backport json-related part of #17469

Author: narimiran

lib/pure/json.nim

@@ -1064,12 +1064,13 @@ when defined(nimFixedForwardGeneric):
     dst = jsonNode.copy
 
   proc initFromJson[T: SomeInteger](dst: var T; jsonNode: JsonNode, jsonPath: var string) =
-    when T is uint|uint64:
+    when T is uint|uint64 or (not defined(js) and int.sizeof == 4):
+      verifyJsonKind(jsonNode, {JInt, JString}, jsonPath)
       case jsonNode.kind
       of JString:
-        dst = T(parseBiggestUInt(jsonNode.str))
+        let x = parseBiggestUInt(jsonNode.str)
+        dst = cast[T](x)
       else:
-        verifyJsonKind(jsonNode, {JInt}, jsonPath)
         dst = T(jsonNode.num)
     else:
       verifyJsonKind(jsonNode, {JInt}, jsonPath)

tests/stdlib/tjsonutils.nim

@@ -72,16 +72,16 @@ template fn() =
     block:
       let a = (int32.high, uint32.high)
       testRoundtrip(a): "[2147483647,4294967295]"
-    when not defined(js):
+    when int.sizeof > 4:
       block:
         let a = (int64.high, uint64.high)
         testRoundtrip(a): "[9223372036854775807,18446744073709551615]"
-      block:
-        let a = (int.high, uint.high)
-        when int.sizeof == 4:
-          testRoundtrip(a): "[2147483647,4294967295]"
-        else:
-          testRoundtrip(a): "[9223372036854775807,18446744073709551615]"
+    block:
+      let a = (int.high, uint.high)
+      when int.sizeof == 4:
+        testRoundtrip(a): "[2147483647,4294967295]"
+      else:
+        testRoundtrip(a): "[9223372036854775807,18446744073709551615]"
 
   block: # case object
     type Foo = object