Update system requirements (including INSTALL.txt) for D7

Looks like support for PHP 5.x is over in Debian - https://wiki.debian.org/PHP says Jessie 8 had PHP 5.6 but that went EOL mid 2020.

Ubuntu 16.04 which is still supported under ESM shipped with PHP 7.0, but actually 14.04 is covered by ESM until April 2024 now ( https://canonical.com/blog/ubuntu-14-04-and-16-04-lifecycle-extended-to-... ). Trusty (14.04) shipped with PHP 5.5.

Centos7 shipped with PHP 5.4 and still seems to be supported until mid-2024 according to https://wiki.centos.org/About/Product

So as of late 2022 it looks like a couple of the major distros still have some support for PHP 5.4 and PHP 5.5 for another ~18 months or so.

I'm inclined to say that any PHP features introduced in PHP 5.3 (or later) are okay to use, and in practical terms PHP 5.x in general is likely to receive minimal testing (I don't really expect any contrib projects are that careful about testing on such old versions).

I think the recommendation should be (/ remain) PHP 7.x or later.

I managed to get a PHP 5.2 environment going in docker (https://github.com/clagomess/docker-php-5.2 with the oracle stuff commented out FWIW).

It looks a lot like D7 doesn't work under PHP 5.2 at the moment anyway, which is not hugely surprising when we don't have automated testing available.

It probably wouldn't be a big deal to fix the initial problems that I ran across, as they're a few variations on this:

PHP Warning:  Unexpected character in input:  '\\' (ASCII=92) state=1 in /usr/local/apache2/htdocs/drupal/includes/bootstrap.inc on line 3948

PHP Warning:  Unexpected character in input:  '\\' (ASCII=92) state=1 in /usr/local/apache2/htdocs/drupal/includes/bootstrap.inc on line 3971

PHP Warning:  Unexpected character in input:  '\\' (ASCII=92) state=1 in /usr/local/apache2/htdocs/drupal/modules/system/system.install on line 545

PHP Warning:  Unexpected character in input:  '\\' (ASCII=92) state=1 in /usr/local/apache2/htdocs/drupal/includes/session.inc on line 293

It looks like this is down to namespaces which are not supported in PHP 5.2 so e.g.

$dom = new \DOMDocument('1.0', 'UTF-8');

...and:

if (\PHP_VERSION_ID >= 70300) {

...cause problems.

We could fix these, but I'm not sure we should. If nobody has complained (AFAIK) about this since these changes were made...

There may be other issues too, and I don't think we should devote any resources to this.

That makes me think drawing the line at PHP 5.3 (with a recommendation to upgrade beyond PHP 5.x) is fine.

First pass at updating INSTALL.txt

I've removed some of the specifics about MySQL alternatives and generally based the minimum requirements on what we know D7 core currently passes tests with.

Thanks - updated the links as suggested. I've not gone through and changed every URL but the new ones we're adding should all be https now.

I've also updated the DRUPAL_MINIMUM_PHP constant, and another check that happens in install.php before the constant is defined.

There are a few other mentions of PHP 5.2 dotted around - e.g.:

/var/www/drupal-7.x$ grep -rn 'PHP 5\.2' *

includes/stream_wrappers.inc:13: * Note that PHP 5.2 fopen() only supports URIs of the form "scheme://target"
includes/filetransfer/filetransfer.inc:395: * available in PHP 5.2.
includes/authorize.inc:323:      // PHP 5.2 doesn't support $class::factory() syntax, so we have to
includes/password.inc:177:  // We rely on the hash() function being available in PHP 5.2+.
includes/file.inc:2418:  // Check that the URI has a value. There is a bug in PHP 5.2 on *BSD systems
includes/file.inc:2421:  // @todo Remove when Drupal drops support for PHP 5.2.
modules/simpletest/tests/file.test:2627:    // rawurlencode() in PHP 5.2 but not in PHP 5.3, as per RFC 3986.
modules/simpletest/drupal_web_test_case.php:582:      // backwards compatibility with PHP 5.2.
modules/system/system.install:76:  // 8.04 ships with PHP 5.2.4, but includes the necessary security patch.
modules/system/system.install:78:    $requirements['php']['description'] = $t('Your PHP installation is too old. Drupal requires at least PHP 5.2.5, or PHP @version with the htmlspecialchars security patch backported.', array('@version' => DRUPAL_MINIMUM_PHP));

Some of these could now be removed, but I think that could be looked at in a followup.

As for updating the system requirements docs page, there's the issue of whether PHP versions still have upstream support from the PHP maintainers (which will soon mean only PHP 8.x) but then of course there are lots of providers that do provide extended support of one form or another.

I'd say it's sufficient to mention that it's not a good idea to run a version without some ongoing upstream / provider support but we don't really need to get into tracking those details. Newer is generally more better :)

Draft CR: https://www.drupal.org/node/3322488 ... it's fairly light on detail so far - do we need to add more about what the increased minimum constraint actually means in practice?

Committed - thanks!