jsonutils.toJson now serializes JsonNode as is by default (#18097)

* jsonutils.toJson now serializes JsonNode as is (without deep copy nor treating it as a regular ref object)

* JsonNodeMode

changelog.md

@@ -69,7 +69,9 @@
   previous behavior for a transition time, see PR #17467.
 
 - `jsonutils` now serializes/deserializes holey enums as regular enums (via `ord`) instead of as strings.
-  Use `-d:nimLegacyJsonutilsHoleyEnum` for a transition period.
+  Use `-d:nimLegacyJsonutilsHoleyEnum` for a transition period. `toJson` now serializes `JsonNode`
+  as is via reference (without a deep copy) instead of treating `JsonNode` as a regular ref object,
+  this can be customized via `jsonNodeMode`.
 
 - `json` and `jsonutils` now serialize NaN, Inf, -Inf as strings, so that
   `%[NaN, -Inf]` is the string `["nan","-inf"]` instead of `[nan,-inf]` which was invalid json.

lib/std/jsonutils.nim

@@ -48,13 +48,18 @@ type
     joptEnumOrd
     joptEnumSymbol
     joptEnumString
+  JsonNodeMode* = enum ## controls `toJson` for JsonNode types
+    joptJsonNodeAsRef ## returns the ref as is
+    joptJsonNodeAsCopy ## returns a deep copy of the JsonNode
+    joptJsonNodeAsObject ## treats JsonNode as a regular ref object
   ToJsonOptions* = object
     enumMode*: EnumMode
-    # xxx charMode
+    jsonNodeMode*: JsonNodeMode
+    # xxx charMode, etc
 
 proc initToJsonOptions*(): ToJsonOptions =
   ## initializes `ToJsonOptions` with sane options.
-  ToJsonOptions(enumMode: joptEnumOrd)
+  ToJsonOptions(enumMode: joptEnumOrd, jsonNodeMode: joptJsonNodeAsRef)
 
 proc isNamedTuple(T: typedesc): bool {.magic: "TypeTrait".}
 proc distinctBase(T: typedesc): typedesc {.magic: "TypeTrait".}
@@ -286,8 +291,15 @@ proc toJson*[T](a: T, opt = initToJsonOptions()): JsonNode =
       result = newJArray()
       for v in a.fields: result.add toJson(v, opt)
   elif T is ref | ptr:
+    template impl =
       if system.`==`(a, nil): result = newJNull()
       else: result = toJson(a[], opt)
+    when T is JsonNode:
+      case opt.jsonNodeMode
+      of joptJsonNodeAsRef: result = a
+      of joptJsonNodeAsCopy: result = copy(a)
+      of joptJsonNodeAsObject: impl()
+    else: impl()
   elif T is array | seq | set:
     result = newJArray()
     for ai in a: result.add toJson(ai, opt)

tests/stdlib/tjsonutils.nim

@@ -91,6 +91,28 @@ template fn() =
     doAssert b2.ord == 1 # explains the `1`
     testRoundtrip(a): """[1,2,3]"""
 
+  block: # JsonNode
+    let a = ((1, 2.5, "abc").toJson, (3, 4.5, "foo"))
+    testRoundtripVal(a): """[[1,2.5,"abc"],[3,4.5,"foo"]]"""
+
+    block:
+      template toInt(a): untyped = cast[int](a)
+
+      let a = 3.toJson
+      let b = (a, a)
+
+      let c1 = b.toJson
+      doAssert c1[0].toInt == a.toInt
+      doAssert c1[1].toInt == a.toInt
+
+      let c2 = b.toJson(ToJsonOptions(jsonNodeMode: joptJsonNodeAsCopy))
+      doAssert c2[0].toInt != a.toInt
+      doAssert c2[1].toInt != c2[0].toInt
+      doAssert c2[1] == c2[0]
+
+      let c3 = b.toJson(ToJsonOptions(jsonNodeMode: joptJsonNodeAsObject))
+      doAssert $c3 == """[{"isUnquoted":false,"kind":2,"num":3},{"isUnquoted":false,"kind":2,"num":3}]"""
+
   block: # ToJsonOptions
     let a = (me1, me2)
     doAssert $a.toJson() == "[1,2]"