Fix #4098: Check that refinements have good bounds

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

@@ -30,8 +30,8 @@ object CheckRealizable {
   class NotFinal(sym: Symbol)(implicit ctx: Context)
   extends Realizability(i" refers to nonfinal $sym")
 
-  class HasProblemBounds(typ: SingleDenotation)(implicit ctx: Context)
-  extends Realizability(i" has a member $typ with possibly conflicting bounds ${typ.info.bounds.lo} <: ... <: ${typ.info.bounds.hi}")
+  class HasProblemBounds(name: Name, info: Type)(implicit ctx: Context)
+  extends Realizability(i" has a member $name with possibly conflicting bounds ${info.bounds.lo} <: ... <: ${info.bounds.hi}")
 
   class HasProblemBaseArg(typ: Type, argBounds: TypeBounds)(implicit ctx: Context)
   extends Realizability(i" has a base type $typ with possibly conflicting parameter bounds ${argBounds.lo} <: ... <: ${argBounds.hi}")
@@ -96,6 +96,14 @@ class CheckRealizable(implicit ctx: Context) {
       else boundsRealizability(tp).andAlso(memberRealizability(tp))
   }
 
+  private def refinedNames(tp: Type): Set[Name] = tp.dealias match {
+    case tp: RefinedType => refinedNames(tp.parent) + tp.refinedName
+    case tp: AndType => refinedNames(tp.tp1) ++ refinedNames(tp.tp2)
+    case tp: OrType  => refinedNames(tp.tp1) ++ refinedNames(tp.tp2)
+    case tp: TypeProxy => refinedNames(tp.underlying)
+    case _ => Set.empty
+  }
+
   /** `Realizable` if `tp` has good bounds, a `HasProblem...` instance
    *  pointing to a bad bounds member otherwise. "Has good bounds" means:
    *
@@ -107,12 +115,22 @@ class CheckRealizable(implicit ctx: Context) {
    *       also lead to base types with bad bounds).
    */
   private def boundsRealizability(tp: Type) = {
-    val mbrProblems =
+
+    val memberProblems =
       for {
         mbr <- tp.nonClassTypeMembers
         if !(mbr.info.loBound <:< mbr.info.hiBound)
       }
-      yield new HasProblemBounds(mbr)
+      yield new HasProblemBounds(mbr.name, mbr.info)
+
+    val refinementProblems =
+      for {
+        name <- refinedNames(tp)
+        if (name.isTypeName)
+        mbr <- tp.member(name).alternatives
+        if !(mbr.info.loBound <:< mbr.info.hiBound)
+      }
+      yield new HasProblemBounds(name, mbr.info)
 
     def baseTypeProblems(base: Type) = base match {
       case AndType(base1, base2) =>
@@ -126,12 +144,13 @@ class CheckRealizable(implicit ctx: Context) {
     val baseProblems =
       tp.baseClasses.map(_.baseTypeOf(tp)).flatMap(baseTypeProblems)
 
-    (((Realizable: Realizability)
-      /: mbrProblems)(_ andAlso _)
+    ((((Realizable: Realizability)
+      /: memberProblems)(_ andAlso _)
+      /: refinementProblems)(_ andAlso _)
       /: baseProblems)(_ andAlso _)
   }
 
-  /** `Realizable` if all of `tp`'s non-struct fields have realizable types,
+  /** `Realizable` if all of `tp`'s non-strict fields have realizable types,
    *  a `HasProblemField` instance pointing to a bad field otherwise.
    */
   private def memberRealizability(tp: Type) = {

compiler/src/dotty/tools/dotc/typer/Dynamic.scala

@@ -11,6 +11,7 @@ import dotty.tools.dotc.core.Names.{Name, TermName}
 import dotty.tools.dotc.core.StdNames._
 import dotty.tools.dotc.core.Types._
 import dotty.tools.dotc.core.Decorators._
+import util.Positions._
 import core.Symbols._
 import core.Definitions
 import Inferencing._
@@ -49,7 +50,7 @@ trait Dynamic { self: Typer with Applications =>
    *    foo.bar[T0, ...](x = bazX, y = bazY, baz, ...) ~~> foo.applyDynamicNamed[T0, ...]("bar")(("x", bazX), ("y", bazY), ("", baz), ...)
    */
   def typedDynamicApply(tree: untpd.Apply, pt: Type)(implicit ctx: Context): Tree = {
-    def typedDynamicApply(qual: untpd.Tree, name: Name, targs: List[untpd.Tree]): Tree = {
+    def typedDynamicApply(qual: untpd.Tree, name: Name, selPos: Position, targs: List[untpd.Tree]): Tree = {
       def isNamedArg(arg: untpd.Tree): Boolean = arg match { case NamedArg(_, _) => true; case _ => false }
       val args = tree.args
       val dynName = if (args.exists(isNamedArg)) nme.applyDynamicNamed else nme.applyDynamic
@@ -62,19 +63,19 @@ trait Dynamic { self: Typer with Applications =>
           case arg => namedArgTuple("", arg)
         }
         val args1 = if (dynName == nme.applyDynamic) args else namedArgs
-        typedApply(untpd.Apply(coreDynamic(qual, dynName, name, targs), args1), pt)
+        typedApply(untpd.Apply(coreDynamic(qual, dynName, name, selPos, targs), args1), pt)
       }
     }
 
