[5.0] b/c plugin for deprecation

[HLeithner]

Add a plugin which provides backward compatibility for the deprecation which has been deprecated prior Joomla! 5.0. This plugin will be activated for upgrades automatically and maybe be disabled for new Joomla! 5 installations.
At this point in time it's not clear we introduce an additional XML parameter which defines the needed b/c plugin version (for example 4.0 means that the extension needs the backward compatible polyfills based on Joomla 4.0 version and needs the plugin in Joomla 5).

Cleanup is still needed

• For example some version strings in the plugin are not correct.

Summary of Changes

Current Status of the plugin:

• Add the plugin
• Remove the automatically loaded classmap for J-prefixed classes and moves it to the plugin
• Fix HTMLHelper using the correct Namespace and by default not longer the JHtml Namespace with fallback
• Fix JTable using the correct Namespace and by default not longer the JTable Namespace with fallback
• Update Tests to use correct namespaces

Testing Instructions

Use an joomla 4 extension which needs one or all of the polyfills and try it with activated and disabled plugin.

Actual result BEFORE applying this Pull Request

Works.

Expected result AFTER applying this Pull Request

Works with active plugin, may crash without active plugin if the extension uses b/c code.

Link to documentations

Please select:

• Documentation link for docs.joomla.org:

• No documentation changes for docs.joomla.org needed

• Pull Request link for manual.joomla.org:

• No documentation changes for manual.joomla.org needed

[brianteeman]

Please can you suggest an extension that can be used to test the plugin with

[HLeithner]

at the moment I think not even Joomla it self works without the plugin... I will change it to draft for the moment.

[laoneo]

Can we not leave the old file and do a n include of the new location for BC reasons? This looks for me like a rather hard break.

[HLeithner]

That's the whole point of the plugin, that you are able to disable deprecation. just require it from the new location would make no difference to now and make the plugin useless.

[brianteeman]

Speaking from past experience the main problem that we have to avoid with this plugin is not the code but the communication of what it does. If it is not enabled by default then we will get lots of issues reported on forums etc where the first response to any issue will always be to enable the plugin even if it is completely unrelated

[HLeithner]

Speaking from past experience the main problem that we have to avoid with this plugin is not the code but the communication of what it does. If it is not enabled by default then we will get lots of issues reported on forums etc where the first response to any issue will always be to enable the plugin even if it is completely unrelated

True, that's one of the concerns I was thinking about and started to talk to benjamin.

For upgrades, I think having it always active is the safest way for us and the b/c promise

Multiple options came to my mind on new installations (which may also could effect upgrades)

1. Auto activate on new installs (that would make the plugin less useful because you need to be proactive. But wouldn't be to worse in combination with quick icon and deprecation report.
2. Not activate it on new installs and add a xml parameter to the extensions which defines the combat version. As explained in the description. Set your extension to be fully compatible with 5.0 would not enable the plugin in j5. Set the extension to 4.0 would automatically activate the b/c plugin on installation/upgrade of the extension. This would also allow us to show extensions which need the plugin.
3. Automatically activate the plugin on extension installation.
4. Disable the plugin and add post installation message
5. Let the extension activate the plugin when it needs it.

Options 3-4 are not so good options in my opinion. 1 or 2 would work. In both cases I would like to add a quick Icon telling the site owner that the plugin is enabled and that x extensions doesn't announce full compatibility with Joomla 5.

I would also like to collect the calls to deprecated functions (based on our existing deprecation log) and show it to the user and of course to the extension developer. Not sure if this works in all situation but could provide some help.

[brianteeman]

please add the plugin to libraries\src\Extension\ExtensionHelper.php

[HLeithner]

please add the plugin to libraries\src\Extension\ExtensionHelper.php

do you mean this entry? https://github.com/joomla/joomla-cms/pull/40664/files#diff-45688fa5398ae3d4bab3daa80bc4d2ea4785370233b82a7326f9676f965ec9ebR286

[brianteeman]

my bad - i missed it

[HLeithner]

I'm merging this for now for a minimal impact version of the plugin as base for other deprecations.