I've just enabled Diff and not done anything else. It looks like the default value for some config settings is NULL, when the code is expecting an array.

On the home page node of my site, I'm seeing

Warning: in_array() expects parameter 2 to be array, null given in diff_node_view_alter() (line 314 of /path/to/backdrop/modules/contrib/diff/diff.module).

going to the Diff entities config tab, I get

Warning: Invalid argument supplied for foreach() in form_type_checkboxes_value() (line 2434 of /path/to/backdrop/core/includes/form.inc).

Saving the config pages, without making any changes, make the warnings there go away.

I enabled revisions on a content type but the home page warning is still there.

TypeError: in_array(): Argument #2 ($haystack) must be of type array, null given in in_array() (line 300 of /app/modules/contrib/diff/diff.module).

I'm not exactly sure where this is coming from yet but will update as I find out more.

Need to take account of use of config settings.

Similarly to #26 it's giving:

The function diff_compare_entities() (diff.pages.inc:480) called deprecated function element_sort(). It will be removed in the next major release of Backdrop.

Replacing element_sort() with backdrop_sort() didn't work. So until #27 is resolved, I need Comment Alter module (which depends on Diff) to work properly without flooding the log with the above error and therefore came up with a temporary solution in the PR offered below.

Incorporate available commits from Drupal module up to v7.x-3.4.

Now that entity reference is in core could include https://git.drupalcode.org/project/entityreference/-/blob/7.x-1.x/entityreference.diff.inc here.

Hey @Graham-72 👋🏼 not sure if you are around, but there are a few issues with this module that I would like to help fix, and I'm generally interested in helping you maintain the module. Do you accept?

I'm splitting this from #16

• D7 (notice how the "Standard" diff mode is also denoted as the currently selected one, by making it not look like a link 👍🏼 ):
  
• Backdrop (both options are shown as links - can you tell which diff mode is active?? 👎🏼 ):
  

There's a @todo item in https://github.com/backdrop-contrib/diff/blob/1.x-1.x/diff.pages.inc#L250

  $links = array();
  foreach (diff_available_states('node') as $alternative_state => $label) {
    if ($alternative_state == $state) {
      // @todo: Should we show both or just alternatives?
    }
    $links[$alternative_state] = array(
      'title' => $label,
      'href' => ...,
    );
  }

That @todo item seems to have been placed there in order to skip adding the currently selected diff mode as a link, but I think that we should still show it, but denote the active vs available diff modes differently. I propose that we make them look like secondary buttons instead.

Rough mockup:

...or with smaller buttons:

Tested on text and integer types fields, unfortunately whatever change I make it always shows 'No visible changes'. Tried both dev and the officially released versions. Am I doing something wrong? Anyone using this module successfully?

This is a deprecated function in Backdrop.

Backdrop core includes a diff engine that is more up-to-date and compatible with PHP 8+, which would avoid problems like #26. Right now Diff module duplicates the entire DiffEngine which is directly available in core (used by the config sync form). This module should stop shipping it's own copy and use the one in core instead.

Apologies for releasing this prematurely. Something has gone wrong and requires more work.

Other user that user/1 don't have access to the revision tab even with the revision permission. However, disabling diff module get thinks to normal again and revisions tab is there again.

Testing Diff 7.x-3.3 in a D7.82 sandbox

1. When I compared revisions, I got the "HTML" (raw) mode shown out of the box:
   
   The path I was at was node/1/revisions/view/1/2.
2. I switched to "Marked down" mode, which took me to node/1/revisions/view/1/2/raw-plain
3. I switched back to "Standard" mode, which took me to node/1/revisions/view/1/2 (notice: no /raw added to the end of the path)
4. I then navigated to admin/config/content/diff/entities and switched the "Diff default state" setting to "- None -" (which I find of no use at all by the way), and saved settings.
5. When I compared revisions again, I got this:
   

Testing Diff 3.4.0 in a Backdrop 1.20.0 demo sandbox

1. I navigated to admin/config/content/diff/entities and confirmed that the "Diff default state" setting was set to "HTML view" (raw) out of the box.
2. When I compared revisions, I got this (which is basically the "- None -" diff mode 👎🏼 ):
   
   The path I was at was node/1/revisions/view/1/2.
3. I switched to "Marked down" mode, which took me to node/1/revisions/view/1/2/raw-plain 👍🏼
4. I switched back to "Standard" mode, which took me to node/1/revisions/view/1/2/raw (differs compared to the 7.x behavior, which is that no /raw is being added to the end of the path)
5. I navigated to admin/config/content/diff/entities and changed the "Diff default state" setting to "Plain view" (raw-plain).
6. When I compared revisions, I got the "- None -" diff mode again 👎🏼

Diff requires three settings for each node type and these are displayed and administered on the administration form for the content type under a new entry 'Content revisions'.

In porting this module from Drupal I have added these config settings to the json file for the node type in order that they are updated through the normal saving of the content type. Maybe they should instead be stored in diff.settings.json?

In order to initiate these three settings if they have not yet been set, I have added code to function diff_form_node_type_form_alter. Is this the right way to deal with this?

There is no implementation of hook_autoload_info in diff.module. This is needed because several classes are defined in DiffEngine.php.

Steps to reproduce:

1. In a vanilla backdrop installation, install and enable the Diff module.
2. Go to admin/config/content/diff/entities and make sure that the "Use administration theme" setting is on.
3. Compare two revisions of a node -> the Basis theme is being used instead of Seven 👎🏼
4. Go to admin/config/content/diff/entities and disable the "Use administration theme" setting. Save.
5. Compare two revisions of a node -> the Basis theme is being used 🤷🏼

When viewing a diff in Standard mode, I get the following error message:

Deprecated function: The each() function is deprecated. This message will be suppressed on further calls in _DiffEngine->_diag() (line 315 of /var/www/html/web/modules/contrib/diff/DiffEngine.php). 

I'm running PHP 7.4, and it looks like this function was removed entirely in PHP 8.0 (meaning Diff probably doesn't work in PHP 8)

See https://www.php.net/manual/en/function.each.php

The initial port of this module (release 1.x-3.2.0) does not create and maintain config settings completely and correctly.