Merge pull request #1461 from dotty-staging/fixes-gadts

Fixes of GADTs and test recategorization.

6 files changed, 77 insertions, 26 deletions

diff --git a/src/dotty/tools/dotc/ast/Desugar.scala b/src/dotty/tools/dotc/ast/Desugar.scala
index 346af42b8..500b28233 100644
--- a/src/dotty/tools/dotc/ast/Desugar.scala
+++ b/src/dotty/tools/dotc/ast/Desugar.scala
@@ -8,6 +8,7 @@ import SymDenotations._, Symbols._, StdNames._, Annotations._, Trees._
 import Decorators._
 import language.higherKinds
 import collection.mutable.ListBuffer
+import util.Attachment
 import config.Printers._
 
 object desugar {
@@ -17,6 +18,11 @@ object desugar {
 
   import untpd._
 
+  /** Tags a .withFilter call generated by desugaring a for expression.
+   *  Such calls can alternatively be rewritten to use filter.
+   */
+  val MaybeFilter = new Attachment.Key[Unit]
+
   /** Info of a variable in a pattern: The named tree and its type */
   private type VarInfo = (NameTree, Tree)
 
@@ -773,6 +779,12 @@ object desugar {
           (Bind(name, pat), Ident(name))
       }
 
+      /** Add MaybeFilter attachment */
+      def orFilter(tree: Tree): tree.type = {
+        tree.putAttachment(MaybeFilter, ())
+        tree
+      }
+
       /** Make a pattern filter:
        *    rhs.withFilter { case pat => true case _ => false }
        *
@@ -803,7 +815,7 @@ object desugar {
         val cases = List(
           CaseDef(pat, EmptyTree, Literal(Constant(true))),
           CaseDef(Ident(nme.WILDCARD), EmptyTree, Literal(Constant(false))))
-        Apply(Select(rhs, nme.withFilter), makeCaseLambda(cases))
+        Apply(orFilter(Select(rhs, nme.withFilter)), makeCaseLambda(cases))
       }
 
       /** Is pattern `pat` irrefutable when matched against `rhs`?
@@ -858,7 +870,7 @@ object desugar {
           val vfrom1 = new IrrefutableGenFrom(makeTuple(allpats), rhs1)
           makeFor(mapName, flatMapName, vfrom1 :: rest1, body)
         case (gen: GenFrom) :: test :: rest =>
-          val filtered = Apply(rhsSelect(gen, nme.withFilter), makeLambda(gen.pat, test))
+          val filtered = Apply(orFilter(rhsSelect(gen, nme.withFilter)), makeLambda(gen.pat, test))
           val genFrom =
             if (isIrrefutableGenFrom(gen)) new IrrefutableGenFrom(gen.pat, filtered)
             else GenFrom(gen.pat, filtered)
diff --git a/src/dotty/tools/dotc/core/TypeComparer.scala b/src/dotty/tools/dotc/core/TypeComparer.scala
index 8d7e9d164..538a74198 100644
--- a/src/dotty/tools/dotc/core/TypeComparer.scala
+++ b/src/dotty/tools/dotc/core/TypeComparer.scala
@@ -76,6 +76,19 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
     myNothingType
   }
 
+  /** Indicates whether a previous subtype check used GADT bounds */
+  var GADTused = false
+
+  /** Record that GADT bounds of `sym` were used in a subtype check.
+   *  But exclude constructor type parameters, as these are aliased
+   *  to the corresponding class parameters, which does not constitute
+   *  a true usage of a GADT symbol.
+   */
+  private def GADTusage(sym: Symbol) = {
+    if (!sym.owner.isConstructor) GADTused = true
+    true
+  }
+
   // Subtype testing `<:<`
 
