Bad error message when a strong dep features's depedency is an unused optional dependency about cargo HOT 4 OPEN

#14010 (comment)

This makes me worried about dep_name/feature_name syntax on Edition 2024. It now requires also adding dep:dep_name at which point it isn't much different than dep_name?/feature_name.

I had missing this part in past discussions (e.g. this zulip topic). It seems like we should have either changed it in Edition 2024 to not need dep:dep_name or transition out the syntax according to #10556. I worry that changing the meaning of dep_name/feature_name would be too subtle. Maybe we should at least go forward with the deprecation of dep_name/feature_name as mentioned in the comments of #10556?

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#14010 (comment)

Also, another reason why deprecating implicit features doesn't play well with dep_name/feature_name is that

[features]
foo = ["dep:dep_name"]
bar = ["dep_name/feature_name"]

and

[features]
bar = ["dep:dep_name", "dep_name/feature_name"]

are valid while the following is not

[features]
bar = ["dep_name/feature_name"]

That inconsistency feels weird.

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We discussed this in today's team meeting and lean towards "dep_name/feature_name" implying "dep:dep_name" in Edition 2024 with it being normalized in the published Cargo.toml file.

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Re-opened due to #14295. See #14283 for more context.

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