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.

8 files changed, 145 insertions, 53 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)
     } {
diff --git a/src/reflect/scala/reflect/api/BuildUtils.scala b/src/reflect/scala/reflect/api/BuildUtils.scala
index ec20a89a10..57dc7da6cc 100644
--- a/src/reflect/scala/reflect/api/BuildUtils.scala
+++ b/src/reflect/scala/reflect/api/BuildUtils.scala
@@ -220,6 +220,12 @@ private[reflect] trait BuildUtils { self: Universe =>
       def unapply(tree: Tree): Option[(Modifiers, TermName, Tree, Tree)]
     }
 
+    val SyntacticPatDef: SyntacticPatDefExtractor
+
+    trait SyntacticPatDefExtractor {
+      def apply(mods: Modifiers, pat: Tree, tpt: Tree, rhs: Tree): List[ValDef]
+    }
+
     val SyntacticAssign: SyntacticAssignExtractor
 
     trait SyntacticAssignExtractor {
diff --git a/src/reflect/scala/reflect/internal/BuildUtils.scala b/src/reflect/scala/reflect/internal/BuildUtils.scala
index c5581601de..6f1e4d2e32 100644
--- a/src/reflect/scala/reflect/internal/BuildUtils.scala
+++ b/src/reflect/scala/reflect/internal/BuildUtils.scala
@@ -193,9 +193,9 @@ trait BuildUtils { self: SymbolTable =>
     // recover constructor contents generated by gen.mkTemplate
     protected object UnCtor {
       def unapply(tree: Tree): Option[(Modifiers, List[List[ValDef]], List[Tree])] = tree match {
-        case DefDef(mods, nme.MIXIN_CONSTRUCTOR, _, _, _, Block(lvdefs, _)) =>
+        case DefDef(mods, nme.MIXIN_CONSTRUCTOR, _, _, _, SyntacticBlock(lvdefs :+ _)) =>
           Some((mods | Flag.TRAIT, Nil, lvdefs))
-        case DefDef(mods, nme.CONSTRUCTOR, Nil, vparamss, _, Block(lvdefs :+ _, _)) =>
+        case DefDef(mods, nme.CONSTRUCTOR, Nil, vparamss, _, SyntacticBlock(lvdefs :+ _ :+ _)) =>
           Some((mods, vparamss, lvdefs))
         case _ => None
       }
@@ -474,10 +474,9 @@ trait BuildUtils { self: SymbolTable =>
     }
 
     protected class SyntacticValDefBase(isMutable: Boolean) extends SyntacticValDefExtractor {
-      def apply(mods: Modifiers, name: TermName, tpt: Tree, rhs: Tree) = {
-        val mods1 = if (isMutable) mods | MUTABLE else mods
-        ValDef(mods1, name, tpt, rhs)
-      }
+      def modifiers(mods: Modifiers): Modifiers = if (isMutable) mods | MUTABLE else mods
+
+      def apply(mods: Modifiers, name: TermName, tpt: Tree, rhs: Tree): ValDef = ValDef(modifiers(mods), name, tpt, rhs)
 
       def unapply(tree: Tree): Option[(Modifiers, TermName, Tree, Tree)] = tree match {
         case ValDef(mods, name, tpt, rhs) if mods.hasFlag(MUTABLE) == isMutable =>
@@ -547,25 +546,57 @@ trait BuildUtils { self: SymbolTable =>
 
