Change some occurrences of <:< to frozen_<:<

Some subtype tests should not instantiate type variables, in particular
those having to do with & and |.

3 files changed, 15 insertions, 10 deletions

diff --git a/src/dotty/tools/dotc/core/Denotations.scala b/src/dotty/tools/dotc/core/Denotations.scala
index fff447803..b223a8086 100644
--- a/src/dotty/tools/dotc/core/Denotations.scala
+++ b/src/dotty/tools/dotc/core/Denotations.scala
@@ -339,8 +339,8 @@ object Denotations {
           val info1 = denot1.info
           val info2 = denot2.info
           val sameSym = sym1 eq sym2
-          if (sameSym && info1 <:< info2) denot2
-          else if (sameSym && info2 <:< info1) denot1
+          if (sameSym && (info1 frozen_<:< info2)) denot2
+          else if (sameSym && (info2 frozen_<:< info1)) denot1
           else {
             val jointSym =
               if (sameSym) sym1
diff --git a/src/dotty/tools/dotc/core/TypeApplications.scala b/src/dotty/tools/dotc/core/TypeApplications.scala
index 927c4fcc5..47935f79e 100644
--- a/src/dotty/tools/dotc/core/TypeApplications.scala
+++ b/src/dotty/tools/dotc/core/TypeApplications.scala
@@ -497,7 +497,7 @@ class TypeApplications(val self: Type) extends AnyVal {
       val boundss = new mutable.ListBuffer[TypeBounds]
       for (sym <- boundSyms) {
         val bounds = sym.info.bounds
-        if (!(TypeBounds.empty <:< bounds)) {
+        if (!(TypeBounds.empty frozen_<:< bounds)) {
           boundNames += sym.name
           boundss += bounds
         }
@@ -574,7 +574,7 @@ class TypeApplications(val self: Type) extends AnyVal {
                 // we have a binding T = Lambda$XYZ{...}.this.hk$i where hk$i names the current `tparam`.
                 val pcore = etaCore(tp.parent, otherParams)
                 val hkBounds = self.member(rname).info.bounds
-                if (TypeBounds.empty <:< hkBounds) pcore
+                if (TypeBounds.empty frozen_<:< hkBounds) pcore
                 else tp.derivedRefinedType(pcore, tp.refinedName, hkBounds)
               case _ =>
                 val pcore = etaCore(tp.parent, tparams)
diff --git a/src/dotty/tools/dotc/core/Types.scala b/src/dotty/tools/dotc/core/Types.scala
index bce57ae23..8ad694ea2 100644
--- a/src/dotty/tools/dotc/core/Types.scala
+++ b/src/dotty/tools/dotc/core/Types.scala
@@ -595,6 +595,11 @@ object Types {
       ctx.typeComparer.topLevelSubType(this, that)
     }
 
+    /** Is this type a subtype of that type? */
+    final def frozen_<:<(that: Type)(implicit ctx: Context): Boolean = track("frozen_<:<") {
+      ctx.typeComparer.isSubTypeWhenFrozen(this, that)
+    }
+
     /** Is this type the same as that type?
      *  This is the case iff `this <:< that` and `that <:< this`.
      */
@@ -625,9 +630,9 @@ object Types {
         case ExprType(_) | MethodType(Nil, _) => tp.resultType
         case _ => tp
       }
-      this <:< that || {
+      (this frozen_<:< that) || {
         val rthat = result(that)
-        (rthat ne that) && result(this) <:< rthat
+        (rthat ne that) && (result(this) frozen_<:< rthat)
       }
     }
 
@@ -2652,13 +2657,13 @@ object Types {
     }
 
     def & (that: TypeBounds)(implicit ctx: Context): TypeBounds =
-      if (this.lo <:< that.lo && that.hi <:< this.hi) that
-      else if (that.lo <:< this.lo && this.hi <:< that.hi) this
+      if ((this.lo frozen_<:< that.lo) && (that.hi frozen_<:< this.hi)) that
+      else if ((that.lo frozen_<:< this.lo) && (this.hi frozen_<:< that.hi)) this
       else TypeBounds(this.lo | that.lo, this.hi & that.hi)
 
     def | (that: TypeBounds)(implicit ctx: Context): TypeBounds =
-      if (this.lo <:< that.lo && that.hi <:< this.hi) this
-      else if (that.lo <:< this.lo && this.hi <:< that.hi) that
+      if ((this.lo frozen_<:< that.lo) && (that.hi frozen_<:< this.hi)) this
+      else if ((that.lo frozen_<:< this.lo) && (this.hi frozen_<:< that.hi)) that
       else TypeBounds(this.lo & that.lo, this.hi | that.hi)
 
     override def & (that: Type)(implicit ctx: Context) = that match {