Feature Name: super_hyphens
Start Date: (fill me in with today's date, YYYY-MM-DD)
RFC PR: (leave this empty)
Rust Issue: (leave this empty)

Summary

Treat hyphens - in crate names as path separators :: in Rust.

For example, the crate rustc-serialize would be imported as

extern crate rustc::serialize;

which is desugared to:

mod rustc {
    pub mod serialize {
        extern crate "rustc-serialize" as krate;
        pub use krate::*;
    }
}

The old syntax (extern crate "foo" as foo) will remain as-is.

Motivation

This RFC aims to solve two issues, which at first glance seem unrelated.

Hyphens are awkward to use

Currently, hyphens in crate names – foo-bar – are an ergonomic nightmare. Since hyphens are not allowed in identifiers, anyone who uses such a crate must rename it on import:

extern crate "rustc-serialize" as rustc_serialize;

This boilerplate confers no additional meaning, and is a common source of confusion for beginners. It is without question a Bad Thing.

However, as of January 2015 there are 589 packages with hyphens on crates.io. Any proposal will need to account for these packages, and it is not clear how a total ban on hyphenated names will play out. That we recently established a -sys convention for C bindings muddies the situation further.

Crate namespaces are useful

Package namespaces are an oft-requested feature for Cargo.

One use case is the Iron web framework, which consists of multiple small packages extending a common core. Since most of these packages don't make sense outside of Iron, it would be beneficial to put them under an iron namespace. Other package "families", such as retep998's Windows API bindings, could make use of this feature as well.

On platforms which don't implement namespacing, users tend to overload the hyphen - for this purpose. For example in Python, a quick search yields countless packages prefixed with django-. A solution for Rust should take this existing convention into account.

Detailed design

Currently, the syntax for extern crate is:

EXTERN_CRATE = 'extern' 'crate' ( STRING 'as' IDENT | IDENT )

This RFC proposes it be changed to:

EXTERN_CRATE = 'extern' 'crate' ( STRING 'as' EC_PATH | EC_PATH )
EC_PATH = IDENT ( '::' IDENT )*

This syntax will be desugared as follows:

TODO: Write something clever here

Drawbacks

More complexity in the compiler. However, the changes are bounded to the parser and shouldn't touch other parts of the system.

Alternatives

Do nothing

Ban hyphens altogether

Rename the crate in `Cargo.toml`

Use `/` or `.` for namespacing

Both of these characters have their own drawbacks:

/ is also a path separator. This will cause problems in filenames and URLs:
- Currently, a package named foo-bar compiles to a library named libfoo-bar.rlib by default. Under this scheme, it is unclear what foo/bar would map to.
- On crates.io, you can look up the versions of a package via the path /crates/<name>/versions. If we allow slashes in package names, then /crates/foo/versions will be ambiguous: does it show the versions of foo, or the package named foo/versions? We can solve this problem using an extra sigil (e.g. /crates/foo/+versions), but other solutions don't need such hacks at all.
. is a namespace delimiter in TOML files. Consider the syntax for custom dependencies:
```
[dependencies.apple-fritter]
git = "..."
```
If we allow dots in package names, we'll need to quote the name every time it is used:
```
[dependencies."apple.fritter"]  # Ugly!
git = "..."
```
This syntax is not obvious, and will trip up newcomers to the language.

Unresolved questions

What parts of the design are still TBD?

lfairy/rfcs forked from rust-lang/rfcs

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