# \[Pre-RFC\] Hyphens in crate names, redux

**URL:** <https://internals.rust-lang.org/t/pre-rfc-hyphens-in-crate-names-redux/1655>\
**Category:** ideas (deprecated)\
**Created:** [February 25, 2015, 7:31am UTC](https://internals.rust-lang.org/t/pre-rfc-hyphens-in-crate-names-redux/1655 "2015-02-25T07:31:35Z")\
**Posts on this page:** 10\
**Page:** 1

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**Author:** ![lambda-fairy](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/lambda-fairy/32/2045_2.png) [@lambda-fairy](https://internals.rust-lang.org/u/lambda-fairy)\
**Post date:** [February 25, 2015, 7:31am UTC](https://internals.rust-lang.org/t/pre-rfc-hyphens-in-crate-names-redux/1655/1 "2015-02-25T07:31:35Z")

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At the request of @DanielKeep, I've fleshed out and finished off his [original proposal](http://internals.rust-lang.org/t/pre-rfc-resolve-support-for-hyphens-in-crate-names/1459).

* * *

- Feature Name: `hyphens_considered_harmful`
- Start Date: 2015-02-25
- RFC PR: (leave this empty)
- Rust Issue: (leave this empty)

# Summary

Disallow hyphens in package and crate names. Propose a clear transition path for existing packages.

# Motivation

Currently, Cargo packages and Rust crates both allow hyphens in their names. This is not good, for two reasons:

1. **Usability** : Since hyphens are not allowed in identifiers, anyone who uses such a crate must rename it on import:

2. **Consistency** : Nowhere else do we allow hyphens in names, so having them in crates is inconsistent with the rest of the language.

For these reasons, we should work to remove this feature before the beta.

However, as of January 2015 there are 589 packages with hyphens on [crates.io](http://crates.io). It is unlikely that simply removing hyphens from the syntax will work, given all the code that depends on them. In particular, we need a plan that:

- Is easy to implement and understand;

- Accounts for the existing packages on [crates.io](http://crates.io); and

- Gives as much time as possible for users to fix their code.

# Detailed design

1. On **[crates.io](http://crates.io)**:

2. In **Cargo** :

3. In **rustc** :

4. Announce the change on the users forum and /r/rust. Tell users to update to the latest Cargo and rustc, and to begin transitioning their packages to the new system. Party.

5. Some time between the beta and 1.0 release, remove support for hyphens from Cargo and rustc.

## C dependency (`*-sys`) packages

[RFC 403](https://github.com/rust-lang/rfcs/blob/master/text/0403-cargo-build-command.md) introduced a `*-sys` convention for wrappers around C libraries. Under this proposal, we will use `*_sys` instead.

# Drawbacks

## Code churn

While most code should not break from these changes, there will be much churn as maintainers fix their packages. However, the work should not amount to more than a simple find/replace. Also, because old packages are migrated automatically, maintainers can delay fixing their code until they need to publish a new version.

## Loss of hyphens

There are two advantages to keeping hyphens around:

- Aesthetics: Hyphens do look nicer than underscores.

- Namespacing: Hyphens are often used for pseudo-namespaces. For example in Python, the Django web framework has a wealth of addon packages, all prefixed with `django-`.

The author believes the disadvantages of hyphens outweigh these benefits.

# Alternatives

## Do nothing

As with any proposal, we can choose to do nothing. But given the reasons outlined above, the author believes it is important that we address the problem before the beta release.

## Disallow hyphens in crates, but allow them in packages

What we often call "crate name" is actually two separate concepts: the _package name_ as seen by Cargo and [crates.io](http://crates.io), and the _crate name_ used by rustc and `extern crate`. While the two names are usually equal, Cargo lets us set them separately.

For example, if we have a package named `lily-valley`, we can rename the inner crate to `lily_valley` as follows:

```toml
[package]
name = "lily-valley" # Package name
# ...

[lib]
name = "lily_valley" # Crate name

```

This will let us import the crate as `extern crate lily_valley` while keeping the hyphenated name in Cargo.

