[Discussion] no_std support

[SimonIT]

Hey @NicolasDP,
@connectety and I want to use cddl-codegen with constrained devices.
For this, we need no_std compatibility.
We started making the changes in our fork.

It seems that everything is compatible with no_std except BufRead.
For BufRead exists a drop-in replacement called acid_io.

So I want to get some opinions from you maintainers about this.
Especially because of your statement:

this crate has zero dependencies (and should not need any in the future)

[NicolasDP]

hello @SimonIT , thanks for the effort in adding no_std support to the crate. I believe you are adding this so that you can use the output of the cddl_codegen to add cardano support on hardware wallets.

The acid_io crate is interesting though I am not sure this is the approach I would have looked at first. I think we should consider a rework of the core component to add the right type of support. I'd like to offer another approach instead:

please have a look at the following: #14

This way the array and bytes data are completely left to the user of the crates and we don't need the BufRead dependency. What do you think?

[SimonIT]

Good idea.

Another problem I came across is the error handling:

1. The trait Error in core is not stable Tracking Issue for Error in core rust-lang/rust#103765
2. Because the trait is not sized, something like Box has to be used
   

   cbor_event/src/error.rs

   Line 33 in b086ad4

   IoError(Box<dyn error::Error>),

   
   This is kinda ugly in my opinion.
3. There seem to be a problem with thread safety and errors?

  error[E0277]: `(dyn core::error::Error + 'static)` cannot be sent between threads safely
   --> src/de.rs:23:17
    |
    23 |             Err(Box::new(Error::ExpectedU8))
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^ `(dyn core::error::Error + 'static)` cannot be sent between threads safely
    |
    = help: the trait `Send` is not implemented for `(dyn core::error::Error + 'static)`
    = note: required for `Unique<(dyn core::error::Error + 'static)>` to implement `Send`
    = note: required because it appears within the type `Box<dyn Error>`
   note: required because it appears within the type `Error`
   --> src/error.rs:11:10
    |
   11 | pub enum Error {
    |          ^^^^^
    = note: required for the cast from `error::Error` to the object type `dyn core::error::Error + Send + Sync`

[NicolasDP]

if we go the path I'm suggesting we don't need IO anymore. We will not need to do things like IoError(Box<dyn error::Error>).

[SimonIT]

We think everything is resolved. Our PR is working. Feel free to make some suggestions there #13 .