Accept hyphen in crate name in place of underscore

[dtolnay]

Crates.io currently accepts hyphens for crates that use underscores, both in the web interface and in the API.

Cargo does not, but should.

error: no matching package named `serde-codegen` found (required by `testing`)
location searched: registry https://github.com/rust-lang/crates.io-index
version required: *

[alexcrichton]

Cargo is somewhat agnostic between - and _, but it doesn't consider the two characters equivalent. Crates decide whether they want - or _ to begin with and then they must be referenced through that name, disallowing usage of the other.

I'd personally prefer to not accept both serde-codegen and serde_codegen as it can be confusing to see two different values which mean the same thing in practice from time to time.

[dtolnay]

Makes sense, and I don't have a strong preference myself. I saw this comment from @steveklabnik and figured this would be a step toward tooling that reflects the conventions we would like developers to use.

Is there a rationale for crates.io vs cargo behaving differently from each other?

I'd personally prefer to not accept both serde-codegen and serde_codegen as it can be confusing to see two different values which mean the same thing in practice from time to time.

Fair, but I would rather see serde-codegen and serde_codegen and not need to care, vs see library-a and library_b and need to remember which one to use in each case. "They mean the same thing" is a thing you learn once, while library-a and library_b is a thing that will bite you for as long as you use Rust.

[alexcrichton]

I don't really know why crates.io is agnostic, it wasn't originally and I think that was a patch added after the fact, would have to track that down.

Yeah it's easier to not have to remember, but to me it's more of a downside as it's disguising what's actually happening under the hood.

[dtolnay]

The crates.io change was rust-lang/crates.io@89bc5dd.

[lambda-fairy]

I don't really know why crates.io is agnostic, it wasn't originally and I think that was a patch added after the fact, would have to track that down.

The current behavior of crates.io is defined by RFC 940:

Right now, crates.io compares package names case-insensitively. This means, for example, you cannot upload a new package named RUSTC-SERIALIZE because rustc-serialize already exists.

Under this proposal, we will extend this logic to identify - and _ as well.

[withoutboats]

I'd like to re-open this issue, I think this is a bug and we should fix it. (Maybe we can talk about it in a cargo meeting).

I'd personally prefer to not accept both serde-codegen and serde_codegen as it can be confusing to see two different values which mean the same thing in practice from time to time.

At first glance, this makes sense, but I think it doesn't hold as much water when you consider:

• In practice, the name almost always appears in your Cargo.toml exactly once, so its not like they'll mean the same thing in the same file, just that some crates will write them differently.
• If the name contains - (which I believe is prefered), both names will already appear, one in the source and one in the manifest, because - is not valid in source.

In contrast, users who accidentally add serde-json always know what they meant, and because of the conversion users are taught that - and _ are interchangeable in package names. In practice, this seems to be a frustrating wart of cargo which is not adding any clarity for people & possibly even confusing them (if they don't guess that the reason adding error_chain failed was that its actually called error-chain).

[dtolnay]

Reopened. I have also come to feel much more strongly about this in the past year.

[alexcrichton]

I also agree this is worthwhile to fix.

Implementation-wise this won't be easy though, I think, as it'll require changes to the crate index. The changes in Cargo itself after that, though, are likely nominal.

[withoutboats]

@alexcrichton That would be a problem, why isn't it sufficient to change how we match the dependency name against the index file to be neutral to underscores (e.g. retry if there's no file with the characters swapped)?

(It'd be better if the index were normalized, but that seems quite challenging).

[alexcrichton]

Right now we don't load the entire index in-memory and we currently also don't try to browse the entire index, rather given a crate we drill into exactly which file it's supposed to be. If we have - and _ normalization we'd have a set of filenames that would be the plausible right one, and we'd in theory have to try to check all of them. That's ok on first builds, but we'd need to ensure that if you've got a lock file that this fallback behavior doesn't happen a lot, as it could add up time-wise I think.

[withoutboats]

Makes sense, so I think what we should do:

• If the index file for the given ident doesn't exist, fall back by substituting underscores/hyphens in the name
• When generating the lock file, be sure to generate it with the index name, not the name in the toml

Is a divergence between the name in the lock and the toml going to be a problem?

EDIT: Also I'd like to write the PR for this to get more acquainted with cargo's codebase :)

[alexcrichton]

Yeah that sounds like it could work!

I think we'll have to maek sure that a Dependency::name isn't compared to a PackageId::name, although we can perhaps either assume that doesn't happen or otherwise use separate types there if necessary. Sounds plausible at least!