Drop phase.isTyper use in isLegalPrefix/asf

Note that "asSeenFrom" (aka asf) is used by SymDenotation#findMember,
which is used by TypeComparer's "hasMatchingMember", as a part of
"compareRefinedSlow".

Previously (using the minimisation in i17222.8.scala) `summonOne` is
inlined during the "inlining" phase, while "summonInline" is inlined
during typing.  The result is that during inlining we fail to find
`Reader[BC, Int]` because we incorrectly consider `A{type F = Int}` as
stable.

Author: dwijnand

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

@@ -346,7 +346,8 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
         }
         compareWild
       case tp2: LazyRef =>
-        isBottom(tp1) || !tp2.evaluating && recur(tp1, tp2.ref)
+        isBottom(tp1)
+        || !tp2.evaluating && recur(tp1, tp2.ref)
       case CapturingType(_, _) =>
         secondTry
       case tp2: AnnotatedType if !tp2.isRefining =>
@@ -466,7 +467,7 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
         // If `tp1` is in train of being evaluated, don't force it
         // because that would cause an assertionError. Return false instead.
         // See i859.scala for an example where we hit this case.
-        tp2.isRef(AnyClass, skipRefined = false)
+        tp2.isAny
         || !tp1.evaluating && recur(tp1.ref, tp2)
       case AndType(tp11, tp12) =>
         if (tp11.stripTypeVar eq tp12.stripTypeVar) recur(tp11, tp2)

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

@@ -123,7 +123,7 @@ object TypeOps:
   }
 
   def isLegalPrefix(pre: Type)(using Context): Boolean =
-    pre.isStable || !ctx.phase.isTyper
+    pre.isStable
 
   /** Implementation of Types#simplified */
   def simplify(tp: Type, theMap: SimplifyMap | Null)(using Context): Type = {

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

@@ -95,12 +95,8 @@ object Types extends TypeUtils {
 // ----- Tests -----------------------------------------------------
 
 //    // debug only: a unique identifier for a type
-//    val uniqId = {
-//      nextId = nextId + 1
-//      if (nextId == 19555)
-//        println("foo")
-//      nextId
-//    }
+//    val uniqId = { nextId = nextId + 1; nextId }
+//    if uniqId == 19555 then trace.dumpStack()
 
     /** A cache indicating whether the type was still provisional, last time we checked */
     @sharable private var mightBeProvisional = true
@@ -5249,24 +5245,25 @@ object Types extends TypeUtils {
     }
 
     def & (that: TypeBounds)(using Context): TypeBounds =
+      val lo1 = this.lo.stripLazyRef
+      val lo2 = that.lo.stripLazyRef
+      val hi1 = this.hi.stripLazyRef
+      val hi2 = that.hi.stripLazyRef
+
       // This will try to preserve the FromJavaObjects type in upper bounds.
       // For example, (? <: FromJavaObjects | Null) & (? <: Any),
       // we want to get (? <: FromJavaObjects | Null) intead of (? <: Any),
       // because we may check the result <:< (? <: Object | Null) later.
-      if this.hi.containsFromJavaObject
-        && (this.hi frozen_<:< that.hi)
-        && (that.lo frozen_<:< this.lo) then
+      if hi1.containsFromJavaObject && (hi1 frozen_<:< hi2) && (lo2 frozen_<:< lo1) then
         // FromJavaObject in tp1.hi guarantees tp2.hi <:< tp1.hi
         // prefer tp1 if FromJavaObject is in its hi
         this
-      else if that.hi.containsFromJavaObject
-        && (that.hi frozen_<:< this.hi)
-        && (this.lo frozen_<:< that.lo) then
+      else if hi2.containsFromJavaObject && (hi2 frozen_<:< hi1) && (lo1 frozen_<:< lo2) then
         // Similarly, prefer tp2 if FromJavaObject is in its hi
         that
-      else if (this.lo frozen_<:< that.lo) && (that.hi frozen_<:< this.hi) then that
-      else if (that.lo frozen_<:< this.lo) && (this.hi frozen_<:< that.hi) then this
-      else TypeBounds(this.lo | that.lo, this.hi & that.hi)
+      else if (lo1 frozen_<:< lo2) && (hi2 frozen_<:< hi1) then that
+      else if (lo2 frozen_<:< lo1) && (hi1 frozen_<:< hi2) then this
+      else TypeBounds(lo1 | lo2, hi1 & hi2)
 
     def | (that: TypeBounds)(using Context): TypeBounds =
       if ((this.lo frozen_<:< that.lo) && (that.hi frozen_<:< this.hi)) this
@@ -5275,7 +5272,7 @@ object Types extends TypeUtils {
 
     override def & (that: Type)(using Context): Type = that match {
       case that: TypeBounds => this & that
-      case _ => super.& (that)
+      case _ => super.&(that)
     }
 
     override def | (that: Type)(using Context): Type = that match {

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

@@ -194,10 +194,10 @@ abstract class Recheck extends Phase, SymTransformer:
         sharpen: Denotation => Denotation)(using Context): Type =
       if name.is(OuterSelectName) then tree.tpe
       else
-        //val pre = ta.maybeSkolemizePrefix(qualType, name)
+        val pre = ta.maybeSkolemizePrefix(qualType, name)
         val mbr = normalizeByName(
           sharpen(
-            qualType.findMember(name, qualType,
+            qualType.findMember(name, pre,
               excluded = if tree.symbol.is(Private) then EmptyFlags else Private
           )).suchThat(tree.symbol == _))
         val newType = tree.tpe match

