Add WASM support for json.is_valid built-in.

[kristiansvalland]

wasm: Add support for WASM and simple tests.
internal: Add opa_json_is_valid to map of wasm built-ins.
docs: Indicate that WASM support is now available for json.is_valid.

This code could also benefit from an allocation-less implementation as the change in #4203 was motivated by, but since that is not readily available I opted for this low-hanging version which I still think improves the codebase, and that can be changed to an allocation-less implementation at a later time by someone with capacity and know-how.

Fixes #4140

[srenatus]

Wonderful. Thanks a lot for picking this up! I've got a couple of nitpicks but nothing major really.

Thanks again 🚀

[srenatus]

[nit] I'd probably go with

Suggested change

	if (r == NULL)
	{
	return opa_boolean(false);
	}
	return opa_boolean(true);
	return opa_boolean(r != NULL);

but it really doesn't matter. I guess it's all the same to the compiler.

[srenatus]

Thinking about this more, maybe a free wouldn't hurt?

Suggested change

	if (r == NULL)
	{
	return opa_boolean(false);
	}
	return opa_boolean(true);
	if (r == NULL)
	{
	return opa_boolean(false);
	}
	opa_free(r);
	return opa_boolean(true);

WDYT? It's been a while since I've played with those parts of the code base 🤔

[kristiansvalland]

I like both suggestions. The latter probably don't hurt, as it did not break the tests at least, so I went with that. After all, we do not need the content of r, so we can free it.

I am not too familiar with the GC of WASM/C though.

[srenatus]

[nit] We're already dealing with booleans, can we do

Suggested change

	test("json/is_valid_true", opa_value_compare(opa_json_is_valid(opa_string_terminated("\"string\"")), opa_boolean(true)) == 0);
	test("json/is_valid_true", opa_cast_boolean(opa_json_is_valid(opa_string_terminated("\"string\"")));

and !opa_cast_boolean(...) here?

[kristiansvalland]

Hmm, seems that it does not work the way we would expect for opa_boolean_t. The following fails
test("json/false_is_false", !opa_cast_boolean(opa_boolean(false)));

But the following seems to work by referencing the bool field v of opa_boolean_t,
test("json/false_is_false", !opa_cast_boolean(opa_boolean(false))->v);

I am not entirely sure that this is the correct way?

[kristiansvalland]

Thanks for your feedback and review :)

[srenatus]

@kristiansvalland thanks for picking this up! Have you been trying to improve the state of the world, or do you have a specific interest in Wasm? (Sorry, I'm just curious)

[kristiansvalland]

@srenatus I recently started using OPA professionally, and thought that I might as well contribute some back to the project and learn something along the way. While I do find Wasm interesting, that was not the main motivation for me picking this up -- I thought that the suggested steps in the original issue was quite helpful and gave it a go.

But I like the sound of "improve the state of the world", so I will consider using that moving forward 😄