UPGRADING

PHP 7.4 UPGRADE NOTES

1. Backward Incompatible Changes
2. New Features
3. Changes in SAPI modules
4. Deprecated Functionality
5. Changed Functions
6. New Functions
7. New Classes and Interfaces
8. Removed Extensions and SAPIs
9. Other Changes to Extensions
10. New Global Constants
11. Changes to INI File Handling
12. Windows Support
13. Migration to pkg-config
14. Other Changes
15. Performance Improvements


========================================
1. Backward Incompatible Changes
========================================

- Core:
  . Trying to use values of type null, bool, int, float or resource as an
    array (such as $null["key"]) will now generate a notice. This does not
    affect array accesses performed by list().
    RFC: https://wiki.php.net/rfc/notice-for-non-valid-array-container
  . get_declared_classes() no longer returns anonymous classes that haven't
    been instantiated yet.
  . "fn" is now a reserved keyword. In particular it can no longer be used as a
    function or class name. It can still be used as a method or class constant
    name.
  . Passing the result of a (non-reference) list() assignment by reference is
    consistently disallowed now. Previously this worked if the right hand side
    was a simple (CV) variable and did not occur as part of the list().
  . `<?php` at the end of the file (without trailing newline) will now be
    interpreted as an opening PHP tag. Previously it was interpreted either as
    `<? php` and resulted in a syntax error (with short_open_tag=1) or was
    interpreted as a literal `<?php` string (with short_open_tag=0).
  . When using include/require on a stream, stream_set_option() will be invoked
    with the STREAM_OPTION_READ_BUFFER option. Custom stream wrapper
    implementations may need to implement the stream_set_option() method to
    avoid a warning (always returning false is a sufficient implementation).

- BCMath:
  . BCMath functions will now warn if a non well-formed number is passed, such
    as "32foo". The argument will be interpreted as zero (as before).

- Curl:
  . Attempting to serialize a CURLFile class will now generate an exception.
    Previously the exception was only thrown on unserialization.
  . Using CURLPIPE_HTTP1 is deprecated, and is no longer supported as of cURL
    7.62.0.
  . The $version parameter of curl_version() is deprecated. If any value not
    equal to the default CURLVERSION_NOW is passed, a warning is raised and the
    parameter is ignored.

- Date:
  . Calling var_dump() or similar on a DateTime(Immutable) instance will no
    longer leave behind accessible properties on the object.
  . Comparison of DateInterval objects (using ==, < and so on) will now generate
    a warning and always return false. Previously all DateInterval objects were
    considered equal, unless they had properties.

- Intl:
  . The default parameter value of idn_to_ascii() and idn_to_utf8() is now
    INTL_IDNA_VARIANT_UTS46 instead of the deprecated INTL_IDNA_VARIANT_2003.

- MySQLi:
  . The embedded server functionality has been removed. It was broken since
    at least PHP 7.0.
  . The undocumented mysqli::$stat property has been removed in favor of
    mysqli::stat().

- Openssl:
  . The openssl_random_pseudo_bytes() function will now throw an exception in
    error situations, similar to random_bytes(). In particular, an Error is
    thrown if the number of requested bytes is less than *or equal to* zero,
    and an Exception is thrown if sufficient randomness cannot be gathered.
    The $crypto_strong output argument is guaranteed to always be true if the
    function does not throw, so explicitly checking it is not necessary.
    RFC: http://php.net/manual/de/function.openssl-random-pseudo-bytes.php

- PCRE:
  . When PREG_UNMATCHED_AS_NULL mode is used, trailing unmatched capturing
    groups will now also be set to null (or [null, -1] if offset capture is
    enabled). This means that the size of the $matches will always be the same.

- PEAR:
  . Installation of PEAR (including PECL) is no longer enabled by default. It
    can be explicitly enabled using --with-pear. This option is deprecated and
    may be removed in the future.

- PDO:
  . Attempting to serialize a PDO or PDOStatement instance will now generate
    an Exception rather than a PDOException, consistent with other internal
    classes which do not support serialization.

- Reflection:
  . Reflection objects will now generate an exception if an attempt is made
    to serialize them. Serialization for reflection objects was never
    supported and resulted in corrupted reflection objects. It has been
    explicitly prohibited now.

