Actually have a chance to reuse optional property signatures in the node builder

[weswigham]

As you can see, I'd forgotten PropertyDeclaration and PropertySignature were not caught by the same check when I originally wrote this comparison, so optional property signatures (that didn't have an explicit undefined written out) never got reused in the node builder. And PropertySignatures are the ones actually within type nodes!

[jakebailey]

I feel nervous about this one in the same way I felt nervous about other reuses when exactOptionalPropertyTypes gets involved. Makes me wonder if all of these sorts of things have accidentally made the flag easier to use...

[weswigham]

Makes me wonder if all of these sorts of things have accidentally made the flag easier to use...

Hope not, since if you write a declaration at the top level, it's already appropriately kept in the fashion in which it was written. Here's a demonstration:

// @declaration: true
// @strict: true
export const a: { key?: { x?: number } } = {};
                 //^?


export const b = () => ([null as any as { key?: { x?: number } }][0]);
           //^?

Workbench Repro

Despite being declared in the exact same way, a lacks | undefined on its' optional properties in the declaration emit (because it was defined without them and we used those nodes), while b has | undefined in all its' optional types (and quickinfo for both has | undefined). The irony here is that when you set exactOptionalPropertyTypes, this is corrected, and the | undefined is removed from both because of the missing-type-removal calls inserted to handle it. (And yes, before you ask, the inline hint for the //^? has different text than the assertion result in the sidebar - I could not tell you why; maybe inline hints in the workbench get calculated without the compiler options set?)

We already respect user intent and keep their nodes as-is sometimes, all this does is make us do it more often - that probably makes this a (at least partial) bugfix, and not just an experience improvement 🤷‍♂️

[jakebailey]

Yeah, I guess for isolated declarations we weren't going to throw | undefined on everything randomly...