SI-8076 improve support for implicit argument list

This adds support for construction and deconstruction
of implicit argument list which was originally suggested
by @cvogt.

1. Splicing vale into implicit argument list automatically
   adds implicit flag to them:

     val x = q"val x: Int"
     q"def foo(implicit $x)"
     // <=> q"def foo(implicit x: Int)"

2. One might extract implicit argument list separately from
   other argument lists:

     val q”def foo(...$argss)(implicit ..$impl)" =
       q"def foo(implicit x: Int)
     // argss is Nil, impl contains valdef for x

   But this doesn't require you to always extract it separatly:

     val q”def foo(...$argss)" =
       q"def foo(implicit x: Int)
     // argss contains valdef for x

4 files changed, 28 insertions, 2 deletions

diff --git a/src/compiler/scala/tools/reflect/quasiquotes/Reifiers.scala b/src/compiler/scala/tools/reflect/quasiquotes/Reifiers.scala
index 58baad01a1..9c0a036541 100644
--- a/src/compiler/scala/tools/reflect/quasiquotes/Reifiers.scala
+++ b/src/compiler/scala/tools/reflect/quasiquotes/Reifiers.scala
@@ -160,8 +160,12 @@ trait Reifiers { self: Quasiquotes =>
         reifyBuildCall(nme.SyntacticObjectDef, mods, name, earlyDefs, parents, selfdef, body)
       case SyntacticNew(earlyDefs, parents, selfdef, body) =>
         reifyBuildCall(nme.SyntacticNew, earlyDefs, parents, selfdef, body)
-      case SyntacticDefDef(mods, name, tparams, vparamss, tpt, rhs) =>
-        reifyBuildCall(nme.SyntacticDefDef, mods, name, tparams, vparamss, tpt, rhs)
+      case SyntacticDefDef(mods, name, tparams, build.ImplicitParams(vparamss, implparams), tpt, rhs) =>
+        if (implparams.nonEmpty)
+          mirrorBuildCall(nme.SyntacticDefDef, reify(mods), reify(name), reify(tparams), 
+                          reifyBuildCall(nme.ImplicitParams, vparamss, implparams), reify(tpt), reify(rhs))
+        else
+          reifyBuildCall(nme.SyntacticDefDef, mods, name, tparams, vparamss, tpt, rhs)
       case SyntacticValDef(mods, name, tpt, rhs) if tree != noSelfType =>
         reifyBuildCall(nme.SyntacticValDef, mods, name, tpt, rhs)
       case SyntacticVarDef(mods, name, tpt, rhs) =>
diff --git a/src/reflect/scala/reflect/api/BuildUtils.scala b/src/reflect/scala/reflect/api/BuildUtils.scala
index 89492e75c4..d70fa01ae6 100644
--- a/src/reflect/scala/reflect/api/BuildUtils.scala
+++ b/src/reflect/scala/reflect/api/BuildUtils.scala
@@ -94,6 +94,13 @@ private[reflect] trait BuildUtils { self: Universe =>
 
     def freshTypeName(prefix: String): TypeName
 
+    val ImplicitParams: ImplicitParamsExtractor
+
+    trait ImplicitParamsExtractor {
+      def apply(paramss: List[List[ValDef]], implparams: List[ValDef]): List[List[ValDef]]
+      def unapply(vparamss: List[List[ValDef]]): Some[(List[List[ValDef]], List[ValDef])]
+    }
+
     val ScalaDot: ScalaDotExtractor
 
     trait ScalaDotExtractor {
diff --git a/src/reflect/scala/reflect/internal/BuildUtils.scala b/src/reflect/scala/reflect/internal/BuildUtils.scala
index 657b098952..292413674b 100644
--- a/src/reflect/scala/reflect/internal/BuildUtils.scala
+++ b/src/reflect/scala/reflect/internal/BuildUtils.scala
@@ -86,6 +86,10 @@ trait BuildUtils { self: SymbolTable =>
                                             """consider reformatting it into q"val $name: $T = $default" shape""")
     }
 
+    def mkImplicitParam(args: List[Tree]): List[ValDef] = args.map(mkImplicitParam)
+
+    def mkImplicitParam(tree: Tree): ValDef = mkParam(tree, IMPLICIT | PARAM)
+
     def mkTparams(tparams: List[Tree]): List[TypeDef] =
       tparams.map {
         case td: TypeDef => copyTypeDef(td)(mods = (td.mods | PARAM) & (~DEFERRED))
@@ -143,6 +147,16 @@ trait BuildUtils { self: SymbolTable =>
 
     protected implicit def fresh: FreshNameCreator = self.currentFreshNameCreator
 
+    object ImplicitParams extends ImplicitParamsExtractor {
+      def apply(paramss: List[List[ValDef]], implparams: List[ValDef]): List[List[ValDef]] =
+        if (implparams.nonEmpty) paramss :+ mkImplicitParam(implparams) else paramss
+
+      def unapply(vparamss: List[List[ValDef]]): Some[(List[List[ValDef]], List[ValDef])] = vparamss match {
+        case init :+ (last @ (initlast :: _)) if initlast.mods.isImplicit => Some((init, last))
+        case _ => Some((vparamss, Nil))
+      }
+    }
+
     object FlagsRepr extends FlagsReprExtractor {
       def apply(bits: Long): FlagSet = bits
       def unapply(flags: Long): Some[Long] = Some(flags)
diff --git a/src/reflect/scala/reflect/internal/StdNames.scala b/src/reflect/scala/reflect/internal/StdNames.scala
index 73ad9def73..49c26ca58d 100644
--- a/src/reflect/scala/reflect/internal/StdNames.scala
+++ b/src/reflect/scala/reflect/internal/StdNames.scala
@@ -576,6 +576,7 @@ trait StdNames {
     val Flag : NameType                = "Flag"
     val FlagsRepr: NameType            = "FlagsRepr"
     val Ident: NameType                = "Ident"
+    val ImplicitParams: NameType       = "ImplicitParams"
     val Import: NameType               = "Import"
     val Literal: NameType              = "Literal"
     val LiteralAnnotArg: NameType      = "LiteralAnnotArg"