2024 implicit feature migration deletes dependency features

[ehuss]

Problem

Migrating to 2024 causes foo/feature_name features to get removed for optional dependencies. Those need to be preserved.

Steps

Example manifest:

cargo-features = ["edition2024"]
[package]
name = "foo"
version = "0.1.0"
edition = "2021"

[dependencies]
serde = { version = "1.0.203", optional = true }

[features]
serde = ["serde/derive"]

Running cargo fix --edition on this will result in:

serde = ["dep:serde"]

Note that the /derive feature got removed.

Possible Solution(s)

When there is a ["foo/feature_name"] syntax in the [features] table, and dep:foo isn't found anywhere in the [features] table, it should be rewritten to be ["dep:foo", "foo/feature_name"]. Some things to be careful of:

• Adjust all places that foo/xxx is found (such as x = ["foo/a"] and y = ["foo/b"], both x and y need a "dep:foo")
• Should not disturb any other features (like ["foo/feature_name", "bar"] would be rewritten to ["dep:foo", "foo/feature_name", "bar"])
• Should avoid duplicates (["foo/a", "foo/b"] should not have two dep:foo entries added).

Notes

No response

Version

cargo 1.80.0-nightly (7a6fad098 2024-05-31)
release: 1.80.0-nightly
commit-hash: 7a6fad0984d28c8330974636972aa296b67c4513
commit-date: 2024-05-31
host: aarch64-apple-darwin
libgit2: 1.7.2 (sys:0.18.3 vendored)
libcurl: 8.6.0 (sys:0.4.72+curl-8.6.0 system ssl:(SecureTransport) LibreSSL/3.3.6)
ssl: OpenSSL 1.1.1w  11 Sep 2023
os: Mac OS 14.5.0 [64-bit]

[linyihai]

So "dep_name/feature_name" is different from "dep:dep_name", "dep_name?/feature_name" in that the implicit feature doesn't get suppressed.
Yes, I suppose so.

And then the most important step is:
Then If the dep_name/dep_name_feature or dep_name?/dep_name_feature exists, then we should keep them when applying Cargo fix ?