Need to have structopt/serde as peer dependency

[killercup]

The structopt derive macro doesn't work unless the current project allows extern crate structopt;.

This means, user of quicli must cargo add structopt, which is not that cool.

This is part of this code which expands to something like:

const _IMPL_STRUCTOPT_FOR_Cli: () = {
    extern crate structopt as _structopt;
    use structopt::StructOpt;
    impl _structopt::StructOpt for Cli {

Maybe we can add a feature to either suppress or customize this upstream?

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Same is also true for serde! (Thanks to this code)

[vitiral]

I'm a bit confused: are you saying that because serde/structopt's derive have macros that themselves have extern crate MYSELF that means that cargo requires the crate to be in Cargo.toml?

Whew... does a workaround for this exist if a fix is made in serde/structopt?

Edit: I see you've opened issues asking that exact question to the authors of those crates.

[killercup]

Let's say you write a crate called "lorem", which has #[derive(Deserialize)] struct Foo { x: i32 }. The proc macro that of the Deserialize derive generates code that has extern crate serde as serde_; in it. This means that post-expansion your "lorem" crate now has extern crate serde … in it. So the compiler will try to load serde from your dependencies – which only works if serde is in your list of dependencies.

See serde-rs/serde#1147 for a few ideas how to solve this.