But while this solution solves the usability problem, it still leaves the package and crate names inconsistent. Given the few use cases for hyphens, it is unclear whether this solution is better than just disallowing them altogether.

## Make `extern crate` match fuzzily

Alternatively, we can have the compiler consider hyphens and underscores as equal while looking up a crate. In other words, the crate `flim-flam` would match both `extern crate flim_flam` and `extern crate "flim-flam" as flim_flam`. This will let us keep the hyphenated names, without having to rename them on import.

The drawback to this solution is complexity. We will need to add this special case to the compiler, guard against conflicting packages on [crates.io](http://crates.io), and explain this behavior to newcomers. That's too much work to support a marginal use case.

## Repurpose hyphens as namespace separators

Alternatively, we can treat hyphens as path separators in Rust.

For example, the crate `hoity-toity` could be imported as

```rust
extern crate hoity::toity;

```

which is desugared to:

```rust
mod hoity {
    mod toity {
        extern crate "hoity-toity" as krate;
        pub use krate::*;
    }
}

```

However, on prototyping this proposal, the author found it too complex and fraught with edge cases. Banning hyphens outright would be much easier to implement and understand.

# Unresolved questions

None so far.

---

<div class="post-metadata">

**Author:** ![jan\_hudec](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/jan_hudec/32/4100_2.png) [@jan\_hudec](https://internals.rust-lang.org/u/jan_hudec)\
**Post date:** [February 25, 2015, 2:10pm UTC](https://internals.rust-lang.org/t/pre-rfc-hyphens-in-crate-names-redux/1655/2 "2015-02-25T14:10:02Z")

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> [@lambda-fairy](#):
>
> extern crate hoity::toity;

I liked the way Perl modules used to be organized in two-level hierarchy. It used to make sense and sounded more professional then the general random project names. But lately CPAN is just as full of “fancy” names as other project sites, so I don't think attempt at organization would have much chance anyway. So not worth it.

---

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**Author:** ![alexcrichton](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/alexcrichton/32/4501_2.png) [@alexcrichton](https://internals.rust-lang.org/u/alexcrichton)\
**Post date:** [February 25, 2015, 7:09pm UTC](https://internals.rust-lang.org/t/pre-rfc-hyphens-in-crate-names-redux/1655/3 "2015-02-25T19:09:11Z")

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Thanks for this! I think this is a well written RFC 😄

> [@lambda-fairy](#):
>
> Drawbacks

This may want to explicitly mention that the `foo-sys` convention will become `foo_sys` (or propose some other alternative). The "Drawbacks" section may not be the right place for it, but it may want to be mentioned somewhere at least.

> [@lambda-fairy](#):
>
> Disallow hyphens in crates, but allow them in packages

Another possible alternative here as well would be for the compiler itself to consider `-` == `_` for the sake of crate name comparison. That way `--extern foo-baz=...` would match against `extern crate foo_baz` or `extern crate "foo-baz" as foo_baz;`

---

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**Author:** ![retep998](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/retep998/32/729_2.png) [@retep998](https://internals.rust-lang.org/u/retep998)\
**Post date:** [February 25, 2015, 8:52pm UTC](https://internals.rust-lang.org/t/pre-rfc-hyphens-in-crate-names-redux/1655/4 "2015-02-25T20:52:16Z")

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If packages with hyphens are going to be renamed, can I explicitly request renames to something else? I’m not entirely a fan of `_sys`.

---

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**Author:** ![DanielKeep](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/danielkeep/32/1332_2.png) [@DanielKeep](https://internals.rust-lang.org/u/DanielKeep)\
**Post date:** [February 26, 2015, 2:20am UTC](https://internals.rust-lang.org/t/pre-rfc-hyphens-in-crate-names-redux/1655/5 "2015-02-26T02:20:06Z")

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Thanks for doing this. Again, apologies for dropping the ball halfway through.

One note: it would be nice to be able to use hyphens in binary crate names (since they can’t be linked against) and maybe static libraries (_i.e._ _not_ `rlib`s), though that could be something that Cargo can do by renaming the output file. By no means is it _necessary_, since it could be allowed in a backward-compatible fashion. (Actually, it might be worth making it a follow-up RFC to allow arbitrary names for _output_ crates; crates that will never be consumed by another Rust program.)

