SI-8008 Make q”f(..$xs)” only match trees with Apply node

Previously it also matched other nodes but returned Nil as value of xs.
This behavior was added for sake of consistentcy with q”f[..$ts]”. On
the other hand q”f[..$Nil]” == q”f” but q”f(..$Nil)” == q”f()” not q”f”.
Due to this deconstruction/construction symmetry was broken.

On the other hand applications also have q"f(...$xss)" option which is
infact similar to q"f[..$ts]". Splicing Nil into it also results in q"f".

Author: densh

src/compiler/scala/tools/reflect/quasiquotes/Reifiers.scala

@@ -161,9 +161,6 @@ trait Reifiers { self: Quasiquotes =>
         reifyBuildCall(nme.SyntacticForYield, enums, body)
       case SyntacticAssign(lhs, rhs) =>
         reifyBuildCall(nme.SyntacticAssign, lhs, rhs)
-      case SyntacticApplied(fun, List(args))
-        if args.forall { case Placeholder(_, _, DotDotDot) => false case _ => true } =>
-        reifyBuildCall(nme.SyntacticApply, fun, args)
       case SyntacticApplied(fun, argss) if argss.nonEmpty =>
         reifyBuildCall(nme.SyntacticApplied, fun, argss)
       case SyntacticTypeApplied(fun, targs) if targs.nonEmpty =>

src/reflect/scala/reflect/api/BuildUtils.scala

@@ -122,13 +122,6 @@ private[reflect] trait BuildUtils { self: Universe =>
       def unapply(tree: Tree): Some[(Tree, List[List[Tree]])]
     }
 
-    val SyntacticApply: SyntacticApplyExtractor
-
-    trait SyntacticApplyExtractor {
-      def apply(tree: Tree, args: List[Tree]): Tree
-      def unapply(tree: Tree): Some[(Tree, List[Tree])]
-    }
-
     val SyntacticClassDef: SyntacticClassDefExtractor
 
     trait SyntacticClassDefExtractor {

src/reflect/scala/reflect/internal/BuildUtils.scala

@@ -165,15 +165,6 @@ trait BuildUtils { self: SymbolTable =>
       }
     }
 
-    object SyntacticApply extends SyntacticApplyExtractor {
-      def apply(tree: Tree, args: List[Tree]): Tree = SyntacticApplied(tree, List(args))
-
-      def unapply(tree: Tree): Some[(Tree, List[Tree])] = tree match {
-        case Apply(fun, args) => Some((fun, args))
-        case other => Some((other, Nil))
-      }
-    }
-
     // recover constructor contents generated by gen.mkTemplate
     protected object UnCtor {
       def unapply(tree: Tree): Option[(Modifiers, List[List[ValDef]], List[Tree])] = tree match {

src/reflect/scala/reflect/internal/StdNames.scala

@@ -588,7 +588,6 @@ trait StdNames {
     val Select: NameType               = "Select"
     val SelectFromTypeTree: NameType   = "SelectFromTypeTree"
     val SyntacticApplied: NameType     = "SyntacticApplied"
-    val SyntacticApply: NameType       = "SyntacticApply"
     val SyntacticAssign: NameType      = "SyntacticAssign"
     val SyntacticBlock: NameType       = "SyntacticBlock"
     val SyntacticClassDef: NameType    = "SyntacticClassDef"

test/files/scalacheck/quasiquotes/TermDeconstructionProps.scala

@@ -3,8 +3,10 @@ import scala.reflect.runtime.universe._, Flag._
 
 object TermDeconstructionProps extends QuasiquoteProperties("term deconstruction") {
   property("f(..x) = f") = test {
-    val q"f(..$args)" = q"f"
-    assert(args ≈ Nil)
+    // see SI-8008
+    assertThrows[MatchError] {
+      val q"f(..$args)" = q"f"
+    }
   }
 
   property("f(x)") = forAll { (x: Tree) =>