     // match a sequence of desugared `val $pat = $value`
     protected object UnPatSeq {
-      def unapply(trees: List[Tree]): Option[List[(Tree, Tree)]] = trees match {
-        case Nil => Some(Nil)
-        // case q"$mods val ${_}: ${_} = ${MaybeUnchecked(value)} match { case $pat => (..$ids) }" :: tail
-        case ValDef(mods, _, _, Match(MaybeUnchecked(value), CaseDef(pat, EmptyTree, SyntacticTuple(ids)) :: Nil)) :: tail
+      def unapply(trees: List[Tree]): Option[List[(Tree, Tree)]] = {
+        val imploded = implodePatDefs(trees)
+        val patvalues = imploded.flatMap {
+          case SyntacticPatDef(_, pat, EmptyTree, rhs) => Some((pat, rhs))
+          case ValDef(_, name, SyntacticEmptyTypeTree(), rhs) => Some((Bind(name, self.Ident(nme.WILDCARD)), rhs))
+          case ValDef(_, name, tpt, rhs) => Some((Bind(name, Typed(self.Ident(nme.WILDCARD), tpt)), rhs))
+          case _ => None
+        }
+        if (patvalues.length == imploded.length) Some(patvalues) else None
+      }
+    }
+
+    // implode multiple-statement desugaring of pattern definitions
+    // into single-statement valdefs with nme.QUASIQUOTE_PAT_DEF name
+    object implodePatDefs extends Transformer {
+      override def transform(tree: Tree) = tree match {
+        case templ: Template => deriveTemplate(templ)(transformStats)
+        case block: Block =>
+          val Block(init, last) = block
+          Block(transformStats(init), transform(last)).copyAttrs(block)
+        case ValDef(mods, name1, SyntacticEmptyTypeTree(), Match(MaybeTyped(MaybeUnchecked(value), tpt), CaseDef(pat, EmptyTree, Ident(name2)) :: Nil))
+          if name1 == name2 =>
+          ValDef(mods, nme.QUASIQUOTE_PAT_DEF, Typed(pat, tpt), transform(value))
+        case _ =>
+          super.transform(tree)
+      }
+      def transformStats(trees: List[Tree]): List[Tree] = trees match {
+        case Nil => Nil
+        case ValDef(mods, _, SyntacticEmptyTypeTree(), Match(MaybeTyped(MaybeUnchecked(value), tpt), CaseDef(pat, EmptyTree, SyntacticTuple(ids)) :: Nil)) :: tail
           if mods.hasFlag(SYNTHETIC) && mods.hasFlag(ARTIFACT) =>
-          tail.drop(ids.length) match {
-            case UnPatSeq(rest) => Some((pat, value) :: rest)
-            case _ => None
+          ids match {
+            case Nil =>
+              ValDef(NoMods, nme.QUASIQUOTE_PAT_DEF, Typed(pat, tpt), transform(value)) :: transformStats(tail)
+            case _   =>
+              val mods = tail.take(1).head.asInstanceOf[ValDef].mods
+              ValDef(mods, nme.QUASIQUOTE_PAT_DEF, Typed(pat, tpt), transform(value)) :: transformStats(tail.drop(ids.length))
           }
-        // case q"${_} val $name1: ${_} = ${MaybeUnchecked(value)} match { case $pat => ${Ident(name2)} }" :: UnPatSeq(rest)
-        case ValDef(_, name1, _, Match(MaybeUnchecked(value), CaseDef(pat, EmptyTree, Ident(name2)) :: Nil)) :: UnPatSeq(rest)
-          if name1 == name2 =>
-          Some((pat, value) :: rest)
-        // case q"${_} val $name: ${SyntacticEmptyTypeTree()} = $value" :: UnPatSeq(rest) =>
-        case ValDef(_, name, SyntacticEmptyTypeTree(), value) :: UnPatSeq(rest) =>
-          Some((Bind(name, self.Ident(nme.WILDCARD)), value) :: rest)
-        // case q"${_} val $name: $tpt = $value" :: UnPatSeq(rest) =>
-        case ValDef(_, name, tpt, value) :: UnPatSeq(rest) =>
-          Some((Bind(name, Typed(self.Ident(nme.WILDCARD), tpt)), value) :: rest)
+        case other :: tail =>
+          transform(other) :: transformStats(tail)
+      }
+      def apply(tree: Tree) = transform(tree)
+      def apply(trees: List[Tree]) = transformStats(trees)
+    }
+
+    object SyntacticPatDef extends SyntacticPatDefExtractor {
+      def apply(mods: Modifiers, pat: Tree, tpt: Tree, rhs: Tree): List[ValDef] = tpt match {
+        case SyntacticEmptyTypeTree() => gen.mkPatDef(mods, pat, rhs)
+        case _                        => gen.mkPatDef(mods, Typed(pat, tpt), rhs)
+      }
+      def unapply(tree: Tree): Option[(Modifiers, Tree, Tree, Tree)] = tree match {
+        case ValDef(mods, nme.QUASIQUOTE_PAT_DEF, Typed(pat,  tpt), rhs) => Some((mods, pat, tpt, rhs))
         case _ => None
       }
     }
@@ -746,6 +777,13 @@ trait BuildUtils { self: SymbolTable =>
       }
     }
 
