POC: use snafu instead of derive_more for errors

[pkhry]

Description

• this is an alternative to Remove derive_more #1600 (see Replace derive_more (and remove syn 1.0 in favour of 2.0)? #1503)
• Replaces derive_more usage with snafu

Changing the library was somewhat easy, however:

• snafu uses its own custom snafu::Error type in no-std contexts, therefore we needed to define a wrapper type that implements snafu::AsErrorSource for external error types and this led to a bit of boilerplate.
• snafu doesn't support tuple variants yet, so its impossible to define an Error enum like this:

#[derive(Snafu)]
enum Error {
 #[snafu(display("example text {0}"))]
  MyEnum(AnotherError) 
}

it will be defined as:

#[derive(Snafu)]
enum Error {
 #[snafu(display("example text {source}"), context(false))]
  MyEnum {
    source: AnotherError
  } 
}
- for external types it will look like example below, given we defined `DisplayError` wrapper for compatibility
```rust
#[derive(Snafu)]
enum Error {
 #[snafu(display("example text {source}"), context(false))]
  MyEnum {
    #[snafu(source(from(AnotherErrorExternal,DisplayError)))]
    source: DisplayError<AnotherError>
  } 
}

• This is a POC to gather some discussion whether it's better to go with snafu or use some other library or define Display/From by hand
• This will also incur dowstream breakage for users of subxt-metadata, subxt-signer, subxt-core

[niklasad1]

This will also incur dowstream breakage for users of subxt-metadata, subxt-signer, subxt-core

It's because that snafu uses each variant as a struct instead of tuple?

// snafu
#[derive(Debug, snafu::Snafu)]
pub enum Error {
    #[snafu(display("Metadata Error: {source}"), context(false))]
    Metadata {
        /// Error source
        source: MetadataError,
    }
}

// dervive_more
#[derive(Debug, dervive_more::Display)]
enum Error {
    #[display(fmt = "Metadata Error: {_0}")]
    Metadata(MetadataError),
}

In downstream code then one has to do:

   // snafu
   if let Err(Error::Metadata { e }) = my_err {}

   // derive_more
   if let Err(Error::Metadata(e)) = my_err {}

Looks like a good solution to me :)
Would be nice to use context(false) globally on the Error type but that doesn't seem possible
because it depends on display attribute is used....

[niklasad1]

Looks good to me

[lexnv]

LGTM! This approach also looks good, nice 👍

[jsdw]

Offhand I can't quite see what the reason for this is?

[niklasad1]

snafu uses its own custom snafu::Error type in no-std contexts, therefore we needed to define a wrapper type that implements snafu::AsErrorSource for external error types and this led to a bit of boilerplate.snafu uses its own custom snafu::Error type in no-std contexts, therefore we needed to define a wrapper type that implements snafu::AsErrorSource for external error types and this led to a bit of boilerplate.

Most likely ☝️

[jsdw]

Ahh, I should have paid more attention reading :)

[pkhry]

closing in favor of #1600