In the following query, all directives declared in the ancestor fields are lost, only the ones in the leaf fields are parsed correctly from the AST:

query {
  ancestorField @thisDirectiveIsLost { 
    leafField @thisDirectiveWorksWell
  }
}

For instance, in this query the @include directive is lost, and title is included when it should not:

query {
  post(id:1) @include(if: false) { 
    title
  }
}

Inspecting the code, I found out that in Parser/Parser.php, function parseOperation, the operation type directive is being set into $operation:

$operation->setDirectives($directives);

However, the $operation already had its own directives, parsed through parseBodyItem. Hence, these are being overridden.

Merging the 2 sets of directives, instead, it works well:

$operation->setDirectives(array_merge(
    $directives,
    $operation->getDirectives()
));

Is that the right solution? Must directives defined next to the operation type be copied into all ancestor fields? And what about leaf fields, which currently have no problem with their own directives? (This solution seems to fix the bug, but I don't know if I may be creating another one? I can't find any reference in the GraphQL spec to what is the expected behavior for operation type directives...)