Making core no_std compatible

[pranav-bhatt]

#72
Things left to do:

• Remove DisplayError (chrono example, serde-json example), and generally clean up error.rs
• Create default hostname return value for no_std environments
• Investigate removing serde-value #105
• Replace url::Url with something like

#[] // no_std
pub use String as Url;
#[] // std
pub use url::Url;

[elpiel]

For what I've checked, snafu has it's own trait Error that it's implemented in no_std. Since thiserror doesn't have no_std support I would say to just leave snafu for now (if it ain't broken, don't fix it).

[pranav-bhatt]

For what I've checked, snafu has it's own trait Error that it's implemented in no_std. Since thiserror doesn't have no_std support I would say to just leave snafu for now (if it ain't broken, don't fix it).

Mhmm! The main reason behind wanting to explore thiserror was that it was simpler compared to snafu. If you've worked with any other error handling library that can complement no_std and do the trick, it would be amazing if you could help :)
Would you mind joining the Slack channel so we can continue talking on the #cloudevents-sdk-rust channel? (I promise this is the last switch xD)

[slinkydeveloper]

@pranav-bhatt you need to configure the ci to run the no_std builds/tests too

[slinkydeveloper]

Why do we need that?

[pranav-bhatt]

This basically is a work around for std::io::Error and std::io::Result<>. If you're asking about the link, then I forgot to remove it :P

[slinkydeveloper]

Well, why we need io::Error? Can you just disable it in no_std envs?

[slinkydeveloper]

Can we enable these imports around the sdk only if the no_std feature is enabled?

[slinkydeveloper]

In the Cargo.toml, you need to define the std feature, like in https://github.com/KodrAus/rust-no-std/blob/master/Cargo.toml and https://github.com/shepmaster/snafu/blob/master/Cargo.toml and enable it by default.

Then try to create an embedded project in your machine and try to import this library

[slinkydeveloper]

In case of no_std env, you need to import snafu like below (no need to include guide feature)

[slinkydeveloper]

I don't think we need this variant (and the one below) in no_std envs

[slinkydeveloper]

Can you rebase?

[slinkydeveloper]

@pranav-bhatt you should look at this #107

[slinkydeveloper]

@pranav-bhatt can you start cleaning up this pr removing history files etc and rebasing with master? This branch diverged quite a bit from master