      tree.fun match {
-      case Select(qual, name) if !isDynamicMethod(name) =>
-        typedDynamicApply(qual, name, Nil)
-      case TypeApply(Select(qual, name), targs) if !isDynamicMethod(name) =>
-        typedDynamicApply(qual, name, targs)
+      case sel @ Select(qual, name) if !isDynamicMethod(name) =>
+        typedDynamicApply(qual, name, sel.pos, Nil)
+      case TypeApply(sel @ Select(qual, name), targs) if !isDynamicMethod(name) =>
+        typedDynamicApply(qual, name, sel.pos, targs)
       case TypeApply(fun, targs) =>
-        typedDynamicApply(fun, nme.apply, targs)
+        typedDynamicApply(fun, nme.apply, fun.pos, targs)
       case fun =>
-        typedDynamicApply(fun, nme.apply, Nil)
+        typedDynamicApply(fun, nme.apply, fun.pos, Nil)
     }
   }
 
@@ -86,26 +87,26 @@ trait Dynamic { self: Typer with Applications =>
    *  through an existing transformation of in typedAssign [foo.bar(baz) = quux ~~> foo.bar.update(baz, quux)].
    */
   def typedDynamicSelect(tree: untpd.Select, targs: List[Tree], pt: Type)(implicit ctx: Context): Tree =
-    typedApply(coreDynamic(tree.qualifier, nme.selectDynamic, tree.name, targs), pt)
+    typedApply(coreDynamic(tree.qualifier, nme.selectDynamic, tree.name, tree.pos, targs), pt)
 
   /** Translate selection that does not typecheck according to the normal rules into a updateDynamic.
    *    foo.bar = baz ~~> foo.updateDynamic(bar)(baz)
    */
   def typedDynamicAssign(tree: untpd.Assign, pt: Type)(implicit ctx: Context): Tree = {
-    def typedDynamicAssign(qual: untpd.Tree, name: Name, targs: List[untpd.Tree]): Tree =
-      typedApply(untpd.Apply(coreDynamic(qual, nme.updateDynamic, name, targs), tree.rhs), pt)
+    def typedDynamicAssign(qual: untpd.Tree, name: Name, selPos: Position, targs: List[untpd.Tree]): Tree =
+      typedApply(untpd.Apply(coreDynamic(qual, nme.updateDynamic, name, selPos, targs), tree.rhs), pt)
     tree.lhs match {
-      case Select(qual, name) if !isDynamicMethod(name) =>
-        typedDynamicAssign(qual, name, Nil)
-      case TypeApply(Select(qual, name), targs) if !isDynamicMethod(name) =>
-        typedDynamicAssign(qual, name, targs)
+      case sel @ Select(qual, name) if !isDynamicMethod(name) =>
+        typedDynamicAssign(qual, name, sel.pos, Nil)
+      case TypeApply(sel @ Select(qual, name), targs) if !isDynamicMethod(name) =>
+        typedDynamicAssign(qual, name, sel.pos, targs)
       case _ =>
         errorTree(tree, ReassignmentToVal(tree.lhs.symbol.name))
     }
   }
 
-  private def coreDynamic(qual: untpd.Tree, dynName: Name, name: Name, targs: List[untpd.Tree])(implicit ctx: Context): untpd.Apply = {
-    val select = untpd.Select(qual, dynName)
+  private def coreDynamic(qual: untpd.Tree, dynName: Name, name: Name, selPos: Position, targs: List[untpd.Tree])(implicit ctx: Context): untpd.Apply = {
+    val select = untpd.Select(qual, dynName).withPos(selPos)
     val selectWithTypes =
       if (targs.isEmpty) select
       else untpd.TypeApply(select, targs)
@@ -134,7 +135,7 @@ trait Dynamic { self: Typer with Applications =>
     def structuralCall(selectorName: TermName, formals: List[Tree]) = {
       val selectable = adapt(qual, defn.SelectableType)
       val scall = untpd.Apply(
-        untpd.TypedSplice(selectable.select(selectorName)),
+        untpd.TypedSplice(selectable.select(selectorName)).withPos(tree.pos),
         (Literal(Constant(name.toString)) :: formals).map(untpd.TypedSplice(_)))
       typed(scall)
     }

tests/neg/i4098.scala

@@ -0,0 +1,16 @@
+object App {
+  import scala.reflect.Selectable.reflectiveSelectable
+
+  def coerce[U, V](u: U): V = {
+    type X = { type R >: U }
+    type Y = { type R = V }
+    type Z = X & Y
+    val u1: Z#R = u // error: not a legal path
+    u1
+  }
+
+  def main(args: Array[String]): Unit = {
+    val x: Int = coerce[String, Int]("a")
+    println(x + 1)
+  }
+}

tests/neg/i4098a.scala

@@ -0,0 +1,16 @@
+object App {
+  import scala.reflect.Selectable.reflectiveSelectable
+
+  def coerce[U, V](u: U): V = {
+    type X = { val x: { type R >: U } }
+    type Y = { val x: { type R = V } }
+    lazy val z: X & Y = z
+    val u1: z.x.R = u  // error: Object { type R >: U | V <: V } is not stable (with arrows under z.x)
+    u1
+  }
+
+  def main(args: Array[String]): Unit = {
+    val x: Int = coerce[String, Int]("a")
+    println(x + 1)
+  }
+}