Faster parsing of small JSON arrays to Vector and IndexSeq collections

Author: plokhotnyuk

jsoniter-scala-macros/shared/src/main/scala-2/com/github/plokhotnyuk/jsoniter_scala/macros/JsonCodecMaker.scala

@@ -1828,6 +1828,10 @@ object JsonCodecMaker {
           val tpe1 = typeArg1(tpe)
           genReadArray(q"{ val x = new _root_.scala.collection.mutable.ListBuffer[$tpe1] }",
             genReadValForGrowable(tpe1 :: types, isStringified), q"x.toList")
+        } else if (tpe <:< typeOf[Vector[_]] || tpe.typeSymbol == typeOf[IndexedSeq[_]].typeSymbol) withDecoderFor(methodKey, default) {
+          val tpe1 = typeArg1(tpe)
+          genReadArray(q"{ val x = new _root_.scala.collection.immutable.VectorBuilder[$tpe1] }",
+            genReadValForGrowable(tpe1 :: types, isStringified), q"x.result()")
         } else if (tpe <:< typeOf[mutable.Iterable[_] with mutable.Builder[_, _]] &&
             !(tpe <:< typeOf[mutable.ArrayStack[_]])) withDecoderFor(methodKey, default) { //ArrayStack uses 'push' for '+=' in Scala 2.12.x
           val tpe1 = typeArg1(tpe)

jsoniter-scala-macros/shared/src/main/scala-3/com/github/plokhotnyuk/jsoniter_scala/macros/JsonCodecMaker.scala

@@ -2526,6 +2526,13 @@ object JsonCodecMaker {
                 if ($tDefault.isEmpty) $tDefault
                 else new mutable.ListBuffer[t1]
               }, x => genReadValForGrowable(tpe1 :: types, isStringified, x, in), tDefault, x => x, in).asExprOf[T]
+        } else if (tpe <:< TypeRepr.of[Vector[_]] || tpe.typeSymbol == TypeRepr.of[IndexedSeq[_]].typeSymbol) withDecoderFor(methodKey, default, in) { (in, default) =>
+          val tpe1 = typeArg1(tpe)
+          tpe1.asType match
+            case '[t1] =>
+              genReadCollection('{ new immutable.VectorBuilder[t1] },
+                x => genReadValForGrowable(tpe1 :: types, isStringified, x, in),
+                default, x => '{ $x.result() }, in).asExprOf[T]
         } else if (tpe <:< TypeRepr.of[mutable.Iterable[_] with mutable.Growable[_]]) withDecoderFor(methodKey, default, in) { (in, default) =>
           val tpe1 = typeArg1(tpe)
           tpe1.asType match