MiniJinja: Learnings from Building a Template Engine in Rust

https://lucumr.pocoo.org/2024/8/27/minijinja/

by todsacerdoti • 2 years ago

115 66 2 years ago

lucumr.pocoo.org

infogulch3• 2 years ago

A templating language would be a great case for using an arena allocator since objects will only live as long as it takes to fulfill the request.

the_mitsuhiko8• 2 years ago

Yes! I did in fact try this but I was unable to find a good way to make the API work.

infogulch3• 2 years ago

Interesting! I suspect a templating engine that uses arenas would be a holy grail for rust web perf, so I'm curious about your experience trying to use them. As for making the API work, do you mean that the arena API was difficult to use, or the object interface you built on top of it was difficult to implement in a way that was accessible to template execution?

HiHelloBolke• 2 years ago

Thank you for this, I just used this to create a rust based cli tool to create j2 yamls. This was motivated because we want to not use ansible j2 yaml generation instead to a standalone binary for it.

Now it feel like helm but it’s j2 and outputs a directory of yamls with base and overlays in kustomization way. So they can be iverriden in gitops by sre if needed

brucecrust• 2 years ago

ha man I hate Jinja. Nothing against this or Rust, just from working in Flask I have borderline nightmares. That might say more about my team that the framework though.

0cf8612b2e1e• 2 years ago

Could you elaborate? I think it’s fine? Although I have always subscribed to the “Two Scoops” philosophy and keep my templates as stupid as possible. Use a variable, simple conditions, etc. Anything more complex should be handled at a higher level.

Go templating on the other hand, that drove me bananas.

murkt4• 2 years ago

I got used to React components, and after that templates feel a bit cumbersome and un-ergonomic in places.

I’ve been using Django templates since 2006. Jinja was designed after Django templates of that era, fixing their most glaring problems. Don’t remember the exact year when I started using Jinja a lot. Maybe 2013.

For example, a pure existence of an {% include %} tag. People use it, implicitly passing many arguments to some other template. Which makes it very hard to understand and change later.

Macros are not that pleasant to use, there are less features in macros then in Python functions, and tools support is much worse too (static analysis, formatting, etc).

Filters… why do I need to write `value|string` instead of `str(value)`?

Etc.

bityard• 2 years ago

Every templating engine has to find a balance between doing what you need it to do, and letting you write business logic in the template itself. (Hey there, PHP.) That said, it's possible to write pathlogical templates in just about anything.

I've used Jinja a lot and always thought that it struck just about the right balance.

The docs are also way better than they used to be.

IshKebab• 2 years ago

The answer is not to use a templating engine. TSX is the gold standard here IMO. Using it with https://fresh.deno.dev/ is soooo much nicer than old school templates.

murkt4• 2 years ago

I’ve been using Jinja2 for years and years, probably around a decade now. I don’t remember any other docs?

golergka• 2 years ago

I worked on a project that implemented static type checking for dbt projects, which are made of SQL templated with jinja and some yaml configs. I'm not sure if I hate it, but it certainly was fun.

snarkyturtle• 2 years ago

Wait until you have to work in Mustache/Handlebars, you'd love Jinja

pietz5• 2 years ago

https://jinjax.scaletti.dev/ cured my pain.

singhrac• 2 years ago

I have the opposite memory :) I remember writing complex applications in Flask and it just worked right away, and as our performance / complexity grew it kind of kept up because it was very modular.

VWWHFSfQ• 2 years ago

I wanted to make a cli tool for rendering templates with mini jinja and also for users to write their own little library of functions/filters etc in Lua using mlua and then be able to use those in their templates. Unfortunately didn't work. All kinds of issues with mini jinja and mlua interactions when trying to add_filter, add_function, etc.

This was awhile ago though. Maybe something changed and I should try it again

the_mitsuhiko8• 2 years ago

You cannot register filters with a non 'static lifetime. However it’s not super hard to work around. Usually an Arc<Mutex> is all you need.

ctoth• 2 years ago

The first thing is that Rust is just not particularly amazing at tree structures.

As someone who doesn't write any Rust I'd like to understand this more. Is it the ownership model that makes trees weird? Is there something you guys do instead? I was working on an R-tree yesterday for something and I'm slightly surprised to read this but obviously Armin knows what he's talking about :)

__s2• 2 years ago

it's a pain if you want children to reference their parents while their parents reference them

Similarly getting a mutable reference to a leaf while parents have references to children is awkward

giancarlostoro• 2 years ago

I know just Rust basics, what specifically makes it awkward? I'm not a heavy Rust user, so I'm having a hard time following, do you have any simple pseudo-Rust code you could share? I'm also a basic CRUD app dev by day, hobbyist by night.

