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

1 files changed, 14 insertions, 1 deletions

diff --git a/test/files/scalacheck/quasiquotes/DefinitionConstructionProps.scala b/test/files/scalacheck/quasiquotes/DefinitionConstructionProps.scala
index 2af656c7c9..3166eb7a99 100644
--- a/test/files/scalacheck/quasiquotes/DefinitionConstructionProps.scala
+++ b/test/files/scalacheck/quasiquotes/DefinitionConstructionProps.scala
@@ -7,6 +7,7 @@ object DefinitionConstructionProps
     with TraitConstruction
     with TypeDefConstruction
     with ValDefConstruction
+    with DefConstruction
     with PackageConstruction {
   property("SI-6842") = test {
     val x: Tree = q"val x: Int"
@@ -349,4 +350,16 @@ trait PackageConstruction { self: QuasiquoteProperties =>
     assertEqAst(q"package object foo extends { ..$edefs } with Any",
                  "package object foo extends { val x = 1; type I = Int } with Any")
   }
-}
\ No newline at end of file
+}
+
+trait DefConstruction { self: QuasiquoteProperties =>
+  property("construct implicit args (1)") = test {
+    val x = q"val x: Int"
+    assertEqAst(q"def foo(implicit $x) = x", "def foo(implicit x: Int) = x")
+  }
+
+  property("construct implicit args (2)") = test {
+    val xs = q"val x1: Int" :: q"val x2: Long" :: Nil
+    assertEqAst(q"def foo(implicit ..$xs) = x1 + x2", "def foo(implicit x1: Int, x2: Long) = x1 + x2")
+  }
+}