Typescript: Should a `new` expression with type arguments need parentheses?

[DanielRosenwasser]

// @target es6

// @filename: file1.ts
let stuff1 = new Array<string>;

// @filename: file2.ts
let stuff2 = new Map<string, number>;

This code currently errors with

'(' expected.

I actually don't care if this code should be allowed or not.

Maybe it should, in which case this is a bug on needing to allow the code.

Maybe it shouldn't, in which case I think we should give a better error message like

A 'new' expression with type arguments must always be followed by a parenthesized argument list.

[RyanCavanaugh]

Approximately infinity years ago we decided that parens were required in this case, to simplify the grammar and reduce the chances of ambiguity.

[hi-rustin]

@DanielRosenwasser I want to working on it, can I take this? Could you please add more info about how to fix it?

[DanielRosenwasser]

1. Add the new error message to src/compiler/diagnosticMessages.json
2. Run npx gulp generate-diagnostics

3. In src/compiler/parser.ts

   https://github.com/microsoft/TypeScript/blob/37569d01f6a67ef4cca4fac46dfbff646137b9d9/src/compiler/parser.ts#L5202

   you'll want to write something like

   if (token() === SyntaxKind.OpenParenToken) {
      node.arguments = parseArgumentList();
   }
   else if (node.typeArguments) {
      // issue the error here using parseErrorAt(fullStart, scanner.getStartPos(), ...)
   }
   

4. Try running npx gulp runtests-parallel. There is at least one test that should break:

   https://github.com/microsoft/TypeScript/blob/37569d01f6a67ef4cca4fac46dfbff646137b9d9/tests/cases/conformance/expressions/newOperator/newOperatorErrorCases.ts#L32

5. Run npx gulp baseline-accept

[DanielRosenwasser]

Thanks @Rustin-Liu!