Symfony Polyfill
================

This project backports features found in the latest PHP versions and provides
compatibility layers for some extensions and functions. It is intended to be
used when portability across PHP versions and extensions is desired.

Polyfills are provided for:
- the `apcu` extension when the legacy `apc` extension is installed;
- the `ctype` extension when PHP is compiled without ctype;
- the `deepclone` extension (`deepclone_to_array` and `deepclone_from_array` functions);
- the `mbstring` and `iconv` extensions;
- the `uuid` extension;
- the `MessageFormatter` class and the `msgfmt_format_message` functions;
- the `Normalizer` class and the `grapheme_*` functions;
- the `utf8_encode` and `utf8_decode` functions from the `xml` extension or PHP-7.2 core;
- the `Collator`, `NumberFormatter`, `Locale`, `IntlDateFormatter` and
  `IntlListFormatter` classes, limited to the "en" locale;
- the `intl_error_name`, `intl_get_error_code`, `intl_get_error_message` and
  `intl_is_failure` functions;
- the `idn_to_ascii` and `idn_to_utf8` functions;
- a `Binary` utility class to be used when compatibility with
  `mbstring.func_overload` is required;
- the `spl_object_id` and `stream_isatty` functions introduced in PHP 7.2;
- the `mb_ord`, `mb_chr` and `mb_scrub` functions introduced in PHP 7.2 from the `mbstring` extension
- the `sapi_windows_vt100_support` function (Windows only) introduced in PHP 7.2;
- the `PHP_FLOAT_*` constant introduced in PHP 7.2;
- the `PHP_OS_FAMILY` constant introduced in PHP 7.2;
- the `is_countable` function introduced in PHP 7.3;
- the `array_key_first` and `array_key_last` functions introduced in PHP 7.3;
- the `hrtime` function introduced in PHP 7.3;
- the `JsonException` class introduced in PHP 7.3;
- the `normalizer_get_raw_decomposition` function introduced in PHP 7.3;
- the `get_mangled_object_vars`, `mb_str_split` and `password_algos` functions
  introduced in PHP 7.4;
- the `fdiv` function introduced in PHP 8.0;
- the `get_debug_type` function introduced in PHP 8.0;
- the `preg_last_error_msg` function introduced in PHP 8.0;
- the `str_contains` function introduced in PHP 8.0;
- the `str_starts_with` and `str_ends_with` functions introduced in PHP 8.0;
- the `ValueError` class introduced in PHP 8.0;
- the `UnhandledMatchError` class introduced in PHP 8.0;
- the `FILTER_VALIDATE_BOOL` constant introduced in PHP 8.0;
- the `get_resource_id` function introduced in PHP 8.0;
- the `Attribute` class introduced in PHP 8.0;
- the `Stringable` interface introduced in PHP 8.0;
- the `PhpToken` class introduced in PHP 8.0 when the tokenizer extension is enabled;
- the `array_is_list` function introduced in PHP 8.1;
- the `enum_exists` function introduced in PHP 8.1;
- the `MYSQLI_REFRESH_REPLICA` constant introduced in PHP 8.1;
- the `ReturnTypeWillChange` attribute introduced in PHP 8.1;
- the `CURLStringFile` class introduced in PHP 8.1 (but only if PHP >= 7.4 is used);
- the `CURLOPT_ISSUERCERT_BLOB` constant introduced in PHP 8.1 when curl 7.47+ is used;
- the `AllowDynamicProperties` attribute introduced in PHP 8.2;
- the `SensitiveParameter` attribute introduced in PHP 8.2;
- the `SensitiveParameterValue` class introduced in PHP 8.2;
- the `Random\Engine` interface introduced in PHP 8.2;
- the `Random\CryptoSafeEngine` interface introduced in PHP 8.2;
- the `Random\Engine\Secure` class introduced in PHP 8.2 (check [arokettu/random-polyfill](https://packagist.org/packages/arokettu/random-polyfill) for more engines);
- the `odbc_connection_string_is_quoted` function introduced in PHP 8.2;
- the `odbc_connection_string_should_quote` function introduced in PHP 8.2;
- the `odbc_connection_string_quote` function introduced in PHP 8.2;
- the `ini_parse_quantity` function introduced in PHP 8.2;
- the `CURLOPT_SSH_HOST_PUBLIC_KEY_SHA256` constant introduced in PHP 8.1 when curl 7.50+ is used;
- the `json_validate` function introduced in PHP 8.3;
- the `Override` attribute introduced in PHP 8.3;
- the `mb_str_pad` function introduced in PHP 8.3;
- the `ldap_exop_sync` function introduced in PHP 8.3;
- the `ldap_connect_wallet` function introduced in PHP 8.3;
- the `stream_context_set_options` function introduced in PHP 8.3;
- the `str_increment` and `str_decrement` functions introduced in PHP 8.3;
- the `Date*Exception/Error` classes introduced in PHP 8.3;
- the `SQLite3Exception` class introduced in PHP 8.3;
- the `mb_ucfirst` and `mb_lcfirst` functions introduced in PHP 8.4;
- the `array_find`, `array_find_key`, `array_any` and `array_all` functions introduced in PHP 8.4;
- the `Deprecated` attribute introduced in PHP 8.4;
- the `mb_trim`, `mb_ltrim` and `mb_rtrim` functions introduced in PHP 8.4;
- the `ReflectionConstant` class introduced in PHP 8.4
- the `CURL_HTTP_VERSION_3` and `CURL_HTTP_VERSION_3ONLY` constants introduced in PHP 8.4;
- the `grapheme_str_split` function introduced in PHP 8.4;
- the `bcceil`, `bcdivmod`, `bcfloor` and `bcround` functions introduced in PHP 8.4;
- the `PDO` driver specific sub-classes introduced in PHP 8.4;
- the `get_error_handler` and `get_exception_handler` functions introduced in PHP 8.5;
- the `NoDiscard` attribute introduced in PHP 8.5;
- the `array_first` and `array_last` functions introduced in PHP 8.5;
- the `DelayedTargetValidation` attribute introduced in PHP 8.5;
- the `Filter\FilterException` class introduced in PHP 8.5;
- the `Filter\FilterFailedException` class introduced in PHP 8.5;
- the `grapheme_levenshtein` function introduced in PHP 8.5;
- the `locale_is_right_to_left` function introduced in PHP 8.5;
- the `clamp` function introduced in PHP 8.6;
- the `ARRAY_FILTER_USE_VALUE` constant introduced in PHP 8.6;
- the `SortDirection` enum introduced in PHP 8.6;
- the `grapheme_strrev` function introduced in PHP 8.6;
- the `Io\Poll` API and `StreamPollHandle` introduced in PHP 8.6 (requires PHP >= 8.1; only the `Poll` backend is available);