   def topLevelSubType(tp1: Type, tp2: Type): Boolean = {
@@ -325,7 +338,8 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
         val gbounds2 = ctx.gadt.bounds(tp2.symbol)
         (gbounds2 != null) &&
           (isSubTypeWhenFrozen(tp1, gbounds2.lo) ||
-            narrowGADTBounds(tp2, tp1, isUpper = false))
+            narrowGADTBounds(tp2, tp1, isUpper = false)) &&
+          GADTusage(tp2.symbol)
       }
       ((frozenConstraint || !isCappable(tp1)) && isSubType(tp1, lo2) ||
         compareGADT ||
@@ -507,7 +521,8 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
             val gbounds1 = ctx.gadt.bounds(tp1.symbol)
             (gbounds1 != null) &&
               (isSubTypeWhenFrozen(gbounds1.hi, tp2) ||
-               narrowGADTBounds(tp1, tp2, isUpper = true))
+               narrowGADTBounds(tp1, tp2, isUpper = true)) &&
+              GADTusage(tp1.symbol)
           }
           isSubType(hi1, tp2) || compareGADT
         case _ =>
@@ -846,11 +861,13 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
     // special case for situations like:
     //    class C { type T }
     //    val foo: C
-    //    foo.type <: C { type T = foo.T }
+    //    foo.type <: C { type T {= , <: , >:} foo.T }
     def selfReferentialMatch = tp1.isInstanceOf[SingletonType] && {
       rinfo2 match {
-        case rinfo2: TypeAlias =>
-          !defn.isBottomType(tp1.widen) && (tp1 select name) =:= rinfo2.alias
+        case rinfo2: TypeBounds =>
+          val mbr1 = tp1.select(name)
+          !defn.isBottomType(tp1.widen) &&
+          (mbr1 =:= rinfo2.hi || (rinfo2.hi ne rinfo2.lo) && mbr1 =:= rinfo2.lo)
         case _ => false
       }
     }
diff --git a/src/dotty/tools/dotc/transform/TreeChecker.scala b/src/dotty/tools/dotc/transform/TreeChecker.scala
index ce160d7b0..18e3a6c8a 100644
--- a/src/dotty/tools/dotc/transform/TreeChecker.scala
+++ b/src/dotty/tools/dotc/transform/TreeChecker.scala
@@ -258,7 +258,7 @@ class TreeChecker extends Phase with SymTransformer {
     }
 
     override def typed(tree: untpd.Tree, pt: Type = WildcardType)(implicit ctx: Context): tpd.Tree = {
-      val tpdTree = super.typed(tree)
+      val tpdTree = super.typed(tree, pt)
       checkIdentNotJavaClass(tpdTree)
       tpdTree
     }
diff --git a/src/dotty/tools/dotc/typer/Applications.scala b/src/dotty/tools/dotc/typer/Applications.scala
index 45ed4d938..099105de3 100644
--- a/src/dotty/tools/dotc/typer/Applications.scala
+++ b/src/dotty/tools/dotc/typer/Applications.scala
@@ -775,14 +775,13 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
      *  The generalizations of a type T are the smallest set G such that
      *
      *   - T is in G
-     *   - If a typeref R in G represents a trait, R's superclass is in G.
+     *   - If a typeref R in G represents a class or trait, R's superclass is in G.
      *   - If a type proxy P is not a reference to a class, P's supertype is in G
      */
     def isSubTypeOfParent(subtp: Type, tp: Type)(implicit ctx: Context): Boolean =
       if (subtp <:< tp) true
       else tp match {
-        case tp: TypeRef if tp.symbol.isClass =>
-          tp.symbol.is(Trait) && isSubTypeOfParent(subtp, tp.firstParent)
+        case tp: TypeRef if tp.symbol.isClass => isSubTypeOfParent(subtp, tp.firstParent)
         case tp: TypeProxy => isSubTypeOfParent(subtp, tp.superType)
         case _ => false
       }
diff --git a/src/dotty/tools/dotc/typer/Namer.scala b/src/dotty/tools/dotc/typer/Namer.scala
index 3c0a45e94..d90f37860 100644
--- a/src/dotty/tools/dotc/typer/Namer.scala
+++ b/src/dotty/tools/dotc/typer/Namer.scala
@@ -726,7 +726,7 @@ class Namer { typer: Typer =>
       // the parent types are elaborated.
       index(constr)
       symbolOfTree(constr).ensureCompleted()
-      
+
       index(rest)(inClassContext(selfInfo))
 