- SPL:
  . Calling get_object_vars() on an ArrayObject instance will now always return
    the properties of the ArrayObject itself (or a subclass). Previously it
    returned the values of the wrapped array/object unless the STD_PROP_LIST
    flag was specified. Other affected operations are:

     * ReflectionObject::getProperties()
     * reset(), current(), etc. Use Iterator methods instead.
     * Potentially others working on object properties as a list.

    (array) casts are *not* affected. They will continue to return either the
    wrapped array, or the ArrayObject properties, depending on whether the
    STD_PROP_LIST flag is used.
  . SplPriorityQueue::setExtractFlags() will throw an exception if zero is
    passed. Previously this would generate a recoverable fatal error on the
    next extraction operation.
  . ArrayObject, ArrayIterator, SplDoublyLinkedList and SplObjectStorage now
    support the __serialize() + __unserialize() mechanism in addition to the
    Serializable interface. This means that serialization payloads created on
    older PHP versions can still be unserialized, but new payloads created by
    PHP 7.4 will not be understood by older versions.

- Standard:
  . The "o" serialization format has been removed. As it is never produced by
    PHP, this may only break unserialization of manually crafted strings.
  . Password hashing algorithm identifiers are now nullable strings rather
    than integers.

     * PASSWORD_DEFAULT was int 1; now is null
     * PASSWORD_BCRYPT was int 1; now is string '2y'
     * PASSWORD_ARGON2I was int 2; now is string 'argon2i'
     * PASSWORD_ARGON2ID was int 3; now is string 'argon2id'

    Applications correctly using the constants PASSWORD_DEFAULT,
    PASSWORD_BCRYPT, PASSWORD_ARGON2I, and PASSWORD_ARGON2ID will continue to
    function correctly.
  . htmlentities() will now throw a notice (instead of a strict standards
    warning) if it is used with an encoding for which only basic entity
    substitution is supported, in which case it is equivalent to
    htmlspecialchars().
  . fread() and fwrite() will now return false if the operation failed.
    Previously an empty string or 0 was returned. EAGAIN/EWOULDBLOCK are not
    considered failures.
  . fread() and fwrite() on plain files will now throw a notice on failure,
    such as when trying to write to a read-only file resource.

- Tokenizer:
  . token_get_all() will now emit a T_BAD_CHARACTER token for unexpected
    characters instead of leaving behind holes in the token stream.

========================================
2. New Features
========================================

- Core:
  . Added support for typed properties. For example:

        class User {
            public int $id;
            public string $name;
        }

    This will enforce that $user->id can only be assigned integers and
    $user->name can only be assigned strings. For more information see the
    RFC: https://wiki.php.net/rfc/typed_properties_v2

  . Added support for arrow functions with implicit by-value scope binding.
    For example:

        $factor = 10;
        $nums = array_map(fn($num) => $num * $factor, $nums);

    RFC: https://wiki.php.net/rfc/arrow_functions_v2

  . Added support for limited return type covariance and argument type
    contravariance. The following code will now work:

        class A {}
        class B extends A {}

        class Producer {
            public function method(): A {}
        }
        class ChildProducer extends Producer {
            public function method(): B {}
        }

    Full variance support is only available if autoloading is used. Inside a
    single file only non-cyclic type references are possible, because all
    classes need to be available before they are referenced.
    RFC: https://wiki.php.net/rfc/covariant-returns-and-contravariant-parameters

  . Added support for coalesce assign (??=) operator. For example:

        $array['key'] ??= computeDefault();
        // is roughly equivalent to
        if (!isset($array['key'])) {
            $array['key'] = computeDefault();
        }

    RFC: https://wiki.php.net/rfc/null_coalesce_equal_operator

  . Added support for unpacking inside arrays. For example:

        $arr1 = [3, 4];
        $arr2 = [1, 2, ...$arr1, 5];
        // $arr2 == [1, 2, 3, 4, 5]

    RFC: https://wiki.php.net/rfc/spread_operator_for_array

  . Added support for underscore separators in numeric literals. Some examples:

        6.674_083e-11; // float
        299_792_458;   // decimal
        0xCAFE_F00D;   // hexadecimal
        0b0101_1111;   // binary

    RFC: https://wiki.php.net/rfc/numeric_literal_separator

  . Support for WeakReferences has been added.
    RFC: https://wiki.php.net/rfc/weakrefs

  . Throwing exceptions from __toString() is now permitted. Previously this
    resulted in a fatal error. Existing recoverable fatals in string conversions
    have been converted to Error exceptions.
    RFC: https://wiki.php.net/rfc/tostring_exceptions

- CURL:
  . CURLFile now supports stream wrappers in addition to plain file names, if
    the extension has been built against libcurl >= 7.56.0.  The streams may
    need to be seekable.

