Provide a type guard to distinguish between ResolveTree and FieldsByTypeName

[Nargonath]

Feature description

parseResolveInfo return type is ResolveTree | FieldsByTypeName | null | undefined. You can get rid of null | undefined with an if condition but you're left with ResolveTree | FieldsByTypeName. The problem is that simplifyParsedResolveInfoFragmentWithType expects a ResolveTree as its first argument. We need a way to tell them apart. Right now I'm using this:

function isResolveTree(
  value: ResolveTree | FieldsByTypeName,
): value is ResolveTree {
  return typeof value.name === "string" && Boolean(value.fieldsByTypeName);
}

Motivating example

It's hard to use simplifyParsedResolveInfoFragmentWithType when using TypeScript without this type guard, unless I'm doing something wrong here.

Supporting development

I [tick all that apply]:

• am interested in building this feature myself
• am interested in collaborating on building this feature
• am willing to help testing this feature before it's released
• am willing to write a test-driven test suite for this feature (before it exists)
• am a Graphile sponsor ❤️
• have an active support or consultancy contract with Graphile

[benjie]

Sure; go ahead and raise a PR for it. I'd soften the argument to value: ResolveTree | FieldsByTypeName | null | undefined personally.

[Nargonath]

Alright, thank you. I'll add it to my TODO list and I'll aim to do it ASAP.