       val tparamAccessors = decls.filter(_ is TypeParamAccessor).toList
@@ -807,20 +807,27 @@ class Namer { typer: Typer =>
           lazy val schema = paramFn(WildcardType)
           val site = sym.owner.thisType
           ((NoType: Type) /: sym.owner.info.baseClasses.tail) { (tp, cls) =>
-            val iRawInfo =
-              cls.info.nonPrivateDecl(sym.name).matchingDenotation(site, schema).info
-            val iInstInfo = iRawInfo match {
-              case iRawInfo: PolyType =>
-                if (iRawInfo.paramNames.length == typeParams.length)
-                  iRawInfo.instantiate(typeParams map (_.typeRef))
+            def instantiatedResType(info: Type, tparams: List[Symbol], paramss: List[List[Symbol]]): Type = info match {
+              case info: PolyType =>
+                if (info.paramNames.length == typeParams.length)
+                  instantiatedResType(info.instantiate(tparams.map(_.typeRef)), Nil, paramss)
                 else NoType
+              case info: MethodType =>
+                paramss match {
+                  case params :: paramss1 if info.paramNames.length == params.length =>
+                    instantiatedResType(info.instantiate(params.map(_.termRef)), tparams, paramss1)
+                  case _ =>
+                    NoType
+                }
               case _ =>
-                if (typeParams.isEmpty) iRawInfo
+                if (tparams.isEmpty && paramss.isEmpty) info.widenExpr
                 else NoType
             }
-            val iResType = iInstInfo.finalResultType.asSeenFrom(site, cls)
+            val iRawInfo =
+              cls.info.nonPrivateDecl(sym.name).matchingDenotation(site, schema).info
+            val iResType = instantiatedResType(iRawInfo, typeParams, paramss).asSeenFrom(site, cls)
             if (iResType.exists)
-              typr.println(i"using inherited type for ${mdef.name}; raw: $iRawInfo, inst: $iInstInfo, inherited: $iResType")
+              typr.println(i"using inherited type for ${mdef.name}; raw: $iRawInfo, inherited: $iResType")
             tp & iResType
           }
         }
diff --git a/src/dotty/tools/dotc/typer/Typer.scala b/src/dotty/tools/dotc/typer/Typer.scala
index 7eb022b51..f0086b0ab 100644
--- a/src/dotty/tools/dotc/typer/Typer.scala
+++ b/src/dotty/tools/dotc/typer/Typer.scala
@@ -346,11 +346,17 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
       }
     }
 
-    if (ctx.compilationUnit.isJava && tree.name.isTypeName) {
+    def selectWithFallback(fallBack: => Tree) =
+      tryEither(tryCtx => asSelect(tryCtx))((_, _) => fallBack)
+
+    if (ctx.compilationUnit.isJava && tree.name.isTypeName)
       // SI-3120 Java uses the same syntax, A.B, to express selection from the
       // value A and from the type A. We have to try both.
-      tryEither(tryCtx => asSelect(tryCtx))((_, _) => asJavaSelectFromTypeTree(ctx))
-    } else asSelect(ctx)
+      selectWithFallback(asJavaSelectFromTypeTree(ctx))
+    else if (tree.name == nme.withFilter && tree.getAttachment(desugar.MaybeFilter).isDefined)
+      selectWithFallback(typedSelect(untpd.cpy.Select(tree)(tree.qualifier, nme.filter), pt))
+    else
+      asSelect(ctx)
   }
 
   def typedSelectFromTypeTree(tree: untpd.SelectFromTypeTree, pt: Type)(implicit ctx: Context): Tree = track("typedSelectFromTypeTree") {
@@ -1066,8 +1072,9 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
   def completeAnnotations(mdef: untpd.MemberDef, sym: Symbol)(implicit ctx: Context): Unit = {
     // necessary to force annotation trees to be computed.
     sym.annotations.foreach(_.tree)
+    val annotCtx = ctx.outersIterator.dropWhile(_.owner == sym).next
     // necessary in order to mark the typed ahead annotations as definitely typed:
-    untpd.modsDeco(mdef).mods.annotations.foreach(typedAnnotation)
+    untpd.modsDeco(mdef).mods.annotations.foreach(typedAnnotation(_)(annotCtx))
   }
 
   def typedAnnotation(annot: untpd.Tree)(implicit ctx: Context): Tree = track("typedAnnotation") {
@@ -1715,6 +1722,7 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
         else
           missingArgs
       case _ =>
+        ctx.typeComparer.GADTused = false
         if (ctx.mode is Mode.Pattern) {
           tree match {
             case _: RefTree | _: Literal if !isVarPattern(tree) =>
@@ -1723,7 +1731,15 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
           }
           tree
         }
-        else if (tree.tpe <:< pt) tree
+        else if (tree.tpe <:< pt)
+          if (ctx.typeComparer.GADTused && pt.isValueType)
+            // Insert an explicit cast, so that -Ycheck in later phases succeeds.
+            // I suspect, but am not 100% sure that this might affect inferred types,
+            // if the expected type is a supertype of the GADT bound. It would be good to come
+            // up with a test case for this.
+            tree.asInstance(pt)
+          else
+            tree
         else if (wtp.isInstanceOf[MethodType]) missingArgs
         else {
           typr.println(i"adapt to subtype ${tree.tpe} !<:< $pt")