Hygienic desugaring

Made desugaring hygienic. Trees that are derived from some other tree are no longer stored as simple
untyped Ident trees, but as TypeTrees that know how to derive their types from some other type.

Test cases in pos: hygiene.scala, t0054.scala and t0085.scala.

The comment in hygiene.scala points to the difficulties we are facing. In particular, we need type
trees that can rebind some references of a source type to local occurrences with the same name. t0054.scala is similar to hygiene.scala. t0085.scala is trickier, but also related. Essentially the problem there is that we have a class
that inherits its outer class. In this case it is important to resolve an identifier in the right context. The identifier added to the copy method of a case class must be resolved outside the class (just like the same
identifier in the constructor of that case class).

1 files changed, 21 insertions, 13 deletions

diff --git a/src/dotty/tools/dotc/typer/Namer.scala b/src/dotty/tools/dotc/typer/Namer.scala
index 162e13bbc..7885e85ac 100644
--- a/src/dotty/tools/dotc/typer/Namer.scala
+++ b/src/dotty/tools/dotc/typer/Namer.scala
@@ -72,6 +72,13 @@ trait NamerContextOps { this: Context =>
     }
     go(this)
   }
+
+  /** Context where `sym` is defined, assuming we are in a nested context. */
+  def defContext(sym: Symbol) =
+    outersIterator
+      .dropWhile(_.owner != sym)
+      .dropWhile(_.owner == sym)
+      .next
 }
 
 /** This class creates symbols from definitions and imports and gives them
@@ -173,10 +180,10 @@ class Namer { typer: Typer =>
       enclosingClassNamed(mods.privateWithin, mods.pos)
 
     def record(sym: Symbol): Symbol = {
-      val refs = tree.attachmentOrElse(desugar.References, Nil)
+      val refs = tree.attachmentOrElse(References, Nil)
       if (refs.nonEmpty) {
-        tree.removeAttachment(desugar.References)
-        refs foreach (_.pushAttachment(desugar.OriginalSymbol, sym))
+        tree.removeAttachment(References)
+        refs foreach (_.pushAttachment(OriginalSymbol, sym))
       }
       tree.pushAttachment(SymOfTree, sym)
       sym
@@ -449,17 +456,25 @@ class Namer { typer: Typer =>
         if (self.isEmpty) NoType
         else if (cls is Module) cls.owner.thisType select sourceModule
         else createSymbol(self)
+
       // pre-set info, so that parent types can refer to type params
       denot.info = ClassInfo(cls.owner.thisType, cls, Nil, decls, selfInfo)
+
+      // Ensure constructor is completed so that any parameter accessors
+      // which have type trees deriving from its parameters can be
+      // completed in turn. Note that parent types access such parameter
+      // accessors, that's why the constructor needs to be completed before
+      // the parent types are elaborated.
+      index(constr)
+      symbolOfTree(constr).ensureCompleted()
+
       val parentTypes = ensureFirstIsClass(parents map checkedParentType)
       val parentRefs = ctx.normalizeToClassRefs(parentTypes, cls, decls)
       typr.println(s"completing $denot, parents = $parents, parentTypes = $parentTypes, parentRefs = $parentRefs")
 
-      index(constr)
       index(rest)(inClassContext(selfInfo))
       denot.info = ClassInfo(cls.owner.thisType, cls, parentRefs, decls, selfInfo)
       // make sure constr parameters are all entered because we refer to them in desugarings:
-      symbolOfTree(constr).ensureCompleted()
     }
   }
 
@@ -509,13 +524,6 @@ class Namer { typer: Typer =>
       if (!mdef.tpt.isEmpty) WildcardType
       else {
 
-        /** Context where `sym` is defined */
-        def defContext(sym: Symbol) =
-          ctx.outersIterator
-            .dropWhile(_.owner != sym)
-            .dropWhile(_.owner == sym)
-            .next
-
         /** An type for this definition that might be inherited from elsewhere:
          *  If this is a setter parameter, the corresponding getter type.
          *  If this is a class member, the conjunction of all result types
@@ -561,7 +569,7 @@ class Namer { typer: Typer =>
               if (original.isConstructorName && (sym.owner is ModuleClass))
                 sym.owner.companionClass.info.decl(nme.CONSTRUCTOR)
               else
-                defContext(sym).denotNamed(original)
+                ctx.defContext(sym).denotNamed(original)
             def paramProto(paramss: List[List[Type]], idx: Int): Type = paramss match {
               case params :: paramss1 =>
                 if (idx < params.length) wildApprox(params(idx))