💡 Node assert❔

[smnandre]

Acting as a spinoff to #4165 Add tag to declare variable types
(as I don't want to disrupt the main conversation too much 😅)

The idea is to introduce assertions.

I'm opening this to gather feedback and ideas. I'd like to see if there's something interesting here—or not. :)

This could enhance static analysis, define contracts in templates, and serve as a validator during includes/rendering.

{% assert name string %}
{% assert size in ['sm', 'md', 'lg'] %}

Open to any feedback :)

[smnandre]

Usage / syntax examples

Langage	Code example
PHP	assert(in_array($size, ['sm', 'md']));
Python	assert size in ['sm', 'md']
Java	assert java.util.Arrays.asList("sm", "md").contains(size);
C	assert(strcmp(size, "sm") == 0 || strcmp(size, "md") == 0);
JavaScript	console.assert(["sm", "md"].includes(size));
C++	assert(size == "sm" || size == "md");
Ruby	raise 'Assertion failed' unless ['sm', 'md'].include?(size)

(Table made with some gpt - for representational purposes only)

[Kocal]

What about using assert() function?
With OPcache configuration, you can literally remove assert() calls from the code... or here you planned to not write anything if production?

[smnandre]

That's an idea too ! I would say a node would be easier to parse / use by node visitors but i may be wrong here 😅

or here you planned to not write anything if production?

I planned... nothing 🙃 the "idea" just emerged earlier tonight during the "var/type" discussion

[stof]

The suggestion is about the compiled code, not about the Twig API

Actually, to be able to use PHP's assert function which is a no-op at runtime in production mode, it needs to be a Twig tag and not Twig function usable in an expression.

[smnandre]

👍

[drjayvee]

When it comes to asserting variable types, that can be left over to extensions like TwigStan, once types is merged.

I do like the idea of using assert for expressions.

There's currently no way to intentionally throw an Exception of trigger a warning (aside from something silly like {{ [].foo }}).

I'd propose that the assert tag should have an optional message as part of its spec:

{% assert <expression> [message string] %}

@ruudk is working on compiling Twig templates to PHP in such a way that PHPStan can work its magic. If the assert tag gets a similar treatment, with properly typed variables, we can take a huge leap in template quality.

[fabpot]

@ruudk is working on compiling Twig templates to PHP in such a way that PHPStan can work its magic. If the assert tag gets a similar treatment, with properly typed variables, we can take a huge leap in template quality.

I'm curious to see how that would look like... but also if that's something we can include in the "default" Twig compilation (I suppose this is based on attributes/annotations with no runtime side-effects).

[ruudk]

You can read more about TwigStan here: #4233