---

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**Author:** ![lambda-fairy](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/lambda-fairy/32/2045_2.png) [@lambda-fairy](https://internals.rust-lang.org/u/lambda-fairy)\
**Post date:** [February 26, 2015, 5:29am UTC](https://internals.rust-lang.org/t/pre-rfc-hyphens-in-crate-names-redux/1655/6 "2015-02-26T05:29:10Z")

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Cheers for the review, @alexcrichton! I've addressed both your points.

> [@retep998](#):
>
> If packages with hyphens are going to be renamed, can I explicitly request renames to something else? I'm not entirely a fan of \_sys.

Though I agree with you on `_sys`, I'd rather not allow these requests. Under the current proposal, the instructions will simply be "change all hyphens to underscores". If we allow custom renames, it'll end up as "change all hyphens to underscores... unless someone chose a different name, in which case spend a few minutes looking it up".

It'll already be annoying having to fix all those hyphens, and I don't want to make it harder for everyone involved.

If you'd like to change the convention, then we can do that in a separate RFC.

> [@DanielKeep](#):
>
> One note: it would be nice to be able to use hyphens in binary crate names (since they can't be linked against) and maybe static libraries (i.e. not rlibs), though that could be something that Cargo can do by renaming the output file. By no means is it necessary, since it could be allowed in a backward-compatible fashion. (Actually, it might be worth making it a follow-up RFC to allow arbitrary names for output crates; crates that will never be consumed by another Rust program.)

We can already override the output filename in rustc using `-o`, but yes it would be nice to have something like that in Cargo.

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**Author:** ![mikedilger](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/mikedilger/32/261_2.png) [@mikedilger](https://internals.rust-lang.org/u/mikedilger)\
**Post date:** [March 8, 2015, 7:55am UTC](https://internals.rust-lang.org/t/pre-rfc-hyphens-in-crate-names-redux/1655/7 "2015-03-08T07:55:17Z")

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If the only counterargument to “Disallow hyphens in crates, but allow them in packages” is that it leaves the package name and crate name inconsistent, then I would argue that Cargo shouldn’t be allowing us to specify them separately. That is, either we wholly believe that having two names (one for package, one for crate) is a bad thing, and we follow that to its logical conclusion, or else … (tada!) there is no valid counter-argument remaining to “Disallow hyphens in crates, but allow them in packages,” and yet several pro-arguments (no package renaming, aesthetics, pseudo-namespacing).

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**Author:** ![gilescope](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/gilescope/32/2798_2.png) [@gilescope](https://internals.rust-lang.org/u/gilescope)\
**Post date:** [September 28, 2017, 10:37pm UTC](https://internals.rust-lang.org/t/pre-rfc-hyphens-in-crate-names-redux/1655/8 "2017-09-28T22:37:59Z")

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Two years on and there’s more crates with hyphens AND underscores though I haven’t seen any yet that use both. Could we please prevent new crates from having hyphens. This way in a decade we’ll be able to say look - 90% of the crates are using underscores, we should standardise on that. Think of the children!

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**Author:** ![dtolnay](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/dtolnay/32/1447_2.png) [@dtolnay](https://internals.rust-lang.org/u/dtolnay)\
**Post date:** [October 2, 2017, 7:56pm UTC](https://internals.rust-lang.org/t/pre-rfc-hyphens-in-crate-names-redux/1655/9 "2017-10-02T19:56:13Z")

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We plan to make it not matter which one you use. [rust-lang/cargo#2775](https://github.com/rust-lang/cargo/issues/2775)

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**Author:** ![system](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/system/32/14092_2.png) [@system](https://internals.rust-lang.org/u/system)\
**Post date:** [March 25, 2019, 8:23am UTC](https://internals.rust-lang.org/t/pre-rfc-hyphens-in-crate-names-redux/1655/10 "2019-03-25T08:23:59Z")

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Closed on March 25, 2019, 8:23am UTC

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