When assigning type cases, substitute any instances of type parameter…

…s for the applied arguments
scala · Mar 8, 2022 · 0e578f1 · 0e578f1
1 parent 5a4a571
commit 0e578f1
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Showing 4 changed files with 17 additions and 17 deletions.
diff --git a/compiler/src/dotty/tools/dotc/typer/TypeAssigner.scala b/compiler/src/dotty/tools/dotc/typer/TypeAssigner.scala
@@ -401,15 +401,19 @@ trait TypeAssigner {
   def assignType(tree: untpd.CaseDef, pat: Tree, body: Tree)(using Context): CaseDef = {
     val ownType =
       if (body.isType) {
-        val params = new TreeAccumulator[mutable.ListBuffer[TypeSymbol]] {
+        val getParams = new TreeAccumulator[mutable.ListBuffer[TypeSymbol]] {
           def apply(ps: mutable.ListBuffer[TypeSymbol], t: Tree)(using Context) = t match {
             case t: Bind if t.symbol.isType => foldOver(ps += t.symbol.asType, t)
             case _ => foldOver(ps, t)
           }
         }
-        HKTypeLambda.fromParams(
-          params(new mutable.ListBuffer[TypeSymbol](), pat).toList,
-          defn.MatchCase(pat.tpe, body.tpe))
+        val params = getParams(new mutable.ListBuffer[TypeSymbol](), pat).toList
+        pat.tpe match
+          case AppliedType(tycon, args) =>
+            val tparams = tycon.typeParamSymbols
+            for param <- params do param.info = param.info.subst(tparams, args))
+          case _ =>
+        HKTypeLambda.fromParams(params, defn.MatchCase(pat.tpe, body.tpe))
       }
       else body.tpe
     tree.withType(ownType)

diff --git a/tests/neg/6697.check b/tests/neg/6697.check
diff --git a/tests/neg/6697.scala → tests/pos/6697.scala b/tests/neg/6697.scala → tests/pos/6697.scala
diff --git a/tests/pos/i14477.scala b/tests/pos/i14477.scala
@@ -0,0 +1,9 @@
+sealed trait Foo[A, X <: A]
+
+type FooX[F] = F match {
+  case Foo[a, x] => x
+}
+
+type MyFoo = Foo[String, "hello"]
+
+val hello: FooX[MyFoo] = "hello"