# 2024 Deprecations

# Problem

Cargo has been emitting a bunch deprecation message for a (long?) while. Since edition 2024 is approaching (1.82.0 anticipated), and a Cargo linting system is on the way (<https://github.com/rust-lang/cargo/pull/13621>), we might want to take advantage of this timing to evaluate whether this deprecations could be turned into a hard error.

The main risk here is CI automation might fail. Unlike rustc and clippy lints, people hardly noticed Cargo warnings becuase because there was no way to set `-D` on them.

# Deprecations

## 2024 Edition

### dependency without `path`, `version`, `git`, `workspace` specified

https://github.com/rust-lang/cargo/blob/8bcecfeed464c990733ff680e0b4546a73fbed44/src/cargo/util/toml/mod.rs#L1914-L1918

* Warn since: Merged on 2016-01-20
* May become a hard error? ✅
* Risk: Old crates and deps fail to build. See <https://github.com/rust-lang/cargo/issues/9885>
* <https://github.com/rust-lang/cargo/pull/2270>
* Next step:
* Check all `Cargo.toml` and latest `Cargo.toml.orig` on crates.io
* Was this a bug?
* Yes
* https://github.com/rust-lang/cargo/issues/2147#issuecomment-156879677
* Disposition: leaning towards removal without worrying about Edition
* Maybe back off if something needs fixed in ecosystem first
* Could slow introduce using Editions

### `license-file` and `readme` pointing to a non-existent file

https://github.com/rust-lang/cargo/blob/f0ae76519127d16d87362c6d88416d92cba86c6a/src/cargo/ops/cargo_package.rs#L416-L418

* Warn since: 1.43.0 (2020-04-23) for `license-file`; 1.71.0 (2023-08-03) for `readme`
* may become a hard error? ✅ )
* Risk: Publish might fail. Easy to fix in normal cases.
* <https://github.com/rust-lang/cargo/pull/7905>
* <https://github.com/rust-lang/cargo/pull/12036>
* Next step:
* Check with ehuss for context on why it could become a hard error in #7905
* Otherwise, use Edition 2024

### `dev_dependencies`/`build_dependencies`/`default_features`/`crate_types`/`proc_macro`

https://github.com/rust-lang/cargo/blob/f0ae76519127d16d87362c6d88416d92cba86c6a/src/cargo/util/toml/mod.rs#L198-L199

* Warn since: 1.61 (2022-05-19) but only when conflicting with dash ones
* may become a hard error? NO
* Risk: Old crates fail to compile. Might need an edition boundary.
* <https://github.com/rust-lang/cargo/pull/10316>
* Next step:
* Error on 2024 edition

### good old `[project]` (replaced with `[package]`)

https://github.com/rust-lang/cargo/blob/f0ae76519127d16d87362c6d88416d92cba86c6a/src/cargo/util/toml/mod.rs#L497-L498

* Warn since: 1.66 (2022-12-15)
* may become a hard error? ✅
* Risk: Old crates fail to compile. Require an edition boundary.
* <https://github.com/rust-lang/cargo/pull/11135>
* Next step:
* Error on 2024 edition

### `default-features` in inherited dependencies

https://github.com/rust-lang/cargo/blob/f0ae76519127d16d87362c6d88416d92cba86c6a/src/cargo/util/toml/mod.rs#L1801-L1803

* Warn since: 1.69.0 (2023-04-29)
* may become a hard error? ✅
* Risk: Build failures. Easy to fix.
* <https://github.com/rust-lang/cargo/pull/11409>
* Next step:
* Error in 2024 Edition

### `plugin` support

https://github.com/rust-lang/cargo/blob/f0ae76519127d16d87362c6d88416d92cba86c6a/src/cargo/util/toml/targets.rs#L211-L216

* Warn since: 1.77.0 (2024-03-21)
* may become a hard error? ✅ (stop supporting `plugin`)
* Risk: Too new.
* <https://github.com/rust-lang/cargo/pull/13248>
* Next step:
* Wait until 2024 release
* Remove key, making it an "unused key" warning

## Independent of Edition

### `--release` is ignored when paired with `--profile`

https://github.com/rust-lang/cargo/blob/8bcecfeed464c990733ff680e0b4546a73fbed44/src/cargo/util/command_prelude.rs#L570-L573

* Warn since: 1.57.0 (2021-12-02)
* may become a hard error? ✅
* Risk: Break people's build. Easy to fix by themselves.
* <https://github.com/rust-lang/cargo/pull/9943>
* Next step:
* Check with ehuss, is hard error justified? If accepted for long time and no indication to user its a bug, then maybe keep as warning?

### `cargo read-manifest`

https://github.com/rust-lang/cargo/blob/8bcecfeed464c990733ff680e0b4546a73fbed44/src/bin/cargo/commands/read_manifest.rs#L9

* Warn since: Merged on 2016-10-03.
* Become a hard error? NO
* Risk: Automations might still rely on it. `cargo metadata --no-deps` should cover its use cases.
* <https://github.com/rust-lang/cargo/pull/3150>
* Next step:
* Add runtime warning saying its deprecated (not just help)
* CLI, so no further steps

### `[replace]` is deprecated

https://github.com/rust-lang/cargo/blob/8bcecfeed464c990733ff680e0b4546a73fbed44/src/doc/src/reference/overriding-dependencies.md?plain=1#L300-L301

