Improve error when composeAndValidate is provided empty SDL

[EverlastingBugstopper]

If you pass an empty string to harmonizer::harmonize, you get this error:

UNKNOWN: Syntax Error: Unexpected <EOF>

Edit by @abernix: see my comment below for where this is probably buried.

[abernix]

Agree we can guard against this.

I suspect the fix for this lives upstream from harmonizer in (the JS) @apollo/federation to benefit both implementations. It could guard against the production of this error which is (I believe) a result of the invocation of graphql's parse on the empty input.

[abernix]

@trevor-scheer I believe you may be working around improving error messages already, so perhaps this is a low-hanging fruit. I surface this only if it's convenient; if it's not easily within reach don't worry about it!

[trevor-scheer]

Thanks @abernix. @EverlastingBugstopper I've got another issue (#605) immediately related to this error, but it's not at the top of my priority list for now. Is this something that can wait, or is it blocking / problematic in a way that can't be worked around for the time being?

[EverlastingBugstopper]

oh it can totally be worked around, not blocking at all. this is mostly just to bring it to y'alls attention for sanding down some of these rough edges 😄

[abernix]

do we want to transfer this back to federation for next steps?