duplicate GraphQL Variables for compound queries

[mdugue]

First of all, great work on grahql mesh and hive gateway. I'd love to help making it a robust open source solution. Hence I'll try to share some broken edge case I stumbled upon.

Hive Gateway seems to forward broken variables to subgraphs when variables are optional and not provided by the query.

Example

this works fine ✅

query TestOK($a:String, $b:String) {
  params1(a: $a, b:$b)
}

#variables
{}

this breaks ❌

query TestBroken($a:String, $b:String) {
  params1(a: $a, b:$b)
  o: params1(a: $a, b:$b)
}

#variables
{}

Apparently the variables get repeatedly appended for each top-level query field, so that the subgraph receives the following query:

"query TestBroken($a:String$b:String$a:String$b:String){_0___typename:__typename _0_params1:params1(a:$a b:$b)_1___typename:__typename _1_params1:params1(a:$a b:$b)}"

Note the duplication in the variables $a:String$b:String$a:String$b:String

Observations

• the problematic query in is correctly forwarded if variables are set, eg. {"a": "foo"} or even {"a": null}
• if 3 top level query fields are set, the variable definition is also 3x
• it does not make a difference if the used top level fields are the same with an alias or another field

In case you need some reproduction deployment I'm more than happy to provide one, but I'm not sure what to use as I assume CodeSandbox will not work easily. Do you have any guidelines therefore?

Thanks a lot in advance!