Add rlpFieldsCount helper and the ability to read objects not wrapped in lists

rlp.nim

@@ -354,7 +354,7 @@ proc readImpl[E](rlp: var Rlp, T: type openarray[E]): seq[E] =
   result = readImpl(rlp, seq[E])
 
 proc readImpl(rlp: var Rlp, T: type[object|tuple],
-              wrappedInList = wrapObjectsInList): T =
+              wrappedInList = wrapObjsInList): T =
   mixin enumerateRlpFields, read
 
   if wrappedInList:
@@ -391,6 +391,9 @@ proc toNodes*(self: var Rlp): RlpNode =
 template read*(rlp: var Rlp, T: type): auto =
   readImpl(rlp, T)
 
+template readRecordType*(rlp: var Rlp, T: type, wrappedInList: bool): auto =
+  readImpl(rlp, T, wrappedInList)
+
 proc decode*(bytes: openarray[byte]): RlpNode =
   var
     bytesCopy = @bytes

rlp/object_serialization.nim

@@ -18,6 +18,17 @@ template enumerateRlpFields*[T](x: T, op: untyped) =
     when not hasCustomPragma(f, rlpIgnore):
       op(f)
 
+proc rlpFieldsCount*(T: type): int =
+  mixin enumerateRlpFields
+
+  proc helper: int =
+    var dummy: T
+    template countFields(x) = inc result
+    enumerateRlpFields(dummy, countFields)
+
+  const res = helper()
+  return res
+
 macro rlpFields*(T: typedesc, fields: varargs[untyped]): untyped =
   var body = newStmtList()
   let

rlp/writer.nim

@@ -32,7 +32,7 @@ type
   Integer* = SomeInteger # or IntLike
 
 const
-  wrapObjectsInList* = true
+  wrapObjsInList* = true
 
 proc bytesNeeded(num: Integer): int =
   type IntType = type(num)
@@ -214,16 +214,11 @@ proc appendImpl[T](self; listOrBlob: openarray[T]) =
     for i in 0 ..< listOrBlob.len:
       self.append listOrBlob[i]
 
-proc appendTupleOrObject(self; obj: object|tuple, wrapInList: bool) =
+proc appendRecordType*(self; obj: object|tuple, wrapInList = wrapObjsInList) =
   mixin enumerateRlpFields, append
 
-  const wrapInList = wrapObjectsInList
-
   if wrapInList:
-    var fieldsCount = 0
-    template countFields(x) = inc fieldsCount
-    enumerateRlpFields(obj, countFields)
-    self.startList(fieldsCount)
+    self.startList(static obj.type.rlpFieldsCount)
 
   template op(field) =
     when hasCustomPragma(field, rlpCustomSerialization):
@@ -233,16 +228,16 @@ proc appendTupleOrObject(self; obj: object|tuple, wrapInList: bool) =
 
   enumerateRlpFields(obj, op)
 
-proc appendImpl(self; data: object, wrapInList = wrapObjectsInList) {.inline.} =
+proc appendImpl(self; data: object) {.inline.} =
   # TODO: This append proc should be overloaded by `BytesRange` after
   # nim bug #7416 is fixed.
   when data is BytesRange:
     self.appendBytesRange(data)
   else:
-    self.appendTupleOrObject(data, wrapInList)
+    self.appendRecordType(data)
 
-proc appendImpl(self; data: tuple, wrapInList = wrapObjectsInList) {.inline.} =
-  self.appendTupleOrObject(data, wrapInList)
+proc appendImpl(self; data: tuple) {.inline.} =
+  self.appendRecordType(data)
 
 # We define a single `append` template with a pretty low specifity
 # score in order to facilitate easier overloading with user types:

tests/test_object_serialization.nim

@@ -74,3 +74,9 @@ test "custom field serialization":
     origVal.customFoo.y.len == restored.customFoo.y.len
     restored.ignored == 10
 
+test "RLP fields count":
+  check:
+    Bar.rlpFieldsCount == 2
+    Foo.rlpFieldsCount == 3
+    Transaction.rlpFieldsCount == 3
+