* Warn since: 1.42.0 (2020-03-12)
* may become a hard error? NO
* Risk: Can we patch `[patch]` to fully replace `[repalce]`?
* <https://github.com/rust-lang/cargo/pull/7733>
* Next step
* Deprecation warning using lint system (since restricted `Cargo.toml`)
* Maybe with future edition turn it into forbid (based on people's reaction to warning)

### old `cargo tree` flags: `--all`, `no-dev-dependencies`, `--no-indent`, `--prefix-depth`, `--all-targets`

https://github.com/rust-lang/cargo/blob/8bcecfeed464c990733ff680e0b4546a73fbed44/src/bin/cargo/commands/tree.rs#L144-L146

* Warn since: 1.44.0 (2020-06-04)
* may become a hard error? ✅ for `all`; NO for others
* Risk: Have alternatives. Easy to fix.
* <https://github.com/rust-lang/cargo/pull/8115>
* Next step:
* Downgrade to consistent deprecation (no point removing one when others would be kept)

### path override modifying dependency graph

https://github.com/rust-lang/cargo/blob/f0ae76519127d16d87362c6d88416d92cba86c6a/src/cargo/core/registry.rs#L535-L538

* Warn since: Merged on 2016-10-05 (1.14 or so)
* may become a hard error? ✅ (was a bug)
* Risk: Assuming people seldom use it?
* <https://github.com/rust-lang/cargo/pull/3136>
* Next step:
* Turn into error because it was a bug with buggy behavior and people using this went into it knowing its bad (since they likely started post-1.14), and we've not been getting necro-posts for people saying they need this (like depending on bins)

### `rustc-cdylib-link-arg` used in non-cdylib target

https://github.com/rust-lang/cargo/blob/f0ae76519127d16d87362c6d88416d92cba86c6a/src/cargo/core/compiler/custom_build.rs#L850-L856

* Warn since: 1.54.0 (2021-07-29)
* may become a hard error? ✅ (may become)
* Risk: crates might depends on this heavily; might need a way to toggle like <https://github.com/rust-lang/cargo/issues/9094> or [Pre-RFC for mutually-exclusive, global features](https://internals.rust-lang.org/t/pre-rfc-mutually-excusive-global-features/19618)
* <https://github.com/rust-lang/cargo/pull/9563>
* Next step:
* Hard error, independent of edition, because this was never intended, we warning for a while, and no has brought up a concrete case of the warning firing when they need it

### user-defined alias is shadowing an external subcommand found:

https://github.com/rust-lang/cargo/blob/f0ae76519127d16d87362c6d88416d92cba86c6a/src/bin/cargo/cli.rs#L321-L323

* Warn since: 1.58.0 (2022-01-13)
* may become a hard error? ✅
* Risk: Custom workflow might fail. `cargo clippy` and `cargo fmt` are what we concerned.
* #10049
* <https://github.com/rust-lang/cargo/pull/10082>
* Next step:
* Turn into hard error. Aliases are generally for user interaction, rather than automation (except for things like xtasks) so the impact is low

### output artifact name collisions

https://github.com/rust-lang/cargo/blob/f0ae76519127d16d87362c6d88416d92cba86c6a/src/cargo/core/compiler/build_runner/mod.rs#L472-L474

* Warn since: 1.32.0 (2019-01-17)
* may become a hard error? ✅
* Risk: Workaround could be quite complicated.
* <https://github.com/rust-lang/cargo/pull/6308>
* Next step:
* Maybe in a future Edition, switch to forbid by default?
* Or just warn because this is implementation-defined for when a collision may occur and new collisions may come up in the future

### Bail out when trying to link to a library that is not linkable

https://github.com/rust-lang/cargo/blob/f0ae76519127d16d87362c6d88416d92cba86c6a/src/cargo/core/compiler/mod.rs#L1427-L1430

* Warn since: 1.24.0 (2018-02-15)
* may become a hard error? ✅
* Risk: People depend on this in a quirky way.
* <https://github.com/rust-lang/cargo/pull/4797>
* Next step:
* Needs investigation into replacement feature for those relying on it
* Likely should instead be hard error conditioned on Edition

### Ambiguous package name in git dependency

https://github.com/rust-lang/cargo/blob/bd1cf584af2c356eeb3980c3c9bb0fea190ed633/src/cargo/ops/cargo_read_manifest.rs#L225-L234

* Warn since: 1.63
* may become a hard error? NO
* Risk: too many false positives, see #10752
* #10701, #10767
* Next step:
* Address #10752
* Turn into error on edition

## No further steps

### deprecate `--all` (alias to `--workspace`)

https://github.com/rust-lang/cargo/blob/8bcecfeed464c990733ff680e0b4546a73fbed44/src/cargo/util/command_prelude.rs#L54

* Warn since: 1.39.0 (2019-11-07)
* may become a hard error? NO
* Risk: Automations might still rely on it. Some users use it exclusively due to brevity (see also #11554)
* <https://github.com/rust-lang/cargo/pull/7241>
* Next step:
* CLI, so no further steps
* Not doing runtime warning because of pervasive use by people who really like it for brevity

### Deprecate `.cargo/config`

https://github.com/rust-lang/cargo/blob/8bcecfeed464c990733ff680e0b4546a73fbed44/src/cargo/util/context/mod.rs#L1563-L1567

* Warn since: 1.78 (2024-05-02)
* may become a hard error? NO
* Risk: Way too new.
* <https://github.com/rust-lang/cargo/pull/13349>
* Next step:
* No further steps