So Doctrine annotations are based on JSON but as PHP arrays allow for dangling commas Drupal people are much used to this and to be honest, it's much easier to edit
(
"foo" => "bar",
"foo1" => "bar1",
)
so that the rows can be switched, another row added etc than if that comma after bar1 were missing.
So I am trying to patch Doctrine to allow for this. The maintainer claims
you are mixing grammar rules by checking a token that is not part of "Values", but its parent, "Annotation".
And he is right. So, we are looking for a better grammar.
Annotation ::= "@" AnnotationName ["(" [Values] ")"]
Values ::= Array | Value {"," Value}*
How would you allow for a trailing comma in Values?
The modified grammar is not LL(1) anymore. As a consequence the simple recursive descent parser implemented by Doctrine requires backtracking.
In this case, you need to make sure that ::Value() can backtrack, ie. trigger an exception and reset the parsing to the position it was in before entering ::Value(). You catch this exception and just ignore it in ::Values() as soon as you already have one valid value.
That requires to be able to seek in the lexer, and I don't know how practical it is. AbstractLexer is quite a bit weird.
Edit: The easiest way forward would be to keep the grammar in a LL(1) form. One way of doing that is to move the parenthesis inside Values:
Values ::= "(" [Array | Value {"," Value}* [","] ] ")"