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const TemplateStringsArray for TaggedTemplateExpression #31422

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@xialvjun

Description

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TemplateStringsArray, TaggedTemplateExpression

Suggestion

There shouldn't be a type TemplateStringsArray, it should be a const string tuple type, so we can write code:

interface SQL<TSA, VS> {
  texts: TSA;
  values: VS;
}

function sql<TSA extends readonly string[], VS extends any[]>(texts:TSA, ...values: VS): SQL<TSA, VS> {
  return { texts, values };
}

// then
let s: SQL<['select * from person where a=', ' and b=', ''], [number, Date]> = sql`select * from person where a=${1} and b=${new Date()}`;

Use Cases

Just like in the above code, we can test the sql at compile time or use a TypeScript Language Service Plugin (in fact, I'm writing itts-sql-plugin and then come across this problem).

Examples

Checklist

My suggestion meets these guidelines:

  • This wouldn't be a breaking change in existing TypeScript/JavaScript code
  • This wouldn't change the runtime behavior of existing JavaScript code
  • This could be implemented without emitting different JS based on the types of the expressions
  • This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
  • This feature would agree with the rest of TypeScript's Design Goals.

There is another issue is alike. #16552 (comment)

Besides, TemplateStringsArray is ReadonlyArray<string>, it should be const anyway.

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