- Filter:
  . The FILTER_VALIDATE_FLOAT filter now supports the min_range and max_range
    options, with the same semantics as FILTER_VALIDATE_INT.

- FFI:
  . A new extension which provides a simple way to call native functions, access
    native variables and create/access data structures defined in C libraries.
    RFC: https://wiki.php.net/rfc/ffi

- GD:
  . Added the "scatter" image filter (IMG_FILTER_SCATTER) to apply a scatter
    filter to images. This filter has the following prototype:

        imagefilter($im, IMG_FILTER_SCATTER, int $sub, int $plus, array $colors = []);

    The $colors array can be populated with a set of indexed colors to
    apply the scatter pixel shifting on.

    Note, the result of this filter is always random.

- Hash:
  . Added "crc32c" hash using Castagnoli's polynomial. This crc32 variant is
    used by storage systems, such as iSCSI, SCTP, Btrfs and ext4.

- Mbstring:
  . Added mb_str_split() function, which provides the same functionality as
    str_split(), but operating on code points rather than bytes.
    RFC: https://wiki.php.net/rfc/mb_str_split

- OPcache:
  . Support for preloading code has been added.
    RFC: https://wiki.php.net/rfc/preload

- PCRE:
  . The preg_replace_callback() and preg_replace_callback_array() functions now
    accept an additional $flags argument, with support for the
    PREG_OFFSET_CAPTURE and PREG_UNMATCHED_AS_NULL flags. This influences the
    format of the matches array passed to to the callback function.

- PDO:
  . The username and password can now be specified as part of the PDO DSN for
    the mysql, mssql, sybase, dblib, firebird and oci drivers. Previously this
    was only supported by the pgsql driver. If a username/password is specified
    both in the constructor and the DSN, the constructor takes precedence.

        new PDO("mysql:host=xxx;port=xxx;dbname=xxx;user=xxx;password=xxx");

- PDO_OCI:
  . PDOStatement::getColumnMeta() is now available

- PDO_SQLite:
  . PDOStatement::getAttribute(PDO::SQLITE_ATTR_READONLY_STATEMENT) allows
    checking whether the statement is read-only, i.e. if it doesn't modify
    the database.
  . PDO::setAttribute(PDO::SQLITE_ATTR_EXTENDED_RESULT_CODES, true) enables the
    use of SQLite3 extended result codes in errorInfo().

- SQLite3:
  . Added SQLite3::lastExtendedErrorCode() to fetch the last extended result
    code.
  . Added SQLite3::enableExtendedResultCodes($enable = true), which will make
    SQLite3::lastErrorCode() return extended result codes.

- Standard:
  . strip_tags() now also accepts an array of allowed tags: Instead of
    strip_tags($str, '<a><p>') you can now write strip_tags($str, ['a', 'p']).

  . A new mechanism for custom object serialization has been added, which
    uses two new magic methods:

        // Returns array containing all the necessary state of the object.
        public function __serialize(): array;

        // Restores the object state from the given data array.
        public function __unserialize(array $data): void;

    The new serialization mechanism supersedes the Serializable interface,
    which will be deprecated in the future.

    RFC: https://wiki.php.net/rfc/custom_object_serialization

  . array_merge() and array_merge_recursive() may now be called without any
    arguments, in which case they will return an empty array. This is useful
    in conjunction with the spread operator, e.g. array_merge(...$arrays).

