"verbose-errors" changes nom's API

[jsgf]

Prerequisites

Here are a few things you should provide to help me understand the issue:

• Rust version : 1.29.0
• nom version : 3.2.1
• nom compilation features used:

The verbose-errors feature changes nom's API by changing the definition of the IResult type in a non-compatible way. This means that enabling the feature will break downstream users which don't expect it.

Since cargo always accumulates features across the dependency graph, if there are two users of nom within the same dep graph, and one enabled verbose-errors, it will break the other user which doesn't want it.

This is because in general cargo expects features to extend the functionality of a crate in a compatible way.

It would be better to make the verbose- and simple- explicit separate parts of the exposed API so that you can just use the API you want from a single instance of the crate.

cc: @alexcrichton

[Geal]

hello,

there's a workaround in nom 4: the errors are now an enum, and the one from verbose-errors includes the only case from simple-errors.

[kryptan]

@Geal, what do you mean by workaround? How do I actually handle the error in a way that won't break if verbose-errors is enabled?

match context {
    Context::Code(input, error) => { ... },
    _ => unreachable!(),
}

This generates a warning about unreachable pattern and would panic if verbose-errors is enabled and other variant is returned.

Can you please provide an example how to handle the error properly?

[Geal]

verbose-errors has disappeared in nom 5. Now the error behaviour is completely decided by the error type