Drop incorrect optimization in substituters

The optimization was to disregard a prefix of a named type if its symbol is static
and none of the mapped symbols in `from` is static. This is incorrect, since the
prefix might be a non-static reference to a static object. In that case the prefix
still has to be considered. i2895a.scala contains code that failed when running
with the cbn implementation of `assert` in the next commit.

Author: odersky

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

@@ -12,7 +12,7 @@ trait Substituters { this: Context =>
       case tp: BoundType =>
         if (tp.binder eq from) tp.copyBoundType(to.asInstanceOf[tp.BT]) else tp
       case tp: NamedType =>
-        if (tp.currentSymbol.isStatic || (tp.prefix `eq` NoPrefix)) tp
+        if (tp.prefix `eq` NoPrefix) tp
         else tp.derivedSelect(subst(tp.prefix, from, to, theMap))
       case _: ThisType =>
         tp
@@ -26,7 +26,7 @@ trait Substituters { this: Context =>
       case tp: NamedType =>
         val sym = tp.symbol
         if (sym eq from) return to
-        if (sym.isStatic && !from.isStatic || (tp.prefix `eq` NoPrefix)) tp
+        if (tp.prefix `eq` NoPrefix) tp
         else tp.derivedSelect(subst1(tp.prefix, from, to, theMap))
       case _: ThisType | _: BoundType =>
         tp
@@ -42,7 +42,7 @@ trait Substituters { this: Context =>
         val sym = tp.symbol
         if (sym eq from1) return to1
         if (sym eq from2) return to2
-        if (sym.isStatic && !from1.isStatic && !from2.isStatic || (tp.prefix `eq` NoPrefix)) tp
+        if (tp.prefix `eq` NoPrefix) tp
         else tp.derivedSelect(subst2(tp.prefix, from1, to1, from2, to2, theMap))
       case _: ThisType | _: BoundType =>
         tp
@@ -63,7 +63,7 @@ trait Substituters { this: Context =>
           fs = fs.tail
           ts = ts.tail
         }
-        if (sym.isStatic && !existsStatic(from) || (tp.prefix `eq` NoPrefix)) tp
+        if (tp.prefix `eq` NoPrefix) tp
         else tp.derivedSelect(subst(tp.prefix, from, to, theMap))
       case _: ThisType | _: BoundType =>
         tp
@@ -85,7 +85,7 @@ trait Substituters { this: Context =>
           fs = fs.tail
           ts = ts.tail
         }
-        if (sym.isStatic && !existsStatic(from) || (tp.prefix `eq` NoPrefix)) tp
+        if (tp.prefix `eq` NoPrefix) tp
         else tp.derivedSelect(substSym(tp.prefix, from, to, theMap))
       case tp: ThisType =>
         val sym = tp.cls
@@ -123,7 +123,7 @@ trait Substituters { this: Context =>
       case tp @ RecThis(binder) =>
         if (binder eq from) to else tp
       case tp: NamedType =>
-        if (tp.currentSymbol.isStatic || (tp.prefix `eq` NoPrefix)) tp
+        if (tp.prefix `eq` NoPrefix) tp
         else tp.derivedSelect(substRecThis(tp.prefix, from, to, theMap))
       case _: ThisType | _: BoundType =>
         tp
@@ -137,7 +137,7 @@ trait Substituters { this: Context =>
       case tp: BoundType =>
         if (tp == from) to else tp
       case tp: NamedType =>
-        if (tp.currentSymbol.isStatic || (tp.prefix `eq` NoPrefix)) tp
+        if (tp.prefix `eq` NoPrefix) tp
         else tp.derivedSelect(substParam(tp.prefix, from, to, theMap))
       case _: ThisType =>
         tp
@@ -151,7 +151,7 @@ trait Substituters { this: Context =>
       case tp: ParamRef =>
         if (tp.binder == from) to(tp.paramNum) else tp
       case tp: NamedType =>
-        if (tp.currentSymbol.isStatic || (tp.prefix `eq` NoPrefix)) tp
+        if (tp.prefix `eq` NoPrefix) tp
         else tp.derivedSelect(substParams(tp.prefix, from, to, theMap))
       case _: ThisType =>
         tp
@@ -160,11 +160,6 @@ trait Substituters { this: Context =>
           .mapOver(tp)
     }
 
-  private def existsStatic(syms: List[Symbol]): Boolean = syms match {
-    case sym :: syms1 => sym.isStatic || existsStatic(syms1)
-    case nil => false
-  }
-
   final class SubstBindingMap(from: BindingType, to: BindingType) extends DeepTypeMap {
     def apply(tp: Type) = subst(tp, from, to, this)
   }

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

@@ -643,7 +643,7 @@ object Symbols {
      *  the implicit conversion `sourcePos` will return the wrong result, careful!
      *  TODO: Consider changing this method return type to `SourcePosition`.
      */
-    def pos: Position = if (coord.isPosition) coord.toPosition else NoPosition
+    final def pos: Position = if (coord.isPosition) coord.toPosition else NoPosition
 
     // ParamInfo types and methods
     def isTypeParam(implicit ctx: Context) = denot.is(TypeParam)