PHP RFC: Revisit trailing commas in function arguments

Introduction

Arrays in PHP have long since supported trailing commas.

$foo = [
    'foo',
    'bar',
];

This makes for clean diffs and easy appending of new values in user-land.

Unfortunately, the argument list for function/method declarations and calls do not share the same luxury.

// Parse error
function myFunc(
    $foo,
    $bar,
    ) {
  /* ... */
}

// Parse error
myFunc(
    $foo,
    $bar,
    );

This RFC proposes allowing function/method declarations and calls to allow for trailing commas in order to:

Offer a consistent API and match the existing array functionality.
Make it easy to append new arguments in user-land.
Have cleaner diffs (so only one line shows up as being modified when appending arguments instead of two).
Match what HHVM did a while ago.

This change would have no breaking changes.

PHP 7.1

Project requires a 2/3 majority.