Rule Proposal: newline-in-function-parens

EDIT: I updated options in https://github.com/eslint/eslint/issues/6074#issuecomment-217124523

---

From validateAlignedFunctionParameters.

This will require/disallow line breaks after open parentheses of function parameters and before close parentheses of function parameters.

{
    "newline-in-function-parens": ["error", "always" or "never" or "multiline" or {"minItems": 2}]
}

• "always" (default) - Requires line breaks always.
• "never" - Disallows line breaks always.
• "multiline" - Requires line breaks when the content is multiline. Otherwise, disallows line breaks.
• {"minItems": <integer>} - Requires line breaks when the number of items is more than the specific integer. Otherwise, disallows line breaks.

Valid:

/*eslint newline-in-function-parens: ["error", "always"]*/

function foo(
) {}
function foo(
    a
) {}
function foo(
    a, b
) {}
function foo(
    a,
    b
) {}
function foo(
    a = function() {
        dosomething();
    }
) {}

/*eslint newline-in-function-parens: ["error", "never"]*/

function foo() {}
function foo(a) {}
function foo(a, b) {}
function foo(a,
    b) {}
function foo(a = function() {
    dosomething();
}) {}

/*eslint newline-in-function-parens: ["error", "multiline"]*/

function foo() {}
function foo(a) {}
function foo(a, b) {}
function foo(
    a,
    b
) {}
function foo(
    a = function() {
        dosomething();
    }
) {}

/*eslint newline-in-function-parens: ["error", {"minItems": 2}]*/

function foo() {}
function foo(a) {}
function foo(
    a, b
) {}
function foo(
    a,
    b
) {}
function foo(a = function() {
    dosomething();
}) {}

Invalid:

/*eslint newline-in-function-parens: ["error", "always"]*/

function foo() {}
function foo(a) {}
function foo(a, b) {}
function foo(a,
    b) {}
function foo(a = function() {
    dosomething();
}) {}

/*eslint newline-in-function-parens: ["error", "never"]*/

function foo(
) {}
function foo(
    a
) {}
function foo(
    a, b
) {}
function foo(
    a,
    b
) {}
function foo(
    a = function() {
        dosomething();
    }
) {}

/*eslint newline-in-function-parens: ["error", "multiline"]*/

function foo(
) {}
function foo(
    a
) {}
function foo(
    a, b
) {}
function foo(a,
    b) {}
function foo(a = function() {
    dosomething();
}) {}

/*eslint newline-in-function-parens: ["error", {"minItems": 2}]*/

function foo(
) {}
function foo(
    a
) {}
function foo(a, b) {}
function foo(a,
    b) {}
function foo(
    a = function() {
        dosomething();
    }
) {}

[jesstelford]

Does this also cover newlines between arguments? If not, could we also add:

• between (default is “any”) - Setting for the line break between arguments.

Valid

/*eslint newline-in-function-parens: ["error", {"between": "multiline"}]*/

function foo(
) {}
function foo(
    a
) {}
function foo(a) {}
function foo(
    a,
    b
) {}
function foo(
    a = function() {
        dosomething();
    }
) {}

Invalid

/*eslint newline-in-function-parens: ["error", {"between": "multiline"}]*/

function foo(
    a, b
) {}

---

My use-case: We enforce max-len to 100, and for longer lines we can meet that rule by doing:

someReallyCoolFunction(this.aLongPropertyName.subPropertyNamesToo,
  this.anotherPropertyName.whySoManySubPropertyNames);

Which we would like to enforce being written as:

someReallyCoolFunction(
  this.aLongPropertyName.subPropertyNamesToo,
  this.anotherPropertyName.whySoManySubPropertyNames
);

Ie; When there is a newline anywhere, everything should be newline. Otherwise, nothing should be newline.

[mysticatea]

Original JSCS rule seems to apply this rule to FunctionDeclaration, FunctionExpression, and ArrowFunctionExpression.

I think, we can add overrides option to apply for each kind. (also, original rule can configure each paren of open/close)

{
    "newline-in-function-parens": ["error", "always" or "never" or "multiline" or {"minItems": 2} or "any"]
    // or
    "newline-in-function-parens": ["error", {
        "open": "always" or "never" or "multiline" or {"minItems": 2} or "any",
        "close": "always" or "never" or "multiline" or {"minItems": 2} or "any",
        "overrides": {
            "declaration": null,
            "expression": null,
            "arrow": null
        }
    }]
}

• “always” (default) - Requires line breaks always.

• “never” - Disallows line breaks always.

• “multiline” - Requires line breaks when the content is multiline. Otherwise, disallows line breaks.

• {“minItems”: <integer>} - Requires line breaks when the number of items is more than the specific integer. Otherwise, disallows line breaks.

• "any" - Does not warn.

• open (default is "always") - Setting for the line break after the open parenthesis.

• close (default is "always") - Setting for the line break before the close parenthesis.

• overrides - We can override setting for each kind of functions. For example:

  {
      "newline-in-function-parens": ["error", {
          "open": "multiline",
          "close": "multiline",
          "overrides": {
              "arrow": "never" // or {"open": "never", "close": "never"}
          }
      }]
  }