File, that throws exception: /modules/custom/units/sections/site_domains/e_site_domain_eh.php
File, that is visited in browser to start the process: /admin/index.php
DocumentRoot: /mnt/hd/home/alex/web

File paths from stack trace (if inspecting in debugger in PhpStorm):

• /mnt/hd/home/alex/web/p/catalyst-demo/core/kernel/event_handler.php
• /mnt/hd/home/alex/web/p/catalyst-demo/core/kernel/event_manager.php
• /mnt/hd/home/alex/web/p/catalyst-demo/core/kernel/application.php

It seems, that xdebug tries to figure out common path to replace with "..", but does that too aggressively. Removing DocumentRoot from all paths might be a good idea anyway.

This is not a bug. Xdebug doesn't really mean "parent directory" with "../". It just means there is something before the /. If you hover over the filename, then you get the full path.

Then you should use 3 dots (e.g. ".../filename.php") to indicate that the path is shortened and there is more to see. 3 dots at the end of text (e.g. "some text ...") exactly does that.

In file path the "../" always means parent folder and this is what most of people would think about it, when they see it.

Fact, that I can hover over to see full path isn't obvious either. I surely won't be trying to hover over each cell in stack trace table in hopes to get extra info. Usually if hovering over will show something, then element should be underlined with a dashed line. If clicking on element, then it should be underlined from the beginning or while hovering over on it (usual behavior with links).

Xdebug is great debugging product, but common-sense GUI principles still need to be applied.

P.S.
Could you please be more responsive. I've posted this issue 2 month ago and only now I'm getting the answer that there is nothing to be fixed.

As this is a minor issue, it's not very high on my list of things to look at. I'll see what I can do.

It's that hard to add one dot in path name (will be "..." instead of "..") to make things clearer?

I closed it as fixed last night already..., because I've fixed it: https://github.com/xdebug/xdebug/commit/1e13ca94dd66bbb462fc1dcd4402849377f1592b