Force canonical URLs to include ROS distro

[attu0]

Description

This PR fixes canonical URL generation for sphinx-multiversion builds by
explicitly setting html_baseurl to include the ROS distribution
(e.g. https://docs.ros.org/en/rolling).

This prevents mirrors or alternate build environments from generating
incorrect canonical URLs that omit the ROS distribution or use
non-official domains.

Fixes #6112.

Did you use Generative AI?

Yes — ChatGPT (for guidance and explanation only).

Additional Information

• Implemented as a clean commit on top of rolling
• No unrelated documentation history included

[attu0]

@fujitatomoya Thanks for the guidance!

I’ve recreated the change as a clean commit on top of rolling and opened
a new PR targeting the rolling branch, as requested.

[fujitatomoya]

i do not think replacing this with hardcodes will fix the issue described in #6112, can you explain this why this is the fix from your understanding? (or are you just posting the suggested fix by ChatGPT?)

[attu0]

Thanks for the review

From my understanding of #6112, the issue occurs specifically in
sphinx-multiversion builds where html_baseurl is set to
https://docs.ros.org/en, while the generated pages live under
/en/<distro>/…. In that case, Sphinx generates canonical links that
omit the distro segment, which is what causes incorrect canonicals on
mirrors.

In this repository, canonical URLs are generated by the Sphinx HTML
builder using html_baseurl + the page-relative path. By rewriting
html_baseurl only when smv_current_version is set, the builder
produces canonical URLs of the form >> https://docs.ros.org/en//.html

[attu0]

I agree this only fixes canonicals generated by the HTML builder. If you’d prefer this handled at a different layer (such as template-level canonical generation), I’m happy to change the implementation.