No trailing comma for function calls with only a single argument

This is a formatting request. When I enable trailingCommas: 'all' it always bothers me that Prettier adds a trailing comma to a function call with a single item. I think it would look aesthetically better if Prettier did not include a trailing comma only for function calls with a single argument. Below are two examples of code I wish didn’t include the trailing comma.

Prettier 1.18.2 Playground link

--parser babylon
--trailing-comma all

Input:

client.execute(Post.selectAll().where(Post.id.eq(42)).where(Post.published.eq(true)));

array.map(item => item.reallyReallyReallyReallyReallyReallyReallyReallyLongMethodName());

Output:

client.execute(
  Post.selectAll()
    .where(Post.id.eq(42))
    .where(Post.published.eq(true)),
);

array.map(item =>
  item.reallyReallyReallyReallyReallyReallyReallyReallyLongMethodName(),
);

Desired behavior:

client.execute(
  Post.selectAll()
    .where(Post.id.eq(42))
    .where(Post.published.eq(true))
);

array.map(item =>
  item.reallyReallyReallyReallyReallyReallyReallyReallyLongMethodName()
);

[kaicataldo]

Do you mind explaining why the number of arguments should matter here? The argument I usually see for enforcing trailing commas is to minimize diff noise, and it feels like doing this would defeat the purpose of using trailing commas at all.

[fisker]

I don’t think we can accept this, we print , for array and objects

Prettier 2.0.5 Playground link

--arrow-parens avoid
--parser babel
--trailing-comma all

Input:

a = [
  item => item.reallyReallyReallyReallyReallyReaongMethodNamereallyReallyLongMethodName()
];

a = {
  foo: item => item.reallyReallyReallyReallyReallyReaongMethodNamereallyReallyLongMethodName()
}

Output:

a = [
  item =>
    item.reallyReallyReallyReallyReallyReaongMethodNamereallyReallyLongMethodName(),
];

a = {
  foo: item =>
    item.reallyReallyReallyReallyReallyReaongMethodNamereallyReallyLongMethodName(),
};