[unnecessary-else] Add option to disable error at else-if statements

[timocov]

Feature request

Is your feature request related to a problem? Please describe.

It would be nice to have an option to configure unnecessary-else rule to don't fail on else if statements (only on else).

[JoshuaKGoldberg]

Hi @timocov! Could you explain more on why you want this rule option? It seems rather arbitrary to allow else if but not else.

[timocov]

For me it looks strange to change a code from

if (a > 0) {
  return 1;
} else if (a < 0) {
  return 2;
} else {
  return 3;
}

to

if (a > 0) {
  return 1;
}

if (a < 0) {
  return 2;
}

return 3;

These conditions are related and (for me) they should be in "one flow" (not separated conditions), because if someone decide to add new condition between if (a > 0) { and if (a < 0) { it "breaks" their relating.

But I agree, that else block in this case is unnecessary and should be "removed":

if (a > 0) {
  return 1;
} else if (a < 0) {
  return 2;
}

return 3;

[JoshuaKGoldberg]

Seems reasonable as a style preference. Not very important in the context of linting, but it's nice to relax these style preference rules when requested.