It is strongly recommended to upgrade your PHP version and/or install the missing
extensions whenever possible. This polyfill should be used only when there is no
better choice or when portability is a requirement.

Design principles
=================

Polyfills target the API of the latest PHP version and backport it to older ones.
The goal is that code written for a recent PHP runs unchanged on the oldest
supported version; it is not to reproduce the historical behavior of every
intermediate version. In practice:

- New functions, classes, constants and arguments are backported; removed or
  legacy behavior is not. For example, the `is_hex` argument that
  `mb_decode_numericentity()` lost in PHP 8.0 is not accepted by the polyfill.
- A symbol is backported only when defining it carries the native effect.
  A constant whose sole purpose is to switch on behavior in a function that
  cannot be polyfilled is left undefined, so its absence stays usable for feature
  detection, e.g. `FILTER_THROW_ON_FAILURE`, which only configures `filter_var()`.
  Declarative symbols such as attributes are polyfilled even when their runtime
  effect needs engine support, since reflection still conveys their semantics.
- A polyfill runs only when the native symbol is missing, so it reproduces the
  contract of the function it shims rather than a blanket "PHP 7" or "PHP 8"
  behavior. Functions that always raised a `ValueError` on invalid input throw on
  every supported version (a `ValueError` stub is declared on PHP < 8 where
  needed); functions whose native contract returned `false` keep returning
  `false`.
- The signatures declared by the bootstrap files match the native signature of
  the PHP version being run, so the polyfill stays a drop-in that the engine can
  supersede. New arguments that cannot be implemented are accepted and ignored,
  e.g. the `$locale` argument added to the `grapheme_*()` functions in PHP 8.5.
- Extensions that were never bundled with PHP, such as `uuid` and `deepclone`,
  follow the extension's own release history rather than PHP's. Since a polyfill
  cannot influence `extension_loaded()` nor conditionally define constants, it
  mirrors the newest native state, including deprecations: `UUID_TYPE_DCE` and
  `UUID_TYPE_NAME` are defined with a `Deprecated` attribute on PHP 8.5+.
- When a function is provided by both an extension polyfill (`Mbstring`) and a
  version polyfill (`Php74`, `Php83`, `Php84`), both implementations must behave
  identically, because either one may end up registered depending on the PHP
  version and whether the extension is loaded.

