GraphQL federation directives, which allow multiple values, do not match Apollo contract

[alexpoletaev]

Describe the bug

GraphQL federation directives, which allow multiple values, like @provides, @key, etc., do not match Apollo contract. It seems that in Apollo those directives have value of type FieldSet!, which represents whitespace-separated string of values, but Smallrye module represents those directives just as arrays of values. As a result, those directives are not valid for the Apollo server.

Expected behavior

The @provides directive is shown in the schema like that:
@provides(fields : "rating reviews")

Actual behavior

The @provides directive is shown in the schema like that:
@provides(fields : ["rating", "reviews"])

How to Reproduce?

Reproducer: quarkus-graphql-issue.zip

• unzip a reproducer
• start service
• go to graphql UI
• execute next query:
  query { _service { sdl } }
• observe that @provides directive in the graphql schema has a type of array
• uncomment a workaround method in the GraphQLSchemaObserver class
• observe that @provides directive in the graphql schema has a type of whitespace-separated string (FieldSet)

Output of uname -a or ver

No response

Output of java -version

openjdk version "17.0.5" 2022-10-18

GraalVM version (if different from Java)

No response

Quarkus version or git rev

2.15.1.Final

Build tool (ie. output of mvnw --version or gradlew --version)

Gradle 7.5.1

Additional information

This reproducer uses a workaround from the #30129 issue. It also provides a temporary workaround to convert @key and @provides directives from type of array to type of FieldSet (string).

[quarkus-bot]

/cc @jmartisk(graphql), @phillip-kruger(graphql)

[jmartisk]

Here I think we will need the help of @t1 who wrote the code handling these directives -would you be willing to fix this in SmallRye?
It's an API breaking change, but since federation is marked experimental, it shouldn't be a huge deal

[t1]

I'm taking a look into this. The problem is, that the @Key annotation then needs to be repeatable.

[jmartisk]

I think that repeatability would be great to have, but not strictly necessary, no?
As far as I understand, an annotation @Key(fields="a b") is equivalent to @Key(fields="a") plus @Key(fields="b")
The former translates to directive @key(fields: "a b"), the latter to @key(fields: "a") @key(fields: "b")

If we turn the fields parameter into a String that allows multiple values separated by spaces, it will be equivalent to having a repeated annotation for each value separately.

[jmartisk]

But right, there's also the resolvable parameter and if you want to have a different value of it for different fields, then we really need a repeatable annotation.

[t1]

No, @Key(fields="a b") means you can resolve this with the combination of a and b... a compound key, so to speak, while @Key(fields="a") plus @Key(fields="b") means that you can resolve either with a or with b.

[jmartisk]

Ah, ok gotcha.