More intro and outro templates for series

[ZzMzaw]

Hello,

While I was playing with the series feature, I found something which should work (from my perspective at least) but doesn't.

In each of my series' articles, I would like to add some link between the article.

I would like to add an intro like We've seen ... in the previous article of this series and now, we'll see ... for all articles except the first one (because there is no previous article).
I would like to add an outro like We')ve just seen ..., and we'll see ... in the next article of this series. for all articles except the last one (because there is no next article.
Previous and next article point to the relevant previous or next article with a link (which is easy to configure thanks to the template variables).

So far, we have following templates:

• next_only - Used for the first article (has next article but no previous)
• middle - Used for articles with both previous and next articles
• prev_only - Used for the last article (has previous article but no next)
• default - Fallback template used when a specific position template isn’t defined

In order to achieve what I want, I would need to configure middle and prev_only for intro and middle and next_only for outro.

This works if I have multiple articles but fails if I have only one, because the only article is both a next_only and a prev_only.
From my configuration, it inherits the two links which are broken because there is neither a previous article nor a next one.
I discovered that because all the articles of my series are currently draft except the first one.

You can reproduce that with the attached website:
series-intro-outro-test-website.zip

Running zola serve -drafts works as expected but running zola serve has the bad behavior.

I know I could just wait to have multiple articles before commiting my code but all of this made me think we may be missing some templates

We could add a has_prev and a has_next templates.
In terms of precedence, I would go for: next_only/middle/prev_only > has_prev/has_next > default.

I would be happy to get your thoughts about that.

I could have a look at implementing it if you think it is worth it.

Edit: I removed renaming of next_only and prev_only (into first, last) after looking at the code.
We should keep next_only and prev_only for retro-compatibility but I would deprecate them in favor of first and last.