interpreter: Add API to do JSON encoding/decoding for Value

[hunger]

…terpreter

I need to enccode/decode interpreter values into JSON for the viewer and the live-preview.

Extract the from-json code from the viewer into a new crate interpreter-json, so that the normal interpreter does not need to gain a dependency on serde_json.

Extend the from_json code a bit and implement to_json. Add some simple tests while at it.

[ogoffart]

Any reason not to put that in a module in the slint-interpreter crate?
It can be put behind the internal feature flag.
It is annoying that it may be in public API, but additional crates have downsides too (make publishing harder as we may reach rate limit if we publish too many crates at once)
If it has to be in a different crate, its name should be starting by i-slint-

[ogoffart]

so that the normal interpreter does not need to gain a dependency on serde_json

It should be behind a feature flag.
(btw, serde-json is already a build dependency of the interpreter through i-slint-core-macros)

[tronical]

I have the same feeling, I think it makes sense to create a separate crate when there is a need/use for it, but at the moment I think everyone who needs this functionality also needs the interpreter.

[hunger]

OK, I'll merge it into the interpreter.

[ogoffart]

This adds public API, with a public dependency on serde_json when the json feature is added.

Should it be documented, either document it that this is an internal feature (and then it should be renamed with "internal") or polish the documentation (of the feature, and of the functions, and make sure it is on docs.rs)

[hunger]

A bit better docs... not great, but the new functions should be pretty obvious.

[hunger]

This also disambiguates the rust test driver: The workspace turns on the json feature in the slint-interpreter, so that is active in the test as well and causes a build fail there.

[ogoffart]

We'll need to do proper API review on this.

I wonder if a better API wouldn't be to implement the From trait between serde_json::Value and slint_interpreter::Value

Or maybe the best would be to implement manually the serde::Serialize and serde::Deserialize trait for Value

[ogoffart]

I realize that using Serialize/Decerialize or just From don't work because we need the type.
I think we probably need to create a public Type. But we can't just make our Type public.

IMHO it would be better to actually keep this feature internal under the internal feature flag and not having it as public.

Have it under slint-interpreter::internal::value_from_json/value_to_json functions.

That said eventually we would need to expose a proper type for our properties. We could discuss about that

PS: I took the liberty to edit the PR title

[hunger]

So I moved back to the state from late last week, but made json an internal-json feature now. We use the internal type and use that to help us decide how to decode the json strings.

I did keep the Result<_, String> for the error reporting, as that worked pretty well.

I should probably test more error conditions, but most of them are todo items than things that should report an error ;-)

[hunger]

I hope I also fixed the image path test on windows this time round.

[ogoffart]

Thanks. Looks good now.