Compatibility notes
===================

To write portable code between PHP5 and PHP7, some care must be taken:
- `\*Error` exceptions must be caught before `\Exception`;
- after calling `error_clear_last()`, the result of `$e = error_get_last()` must be
  verified using `isset($e['message'][0])` instead of `null !== $e`.

Usage
=====

When using [Composer](https://getcomposer.org/) to manage your dependencies, you
should **not** `require` the `symfony/polyfill` package, but the standalone ones:
- `symfony/polyfill-apcu` for using the `apcu_*` functions,
- `symfony/polyfill-ctype` for using the ctype functions,
- `symfony/polyfill-deepclone` for using the `deepclone_*` functions,
- `symfony/polyfill-php54` for using the PHP 5.4 functions,
- `symfony/polyfill-php55` for using the PHP 5.5 functions,
- `symfony/polyfill-php56` for using the PHP 5.6 functions,
- `symfony/polyfill-php70` for using the PHP 7.0 functions,
- `symfony/polyfill-php71` for using the PHP 7.1 functions,
- `symfony/polyfill-php72` for using the PHP 7.2 functions,
- `symfony/polyfill-php73` for using the PHP 7.3 functions,
- `symfony/polyfill-php74` for using the PHP 7.4 functions,
- `symfony/polyfill-php80` for using the PHP 8.0 functions,
- `symfony/polyfill-php81` for using the PHP 8.1 functions,
- `symfony/polyfill-php82` for using the PHP 8.2 functions,
- `symfony/polyfill-php83` for using the PHP 8.3 functions,
- `symfony/polyfill-php84` for using the PHP 8.4 functions,
- `symfony/polyfill-php85` for using the PHP 8.5 functions,
- `symfony/polyfill-iconv` for using the iconv functions,
- `symfony/polyfill-intl-grapheme` for using the `grapheme_*` functions,
- `symfony/polyfill-intl-idn` for using the `idn_to_ascii` and `idn_to_utf8` functions,
- `symfony/polyfill-intl-icu` for using the intl functions and classes,
- `symfony/polyfill-intl-messageformatter` for using the intl messageformatter,
- `symfony/polyfill-intl-normalizer` for using the intl normalizer,
- `symfony/polyfill-io-poll` for using the `Io\Poll` API and `StreamPollHandle`,
- `symfony/polyfill-mbstring` for using the mbstring functions,
- `symfony/polyfill-util` for using the polyfill utility helpers.
- `symfony/polyfill-uuid` for using the `uuid_*` functions,

Requiring `symfony/polyfill` directly would prevent Composer from sharing
correctly polyfills in dependency graphs. As such, it would likely install
more code than required.

Design
======

This package is designed for low overhead and high quality polyfilling.

It adds only a few lightweight `require` statements to the bootstrap process
to support all polyfills. Implementations are then loaded on-demand when
needed during code execution.

If your project requires a minimum PHP version it is advisable to add polyfills
for lower PHP versions to the `replace` section of your `composer.json`.
This removes any overhead from these polyfills as they are no longer part of your project.
The same can be done for polyfills for extensions that you require.

If your project requires php 7.0, and needs the mb extension, the replace section would look
something like this:

```json
{
    "replace": {
        "symfony/polyfill-php54": "*",
        "symfony/polyfill-php55": "*",
        "symfony/polyfill-php56": "*",
        "symfony/polyfill-php70": "*",
        "symfony/polyfill-mbstring": "*"
    }
}
```

Polyfills are unit-tested alongside their native implementation so that
feature and behavior parity can be proven and enforced in the long run.

License
=======

This library is released under the [MIT license](LICENSE).
