clsTag, _, _, _) =>
-            withMode(Mode.InTypeTest) {
-              Some(typed(untpd.Apply(untpd.TypedSplice(clsTag), untpd.TypedSplice(tree.expr)), pt))
-            }
-          case _ =>
-            None
-      }
-      val tag = withTag(defn.TypeTestClass.typeRef.appliedTo(pt, tref))
-          .orElse(withTag(defn.ClassTagClass.typeRef.appliedTo(tref)))
+  def tryWithTypeTest(tree: Typed, pt: Type)(using Context): Tree =
+    def withTag(tpe: Type): Option[Tree] = {
+      require(ctx.mode.is(Mode.Pattern))
+      withoutMode(Mode.Pattern)(
+        inferImplicit(tpe, EmptyTree, tree.tpt.span)
+      ) match
+        case SearchSuccess(clsTag, _, _, _) =>
+          withMode(Mode.InTypeTest) {
+            Some(typed(untpd.Apply(untpd.TypedSplice(clsTag), untpd.TypedSplice(tree.expr)), pt))
+          }
+        case _ =>
+          None
+    }
+    def tagged(tpe: Type) = {
+      val tag = withTag(defn.TypeTestClass.typeRef.appliedTo(pt, tpe))
+          .orElse(withTag(defn.ClassTagClass.typeRef.appliedTo(tpe)))
           .getOrElse(tree)
       if tag.symbol.owner == defn.ClassTagClass && config.Feature.sourceVersion.isAtLeast(config.SourceVersion.future) then
         report.warning("Use of `scala.reflect.ClassTag` for type testing may be unsound. Consider using `scala.reflect.TypeTest` instead.", tree.srcPos)
       tag
-    case _ => tree
-  }
+    }
+    tree.tpt.tpe.dealias match {
+      case tpe @ AppliedType(tref: TypeRef, _) if !tref.symbol.isClass && !ctx.isAfterTyper && !(tpe =:= pt) => tagged(tpe)
+      case tref: TypeRef if !tref.symbol.isClass && !ctx.isAfterTyper && !(tref =:= pt) => tagged(tref)
+      case _ => tree
+    }
 
 
   def typedNamedArg(tree: untpd.NamedArg, pt: Type)(using Context): NamedArg = {

compiler/test/dotc/run-test-pickling.blacklist

@@ -6,6 +6,8 @@ i7212
 i7868.scala
 i9011.scala
 i9473.scala
+i13433.scala
+i13433b.scala
 macros-in-same-project1
 mixin-forwarder-overload
 t10889
@@ -36,4 +38,4 @@ zero-arity-case-class.scala
 i12194.scala
 i12753
 t6138
-t6138-2
+t6138-2

tests/pos-special/fatal-warnings/i13433.scala

@@ -0,0 +1,28 @@
+import scala.reflect.TypeTest
+
+type Matcher[A] = A match { case String => String }
+
+def patternMatch[A](a: Any)(using tt: TypeTest[Any, Matcher[A]]): Option[Matcher[A]] = {
+  // type T = RDF.Triple[Rdf]
+  a match {
+    case res: Matcher[A] => Some(res)
+    case _ => None
+  }
+}
+
+def patternMatchWithAlias[A](a: Any)(using tt: TypeTest[Any, Matcher[A]]): Option[Matcher[A]] = {
+  type T = Matcher[A]
+  a match {
+    case res: T => Some(res)
+    case _ => None
+  }
+}
+
+
+@main def main = {
+  println(patternMatch[String]("abc"))
+  println(patternMatchWithAlias[String]("abc"))
+
+  println(patternMatch[String](1))
+  println(patternMatchWithAlias[String](1))
+}

tests/pos-special/fatal-warnings/i13433b.scala

@@ -0,0 +1,28 @@
+import scala.reflect.ClassTag
+
+type Matcher[A] = A match { case String => String }
+
+def patternMatch[A](a: Any)(using tt: ClassTag[Matcher[A]]): Option[Matcher[A]] = {
+  // type T = RDF.Triple[Rdf]
+  a match {
+    case res: Matcher[A] => Some(res)
+    case _ => None
+  }
+}
+
+def patternMatchWithAlias[A](a: Any)(using tt: ClassTag[Matcher[A]]): Option[Matcher[A]] = {
+  type T = Matcher[A]
+  a match {
+    case res: T => Some(res)
+    case _ => None
+  }
+}
+
+
+@main def main = {
+  println(patternMatch[String]("abc"))
+  println(patternMatchWithAlias[String]("abc"))
+
+  println(patternMatch[String](1))
+  println(patternMatchWithAlias[String](1))
+}

tests/run/i13433.check

@@ -0,0 +1,4 @@
+Some(abc)
+Some(abc)
+None
+None

tests/run/i13433.scala

@@ -0,0 +1,28 @@
+import scala.reflect.TypeTest
+
+type Matcher[A] = A match { case String => String }
+
+def patternMatch[A](a: Any)(using tt: TypeTest[Any, Matcher[A]]): Option[Matcher[A]] = {
+  // type T = RDF.Triple[Rdf]
+  a match {
+    case res: Matcher[A] => Some(res)
+    case _ => None
+  }
+}
+
+def patternMatchWithAlias[A](a: Any)(using tt: TypeTest[Any, Matcher[A]]): Option[Matcher[A]] = {
+  type T = Matcher[A]
+  a match {
+    case res: T => Some(res)
+    case _ => None
+  }
+}
+
+
+@main def Test = {
+  println(patternMatch[String]("abc"))
+  println(patternMatchWithAlias[String]("abc"))
+
+  println(patternMatch[String](1))
+  println(patternMatchWithAlias[String](1))
+}

tests/run/i13433b.check

@@ -0,0 +1,4 @@
+Some(abc)
+Some(abc)
+None
+None

tests/run/i13433b.scala

@@ -0,0 +1,28 @@
+import scala.reflect.ClassTag
+
+type Matcher[A] = A match { case String => String }
+
+def patternMatch[A](a: Any)(using tt: ClassTag[Matcher[A]]): Option[Matcher[A]] = {
+  // type T = RDF.Triple[Rdf]
+  a match {
+    case res: Matcher[A] => Some(res)
+    case _ => None
+  }
+}
+
+def patternMatchWithAlias[A](a: Any)(using tt: ClassTag[Matcher[A]]): Option[Matcher[A]] = {
+  type T = Matcher[A]
+  a match {
+    case res: T => Some(res)
+    case _ => None
+  }
+}
+
+
+@main def Test = {
+  println(patternMatch[String]("abc"))
+  println(patternMatchWithAlias[String]("abc"))
+
+  println(patternMatch[String](1))
+  println(patternMatchWithAlias[String](1))
+}