Create implicit closures to math expected implicit functions

When the expected type is an implicit function, create an
implicit closure to match it.

3 files changed, 29 insertions, 12 deletions

diff --git a/compiler/src/dotty/tools/dotc/ast/Desugar.scala b/compiler/src/dotty/tools/dotc/ast/Desugar.scala
index 11f8b81eb..def2caabf 100644
--- a/compiler/src/dotty/tools/dotc/ast/Desugar.scala
+++ b/compiler/src/dotty/tools/dotc/ast/Desugar.scala
@@ -123,6 +123,13 @@ object desugar {
     else vdef
   }
 
+  def makeImplicitParameters(tpts: List[Tree], forPrimaryConstructor: Boolean)(implicit ctx: Context) =
+    for (tpt <- tpts) yield {
+       val paramFlags: FlagSet = if (forPrimaryConstructor) PrivateLocalParamAccessor else Param
+       val epname = ctx.freshName(nme.EVIDENCE_PARAM_PREFIX).toTermName
+       ValDef(epname, tpt, EmptyTree).withFlags(paramFlags | Implicit)
+    }
+
   /** Expand context bounds to evidence params. E.g.,
    *
    *      def f[T >: L <: H : B](params)
@@ -143,19 +150,16 @@ object desugar {
     val epbuf = new ListBuffer[ValDef]
     def desugarContextBounds(rhs: Tree): Tree = rhs match {
       case ContextBounds(tbounds, cxbounds) =>
-        for (cxbound <- cxbounds) {
-          val paramFlags: FlagSet = if (isPrimaryConstructor) PrivateLocalParamAccessor else Param
-          val epname = ctx.freshName(nme.EVIDENCE_PARAM_PREFIX).toTermName
-          epbuf += ValDef(epname, cxbound, EmptyTree).withFlags(paramFlags | Implicit)
-        }
+        for (cxbound <- cxbounds)
+          epbuf ++= makeImplicitParameters(cxbounds, isPrimaryConstructor)
         tbounds
       case PolyTypeTree(tparams, body) =>
         cpy.PolyTypeTree(rhs)(tparams, desugarContextBounds(body))
       case _ =>
         rhs
     }
-    val tparams1 = tparams mapConserve { tdef =>
-      cpy.TypeDef(tdef)(rhs = desugarContextBounds(tdef.rhs))
+    val tparams1 = tparams mapConserve { tparam =>
+      cpy.TypeDef(tparam)(rhs = desugarContextBounds(tparam))
     }
 
     val meth1 = addEvidenceParams(cpy.DefDef(meth)(tparams = tparams1), epbuf.toList)
@@ -679,6 +683,11 @@ object desugar {
     Function(param :: Nil, Block(vdefs, body))
   }
 
+  def makeImplicitFunction(formals: List[Type], body: Tree)(implicit ctx: Context): Tree = {
+    val params = makeImplicitParameters(formals.map(TypeTree), forPrimaryConstructor = false)
+    new ImplicitFunction(params, body)
+  }
+
   /** Add annotation with class `cls` to tree:
    *      tree @cls
    */
diff --git a/compiler/src/dotty/tools/dotc/ast/TreeInfo.scala b/compiler/src/dotty/tools/dotc/ast/TreeInfo.scala
index ae7c93784..da83d0644 100644
--- a/compiler/src/dotty/tools/dotc/ast/TreeInfo.scala
+++ b/compiler/src/dotty/tools/dotc/ast/TreeInfo.scala
@@ -290,6 +290,16 @@ trait UntypedTreeInfo extends TreeInfo[Untyped] { self: Trees.Instance[Untyped]
     case _ => false
   }
 
+  /** Is `tree` an implicit function or closure, possibly nested in a block? */
+  def isImplicitClosure(tree: Tree)(implicit ctx: Context): Boolean = unsplice(tree) match {
+    case Function((param: untpd.ValDef) :: _, _) => param.mods.is(Implicit)
+    case Closure(_, meth, _) => true
+    case Block(Nil, expr) => isImplicitClosure(expr)
+    case Block(DefDef(nme.ANON_FUN, _, (param :: _) :: _, _, _) :: Nil, _: Closure) =>
+      param.mods.is(Implicit)
+    case _ => false
+  }
+
   // todo: fill with other methods from TreeInfo that only apply to untpd.Tree's
 }
 
@@ -507,8 +517,6 @@ trait TypedTreeInfo extends TreeInfo[Type] { self: Trees.Instance[Type] =>
     }
   }
 
-  def isClosure(tree: Tree) = closure.unapply(tree).isDefined
-
   /** If tree is a closure, its body, otherwise tree itself */
   def closureBody(tree: Tree)(implicit ctx: Context): Tree = tree match {
     case Block((meth @ DefDef(nme.ANON_FUN, _, _, _, _)) :: Nil, Closure(_, _, _)) => meth.rhs
diff --git a/compiler/src/dotty/tools/dotc/ast/untpd.scala b/compiler/src/dotty/tools/dotc/ast/untpd.scala
index 9707770d5..77755da81 100644
--- a/compiler/src/dotty/tools/dotc/ast/untpd.scala
+++ b/compiler/src/dotty/tools/dotc/ast/untpd.scala
@@ -55,7 +55,9 @@ object untpd extends Trees.Instance[Untyped] with UntypedTreeInfo {
   }
 
   /** An implicit function type */
-  class ImplicitFunction(args: List[Tree], body: Tree) extends Function(args, body)
+  class ImplicitFunction(args: List[Tree], body: Tree) extends Function(args, body) {
+    override def toString = s"ImplicitFunction($args, $body"
+  }
 
   /** A function created from a wildcard expression
    *  @param  placeHolderParams  a list of definitions of synthetic parameters
@@ -274,8 +276,6 @@ object untpd extends Trees.Instance[Untyped] with UntypedTreeInfo {
 
   // ------ Additional creation methods for untyped only -----------------
 
-  // def TypeTree(tpe: Type): TypeTree = TypeTree().withType(tpe) todo: move to untpd/tpd
-
   /**     new pre.C[Ts](args1)...(args_n)
    *  ==>
    *      (new pre.C).<init>[Ts](args1)...(args_n)