Migrate to Zola

[senekor]

closes #1522

A preview is deployed with GitHub Actions on my fork.

A comparison of the output before & aftered (slightly doctored to make it somewhat useful): https://github.com/rust-lang/blog.rust-lang.org/compare/bd43cef553fa63a5fb7fbd311c3e9329f715f1c0..72b0efba957ed22d543406fcce8ad251008c6afc

Rendered

[senekor]

At this point in time, everything is in place at first glance. Both blogs render all their pages, they loook the same, the blog posts themselves look the same, the feeds are there...

However, the output in terms of HTMl files etc. is nowhere near identical to before, so it's super hard to determine if there aren't any regressions. I'll note down some notable things that I know changed:

• Pages moved from slug.html to slug/index.html. There are also hash-preserving redirects at slug.html/index.html so permalinks aren't broken.

• The syntax highlighting is completely changed to Zolas builtin solution. The theme is a different one, I think it looks nice, but that is obviously a prefrence. We can now easily pick one of the other available themes is desired. There's also one clear improvement of syntax highlighting: Previously, code fences without a language specifiers where highlighted as Rust code by default. That might seem resonable for a blog about Rust, but it forced people to put random other specifiers on blocks that weren't Rust code ("console", "text" etc.). Sometimes that was forgotten and the block was highlighted pretty weirdly. One example is this page where console output is sometimes highlighted as Rust code.

• The markdown source files of the content obviously stays mostly the same, but the front matter is migrated automatically. (If there are pending PRs of posts that have the old front matter, they can fix it by running a single command: FIX_FRONT_MATTER=1 cargo test -p front_matter). There are also some slight changes to the markdown files themselves. Namely, section IDs are generated a little differently so links to other sections of the same post were manually fixed. Zola checks internal links on every build, so I'm confident about this. Another content change is that unknown language specifiers on code blocks were removed, because Zola generates a ton of annoying warnings for them. It doesn't make a difference in the output, because unknown languages aren't highlighted anyway. Those languages that were just improperly named were fixed (e.g. rust= -> rust, shell -> sh)

• I'm a little concerned about the feeds. They changed a little bit, for example the releases.json now has foobar/ as the url instead of foobar.html. I'm also not 100% about the atom feed, since I don't use it. Those feeds are probably read by machines, which might be fussy about small differences like that. I don't know all the programs that might be reading these, so it's hard to test if this isn't breaking anything.

• A sitemap and a robots.txt have been added automatically by Zola. I suppose there is no reason to remove them.(?)

[senekor]

Also, it should be noted that we currently have to use a fork of Zola. The maintainer doesn't seem very responsive at the moment, but hopefully the features we need can be upstreamed in a reasonable time frame.

[senekor]

Here is a doctored version of the diff between the output before and after. I removed the generated redirects, those are just noise. And I renamed files in one version so the diff relibly detect them as a single modified file (as opposed to one file being deleted and a slightly different one being created from scratch).

https://github.com/rust-lang/blog.rust-lang.org/compare/bd43cef553fa63a5fb7fbd311c3e9329f715f1c0..72b0efba957ed22d543406fcce8ad251008c6afc

[senekor]

Spent quite a while combing through the output diff, I can't find anything that's wrong anymore.

IMO the riskiest parts of this PR are:

• The atom feed is changed, especially including the IDs of each entry. What's the worst case here? People's RSS readers will spuriously notify them of 10 new blog posts? That would seem acceptable to me.
• The releases.json feed changed. Which tools rely on the url key of that feed to remain stable?
• We have to use a fork of Zola for the time being. The patches aren't big though.

@Manishearth sorry, it's a big one... 😅

[Manishearth]

Landable as is, the issue with code blocks can be figured out later.

Thanks for doing this!!

[senekor]

Great! Only added another commit migrating the front matter of a post that was merged recently.

[Manishearth]

fire at will