Is it always a root level category?

Yes, that's right.
If you want to change the Categories (which you'll probably will later on), you can do that later in the Category Manager.

Thanks for clarifying @pe7er just wanted to double check before testing

OK Several "smaller" comments and a "larger" comment (the plugin thing) but overall nice work. This is a really positive feature :)

What about having a field "parent category" and a second field "child category"
This would improve 2 things:
1) On pages with complex structure it´s easier to find the categories inside the list
2) This great new feature would be able to add categories to existing parent categories

thanks for this great feature!

Without commenting on the code aspects that @wilsonge mentioned

1. Creating categories and alias works (although I did manage at one point to rename an existing category but cant replicate that anymore)
2. As it stands its a bit of a hidden secret. I would suggest updating the tooltip similar to the one for the tags
3. @wilsonge comment that this functionality should be available to all components that use categories makes sense to me. Just as tags works consistently across all uses so should category selection and creation

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   _{This comment was created with the J!Tracker Application at issues.joomla.org/joomla-cms/8623.}

Also what about the acl.
If the user doesnt have access to create a root level category what happens. (Sorry I havent tested this as I am useless setting up the ACL)

Sorry me again

Front end editing
While you can create a new tag on the frontend you cant create a new category

Thanks for your constructive feedback @wilsonge !
I've made some changes, e.g. moved the code to category helper file so that it can be reused with other extensions that use com_categories categories. IMHO it's better to use the helper file and not a plugin.
Roland (thanks @roland-d !) helped me with refactoring the allowAdd to the field.php library.

Thanks for your feedback @designbengel !
I've tried to keep it as simple as possible.
IMHO people can use the Category Manager to further (re)organize their category structure.
The categories created from articles are all assigned to parent level & easy to find.

Maybe we could add a message about that after creating a new category?
For example: "You've created a new category. To organize your categories go to the [Category Manager]" with [Category Manager] linked to the category manager?

Simple is always best

Thanks for your feedback @brianteeman
I'll indeed add this functionality to other components that make use of Categories. Now that the Category Creation method is in the helper file, it's easier to reuse by other components.

Thanks for your tooltip suggestion, I've added it to this PR.

I've reproduced the front-end problem with this PR that @brianteeman reported.
I'll try to fix that...

Please alpha order
+JGLOBAL_ADD_CUSTOM_CATEGORY="Add new Category"

I will do so. Thanks @infograf768

Something else: I've run into an issue with creating a new Category Name with numbers only.
I'll fix that too...

Solved the issue with using a Category name that's only a number. Thanks @roland-d
Alpha ordered new language strings. Thanks @infograf768
Changed tooltip. Thanks @brianteeman

Ok, I've moved some code from fields to categoryedit (Thanks for this advice @wilsonge)
Roland helped me restructuring it (Thanks @roland-d!)

its realy goooooodddd
same think for link menu ?
in article editing view and category editing view => select an existing link or create a new one

@micker yes, after I've created this feature for other components, I'll look into menu item creation.

Almost there :) I think this last comment and you are good from a code perspective. Nice one @pe7er looking forward to seeing this make it into core!

I've changed require_one to JLoader::register. Thanks @wilsonge !

SeemsGood

Tested OK here in monolanguage and multilanguage where the new category picks the article language ( ).
The tip displayed in back-end could also be displayed in front-end I guess.

tested successfuly
nice one @pe7er

Thanks for testing @infograf768 & @alikon and everybody else for improving this PR!

Thought:
after looking more into this, I became conscious of an aspect we may have overseen: ACL.
By default, an Author and up can create articles —normal—, but also categories as the permissions for the component are not separated in Joomla.
As long as this was in back-end, that was not a problem as Authors, Editors, Publishers are not allowed to log in back-end by default, but now that this feature let's create also categories in frontend, it shows the limitations of our ACL. Basically, an Author could create as many new categories as desired...

Is it a real issue? What do you think?

I have tested this item successfully on cf87097

Thanks for testing @Gerlof

Thanks @infograf768 for your comment about this PR & ACL.
This can be a problem indeed, will check it...

This PR has received new commits.

CC: @Gerlof

I've tested the issue with front-end ACL that @infograf768 described:
It was possible for an author to create (unlimited) new categories, however their articles were all created with publish state "unpublished".
IMHO that's unwanted behavior, so I removed the possibility on the front-end to add new categories.

I have tested this item successfully on c055379

Very usable to end-users AND administrators. Tested multi-lingual. Worked fine!

I have tested this item successfully on c055379

Tested successfully.
Verry Nice feature.

I have tested this item successfully on c055379

@test tested succesfully, nice feature!

@pe7er
Do we still need the new strings in frontend?

I have tested this item successfully on c055379

Test OK

RTC - thanks

@pe7er
I still think we do not need the new language strings in frontend.

Merged with b853b6b

With a quick look at the code

• i did not find the ACL check on core.create for the categoryedit form element
• only an attribute 'allowAdd' to enable the feature, ok but that also needs to be complemented with an ACL core.create check

so i decided to test this feature in 3.6.x

Indeed the categoryedit form element does not check it

How to test

• Edit permissions of "manager" usergroup and deny the create at global configuration (and allow to backend access)
• Login as a "manager" user to backend, and edit any article
• Type "Test" into the categoryedit form element, and you see it allows you to add new category
• After saving the article new category is not created which is expected but ... the article category is reset to 1 aka to ROOT category

The problem is that after checking the allowAdd attibute,
we need to go further and also make an core.create ACL check on
the extension (since we are creating a category at root level right ?)

https://github.com/pe7er/joomla-cms/blob/c05537939099d815ec49fb9676c955ec18d61e85/administrator/components/com_categories/models/fields/categoryedit.php#L59

$this->allowAdd = isset($this->element['allowAdd']) ? $this->element['allowAdd'] : '';

if ($this->allowAdd)
{
    $jinput = JFactory::getApplication()->input;
    $user = JFactory::getUser();
    $extension = $this->element['extension'] ? (string) $this->element['extension'] : (string) $jinput->get('extension', 'com_content');
    $this->allowAdd = $user->authorise('core.create', $extension);
}

@wilsonge
@pe7er

can you test this ?

Now if only this option was available on the frontend, communities could create all sorts of structures with this!

@JoshuaLewis What could possibly go wrong!? ;-)

If it was permission based (whether ACL or through a menu item) it could be managed through a select group of people via Joomla's user groups. If the easy creation of categories could be assigned to a parent category, someone attempting to wreck havoc wouldn't be hard to spot and wouldn't really mess up the site structure.