Add support for completions inside string literals

[mhegazy]

Fixes #606

This supports completions in string literals in the following locations:

1. argument to a call expression whose target parameter has a StringLiteralType

   declare function f(a: "A", b: number): void;
   declare function f(a: "B", b: number): void;
   declare function f(a: "C", b: number): void;
   
   f(" // A | B | C

2. argument expression of an element access expression

   var o = {
   "#invlaid identifier name": 1
   };
   
   o["| // #invlaid identifier name

3. a string literal contextually typed by a string literal type

   type Options = "Option 1" | "Option 2" | "Option 3";
   var x: Options = "| // Option 1 | Option 2 | Option 3

This PR does not cover:

• module name completion
• changing o. to o[""] if the completion entry is not a valid identifier name

[DanielRosenwasser]

I think we can eventually generalize this logic to other types as well

[mhegazy]

i suppose if we do pre-selecting of completion entries based on contextual type.

[DanielRosenwasser]

Very cool! Looks like this doesn't include the quote character, right?

[DanielRosenwasser]

This seems like a slightly weird sort of dependency. Ideally there would be an API on the type checker like getPossibleContextualTypes

[mhegazy]

this is not contextual type per se. but sure. If there is another use case for such API we can push it into the checker, but this is the only one, i would keep it at the use site.

[mhegazy]

Very cool! Looks like this doesn't include the quote character, right?

yes. i am assuming here that automatic brace completion would get that done for you, or you have them written already.

we should add replaceText, and replaceRange on CompletionEntry, to allow that. there are some issues with Roslyn API currently that makes this hard, but i believe should be better in next version.

[mhegazy]

@yuit and @DanielRosenwasser any more comments?

[yuit]

Why you have to check this "node.parent.argumentExpression === node"?

[mhegazy]

"expression"["index"] want to make sure we are on "index"

[yuit]

others than the small comments, look good 🍰.

[yuit]

Why you start perform checking for characters?

[mhegazy]

not sure really. this is how it was before adding the argument. let me look more into it.

[Thaina]

Are there any jsdoc comment syntax I could made to use this feature in javascript with salsa?

[DanielRosenwasser]

@Thaina check out #9902 and #9995.