Represent tq"" as SyntacticEmptyTypeTree rather than TypeTree()

Such representation codifies the fact that type tree that doesn't have
embedded syntactic equivalent must have been inferred or otherwise
provided by the compiler rather than specified by the end user.

Additionally it also ensures that we can still match trees without
explicit types (e.g. vals without type) after typechecking. Otherwise
the same quote couldn't be used in situations like:

    val q"val x = 42" = typecheck(q"val x = 42")

3 files changed, 15 insertions, 2 deletions

diff --git a/test/files/scalacheck/quasiquotes/TypeConstructionProps.scala b/test/files/scalacheck/quasiquotes/TypeConstructionProps.scala
index 0984032084..78b54a4e49 100644
--- a/test/files/scalacheck/quasiquotes/TypeConstructionProps.scala
+++ b/test/files/scalacheck/quasiquotes/TypeConstructionProps.scala
@@ -30,7 +30,7 @@ object TypeConstructionProps extends QuasiquoteProperties("type construction")
   }
 
   property("empty tq") = test {
-    val tt: TypeTree = tq" "
+    val tt: TypeTree = tq""
     assert(tt.tpe == null)
     assert(tt.original == null)
   }
diff --git a/test/files/scalacheck/quasiquotes/TypeDeconstructionProps.scala b/test/files/scalacheck/quasiquotes/TypeDeconstructionProps.scala
index 44f110a3d5..0fdcc19052 100644
--- a/test/files/scalacheck/quasiquotes/TypeDeconstructionProps.scala
+++ b/test/files/scalacheck/quasiquotes/TypeDeconstructionProps.scala
@@ -52,4 +52,10 @@ object TypeDeconstructionProps extends QuasiquoteProperties("type deconstruction
     assert(arglast ≈ tq"C")
     assert(restpe ≈ tq"D")
   }
+
+  property("match empty type tree") = test {
+    val tq"" = TypeTree()
+    // matches because type tree isn't syntactic without original
+    val tq"" = tq"${typeOf[Int]}"
+  }
 }
diff --git a/test/files/scalacheck/quasiquotes/TypecheckedProps.scala b/test/files/scalacheck/quasiquotes/TypecheckedProps.scala
index 2f501435e3..3afb47952c 100644
--- a/test/files/scalacheck/quasiquotes/TypecheckedProps.scala
+++ b/test/files/scalacheck/quasiquotes/TypecheckedProps.scala
@@ -75,4 +75,11 @@ object TypecheckedProps extends QuasiquoteProperties("typechecked") {
     assert(f.original ≈ pq"Test.this.Cell")
     assert(args ≈ List(pq"v"))
   }
-}
\ No newline at end of file
+
+  property("extract inferred val type") = test {
+    val typechecked = typecheck(q"val x = 42")
+    val q"val x = 42" = typechecked
+    val q"val x: ${tq""} = 42" = typechecked
+    val q"val x: ${t: Type} = 42" = typechecked
+  }
+}