SkiFire134• 2 years ago

Actually, Rust's rules really wants your data to look like trees. Requiring each value to have exactly one owner is not really different than requiring each node of tree to have exactly one parent.

The problem however comes when you want to reference the parent from a child. In the ownership/reference graph that would also count as an edge, and hence creates a cycle with the parent-to-child edge. There are workarounds like using weak reference counted pointers or indexes into arrays, but ultimately they don't offer the same ergonomics as other languages and it's better to design with only parent-to-child links.

oneshtein14• 2 years ago

Why you want to create cyclic reference from child to parent instead of a bare pointer?

pietz5• 2 years ago

I really don't like Jinja. The syntax is not for me and there's often three different ways of building the same thing. I find it a bit confusing.

Recently I started using JinjaX (https://jinjax.scaletti.dev/), which is weirdly amazing. I think the comparison on the homepage explains it quite well. It feels like what Jinja always should have been and and the multiple ways of doing the same thing converge into one syntax in JinjaX.

I really hope the project gains more traction.

murkt4• 2 years ago

JinjaX components are simple Jinja templates. You use them as if they were HTML tags without having to import them: easy to use and easy to read.

…and impossible to understand and keep track of what goes where.

No, thanks. Components are a good idea, and no imports is a horrible idea.

adontz• 2 years ago

Do I understand JinjaX correctly, that it's specifically for HTML templates, not text templates in general?

pietz5• 2 years ago

Yes

krick2• 2 years ago

IDK. I always though Jinja is the best templating engine and was surprised by your complaints and the Jinja sample on that website. What doesn't he like? Looks totally legit...

After reading JinjaX sample, I see the point. I would agree that it's much cleaner... If not for the fact he uses capitalized tags to distinguish between templates and html. I hate it. First off, it just throws me off, I cannot tell at the glance anymore where is the real text, and where is templating voodoo-magic. How do I find the source files fot layout and pagination? Right, I just have to know the convention. Second, it's remotely justifiable and can be attributed to a matter of getting used to only if it produces html. Templating engines are not restricted to html. It could be producing markdown, it could be producing XML. If only the author of this library restrained himself to be less funky and not introduce any ambiguous idioms, it would be pretty perfect. But as it is, I don't think I could use it.

pietz5• 2 years ago

Different tastes, I guess. It's the same syntax that many JavaScript Frontend frameworks like react and Svelte use. I find it much cleaner.

When using Jinja with HTMX you also run into trouble that it doesn't nicely support partials. You could use the jinja_partials library but I just find JinjaX so much more pleasant.

the_mitsuhiko8• 2 years ago

I don’t think that Jinja is the right way to build HTML heavy anything. Look at JSX for that. However I do find it interesting how this is a constant back and forth.

I remember when the template engine that everybody in Python used was kid (precursor to genshi) which was XML based and looked a lot like vue/jsx does today. Back in the day people did not like it at all because designers found it hard to work with.

Now the situation is a bit different but what do I know where we land in 10 years. It feels like a constant cycle ;)

pietz5• 2 years ago

I think JinjaX was inspired by JSX. Obviously, there's a huge delta, but my "HTML heavy" problems are nicely solved with JinjaX

geenat• 2 years ago

IMHO Jinja was never worth salvaging. It's a bandaid for not being able to mix Python and HTML easily.

Super slow parsing. Unintuitive DSL (opinionated enough to be a PITA). Huge LoC vs the value it contributes to your project.

Adopt a different system.. see: ERB, PHP, EJS- all of these are extremely fast and intuitive (just the native language + an extra tag or two).

Edit:

Of course.. this is authored by the jinja guy.

krick2• 2 years ago

Except no cultured adult programmer would use the original PHP syntax for templating, unless it's some 5-minutes worth development script. It's too powerful and too complicated. People use smarty or twig, which are basically the same thing as Jinja.

lyu07282• 2 years ago

I always liked TAL, it kind of made sense to me that the templating engine itself understands the syntax of the language you are templating. It ought to be impossible to write invalid HTML/XML. It's like the pain you get into when templating YAML with jinja, but if the YAML template also were itself a valid YAML file it would be much cleaner imho.

Jackevansevo• 2 years ago

To add some balance to everyone slating Jinja in the comments, I've personally found it great to use.

Sure you CAN write unmaintainable business logic spaghetti in your templates, doesn't mean you SHOULD (Most criticism appears to come from this angle).

MiniJinja: Learnings from Building a Template Engine in Rust

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