Optional and unused dependencies that are renamed are pulled

[pamaury]

Whenever a crate specified in Cargo.toml specifies an optional dependency that is not used but whose name does not match the original name of the crate, rules_rust still generates a dependency on that crate due to an alias. This can cause rules_rust to pull many unneeded dependencies. One such example is serde_with with indexmap:

indexmap_1 = {package = "indexmap", version = "1.8", optional = true, default-features = false, features = ["serde-1"]}

Even though serde_with does not require this dependency by default, it is still used in the generated BUILD file in aliases (not in the deps):

rust_library(
    name = "serde_with",
    srcs = glob(["**/*.rs"]),
    aliases = {
        "@crate_index__indexmap-1.9.3//:indexmap": "indexmap_1",
    },
   ...
)

I have a minimal reproduction of the problem here using rules_rust 0.30.0.

[nbdd0121]

This is likely caused by use of weak feature dependencies, and cargo still have disabled optional dependency that have weak feature dependencies in Cargo.lock file (rust-lang/cargo#10801)