Feature: Adds Federation 2 Support

[lleadbet]

This PR adds in support for Apollo's Federation 2 standard, as requested per issue #2114.

This adds a new configuration value to set the federation version manually as well as a method to detect federation 2 schemas using a small regex string.

Largely, this doesn't change much about the generated code, but instead allows for graphql-parser to not error by adding the new Federation 2 directives before loading new schemas. Previously, this was panicing due to a missing directive.

By default, this still uses Federation 1 unless detected by aforementioned regex or set by the user to avoid breaking changes.

I have:

• Added tests covering the bug / feature (see testing)
• Updated any relevant documentation (see docs)

[lleadbet]

@frederikhors - Just a small question, as I can't seem to quite understand why it's erroring out on tests/using it.

I have added a Link interface here: plugin/federation/fedruntime/runtime.go, however referencing within the federation file such as:

		builtins["link__Import"] = config.TypeMapEntry{
			Model: config.StringList{"github.com/99designs/gqlgen/fedruntime.Link"},
		}

Still doesn't find the interface.

[frederikhors]

@lleadbet we need to wait @StevenACoffman for this answer.

[kdawgwilk]

Did you want to add a version: 2 key here?

[lleadbet]

We can implicitly pull that from the schema, hence why I left it out; might be worthwhile, however.

[StevenACoffman]

I'm idly wondering if the Link interface should have functions to introspectively answer:

1. What version was imported (currently only "2.0" possible)
2. What imports out of the list: ["@key","@shareable", "@provides", "@external", "@tag", "@extends", "@override", "@inaccessible"]

[lleadbet]

Hmm- I think it might be useful in the future, but since the parser also validates at time of loading, you need to load all directives just in case- the current flow just ensures that the file contains that directive using Regex, which isn't the best solution either.

Not sure if you have any recs on how to handle the pre-parsing problem, though.

[StevenACoffman]

Applying my suggested fix removes one test failure and moves the second to:

=== Failed
=== FAIL: api TestGenerate/federation2 (7.45s)
    generate_test.go:55: Generate() error = validation failed: packages.Load: /Users/steve/Documents/git/gqlgen/api/testdata/federation2/graph/generated/generated.go:4118:17: ec.unmarshalInputlink__Import undefined (type *executionContext has no field or method unmarshalInputlink__Import)
        /Users/steve/Documents/git/gqlgen/api/testdata/federation2/graph/generated/generated.go:4126:12: ec._link__Import undefined (type *executionContext has no field or method _link__Import)
        , wantErr false
    --- FAIL: TestGenerate/federation2 (7.45s)

=== FAIL: api TestGenerate (12.63s)

This is because both the *executionContext methods mentioned unmarshalInputlink__Import and _link__Import have not been added in https://github.com/99designs/gqlgen/blob/master/plugin/federation/federation.gotpl and are not exempted from being required somehow.

[StevenACoffman]

I modified that federation.gotpl to have this chunk to get the tests to succeed after applying the suggested fix in my other comment:

{{ reserveImport "github.com/vektah/gqlparser/v2/ast" }}

{{ reserveImport "github.com/99designs/gqlgen/plugin/federation/fedruntime" }}
{{ reserveImport "github.com/99designs/gqlgen/graphql" }}

var (
	ErrUnknownType = errors.New("unknown type")
	ErrTypeNotFound = errors.New("type not found")
)

func (ec *executionContext) __resolve__service(ctx context.Context) (fedruntime.Service, error) {
	if ec.DisableIntrospection {
		return fedruntime.Service{}, errors.New("federated introspection disabled")
	}

	var sdl []string

	for _, src := range sources {
		if src.BuiltIn {
			continue
		}
		sdl = append(sdl, src.Input)
	}

	return fedruntime.Service{
		SDL: strings.Join(sdl, "\n"),
	}, nil
}

func (ec *executionContext) unmarshalInputlink__Import(ctx context.Context, v  interface{}) (string, error) {
	fmt.Println("Yahoo-hoo-hooey")
	return "", nil
}

func (ec *executionContext) _link__Import(ctx context.Context, sel ast.SelectionSet, v  interface{}) graphql.Marshaler {
	fmt.Println("Yahoo-hoo-hooey")
	return nil
}

These are silly, but something better should go there or have them not be required.

[lleadbet]

These are silly, but something better should go there or have them not be required.

Agreed- was copying Apollo's material, but since those imports are just strings, decided to convert it into [String!] instead of the custom scalar.

[coveralls]

Coverage increased (+0.2%) to 74.735% when pulling 6fbe6f1 on lleadbet:main into cddbf02 on 99designs:master.

[lleadbet]

https://github.com/99designs/gqlgen/runs/6159890288?check_suite_focus=true#step:6:27

I have, however it still fails; would be curious on the fix here.

[StevenACoffman]

You need to run cd ~/_examples/; go generate ./... i think

[StevenACoffman]

Thanks!