Handle splices in quoted patterns

Author: odersky

compiler/src/dotty/tools/dotc/ast/tpd.scala

@@ -1180,8 +1180,10 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
 
   /** An extractor for typed splices */
   object Splice {
-    def apply(tree: Tree)(implicit ctx: Context): Tree =
-      ref(defn.InternalQuoted_exprSplice).appliedTo(tree)
+    def apply(tree: Tree)(implicit ctx: Context): Tree = {
+      val argType = tree.tpe.baseType(defn.QuotedExprClass).argTypesHi.head
+      ref(defn.InternalQuoted_exprSplice).appliedToType(argType).appliedTo(tree)
+    }
     def unapply(tree: Tree)(implicit ctx: Context): Option[Tree] = tree match {
       case Apply(fn, arg :: Nil) if fn.symbol == defn.InternalQuoted_exprSplice => Some(arg)
       case _ => None

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -1963,7 +1963,7 @@ class Typer extends Namer
           val exprTpt = ref(defn.QuotedExprType).appliedToTypeTrees(tpt :: Nil)
           transform(Splice(Typed(pat, exprTpt)))
         case Splice(pat) =>
-          try tasty.TreePickler.Hole(patBuf.length, Nil)
+          try holeForSplice(tree)
           finally patBuf += pat
         case _ =>
           super.transform(tree)
@@ -1973,6 +1973,13 @@ class Typer extends Namer
     (result, splitter.patBuf.toList)
   }
 
+  // TODO: Currently, a hole is expressed as interal.quoted.ExprSplice[T](???)
+  // Settle on a different representation and apply Stagin
+  def holeForSplice(splice: Tree)(implicit ctx: Context): Tree = {
+    val Apply(fn, arg) = splice
+    tpd.cpy.Apply(splice)(fn, ref(defn.Predef_undefined) :: Nil)
+  }
+
   def givenReflection(implicit ctx: Context): Tree = Literal(Constant(null)) // FIXME: fill in
 
   /** Translate `${ t: Expr[T] }` into expression `t.splice` while tracking the quotation level in the context */

tests/pos/quotedPatterns.scala

@@ -2,8 +2,10 @@ object Test {
 
   val x = '{1 + 2}
 
+  def f(x: Int) = x
+
   x match {
-    case '{1 + 2} =>
-    case _ =>
+    case '{1 + 2} => 0
+    case '{f($x)} => x
   }
 }