This has come up before and I still stand by my case of if you need a fallback then the whole point of this method is useless and shouldn't be used at all.

Is there a strong reason you need a fallback?

I'll give you a use case:

In an administrator area, there is a page listing Models of some sort in a table. Next to each item you have an edit button. Each item can be clicked, directing the administrator to the single Model page. Each Model page has an edit button. The edit form has a cancel button.

When the user clicks the edit button from the list page and then clicks the cancel button, the user should return to the list page. When the user clicks the edit button on the Model page and then clicks the cancel button, the user should return to the Model page. Finally, if the user visited the edit page directly, the user should return to the list page.

In the last scenario, the user would be redirected to the root url when I use the UrlGenerator::previous() method.

Note that with this code, getPreviousUrlFromSession has precedence over the provided fallback.

Refs #6293, #10229.

@vlakoff can you explain?

If there is no referer and a fallback is provided, getPreviousUrlFromSession will still be tried before using the fallback. A different approach could be to directly use the fallback, which might be better as it is more predictible.

In addition, $fallback should be wrapped in a $this->to() instead of being used as-is.

It is wrapped in a to when I merged it. I modified the PR.

Got it: a8ca2b7

Thoughts about my previous comments?