  . proc_open() now accepts an array instead of a string for the command. In
    this case the process will be opened directly (without going through a
    shell) and PHP will take care of any necessary argument escaping.

        proc_open(['php', '-r', 'echo "Hello World\n";'], $descriptors, $pipes);

  . proc_open() now supports "redirect" and "null" descriptors. For example:

        // Like 2>&1 on the shell
        proc_open($cmd, [1 => ['pipe', 'w'], 2 => ['redirect', 1]], $pipes);
        // Like 2>/dev/null or 2>nul on the shell
        proc_open($cmd, [1 => ['pipe', 'w'], 2 => ['null']], $pipes);

  . password_hash() has argon2i(d) implementations from ext/sodium when PHP is
    built without libargon.

    RFC: https://wiki.php.net/rfc/sodium.argon.hash

========================================
3. Changes in SAPI modules
========================================

========================================
4. Deprecated Functionality
========================================

- Core:
  . Nesting ternary operators without explicit parentheses is deprecated:

        // Code like
        $a ? $b : $c ? $d : $e
        // should be replaced by (current interpretation)
        ($a ? $b : $c) ? $d : $e
        // or (likely intended interpretation)
        $a ? $b : ($c ? $d : $e)

    RFC: https://wiki.php.net/rfc/ternary_associativity
  . The array and string offset access syntax using curly braces is deprecated.
    Use $str[$idx] instead of $str{$idx}.
    RFC: https://wiki.php.net/rfc/deprecate_curly_braces_array_access
  . The (real) cast is deprecated, use (float) instead.
  . Unbinding $this of a non-static method through a combination of
    ReflectionMethod::getClosure() and closure rebinding is deprecated. Doing
    so is equivalent to calling a non-static method statically, which has been
    deprecated since PHP 7.0.
  . Unbinding $this of a non-static closure that uses $this is deprecated.
  . Using "parent" inside a class without a parent is deprecated, and will throw
    a compile-time error in the future. Currently an error will only be
    generated if/when the parent is accessed at run-time.
  . The allow_url_include ini directive is deprecated. Enabling it will generate
    a deprecation notice at startup.

- COM:
  . Importing type libraries with case-insensitive constant registering has been
    deprecated.

- Filter:
  . FILTER_SANITIZE_MAGIC_QUOTES is deprecated, use FILTER_SANITIZE_ADD_SLASHES
    instead.

- Mbstring:
  . Passing a non-string pattern to mb_ereg_replace() is deprecated. Currently
    non-string patterns are interpreted as ASCII codepoints. In PHP 8 the
    pattern will be interpreted as a string instead.
  . Passing the encoding as 3rd parameter to mb_strrpos() is deprecated. Instead
    pass a 0 offset and encoding as 4th parameter.

- LDAP:
  . ldap_control_paged_result_response and ldap_control_paged_result are
    deprecated. Pagination controls can be sent along with ldap_search instead.

- Reflection:
  . Calls to ReflectionType::__toString() now generate a deprecation notice.
    This method has been deprecated in favor of ReflectionNamedType::getName()
    in the documentation since PHP 7.1, but did not throw a deprecation notice
    for technical reasons.
  . The export() methods on all Reflection classes are deprecated. Construct a
    Reflection object and convert it to string instead:

        // ReflectionClass::export(Foo::class, false) is:
        echo new ReflectionClass(Foo::class), "\n";
        // $str = ReflectionClass::export(Foo::class, true) is:
        $str = (string) new ReflectionClass(Foo::class);

- Socket:
  . The AI_IDN_ALLOW_UNASSIGNED and AI_IDN_USE_STD3_ASCII_RULES flags for
    socket_addrinfo_lookup() are deprecated, due to an upstream deprecation in
    glibc.

- Standard:
  . Passing invalid characters to ''base_convert()'', ''bindec()'', ''octdec()''
    and ''hexdec()'' will now generate a deprecation notice. The result will
    still be computed as if the invalid characters did not exist. Leading and
    trailing whitespace, as well as prefixes of type 0x (depending on base)
    continue to be allowed.
  . Using array_key_exists() on objects is deprecated. Instead either isset()
    or property_exists() should be used.
  . The is_real() function is deprecated, use is_float() instead.
  . The get_magic_quotes_gpc() and get_magic_quotes_runtime() functions are
    deprecated. They always return false.
  . The hebrevc() function is deprecated. It can be replaced with
    nl2br(hebrev($str)), or preferably the use of Unicode RTL support.
  . The convert_cyr_string() function is deprecated. It can be replaced by one
    of mb_convert_string(), iconv() or UConverter.
  . The money_format() function is deprecated. It can be replaced by the
    intl NumberFormatter functionality.
  . The ezmlm_hash() function is deprecated.
  . The restore_include_path() function is deprecated. It can be replaced by
    ini_restore('include_path').
  . Passing parameters to implode() in reverse order is deprecated, use
    implode($glue, $parts) instead of implode($parts, $glue).

