Merge pull request #12971 from dotty-staging/add-rechecker

Add recheck phase

compiler/src/dotty/tools/dotc/Compiler.scala

@@ -103,6 +103,8 @@ class Compiler {
          new TupleOptimizations,     // Optimize generic operations on tuples
          new LetOverApply,           // Lift blocks from receivers of applications
          new ArrayConstructors) ::   // Intercept creation of (non-generic) arrays and intrinsify.
+    List(new PreRecheck) ::
+    List(new TestRecheck) ::
     List(new Erasure) ::             // Rewrite types to JVM model, erasing all type parameters, abstract types and refinements.
     List(new ElimErasedValueType,    // Expand erased value types to their underlying implmementation types
          new PureStats,              // Remove pure stats from blocks

compiler/src/dotty/tools/dotc/config/Printers.scala

@@ -38,6 +38,7 @@ object Printers {
   val pickling = noPrinter
   val quotePickling = noPrinter
   val plugins = noPrinter
+  val recheckr = noPrinter
   val refcheck = noPrinter
   val simplify = noPrinter
   val staging = noPrinter

compiler/src/dotty/tools/dotc/config/ScalaSettings.scala

@@ -311,6 +311,7 @@ private sealed trait YSettings:
   val YcheckInit: Setting[Boolean] = BooleanSetting("-Ysafe-init", "Ensure safe initialization of objects")
   val YrequireTargetName: Setting[Boolean] = BooleanSetting("-Yrequire-targetName", "Warn if an operator is defined without a @targetName annotation")
   val YscalaRelease: Setting[String] = ChoiceSetting("-Yscala-release", "release", "Emit TASTy files that can be consumed by specified version of the compiler. The compilation will fail if for any reason valid TASTy cannot be produced (e.g. the code contains references to some parts of the standard library API that are missing in the older stdlib or uses language features unexpressible in the older version of TASTy format)", ScalaSettings.supportedScalaReleaseVersions, "", aliases = List("--Yscala-release"))
+  val Yrecheck: Setting[Boolean] = BooleanSetting("-Yrecheck", "Run type rechecks (test only)")
 
   /** Area-specific debug output */
   val YexplainLowlevel: Setting[Boolean] = BooleanSetting("-Yexplain-lowlevel", "When explaining type errors, show types at a lower level.")

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

@@ -174,4 +174,24 @@ 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/core/Phases.scala

@@ -298,6 +298,9 @@ object Phases {
     /** If set, implicit search is enabled */
     def allowsImplicitSearch: Boolean = false
 
+    /** If set equate Skolem types with underlying types */
+    def widenSkolems: Boolean = false
+
     /** List of names of phases that should precede this phase */
     def runsAfter: Set[String] = Set.empty
 

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

@@ -738,6 +738,8 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
             false
         }
         compareClassInfo
+      case tp2: SkolemType =>
+        ctx.phase.widenSkolems && recur(tp1, tp2.info) || fourthTry
       case _ =>
         fourthTry
     }

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