Add Recheck

Author: odersky

compiler/src/dotty/tools/dotc/core/NamerOps.scala

@@ -177,4 +177,24 @@ object NamerOps:
     cls.registeredCompanion = modcls
     modcls.registeredCompanion = cls
 
+  /** For secondary constructors, make it known in the context that their type parameters
+   *  are aliases of the class type parameters. This is done by (ab?)-using GADT constraints.
+   *  See pos/i941.scala
+   */
+  def linkConstructorParams(sym: Symbol)(using Context): Context =
+    if sym.isConstructor && !sym.isPrimaryConstructor then
+      sym.rawParamss match
+        case (tparams @ (tparam :: _)) :: _ if tparam.isType =>
+          val rhsCtx = ctx.fresh.setFreshGADTBounds
+          rhsCtx.gadt.addToConstraint(tparams)
+          tparams.lazyZip(sym.owner.typeParams).foreach { (psym, tparam) =>
+            val tr = tparam.typeRef
+            rhsCtx.gadt.addBound(psym, tr, isUpper = false)
+            rhsCtx.gadt.addBound(psym, tr, isUpper = true)
+          }
+          rhsCtx
+        case _ =>
+          ctx
+    else ctx
+
 end NamerOps

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

@@ -0,0 +1,21 @@
+package dotty.tools.dotc
+package transform
+
+import core.Phases.Phase
+import core.DenotTransformers.IdentityDenotTransformer
+import core.Contexts.{Context, ctx}
+
+/** A phase that precedes the rechecker and that allows installing
+ *  new types for local symbols.
+ */
+class PreRecheck extends Phase, IdentityDenotTransformer:
+
+  def phaseName: String = "preRecheck"
+
+  override def isEnabled(using Context) = next.isEnabled
+
+  override def changesBaseTypes: Boolean = true
+
+  def run(using Context): Unit = ()
+
+  override def isCheckable = false