========================================
5. Changed Functions
========================================

- SPL:
  . SplFileObject::fputcsv(), ::fgetcsv() and ::setCsvControl() now accept an
    empty string as $escape argument, which disables the proprietary PHP
    escaping mechanism. SplFileObject::getCsvControl() now may also return an
    empty string for the third array element, accordingly.

- Standard:
  . fputcsv() and fgetcsv() now accept an empty string as $escape argument,
    which disables the proprietary PHP escaping mechanism. The behavior of
    str_getcsv() has been adjusted accordingly (formerly, an empty string was
    identical to using the default).
  . proc_open() on Windows can be passed a "create_process_group" option. It
    is required, if the child process is supposed to handle CTRL events.
  . password_hash() now accepts nullable string and int as $algo argument.
  . password_needs_rehash() now accepts nullable string and int as $algo
    argument.

========================================
6. New Functions
========================================

- Core:
  . Added get_mangled_object_vars($object) function, which returns the mangled
    object properties. It returns the same result as (array) $object, with the
    exception that it ignores overloaded array casts, such as used by
    ArrayObject.

- GD:
  . Added imagecreatefromtga() function, which allows reading images in TGA
    format. TGA support is now also indicated by gd_info() and imagetypes().
    Note that TGA images are not recognized by imagecreatefromstring() and
    getimagesize().

- OpenSSL:
  . Added openssl_x509_verify(mixed cert, mixed key) function that verifies the
    signature of the certificate using a public key. A wrapper around the
    OpenSSL's X509_verify() function.
    See <https://github.com/php/php-src/pull/3624>.

- Pcntl:
  . Added bool pcntl_unshare(int flags) function which allows dissociating
    parts of the process execution context which are currently being shared with
    other processes. Explicitly, it allows you to unshare the mount, IPC, UTS,
    network, PID, user and cgroup namespaces.

- SQLite3:
  . Added SQLite3Stmt::getSQL() to retrieve the SQL of the statement. If true is
    passed as $expanded argument, query parameters will be replaced in the
    return value by their currently bound value, if libsqlite ≥ 3.14 is used.
  . Added SQLite3::backup() to create database backups via the SQLite3 online
    backup API.

- Standard
  . bool sapi_windows_set_ctrl_handler(callable handler, [, bool add = true]) -
    set or remove a handler function upon receiving a CTRL event. The handler
    function is expected to have this signature: "function handler(int $event)".
  . bool sapi_windows_generate_ctrl_event(int type, int pid) - send a CTRL event
    to another process.
  . array password_algos() - return a complete list of all registered password
    hashing algorithms. For more details see the RFC:
    https://wiki.php.net/rfc/password_registry

========================================
7. New Classes and Interfaces
========================================

- Reflection:
  . A new ReflectionReference class has been added, which allows detecting
    references and comparing them for identity. For more details see the RFC:
    https://wiki.php.net/rfc/reference_reflection

========================================
8. Removed Extensions and SAPIs
========================================

- Interbase:
  . The interbase extension has been moved to PECL. Access to an InterBase
    and/or FireBird based database is still available with the PDO_Firebird
    extension. For more details see the RFC:
    https://wiki.php.net/rfc/deprecate-and-remove-ext-interbase

- Recode:
  . The recode extension has been moved to PECL. For character set/encoding
    conversion the iconv or mbstring extensions could be used instead.
    RFC: https://wiki.php.net/rfc/unbundle_recode

- WDDX:
  . The WDDX extension has been deprecated and moved to PECL.
    RFC: https://wiki.php.net/rfc/deprecate-and-remove-ext-wddx

========================================
9. Other Changes to Extensions
========================================

- GD:
  . The behavior of imagecropauto() in the bundled libgd has been synced with
    that of system libgd:
     * IMG_CROP_DEFAULT is no longer falling back to IMG_CROP_SIDES
     * Threshold-cropping now uses the algorithm of system libgd
  . The default $mode parameter of imagecropauto() has been changed to
    IMG_CROP_DEFAULT; passing -1 is now deprecated.
  . imagescale() now supports aspect ratio preserving scaling to a fixed height
    by passing -1 as $new_width.

