Workspace dependencies

What it does

I'm not sure if it is a Clippy responsibility, but I think it would be nice to suggest to use "workspace dependencies" if some library is used in multiple workspace crates.

Perhaps the opposite changes can be suggested if a dependency is used only once or less than some threshold value, though this logic should probably be a separate lint. Ideally both values should be configurable.

Lint Name

workspace_dependencies

Category

pedantic

Advantage

• It is much more convenient to change the dependency version in one place.

Drawbacks

The only disadvantage I can see is that such lint can be noisy for small workspaces, so it probably should be disabled by default.

Example

I don't think this example is needed, but nevertheless:

# [PROJECT_DIR]/Cargo.toml
[workspace]
members = ["foo", "bar"]

# [PROJECT_DIR]/foo/Cargo.toml
[package]
name = "foo"

[dependencies]
rand = "0.8.5"

# [PROJECT_DIR]/bar/Cargo.toml
[package]
name = "bar"

[dependencies]
rand = "0.8.5"

Could be written as:

# [PROJECT_DIR]/Cargo.toml
[workspace]
members = ["foo", "bar"]

[workspace.dependencies]
rand = "0.8.5"

# [PROJECT_DIR]/foo/Cargo.toml
[package]
name = "foo"

[dependencies]
rand.workspace = true

# [PROJECT_DIR]/bar/Cargo.toml
[package]
name = "bar"

[dependencies]
rand.workspace = true

Start with the workspace Cargo.toml, foo/Cargo.toml, and bar/Cargo.toml examples in the issue, then review how Clippy lints inspect Cargo workspace metadata. Define the detection, configurability, default category, and inverse-case behavior before implementation. Done means a lint can identify repeated dependencies and provide appropriate workspace-dependency suggestions with tests covering the stated examples.