…r (mytuny)

This PR was merged into the 6.1 branch.

Discussion
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[ExpressionLanguage] Add support for null-safe operator

| Q             | A
| ------------- | ---
| Branch?       | 6.1
| Bug fix?      | no
| New feature?  | yes
| Deprecations? | no
| Tickets       | Fix #45411, #21691
| License       | MIT
| Doc PR        | symfony/symfony-docs#16630

This is a long-time-lasting feature for the `ExpressionLanguage` component. I've been waiting for the support of `Nullsafe operator` in expressions dealing with mutable objects, until I finally decided to work on it once for all 👍

The lack of [nullsafety feature](https://wiki.php.net/rfc/nullsafe_operator) has been repeatedly reported as a BUG several time  (e.g [#45411](#45411) & [#21691](#21691)) when it is actually a missing feature.

Currently, expressions like `foo.bar` assumes that the property `bar` "always" exists on the object `foo` and if doesn't the parser throws a `RuntimeException`. Although, sometimes, that's exactly the behavior we need, some other times we may work with mutable objects with uncontrolled structure, thus, such assumption is error-prone and will force adding extra checks making the expression uglier and less readable.

The proposed work, introduces the support for the `?.` syntax alongside with the usual `.` syntax to help working with objects with dynamic structure. The two notations works identically in all normal cases. The difference occurs when trying to access non-existant properties and/or methods where the `.` notation will throw a `RuntimeException` as usual and the `?.` notation will return `null` instead and no errors nor exceptions will be thrown. Hence the name "Null-Safe".

PS: This work account ONLY for accessing **object's** properties and methods. It does not account for non-existant **array** items which is a seperate problem that can be addressed by introducing the [null coalescing](https://wiki.php.net/rfc/isset_ternary) operator. Another feature that I'm currently working on as well 💯

Commits
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946c59f [ExpressionLanguage] Add support for null-safe operator

…yntax (mytuny)

This PR was merged into the 6.2 branch.

Discussion
----------

[ExpressionLanguage] Add support for null coalescing syntax

| Q             | A
| ------------- | ---
| Branch?       | 6.1
| Bug fix?      | no
| New feature?  | yes
| Deprecations? | no
| Tickets       | Fix #45411, #21691
| License       | MIT
| Doc PR        | symfony/symfony-docs#16743

This is another waited feature for the syntax of the expression-language component. The [null-coalescing](https://wiki.php.net/rfc/isset_ternary) operator ``??`` becomes a need for variant programming needs these days.

Following my previous PR introducing the null-safe operator (#45795). I'm hereby introducing yet another essential operator to make the syntax even more complete.

The null-coalescing operator is a syntactic sugar for a common use of ternary in conjunction with ``isset()`` (in PHP) or equivalent in other languages. This is such a common use-case to the point that almost all majors programming syntax nowadays support a sort of a short-hand for that operation namely coalescing operator. Now it's time for the syntax of Expression-Language to do so!

Expressions like:

* ``foo.bar ?? 'default'``
* ``foo[3] ?? 'default'``
* ``foo.bar ?? foo['bar'] ?? 'default'``

will default to the expression in the right-hand-side of the ``??`` operator whenever the expression in the left-hand-side of it does not exist or it's ``null``. Note that this coalescing behavior can be chained and the validation logic takes decreasing priority from left to right.

Commits
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8e3c505 [ExpressionLanguage] Add support for null coalescing syntax