CRM-21142 - CiviCRM installer - Check for XML module before install

[MegaphoneJon]

Overview

CiviCRM requires the PHP XML module. We should check for it as part of install requirements.

Before

CiviCRM installer will puke and leave an installation canary. See: https://civicrm.stackexchange.com/questions/20239/wordpress-civi-install-keeps-puking-with-canary-and-simplexml-load-file-erro

After

Installation is blocked by the lack of XML module.

Comments

I tested this on Ubuntu with a buildkit instance by renaming civicrm.settings.php, uninstalling the XML module (sudo apt remove php7.0-xml), restarting Apache, and running the installer. I reversed the changes when done.

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• CRM-21142: Installation fails if PHP XML module isn't installed

[totten]

Thanks, @MegaphoneJon. The test procedure looks good, and the code is clean/consistent with similar tests.

From a communications perspective... I think that PHP actually has several different XML extensions. Here's the list from a MAMP build of PHP 5.6:

$ php -r 'print_r(get_loaded_extensions());' | grep -i xml
    [3] => libxml
    [37] => SimpleXML
    [43] => xml
    [44] => xmlreader
    [45] => xmlwriter

In normal practice, maybe they're all bundled together, but there are some masochists who build their own PHP and tightly manage extensions. (ahem I'm looking at you, portage and arch.) They might read the error and enable xml or libxml... but the installer keeps saying that XML isn't available. Labeling it as "Simple XML" would make the dependency more precise.

[MegaphoneJon]

Good point Tim. I relabeled it and did a Google search on the error to ensure that the first link would lead to a reasonable solution.

[eileenmcnaughton]

Thanks for the quick work on this!