Treat type parameters of secondary constructors as aliases

... of class parameters using the gadt mechanism. Previously they were encoded as aliases
by hardcoding alias bounds in the type parameter declaration, but that then leads to
weird behavior and failures in unpickling.

To make this work, we also need to propagate gadt bounds into the this-call context.

Test case in pickling/i1202a.scala.

1 files changed, 11 insertions, 8 deletions

diff --git a/src/dotty/tools/dotc/typer/Typer.scala b/src/dotty/tools/dotc/typer/Typer.scala
index 3d36905f2..10d7516e6 100644
--- a/src/dotty/tools/dotc/typer/Typer.scala
+++ b/src/dotty/tools/dotc/typer/Typer.scala
@@ -1022,17 +1022,20 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
     val DefDef(name, tparams, vparamss, tpt, _) = ddef
     completeAnnotations(ddef, sym)
     val tparams1 = tparams mapconserve (typed(_).asInstanceOf[TypeDef])
-    // for secondary constructors we need to use that their type parameters
-    // are aliases of the class type parameters. See pos/i941.scala
-    if (sym.isConstructor && !sym.isPrimaryConstructor)
-      (sym.owner.typeParams, tparams1).zipped.foreach {(tparam, tdef) =>
-        tdef.symbol.info = TypeAlias(tparam.typeRef)
-       }
-
     val vparamss1 = vparamss nestedMapconserve (typed(_).asInstanceOf[ValDef])
     if (sym is Implicit) checkImplicitParamsNotSingletons(vparamss1)
     val tpt1 = checkSimpleKinded(typedType(tpt))
-    val rhs1 = typedExpr(ddef.rhs, tpt1.tpe)
+
+    var rhsCtx = ctx
+    if (sym.isConstructor && !sym.isPrimaryConstructor && tparams1.nonEmpty) {
+      // for secondary constructors we need a context that "knows"
+      // that their type parameters are aliases of the class type parameters.
+      // See pos/i941.scala
+      rhsCtx = ctx.fresh.setFreshGADTBounds
+      (tparams1, sym.owner.typeParams).zipped.foreach ((tdef, tparam) =>
+        rhsCtx.gadt.setBounds(tdef.symbol, TypeAlias(tparam.typeRef)))
+    }
+    val rhs1 = typedExpr(ddef.rhs, tpt1.tpe)(rhsCtx)
     assignType(cpy.DefDef(ddef)(name, tparams1, vparamss1, tpt1, rhs1), sym)
     //todo: make sure dependent method types do not depend on implicits or by-name params
   }