Multiline trailing comma rule flags type parameters

[wmrowan]

Bug Report

• TSLint version: 4.0.1
• TypeScript version: 2.1.1
• Running TSLint via: CLI

TypeScript code being linted

somefunction<
  TypeArg1,
  TypeArg2
>(
  arg1,
  arg2,
);

with tslint.json configuration:

{
    "trailing-comma": [true, {"multiline": "always", "singleline": "never"}]
}

Actual behavior

TSLint flags line 3 in the sample code as a lint error. TSLint says that this line should have a trailing comma.

Expected behavior

TSLint should not flag this as a lint failure as a trailing comma is not allowed here by Typescript. Adding a comma to satisfy the linter will result in a Typescript compile error. While I think I personally agree with TSLint that a comma should be allowed here to be consistent with non-type function arguments, Typescript nevertheless disallows this syntax. While I think it would be reasonable to ask Typescript to fix this inconsistency, TSLint should probably be consistent with Typescript in the meantime.

[jmlopez-rod]

Perhaps more options need to be available, see eslint comma-dangle. With TSLint we need an option for generics.

[adidahiya]

yeah, makes sense, if it is not valid TypeScript then TSLint should not flag it as a violation. accepting PRs to fix this in the default rule behavior

[mizunashi-mana]

Missing such case:

var foo = <
    A,
    B
     ~ [Missing trailing comma] // expecting no warnings
>(a: A, b: B) => 42;

This issue should be reopened.
However, this may be caused by syntax parser.

[mizunashi-mana]

I found another case:

function foo(a: [
  number,
  string
  ~ [Missing trailing comma] // expecting no warnings
]): void {
  return 42; 
}

[hitendramalviya]

Is there any workaround to get this fixed or we just need to sicked with // tslint:disable-next-line:trailing-comma ? But due to this my ts file looks ugly.

[adidahiya]

this was fixed by a277873, available in v4.1+

[nchen63]

I tested @mizunashi-mana's 2 test cases above and they're not fixed in 4.3.1

[nchen63]

actually, #1905 was opened to cover those issues