I have tested this item ✅ successfully on 7ba153e

Links are working with and without IDs, even on a multilanguage site.

Multilingual

###NOTE:
I am testing here after correcting the info-block and any file related in order to add the category and parent category language to ContentHelperRoute::getCategoryRoute() as these are missing.

patchcontentcategory.diff.zip

Wanted to make a PR with this but as it is still broken, I will wait...

Results
Setting all types of com_content article or category display (separately or together).
Making sure category and parent category (with links) are set to display in the info-block.

Clicking on the category or parent category link in the infoblock gives correct results depending on the language of the category and its parent category.

If any is set to ALL, the urls are real bad.

I can get:
/en/featured-en-gb?view=category&id=19 Bad
or, if I have a menu item for the article
/en/othercatarticle?view=category&id=18 Bad

If all set to the same Content Language, it will use my hidden All Categories Menu item (alias: allcategories-en-gb) as base (correct result in 3.x with modern router).
/en/allcategories-en-gb/category-all Good.

Briefly said, when anything set to language ALL, sef links in 4.0 are badly broken, even after this patch.

I also tested with a custom menu item to use instead of blog (With xml and all).
I can create the menu item, it will display fine, except for the info-block category and parent category where the layout is appended &layout=cassiopeamyblog for example...

@Hackwar Any idea?

I can get:
/en/featured-en-gb?view=category&id=19 Bad
or, if I have a menu item for the article
/en/othercatarticle?view=category&id=18 Bad

This is another issue, more related to reversed PR #19099 and issue at #19537.

Solved here the issue with info-block and categories set to ALL languages.
Change has to be done in route.php
Will make PR for info-block as it is a separate issue than this PR

See #21916 concerning multilang
For com_content, as long as one has a List All Categories menu item, even hidden, no more 404 afaik.

Requiring a "hidden menu item" is not a real solution

We have 2 issues, one is fixed by your PR another by this PR. Please do not mix it.
This PR is only for URL when there is no any menu item assigned.

@infograf768 Can you say that you have tested this PR?

let me retest in present 4.0-dev + #22022

@csthomas
Multilingual:
Settings
If we have absolutely no menu item to com_content stuff, i.e. if we have for example a home displaying a contact or a com_search menu item.

Then using as url index.php/component/content/categories just gives me a Category not found

Now, if I use the module articles_category, it will display articles and I can click on their title link or their category link.

After your PR, I get links like
/en/component/content/category/category-en-gb?Itemid=112

or
/en/component/content/article/category-en-gb/article-en-gb?Itemid=112

with always the same Itemid=112 , which is the itemid of the Home page whatever the menu item displayed (a contact, a search, whatever) before clicking on the links in the articlescategory module.

I never get the type of links you posted above
en/component/content/article/category-en-gb/article-en-gb

before your patch I do indeed get 404s.

Not sure I can set the test as successful.

Probably J4 start to add an Itemid everywhere, but this is not job for this PR to fix it. IMO this Itemid is redundant. @Hackwar do you want to add something?

@infograf768 Your test has been successful. J4 adds Itemid before and after the patch.

Any consideration about B/C as we had with #19280 ?
@wilsonge @mbabker

This here is a fix for a pretty obvious bug. As it is now ported to 4 it should be fine to be accepted as BC breaks can be tolerated.

I want the unit tests ported as well please @rdeutz can you please work with @csthomas on that. Having stable routing unit tests is going to be super important for j4 so if we do need to make any more changes in the future we can understand the impact clearly

It may be hard to start as I have not found any tests on joomla routing.
https://github.com/joomla/test-unit/ ??
Please contact me at glip.

Idk where the tests are now, but I wrote full tests for all routing code...

They were deleted at joomla/test-unit@f1a5ac8#diff-6862fb1e873b5617da1d3c4dc1447d2b

Try https://github.com/joomla/test-integration (anyone got a map to actually find any of the tests anymore?)

Thanks, I found.

I see that I can use database in tests but I should not as @Hackwar mentioned in older PR.

@wilsonge Should this be followed-up on?

Can anybody pick this up or should we close this PR?

I had the same issue as described in #32248.
The link is: ... /index.php/component/contact/contact/uncategorised/bb?Itemid=101
SEO friendly urls is ON
index.php/component/contact/contact/uncategorised/bb?Itemid=101

before patch: 404, after patch - the contat form is displayed with this url

Closing in favour of #32695 .