compiler/test/dotc/pos-test-pickling.blacklist

@@ -23,6 +23,7 @@ t5031_2.scala
 i16997.scala
 i7414.scala
 i17588.scala
+i8300.scala
 i9804.scala
 i13433.scala
 i16649-irrefutable.scala

tests/neg/6314-6.check

@@ -0,0 +1,16 @@
+-- Error: tests/neg/6314-6.scala:26:3 ----------------------------------------------------------------------------------
+26 |  (new YY {}).boom // error: object creation impossible
+   |   ^
+   |object creation impossible, since def apply(fa: String): Int in trait XX in object Test3 is not defined 
+   |(Note that
+   | parameter String in def apply(fa: String): Int in trait XX in object Test3 does not match
+   | parameter Test3.Bar[X & (X & Y)] in def apply(fa: Test3.Bar[X & YY.this.Foo]): Test3.Bar[Y & YY.this.Foo] in trait YY in object Test3
+   | )
+-- Error: tests/neg/6314-6.scala:52:3 ----------------------------------------------------------------------------------
+52 |  (new YY {}).boom // error: object creation impossible
+   |   ^
+   |object creation impossible, since def apply(fa: String): Int in trait XX in object Test4 is not defined 
+   |(Note that
+   | parameter String in def apply(fa: String): Int in trait XX in object Test4 does not match
+   | parameter Test4.Bar[X & (X & Y)] in def apply(fa: Test4.Bar[X & YY.this.FooAlias]): Test4.Bar[Y & YY.this.FooAlias] in trait YY in object Test4
+   | )

tests/neg/i6225.scala

@@ -1,4 +1,4 @@
-object O1 {
+object O1 { // error: cannot be instantiated
   type A[X] = X
   opaque type T = A // error: opaque type alias must be fully applied
 }

tests/pos/i17222.2.scala

@@ -0,0 +1,30 @@
+import scala.compiletime.*
+
+trait Reader[-In, Out]
+
+trait A:
+  type T
+  type F[X]
+  type Q = F[T]
+
+object Reader:
+
+  given [X]: Reader[A { type Q = X }, X] with {}
+
+object Test:
+
+  trait B[X] extends A:
+    type T = X
+
+  trait C extends A:
+    type F[X] = X
+
+  trait D[X] extends B[X] with C
+
+  val d = new D[Int] {}
+  val bc = new B[Int] with C
+
+  summonAll[(Reader[d.type, Int], Reader[d.type, Int])] // works
+  summonAll[(Reader[bc.type, Int], Reader[bc.type, Int])] // error
+  summonInline[Reader[d.type, Int]] // works
+  summonInline[Reader[bc.type, Int]] // works??

tests/pos/i17222.3.scala

@@ -0,0 +1,39 @@
+import scala.compiletime.*
+
+trait Reader[-In, Out]
+
+trait A:
+  type T
+  type F[X]
+  type Q = F[T]
+
+object Reader:
+
+  given [X]: Reader[A { type Q = X }, X] with {}
+
+object Test:
+
+  trait B[X] extends A:
+    type T = X
+
+  trait C extends A:
+    type F[X] = X
+
+  trait D[X] extends B[X] with C
+
+  val d = new D[Int] {}
+  val bc = new B[Int] with C
+
+  case class Box[T](value: T)
+
+  /** compiletime.summonAll, but with one case */
+  inline def summonOne[T <: Box[?]]: T =
+    val res =
+      inline erasedValue[T] match
+        case _: Box[t] => summonInline[t]
+      end match
+    Box(res).asInstanceOf[T]
+  end summonOne
+
+  summonOne[Box[Reader[d.type, Int]]] // works
+  summonOne[Box[Reader[bc.type, Int]]] // errors

tests/pos/i17222.4.scala

@@ -0,0 +1,71 @@
+import scala.compiletime.*
+
+trait Reader[-In, Out]
+
+trait A:
+  type T
+  type F[X]
+  type Q = F[T]
+
+given [X]: Reader[A { type Q = X }, X] with {}
+
+case class Box[T](x: T)
+
+/** compiletime.summonAll, but with one case */
+inline def summonOne[T]: T =
+  val res =
+    inline erasedValue[T] match
+      case _: Box[t] => summonInline[t]
+    end match
+  Box(res).asInstanceOf[T]
+end summonOne
+
+
+@main def main =
+
+
+  trait B[X] extends A:
+    type T = X
+
+  trait C extends A:
+    type F[X] = X
+
+
+  val bc = new B[Int] with C
+
+  summonOne[Box[Reader[bc.type, Int]]] // errors
+
+
+  val bc2: A { type Q = Int } = new B[Int] with C
+
+  summonOne[Box[Reader[bc2.type, Int]]] // works
+
+
+  object BC extends B[Int] with C
+
+  summonOne[Box[Reader[BC.type, Int]]] // works
+
+
+  val a = new A:
+    type T = Int
+    type F[X] = X
+
+  summonOne[Box[Reader[a.type, Int]]] // works
+
+
+  val b = new B[Int]:
+    type F[X] = X
+
+  summonOne[Box[Reader[b.type, Int]]] // works
+
+
+  val ac = new A with C:
+    type T = Int
+
+  summonOne[Box[Reader[ac.type, Int]]] // works
+
+
+  trait D[X] extends B[X] with C
+  val d = new D[Int] {}
+
+  summonOne[Box[Reader[d.type, Int]]] // works