- Filter:
  . The filter extension no longer exposes --with-pcre-dir for Unix builds and
    can now reliably be built as shared when using ./configure once more.

- Hash:
  . The hash extension cannot be disabled anymore and is always an integral part
    of any PHP build, similar to the date extension.

- Intl:
  . The Intl extension now requires at least ICU 50.1.
  . ResourceBundle now implements Countable.

- Libxml:
  . All libxml based extensions now require libxml 2.7.6 or newer.

- Mbstring:
  . The oniguruma library is no longer bundled with PHP, instead libonig needs
    to be available on the system. Alternatively --disable-mbregex can be used
    to disable the mbregex component.

- OPcache:
  . The --disable-opcache-file|--enable-opcache-file configure options have been
    removed in favor of the opcache.file_cache INI directive.

- PDO:
  . It is now possible to escape question marks in SQL queries to avoid them
    being interpreted as parameter placeholders. Writing "??" allows sending
    a single question mark to the database and e.g. use the PostgreSQL JSON key
    exists "?" operator. For more details see the RFC:
    https://wiki.php.net/rfc/pdo_escape_placeholders

- Reflection:
  . Numeric value of class, property, function and constant modifiers was
    changed. Don't filter methods and properties through
    ReflectionClass::getMethods() and ReflectionClass::getProperties(), or test
    results of Reflection...::getModifiers(), using hard-coded numeric values.
    Use corresponding constants instead (e.g. ReflectionMethod::IS_PUBLIC).

- SimpleXML:
  . SimpleXMLElement now implements Countable.

- SQLite3:
  . The bundled libsqlite has been removed. To build the SQLite3 extension a
    system libsqlite3 ≥ 3.7.4 is now required. To build the PDO_SQLite extension
    a system libsqlite3 ≥ 3.5.0 is now required.
  . (Un)serialization of SQLite3, SQLite3Stmt and SQLite3Result is now
    explicitly forbidden. Formerly, serialization of instances of these classes
    was possible, but unserialization yielded unusable objects.
  . The @param notation can now also be used to denote SQL query parameters.

- Zip:
  . The bundled libzip library has been removed. A system libzip >= 0.11 is now
    necessary to build the extension.

========================================
10. New Global Constants
========================================

- Mbstring:
  . MB_ONIGURUMA_VERSION specifies the version of the oniguruma library against
    which mbregex has been built.

- Socket:
  . Added FreeBSD-specific socket options:
  . SO_LABEL
  . SO_PEERLABEL
  . SO_LISTENQLIMIT
  . SO_LISTENQLEN
  . SO_USER_COOKIE

- Standard:
  . PHP_WINDOWS_EVENT_CTRL_C
  . PHP_WINDOWS_EVENT_CTRL_BREAK

- Tidy:
  . TIDY_TAG_ARTICLE
  . TIDY_TAG_ASIDE
  . TIDY_TAG_AUDIO
  . TIDY_TAG_BDI
  . TIDY_TAG_CANVAS
  . TIDY_TAG_COMMAND
  . TIDY_TAG_DATALIST
  . TIDY_TAG_DETAILS
  . TIDY_TAG_DIALOG
  . TIDY_TAG_FIGCAPTION
  . TIDY_TAG_FIGURE
  . TIDY_TAG_FOOTER
  . TIDY_TAG_HEADER
  . TIDY_TAG_HGROUP
  . TIDY_TAG_MAIN
  . TIDY_TAG_MARK
  . TIDY_TAG_MENUITEM
  . TIDY_TAG_METER
  . TIDY_TAG_NAV
  . TIDY_TAG_OUTPUT
  . TIDY_TAG_PROGRESS
  . TIDY_TAG_SECTION
  . TIDY_TAG_SOURCE
  . TIDY_TAG_SUMMARY
  . TIDY_TAG_TEMPLATE
  . TIDY_TAG_TIME
  . TIDY_TAG_TRACK
  . TIDY_TAG_VIDEO

========================================
11. Changes to INI File Handling
========================================

- zend.exception_ignore_args
  . New INI directive to include or exclude arguments from stack traces
    generated for exceptions.

