Serialize multi-line strings as block strings

[SimonSapin]

Fixes https://github.com/apollographql/apollo-rs/issues/664

[SimonSapin]

Should we also prefer block strings for single-line descriptions? (As opposed to string Values)

[SimonSapin]

It looks like graphql-js:

• Always prefers block strings for descriptions
• StringValue objects can contain a isBLockString boolean flag… but nothing ever sets it?
• Block string printing has some heuristics to decide whether to add leading/trailing newlines

@IvanGoncharov did I miss something?

[goto-bus-stop]

Did the new pushes change something or is it just a rebase?

[SimonSapin]

Rebase to make CI pass + removing the obsolete comment

[IvanGoncharov]

StringValue objects can contain a isBLockString boolean flag… but nothing ever sets it?

@SimonSapin The flag called, block is isBLockString just an alias in this particular destruction. It is set in parser: https://github.com/graphql/graphql-js/blob/0b7590f0a2b65e6210da2e49be0d8e6c27781af2/src/language/parser.ts#L713 This allows graphql-js to do round-trip where block string is parsed and when printed as block string.

Always prefers block strings for descriptions

Yes, note that not every string can be printed as block string.

Block string printing has some heuristics to decide whether to add leading/trailing newlines

Yes, in graphql-js we had a bug where by printing string as block string we were loosing some characters so I spend bunch of time figuring out different heuristics that preserved all characters.

[SimonSapin]

New commit to make stylistic choices closer to graphql-js:

• Prefer block strings for descriptions
• For short single-line values serialize block strings as """example""", except for trailing characters that would make it incorrect