use relative and absolute URLs

[MuxaJIbI4]

see issue #830 for full description.

Now test website (with not empty path after host) looks and works correctly (CSS) => https://muxajibi4.github.io/git.github.io/

---

Not fixed links in older files:

1. ignored (for now?) absolute links (with host) to https://git.github.io in files:

• all .markdown files /_posts
• multiple .md files in /links

2. Didn't add relative_url in links to '/images/*' in files:

• Git-Logo-1788C.png
  SoC-2016-Org-Application.md
  SoC-2017-Org-Application.md
  SoC-2018-Org-Application.md
  SoC-2019-Org-Application.md
  SoC-2020-Org-Application.md
  SoC-2021-Org-Application.md
  SoC-2022-Org-Application.md

• git_merge_2020_cake.jpg
  2020-03-25-edition-61.markdown

• git_merge_2020_timeline.jpg
  2020-03-25-edition-61.markdown

• logo.png
  SoC-2014-Org-Application.md
  SoC-2015-Org-Application.md

[MuxaJIbI4]

@chriscool please review

[chriscool]

Please try to explain the reasons for doing that a bit better than "This removes hard-coded domain name from subpages".

It seems to me that there are some drawbacks to URLs like {{ '/Hacking-Git/' | relative_url }} instead of https://git.github.io/Hacking-Git/, especially:

• it's a bit harder to create, as one cannot just copy-paste them,
• it's harder to check from the source markdown, as one cannot copy-paste them back into a browser.

I agree that it could perhaps help a bit with moving to git-scm.org, but I find the syntax quite complex. Isn't there a simpler syntax?

[MuxaJIbI4]

@chriscool

Please try to explain the reasons for doing that a bit better than "This removes hard-coded domain name from subpages".

Let' separate this into 2 different problems.

1. Remove host from URL to the same website, making relative URLs.
This is actually a good practice - no matter how host (https://git.hithub.io/) changes - it won't be broken. Can be tested on https://locahost:800 - all relative URLs will link to localhost, not git.hithub.io.

2. Add support for additional path after host
For example, my test website https://muxajibi4.github.io/git.github.io (with added path /git.github.io).
Without relative_url link /css/main.css with point to https://muxajibi4.github.io/css/main.css which doesn't exist.

Note. If this website will ALWAYS be located without path, then all relative_url can be deleted (but host should still be removed).

In RSS 'feed.xml' I used absolute_url because in RSS reader it becomes external URL.

I agree that it could perhaps help a bit with moving to git-scm.org,

Didn't think about it.

but I find the syntax quite complex. Isn't there a simpler syntax?

using Jekyll filter relative_url is the simplest form of adding site.url and site.baseurl to the full URL.

You can directly add site.baseurl to the links like in https://github.com/git/git-reference/blob/gh-pages/_layouts/reference.html. This is not recommended compared to relative_url according to docs https://jekyllrb.com/docs/liquid/filters/

[chriscool]

@jnareb, @mjaix, @sivaraam, @To1ne, @stepnem do you have an opinion on this? I think such {{ '/Hacking-Git/' | relative_url }} instead of https://git.github.io/Hacking-Git/ might be a bit cumbersome to create and maintain, but maybe some tools can help us (CI jobs maybe) and it's worth it? What do you think?

[sivaraam]

Sorry. Somehow missed the ping. I think having a way to specify relative URLs would indeed be helpful. It may not be worth it at the moment if the plan to move the site somewhere else isn't particularly in progress.

That said, it may be very much feasible to have a CI tool that would validate existence of such relative URLs while building. We could also explore a more convenient way to specify the relative URL as simply the portion without the domain name rather than having a custom template like the one in this PR. @MuxaJIbI4 have you already explored the possibility of simplifying how relative links are specified?