========================================
12. Windows Support
========================================

- stat:
  . The stat implementation has been refactored.
    - An inode number is delivered and is based on the NTFS file index.
    - The device number is now based on the volume serial number.

  Note that both values are derived from the system and provided as is on 64-bit
  systems. On 32-bit systems, these values might overflow the 32-bit integer in
  PHP, so they're fake.

- CTRL+C and CTRL+BREAK on console can be caught by setting a handler function
  with sapi_windows_set_ctrl_handler().

- configure now regards additional CFLAGS and LDFLAGS set as environment
  variables.

- OPcache now supports an arbitrary amount of separate caches per user via the
  the INI directive opcache.cache_id. All processes with the same cache ID and
  user share an OPcache instance.

========================================
13. Migration to pkg-config
========================================

A number of extensions have been migrated to exclusively use pkg-config for the
detection of library dependencies. Generally, this means that instead of using
--with-foo-dir=DIR or similar only --with-foo is used. Custom library paths can
be specified either by adding additional directories to PKG_CONFIG_PATH or by
explicitly specifying compilation options through FOO_CFLAGS and FOO_LIBS.

The following extensions and SAPIs are affected:

- Curl:
  . --with-curl no longer accepts a directory.

- Enchant:
  . --with-enchant no longer accepts a directory.

- FPM:
  . --with-fpm-systemd now uses only pkg-config for libsystem checks. The
    libsystemd minimum required version is 209.

- GD:
  . --with-gd becomes --enable-gd (whether to enable the extension at all) and
    --with-external-gd (to opt into using an external libgd, rather than the
    bundled one).
  . --with-png-dir has been removed. libpng is required.
  . --with-zlib-dir has been removed. zlib is required.
  . --with-freetype-dir becomes --with-freetype.
  . --with-jpeg-dir becomes --with-jpeg.
  . --with-webp-dir becomes --with-webp.
  . --with-xpm-dir becomes --with-xpm.

- IMAP:
  . --with-kerberos no longer accepts a directory.

- Intl:
  . --with-icu-dir has been removed. If --enable-intl is passed, then libicu is
    always required.

- Ldap:
  . --with-ldap-sasl no longer accepts a directory.

- Libxml:
  . --with-libxml-dir has been removed.
  . --enable-libxml becomes --with-libxml.
  . --with-libexpat-dir has been renamed to --with-expat and no longer accepts a
    directory.

- LiteSpeed:
  . --with-litespeed becomes --enable-litespeed.

- Mbstring:
  . --with-onig has been removed. Unless --disable-mbregex has been passed,
    libonig is required.

- ODBC:
  . --with-iodbc no longer accepts a directory.
  . --with-unixODBC without a directory now uses pkg-config (preferred).
    Directory is still accepted for old versions without libodbc.pc.

- OpenSSL:
  . --with-openssl no longer accepts a directory.
  . --with-kerberos no longer accepts a directory.

- PCRE:
  . --with-pcre-regex has been removed. Instead --with-external-pcre is provided
    to opt into using an external PCRE library, rather than the bundled one.

- PDO_SQLite:
  . --with-pdo-sqlite no longer accepts a directory.

- Readline:
  . --with-libedit no longer accepts a directory.

- Sodium:
  . --with-sodium no longer accepts a directory.

- SQLite3:
  . --with-sqlite3 no longer accepts a directory.

- XSL:
  . --with-xsl no longer accepts a directory.

- Zip:
  . --with-libzip has been removed.
  . --enable-zip becomes --with-zip.

========================================
14. Other Changes
========================================

========================================
15. Performance Improvements
========================================

- Core:
  . A specialized VM opcode for the array_key_exists() function has been added,
    which improves performance of this function if it can be statically
    resolved. In namespaced code, this may require writing \array_key_exists()
    or explicitly importing the function.

- PCRE:
  . When preg_match() in UTF-8 mode ("u" modifier) is repeatedly called on the
    same string (but possibly different offsets), it will only be checked for
    UTF-8 validity once.