+    protected object MaybeTyped {
+      def unapply(tree: Tree): Some[(Tree, Tree)] = tree match {
+        case Typed(v, tpt) => Some((v, tpt))
+        case v             => Some((v, SyntacticEmptyTypeTree()))
+      }
+    }
+
     protected def mkCases(cases: List[Tree]): List[CaseDef] = cases.map {
       case c: CaseDef => c
       case tree => throw new IllegalArgumentException("$tree is not valid representation of pattern match case")
diff --git a/src/reflect/scala/reflect/internal/StdNames.scala b/src/reflect/scala/reflect/internal/StdNames.scala
index 0ac067a399..de582ee5f9 100644
--- a/src/reflect/scala/reflect/internal/StdNames.scala
+++ b/src/reflect/scala/reflect/internal/StdNames.scala
@@ -334,6 +334,7 @@ trait StdNames {
     val QUASIQUOTE_NAME_PREFIX: String     = "nn$"
     val QUASIQUOTE_PACKAGE_STAT: NameType  = "$quasiquote$package$stat$"
     val QUASIQUOTE_PARAM: NameType         = "$quasiquote$param$"
+    val QUASIQUOTE_PAT_DEF: NameType       = "$quasiquote$pat$def$"
     val QUASIQUOTE_PREFIX: String          = "qq$"
     val QUASIQUOTE_REFINE_STAT: NameType   = "$quasiquote$refine$stat$"
     val QUASIQUOTE_TUPLE: NameType         = "$quasiquote$tuple$"
@@ -615,6 +616,7 @@ trait StdNames {
     val SyntacticNew: NameType         = "SyntacticNew"
     val SyntacticObjectDef: NameType   = "SyntacticObjectDef"
     val SyntacticPackageObjectDef: NameType = "SyntacticPackageObjectDef"
+    val SyntacticPatDef: NameType      = "SyntacticPatDef"
     val SyntacticTraitDef: NameType    = "SyntacticTraitDef"
     val SyntacticTry: NameType         = "SyntacticTry"
     val SyntacticTuple: NameType       = "SyntacticTuple"
diff --git a/src/reflect/scala/reflect/internal/TreeGen.scala b/src/reflect/scala/reflect/internal/TreeGen.scala
index 29fdba2781..e7675eb4bf 100644
--- a/src/reflect/scala/reflect/internal/TreeGen.scala
+++ b/src/reflect/scala/reflect/internal/TreeGen.scala
@@ -691,11 +691,11 @@ abstract class TreeGen extends macros.TreeBuilder {
   }
 
   /** Create tree for pattern definition <val pat0 = rhs> */
-  def mkPatDef(pat: Tree, rhs: Tree)(implicit fresh: FreshNameCreator): List[Tree] =
+  def mkPatDef(pat: Tree, rhs: Tree)(implicit fresh: FreshNameCreator): List[ValDef] =
     mkPatDef(Modifiers(0), pat, rhs)
 
   /** Create tree for pattern definition <mods val pat0 = rhs> */
-  def mkPatDef(mods: Modifiers, pat: Tree, rhs: Tree)(implicit fresh: FreshNameCreator): List[Tree] = matchVarPattern(pat) match {
+  def mkPatDef(mods: Modifiers, pat: Tree, rhs: Tree)(implicit fresh: FreshNameCreator): List[ValDef] = matchVarPattern(pat) match {
     case Some((name, tpt)) =>
       List(atPos(pat.pos union rhs.pos) {
         ValDef(mods, name.toTermName, tpt, rhs)
diff --git a/test/files/scalacheck/quasiquotes/DefinitionConstructionProps.scala b/test/files/scalacheck/quasiquotes/DefinitionConstructionProps.scala
index 39e4c48073..5f22925335 100644
--- a/test/files/scalacheck/quasiquotes/DefinitionConstructionProps.scala
+++ b/test/files/scalacheck/quasiquotes/DefinitionConstructionProps.scala
@@ -7,21 +7,22 @@ object DefinitionConstructionProps
     with TraitConstruction
     with TypeDefConstruction
     with ValDefConstruction
+    with PatDefConstruction
     with DefConstruction
-    with PackageConstruction
+    with PackageConstruction 
     with ImportConstruction {
-  property("SI-6842") = test {
-    val x: Tree = q"val x: Int"
-    assertEqAst(q"def f($x) = 0", "def f(x: Int) = 0")
-    assertEqAst(q"class C($x)", "class C(val x: Int)")
-    assertEqAst(q"class C { $x => }", "class C { x: Int => }")
-    assertEqAst(q"trait B { $x => }", "trait B { x: Int => }")
-    assertEqAst(q"object A { $x => }", "object A { x: Int => }")
-    val t: Tree = q"type T"
-    assertEqAst(q"def f[$t] = 0", "def f[T] = 0")
-    assertEqAst(q"class C[$t]", "class C[T]")
-    assertEqAst(q"trait B[$t]", "trait B[T]")
-  }
+
+  val x: Tree = q"val x: Int"
+  property("SI-6842 a1") = test { assertEqAst(q"def f($x) = 0", "def f(x: Int) = 0") }
+  property("SI-6842 a2") = test { assertEqAst(q"class C($x)", "class C(val x: Int)") }
+  property("SI-6842 a3") = test { assertEqAst(q"class C { $x => }", "class C { x: Int => }") }
+  property("SI-6842 a4") = test { assertEqAst(q"trait B { $x => }", "trait B { x: Int => }") }
+  property("SI-6842 a5") = test { assertEqAst(q"object A { $x => }", "object A { x: Int => }") }
+
+  val t: Tree = q"type T"
+  property("SI-6842 b1") = test { assertEqAst(q"def f[$t] = 0", "def f[T] = 0") }
+  property("SI-6842 b2") = test { assertEqAst(q"class C[$t]", "class C[T]") }
+  property("SI-6842 b3") = test { assertEqAst(q"trait B[$t]", "trait B[T]") }
 }
 
