Improve support for patterns in vals

This commits adds construction-only support for splicing patterns into
vals (a.k.a. PatDef). Due to non-locality of the desugaring it would
have been quite expensive to support deconstruction as the only way to
do it with current trees is to perform implodePatDefs transformation on
every single tree.

2 files changed, 20 insertions, 12 deletions

diff --git a/src/compiler/scala/tools/reflect/quasiquotes/Parsers.scala b/src/compiler/scala/tools/reflect/quasiquotes/Parsers.scala
index 2410af49e5..36452c2a6d 100644
--- a/src/compiler/scala/tools/reflect/quasiquotes/Parsers.scala
+++ b/src/compiler/scala/tools/reflect/quasiquotes/Parsers.scala
@@ -14,6 +14,7 @@ import scala.util.Try
  */
 trait Parsers { self: Quasiquotes =>
   import global.{Try => _, _}
+  import build.implodePatDefs
 
   abstract class Parser extends {
     val global: self.global.type = self.global
@@ -182,7 +183,7 @@ trait Parsers { self: Quasiquotes =>
   }
 
   object TermParser extends Parser {
-    def entryPoint = parser => Q(gen.mkTreeOrBlock(parser.templateOrTopStatSeq()))
+    def entryPoint = parser => Q(implodePatDefs(gen.mkTreeOrBlock(parser.templateOrTopStatSeq())))
   }
 
   object TypeParser extends Parser {
@@ -195,7 +196,7 @@ trait Parsers { self: Quasiquotes =>
   }
 
   object CaseParser extends Parser {
-    def entryPoint = _.caseClause()
+    def entryPoint = parser => implodePatDefs(parser.caseClause())
   }
 
   object PatternParser extends Parser {
@@ -209,7 +210,7 @@ trait Parsers { self: Quasiquotes =>
     def entryPoint = { parser =>
       val enums = parser.enumerator(isFirst = false, allowNestedIf = false)
       assert(enums.length == 1)
-      enums.head
+      implodePatDefs(enums.head)
     }
   }
 
diff --git a/src/compiler/scala/tools/reflect/quasiquotes/Reifiers.scala b/src/compiler/scala/tools/reflect/quasiquotes/Reifiers.scala
index 017e966f63..70580adbce 100644
--- a/src/compiler/scala/tools/reflect/quasiquotes/Reifiers.scala
+++ b/src/compiler/scala/tools/reflect/quasiquotes/Reifiers.scala
@@ -194,8 +194,8 @@ trait Reifiers { self: Quasiquotes =>
         reifyBuildCall(nme.SyntacticEmptyTypeTree)
       case SyntacticImport(expr, selectors) =>
         reifyBuildCall(nme.SyntacticImport, expr, selectors)
-      case Q(Placeholder(Hole(tree, DotDot))) =>
-        mirrorBuildCall(nme.SyntacticBlock, tree)
+      case Q(tree) if fillListHole.isDefinedAt(tree) =>
+        mirrorBuildCall(nme.SyntacticBlock, fillListHole(tree))
       case Q(other) =>
         reifyTree(other)
       // Syntactic block always matches so we have to be careful
@@ -311,11 +311,7 @@ trait Reifiers { self: Quasiquotes =>
      */
     def reifyMultiCardinalityList(xs: List[Any])(fill: PartialFunction[Any, Tree])(fallback: Any => Tree): Tree
 
-    /** Reifies arbitrary list filling ..$x and ...$y holeMap when they are put
-     *  in the correct position. Fallbacks to regular reification for non-high cardinality
-     *  elements.
-     */
-    override def reifyList(xs: List[Any]): Tree = reifyMultiCardinalityList(xs) {
+    val fillListHole: PartialFunction[Any, Tree] = {
       case Placeholder(Hole(tree, DotDot)) => tree
       case CasePlaceholder(Hole(tree, DotDot)) => tree
       case RefineStatPlaceholder(h @ Hole(_, DotDot)) => reifyRefineStat(h)
@@ -323,12 +319,23 @@ trait Reifiers { self: Quasiquotes =>
       case PackageStatPlaceholder(h @ Hole(_, DotDot)) => reifyPackageStat(h)
       case ForEnumPlaceholder(Hole(tree, DotDot)) => tree
       case ParamPlaceholder(Hole(tree, DotDot)) => tree
+      case SyntacticPatDef(mods, pat, tpt, rhs) =>
+        reifyBuildCall(nme.SyntacticPatDef, mods, pat, tpt, rhs)
+      case SyntacticValDef(mods, p @ Placeholder(h: ApplyHole), tpt, rhs) if h.tpe <:< treeType =>
+        mirrorBuildCall(nme.SyntacticPatDef, reify(mods), h.tree, reify(tpt), reify(rhs))
+    }
+
+    val fillListOfListsHole: PartialFunction[Any, Tree] = {
       case List(ParamPlaceholder(Hole(tree, DotDotDot))) => tree
       case List(Placeholder(Hole(tree, DotDotDot))) => tree
-    } {
-      reify(_)
     }
 
+    /** Reifies arbitrary list filling ..$x and ...$y holeMap when they are put
+     *  in the correct position. Fallbacks to regular reification for non-high cardinality
+     *  elements.
+     */
+    override def reifyList(xs: List[Any]): Tree = reifyMultiCardinalityList(xs)(fillListHole.orElse(fillListOfListsHole))(reify)
+
     def reifyAnnotList(annots: List[Tree]): Tree = reifyMultiCardinalityList(annots) {
       case AnnotPlaceholder(h @ Hole(_, DotDot)) => reifyAnnotation(h)
     } {