Writer produce correct top-level or in-array optional elem when custom flavor omit optional fields

json_serialization/std/options.nim

@@ -27,7 +27,8 @@ proc writeValue*(writer: var JsonWriter, value: Option) {.raises: [IOError].} =
 
   if value.isSome:
     writer.writeValue value.get
-  elif not flavorOmitsOptionalFields(Flavor):
+  elif not flavorOmitsOptionalFields(Flavor) or 
+      writer.nesting != JsonNesting.WriteObject:
     writer.writeValue JsonString("null")
 
 proc readValue*[T](reader: var JsonReader, value: var Option[T]) =

json_serialization/stew/results.nim

@@ -31,7 +31,8 @@ proc writeValue*[T](
 
   if value.isOk:
     writer.writeValue value.get
-  elif not flavorOmitsOptionalFields(Flavor):
+  elif not flavorOmitsOptionalFields(Flavor) or
+      writer.nesting != JsonNesting.WriteObject:
     writer.writeValue JsonString("null")
 
 proc readValue*[T](reader: var JsonReader, value: var Result[T, void]) =

json_serialization/writer.nim

@@ -22,12 +22,19 @@ type
     RecordStarted
     AfterField
 
+  JsonNesting* {.pure.} = enum
+    TopLevel
+    WriteObject
+    WriteArray
+
   JsonWriter*[Flavor = DefaultFlavor] = object
     stream*: OutputStream
     hasTypeAnnotations: bool
     hasPrettyOutput*: bool # read-only
     nestingLevel*: int     # read-only
     state: JsonWriterState
+    nesting: JsonNesting
+    prevNesting: seq[JsonNesting]
 
 Json.setWriter JsonWriter,
                PreferredOutput = string
@@ -38,7 +45,11 @@ func init*(W: type JsonWriter, stream: OutputStream,
     hasPrettyOutput: pretty,
     hasTypeAnnotations: typeAnnotations,
     nestingLevel: if pretty: 0 else: -1,
-    state: RecordExpected)
+    state: RecordExpected,
+    nesting: JsonNesting.TopLevel)
+
+func nesting*(w: JsonWriter): JsonNesting =
+  w.nesting
 
 proc beginRecord*(w: var JsonWriter, T: type)
 proc beginRecord*(w: var JsonWriter)
@@ -90,6 +101,8 @@ template fieldWritten*(w: var JsonWriter) =
 proc beginRecord*(w: var JsonWriter) =
   doAssert w.state == RecordExpected
 
+  w.prevNesting.add w.nesting
+  w.nesting = JsonNesting.WriteObject
   append '{'
   if w.hasPrettyOutput:
     w.nestingLevel += 2
@@ -109,12 +122,15 @@ proc endRecord*(w: var JsonWriter) =
     indent()
 
   append '}'
+  w.nesting = w.prevNesting.pop()
 
 template endRecordField*(w: var JsonWriter) =
   endRecord(w)
   w.state = AfterField
 
 iterator stepwiseArrayCreation*[C](w: var JsonWriter, collection: C): auto =
+  w.prevNesting.add w.nesting
+  w.nesting = JsonNesting.WriteArray
   append '['
 
   if w.hasPrettyOutput:
@@ -140,6 +156,7 @@ iterator stepwiseArrayCreation*[C](w: var JsonWriter, collection: C): auto =
     indent()
 
   append ']'
+  w.nesting = w.prevNesting.pop()
 
 proc writeIterable*(w: var JsonWriter, collection: auto) =
   mixin writeValue

tests/test_all.nim

@@ -16,4 +16,5 @@ import
   test_spec,
   test_parser,
   test_line_col,
-  test_reader
+  test_reader,
+  test_writer

tests/test_writer.nim

@@ -0,0 +1,101 @@
+# json-serialization
+# Copyright (c) 2024 Status Research & Development GmbH
+# Licensed under either of
+#  * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE))
+#  * MIT license ([LICENSE-MIT](LICENSE-MIT))
+# at your option.
+# This file may not be copied, modified, or distributed except according to
+# those terms.
+
+import
+  unittest2,
+  ../json_serialization/stew/results,
+  ../json_serialization/std/options,
+  ../json_serialization
+
+createJsonFlavor YourJson,
+  omitOptionalFields = false
+
+createJsonFlavor MyJson,
+  omitOptionalFields = true
+
+suite "Test writer":
+  test "stdlib option top level some YourJson":
+    var val = some(123)
+    let json = YourJson.encode(val)
+    check json == "123"
+
+  test "stdlib option top level none YourJson":
+    var val = none(int)
+    let json = YourJson.encode(val)
+    check json == "null"
+
+  test "stdlib option top level some MyJson":
+    var val = some(123)
+    let json = MyJson.encode(val)
+    check json == "123"
+
+  test "stdlib option top level none MyJson":
+    var val = none(int)
+    let json = MyJson.encode(val)
+    check json == "null"
+
+  test "results option top level some YourJson":
+    var val = Opt.some(123)
+    let json = YourJson.encode(val)
+    check json == "123"
+
+  test "results option top level none YourJson":
+    var val = Opt.none(int)
+    let json = YourJson.encode(val)
+    check json == "null"
+
+  test "results option top level some MyJson":
+    var val = Opt.some(123)
+    let json = MyJson.encode(val)
+    check json == "123"
+
+  test "results option top level none MyJson":
+    var val = Opt.none(int)
+    let json = MyJson.encode(val)
+    check json == "null"
+
+  test "stdlib option array some YourJson":
+    var val = [some(123), some(345)]
+    let json = YourJson.encode(val)
+    check json == "[123,345]"
+
+  test "stdlib option array none YourJson":
+    var val = [some(123), none(int), some(777)]
+    let json = YourJson.encode(val)
+    check json == "[123,null,777]"
+
+  test "stdlib option array some MyJson":
+    var val = [some(123), some(345)]
+    let json = MyJson.encode(val)
+    check json == "[123,345]"
+
+  test "stdlib option array none MyJson":
+    var val = [some(123), none(int), some(777)]
+    let json = MyJson.encode(val)
+    check json == "[123,null,777]"
+
+  test "results option array some YourJson":
+    var val = [Opt.some(123), Opt.some(345)]
+    let json = YourJson.encode(val)
+    check json == "[123,345]"
+
+  test "results option array none YourJson":
+    var val = [Opt.some(123), Opt.none(int), Opt.some(777)]
+    let json = YourJson.encode(val)
+    check json == "[123,null,777]"
+
+  test "results option array some MyJson":
+    var val = [Opt.some(123), Opt.some(345)]
+    let json = MyJson.encode(val)
+    check json == "[123,345]"
+
+  test "results option array none MyJson":
+    var val = [Opt.some(123), Opt.none(int), Opt.some(777)]
+    let json = MyJson.encode(val)
+    check json == "[123,null,777]"