Return type generics possible?

[Azarattum]

The Idea

I know this is a huge thing to ask, but would it be even theoretically possible to achieve type-safety with the return type? So you can just:

const todos = await sql`SELECT * FROM todos`;

Where sql manages sql connection, executes query and returns a type-safe result based on schema.

Possible Implementation?

So, there are native intrinsic generic implementation in typescript already for string-manipulation stuff like Uppercase:

type Uppercase<S extends string> = intrinsic;

Would it be possible to add more of these intrinsic types via a plugin?.. So we could have something like:

type SQLResult<T extends TemplateStringsArray> = intrinsic;

That we can then use in our sql template function implementation.

[frigus02]

As far as I know plugins cannot interfere with type checking. They cannot contribute intrinsic types. So this is not possible today.

That said, TypeScript can do some amazing inference on strings. I wonder if you could combine the sql function with something like this:

type SQL<Statement extends string> =
    Statement extends `SELECT ${infer Column} FROM ${infer Table}` ?
    { column: Column, table: Table } : { error: "Cannot parse SQL query" }

type Foo = SQL<"SELECT name FROM users">;
//   ^? type Foo = { column: "name"; table: "users"; }

Playground link

[Azarattum]

The problem is that we cannot get a const string type with template literals due to this: microsoft/TypeScript#33304

So, it's not possible to implement purely in TypeScript currently. I was hoping there were some workarounds for plugins...