Change Diagnostic.code to 'string | number'

[ajafff]

I'm writing a LanguageService plugin for TypeScript that returns custom diagnostics. A Diagnostic needs to have a code property of type number.

I don't have a number. Instead I can provide a string that represents the name of the rule producing the diagnostic. In addition a random number I would choose looks quite ugly in the tooltip VSCode displays for the Diagnostic.

I know TypeScript only ever creates Diagnostics with numeric code, but it's too limiting for plugins.
I looked it up and the LanguageServer protocol specifies it as code?: number | string.

My current workaround is to use a type assertion. Until now nothing bad has happened.

[weswigham]

@DanielRosenwasser I wholeheartedly agree with this - I've made it twice in PRs we never merged about extensibility - it just makes a lot of sense for diagnostics that aren't from us.

[DanielRosenwasser]

Seems pretty reasonable to me.

[ajafff]

Continuing discussion from #28959

it might be better to return a new property on Diagnostic objects.

Does this only affect Diagnostic (DiagnosticRelatedInformation to be precise) or should it also be added to DiagnosticMessageChain and/or DiagnosticMessage?

Does this require a change to the LanguageServerProtocol spec?