json: support tuple (#10010)

lib/pure/json.nim

@@ -142,7 +142,8 @@ runnableExamples:
   doAssert $(%* Foo()) == """{"a1":0,"a2":0,"a0":0,"a3":0,"a4":0}"""
 
 import
-  hashes, tables, strutils, lexbase, streams, unicode, macros, parsejson
+  hashes, tables, strutils, lexbase, streams, unicode, macros, parsejson,
+  typetraits
 
 export
   tables.`$`
@@ -356,6 +357,20 @@ when false:
     assert false notin elements, "usage error: only empty sets allowed"
     assert true notin elements, "usage error: only empty sets allowed"
 
+#[
+Note: could use simply:
+proc `%`*(o: object|tuple): JsonNode
+but blocked by https://github.com/nim-lang/Nim/issues/10019
+]#
+proc `%`*(o: tuple): JsonNode =
+  ## Generic constructor for JSON data. Creates a new `JObject JsonNode`
+  when isNamedTuple(type(o)):
+    result = newJObject()
+    for k, v in o.fieldPairs: result[k] = %v
+  else:
+    result = newJArray()
+    for a in o.fields: result.add(%a)
+
 proc `%`*(o: object): JsonNode =
   ## Generic constructor for JSON data. Creates a new `JObject JsonNode`
   result = newJObject()

tests/stdlib/tjsonmacro.nim

@@ -516,3 +516,7 @@ when true:
       var w = u.to(MyDistRef)
       doAssert v.name == "smith"
       doAssert MyRef(w).name == "smith"
+
+    block test_tuple:
+      doAssert $(%* (a1: 10, a2: "foo")) == """{"a1":10,"a2":"foo"}"""
+      doAssert $(%* (10, "foo")) == """[10,"foo"]"""