Fix completions of optional properties in generic positions

[Andrew Branch (andrewbranch)]

Builds on #32100

Fixes#30507
Fixes#28470

Notable changes from #32100:

• Doesn’t cache an alternative type during inference (Wesley Wigham (@weswigham)’s change request on the original PR)
• Rather than getting the contextual type from the base signature alone, this intersects the types from the base signature and the resolved signature, so that in a case like

typeU={x: boolean};declarefunctionf<TextendsPartial<U>>(x: T,y: T)f({a: true},{/**/});

you get completions for both xanda. Thanks to Daniel Rosenwasser (@DanielRosenwasser) for that suggestion.

[Tim Suchanek (timsuchanek)]

Awesome! Would be great to see this merged!

[Nathan Shively-Sanders (sandersn)]

One test idea plus some nits.

[Avi Vahl (AviVahl)]

Andrew Branch (@andrewbranch) this also fixes #28470

[Andrew Branch (andrewbranch)]

Ugh, committing PR review suggestions from GitHub UI doesn’t work in checker.ts 😑

[Daniel Rosenwasser (DanielRosenwasser)]

🎉

[Tim Suchanek (timsuchanek)]

Very excited to see this merged 🙏
One question: How can I try it out in VSCode?
Unfortunately I'm not able to use this properly yet, even though setting "typescript.tsdk" in my settings.json to node_modules/typescript/lib .

This example should now work in VSCode and show world as a completion:

interfaceMyOptions{hello?: booleanworld?: boolean}declarefunctionbar<TextendsMyOptions>(options?: Partial<T>): voidbar({hello: true,/* cursor */})

Andrew Branch (@andrewbranch) can you confirm that this example is now working for you?

[Tim Suchanek (timsuchanek)]

I added a small PR to add exactly that test case, as it's important for us at Prisma that this one works.

#34559

[Andrew Branch (andrewbranch)]

Tim Suchanek (@timsuchanek) yep, that example works in VS Code for me:

setting "typescript.tsdk" in my settings.json to node_modules/typescript/lib.

If you’re building the source from master, you want to set the path to built/local. The one in the repo’s node_modules is just whatever the nightly was whenever you last did a clean npm install 😄

[Tim Suchanek (timsuchanek)]

Awesome. I didn't know about the built/local. That also works for me.
Thanks a lot!