Create global get_canonical_url function in CMS

[juliandoucette]

Background

See ​codereview.

I would like to be able to output the canonical url (protocol://host.domain:port/path etc) of a page on a page and/or template.

What to change

Create a global function get_canonical_url(page) that accepts a page path and returns a canonical link (that contains no locale component). It should verify that the page exists in default locale and should raise an exception if it doesn't.

Implementation notes:

• The base url should be configurable in the website settings via siteurl variable that already exists.
• Most of the code that generates the links already exists in cms/sources.py:Source.resolve_link.

[juliandoucette]

Note:

This is how I created a canonical url on adblockbrowser.org

link rel="canonical" href="https://adblockbrowser.org/{{ page[:-5] if page.split('/')[-1] == 'index' else page }}" />

I did it this way because:

1. I didn't want a URL ending in "index"
2. I didn't want the language to be part of the canonical URL

I think 1 should be default behaviour and 2 should be configurable. e.g.

get_page_url(page, withLocale)

[kvas]

Everything but get_canonical_link is moved to #5452 (see ​review for the discussion of reasons).

[abpbot]

A commit referencing this issue has landed:
​Fixes 5343 - add global function: get_canonical_url