Disallow floats feature

[MaksymZavershynskyi]

Motivation:
Many modern day blockchains use Rust smart contracts compiled to WebAssembly. Unfortunately, to enforce determinism they have to scan the compiled *.wasm contract before the execution and check whether it uses floats of float operations. This is not a problem for most of the smart contracts that do not actually use floats. However, if smart contract imports serde_json crate and deserializes a struct the compiler has to include some of the code branches that use f64/f32 even if these branches are never entered by the smart contract execution.

JSON is a fundamental format which is a natural choice for smart contract when they need to interact with the front-end (e.g. written in JS). It is highly desirable for smart contracts to be able to import serde_json crate and use it for deserialization.

Solution:
Have a no_floats feature that comments out certain branches of the code sufficiently enough so that when serde_json deserializer is used in a code that does not use f64/f32 no f64/f32 operations are generated in WebAssembly format. This can be implemented like this: nearprotocol#1 (disregard the added test).

Question:
Do serde-rs/json maintainers want to have it as a feature or they want us (https://nearprotocol.com) to create a permanent fork with this feature?

[dtolnay]

Thanks for the explanation. I would not accept a no_floats feature -- I would prefer if this could be maintained outside of serde-rs/json as a fork.

[webmaster128]

Many modern day blockchains use Rust smart contracts compiled to WebAssembly

As we're falling into this category as well, I'd appreciate to learn about the current state of this ticket.

I would not accept a no_floats feature -- I would prefer if this could be maintained outside of serde-rs/json as a fork.

Is this still up to date? If so, I think this issue can be closed, right?

[MaksymZavershynskyi]

Closing the issue.