json: Make fromjson less confusing when used with a decode_value

format/json/json.jq

@@ -2,7 +2,14 @@
 def tojson($opts): _to_json($opts);
 def tojson: _to_json(null);
 # overrides jq's standard fromjson
-# NOTE: should be kept in sync with format_decode.jq
-def fromjson: decode("json") | if ._error then error(._error.error) end;
+# NOTE:
+# should be kept in sync with format_decode.jq and can't use from_json as
+# it's not defined yet.
+# also uses tovalue on it's input to care of the where the input is a decode_value
+# string which without would end up decoding the "backing" binary instead.
+# Ex:
+# $ fq -n '"\"1,2,3\"" | fromjson | tobytes | tostring'
+# "\"1,2,3\""
+def fromjson: tovalue | decode("json") | if ._error then error(._error.error) end;
 
 def _json__todisplay: tovalue;

format/json/testdata/fromjson.fqtest

@@ -0,0 +1,3 @@
+# make sure fromjson decode from value instead of binary for a decode_value
+$ fq -n '"\"123\"" | fromjson | fromjson'
+123