 trait ClassConstruction { self: QuasiquoteProperties =>
@@ -200,19 +201,56 @@ trait TypeDefConstruction { self: QuasiquoteProperties =>
 }
 
 trait ValDefConstruction { self: QuasiquoteProperties =>
-  property("splice term name into val") = forAll { (name: TermName, tpt: Tree, rhs: Tree) =>
+  property("splice into val") = forAll { (name: TermName, tpt: Tree, rhs: Tree) =>
     q"val $name: $tpt = $rhs" ≈ ValDef(Modifiers(), name, tpt, rhs)
   }
 
-  property("splice term name into var") = forAll { (name: TermName, tpt: Tree, rhs: Tree) =>
+  property("splice into var") = forAll { (name: TermName, tpt: Tree, rhs: Tree) =>
     q"var $name: $tpt = $rhs" ≈ ValDef(Modifiers(MUTABLE), name, tpt, rhs)
   }
 
+  // left tree is not a pattern due to Si-8211
   property("SI-8202") = test {
     assertEqAst(q"val (x: Int) = 1", "val x: Int = 1")
   }
 }
 
+trait PatDefConstruction { self: QuasiquoteProperties =>
+  property("splice pattern into pat def") = test {
+    val pat = pq"(a, b)"
+    assertEqAst(q"val $pat = (1, 2)", "val (a, b) = (1, 2)")
+    val tpt = tq"(Int, Int)"
+    assertEqAst(q"val $pat: $tpt = (1, 2)", "val (a, b): (Int, Int) = (1, 2)")
+  }
+
+  property("splice pattern into pat def within other pattern (1)") = test {
+    val pat = pq"(a, b)"
+    assertEqAst(q"val Foo($pat) = Foo((1, 2))", "val Foo((a, b)) = Foo((1, 2))")
+    val tpt = tq"Foo"
+    assertEqAst(q"val Foo($pat): $tpt = Foo((1, 2))", "val Foo((a, b)): Foo = Foo((1, 2))")
+  }
+
+  property("splice patterns into pat def within other pattern (2)") = test {
+    val pat1 = pq"(a, b)"; val pat2 = pq"(c, d)"
+    assertEqAst(q"val ($pat1, $pat2) = ((1, 2), (3, 4))", "val ((a, b), (c, d)) = ((1, 2), (3, 4))")
+    val tpt = tq"((Int, Int), (Int, Int))"
+    assertEqAst(q"val ($pat1, $pat2): $tpt = ((1, 2), (3, 4))", "val ((a, b), (c, d)): ((Int, Int), (Int, Int)) = ((1, 2), (3, 4))")
+  }
+
+  property("splice pattern without free vars into pat def") = test {
+    val pat = pq"((1, 2), 3)"
+    assertEqAst(q"val $pat = ((1, 2), 3)", "{ val ((1, 2), 3) = ((1, 2), 3) }")
+    val tpt = tq"((Int, Int), Int)"
+    assertEqAst(q"val $pat: $tpt = ((1, 2), 3)","{ val ((1, 2), 3): ((Int, Int), Int) = ((1, 2), 3) }")
+  }
+
+  // won't result into pattern match due to SI-8211
+  property("splice typed pat into pat def") = test {
+    val pat = pq"x: Int"
+    assertEqAst(q"val $pat = 2", "{ val x: Int = 2 }")
+  }
+}
+
 trait MethodConstruction { self: QuasiquoteProperties =>
   property("splice paramss into defdef") = test {
     val paramss = List(q"val x: Int") :: List(q"val y: Int = 1") :: Nil
diff --git a/test/files/scalacheck/quasiquotes/QuasiquoteProperties.scala b/test/files/scalacheck/quasiquotes/QuasiquoteProperties.scala
index 589b8d4d72..5d84984514 100644
--- a/test/files/scalacheck/quasiquotes/QuasiquoteProperties.scala
+++ b/test/files/scalacheck/quasiquotes/QuasiquoteProperties.scala
@@ -28,7 +28,7 @@ trait Helpers {
 
     override def transform(tree: Tree): Tree = tree match {
       case Ident(SimplifiedName(name))                  => Ident(name)
-      case ValDef(mods, SimplifiedName(name), tpt, rhs) => ValDef(mods, name, tpt, rhs)
+      case ValDef(mods, SimplifiedName(name), tpt, rhs) => ValDef(mods, name, transform(tpt), transform(rhs))
       case Bind(SimplifiedName(name), rhs)              => Bind(name, rhs)
       case _ =>
         super.transform(tree)