rustdoc does not pickup dev dependencies when the dev-dep adds a feature to an existing dependency

When scraping examples, there is a bug (?) where a dev-dependency that only adds new features does not get used causing example scraping to fail.

This happened in real life here: https://docs.rs/crate/metrique-aggregation/latest/builds/2825680

Code

I made a reproduction package here: https://github.com/rcoh/rustdoc-scrape-examples-reproducer

[package]
name = "example-scrape-bug"
version = "0.1.0"
edition = "2024"

[dependencies]
serde = { version = "1" }

[dev-dependencies]
serde = { version = "1", features = ["rc", "derive"] }
serde_json = "1"

[[example]]
name = "demo"
doc-scrape-examples = true

[package.metadata.docs.rs]
all-features = true
targets = ["x86_64-unknown-linux-gnu"]
rustdoc-args = ["--cfg", "docsrs"]
cargo-args = ["-Zunstable-options", "-Zrustdoc-scrape-examples"]

// examples/demo.rs
use example_scrape_bug::MyStruct;
use serde::Serialize;
use std::rc::Rc;

fn main() {
    let data = MyStruct { value: 42 };
    println!("{:?}", serde_json::to_string(&data).unwrap());

    // This uses the "rc" feature from dev-dependencies
    let _rc_data: Rc<i32> = Rc::new(42);
}

Reproduction Steps

1. Run cargo package, then execute a docs.rs simulated build (e.g. with cargo-docs-rs) on the resulting target:

cargo package && (cd target/package/example-scrape-bug-0.1.0 && cargo +nightly docs-rs)

2. The build will fail because the serialize feature didn't get enabled:

Expected Outcome

Docs build succeeds. NOTE: the docs build does not fail if you run it directly from the package, only if you run it from the packaged crate.

Actual Output

warning: manifest has no description, license, license-file, documentation, homepage or repository
  |
  = note: see https://doc.rust-lang.org/cargo/reference/manifest.html#package-metadata for more info
   Packaging example-scrape-bug v0.1.0 (/Users/rcoh/code/example-scrape-bug)
    Updating crates.io index
    Packaged 8 files, 5.3KiB (2.3KiB compressed)
   Verifying example-scrape-bug v0.1.0 (/Users/rcoh/code/example-scrape-bug)
   Compiling example-scrape-bug v0.1.0 (/Users/rcoh/code/example-scrape-bug/target/package/example-scrape-bug-0.1.0)
error: cannot find derive macro `Serialize` in this scope
 --> src/lib.rs:3:10
  |
3 | #[derive(Serialize)]
  |          ^^^^^^^^^
  |
note: `Serialize` is imported here, but it is only a trait, without a derive macro
 --> src/lib.rs:1:5
  |
1 | use serde::Serialize;
  |     ^^^^^^^^^^^^^^^^

error: could not compile `example-scrape-bug` (lib) due to 1 previous error
error: failed to verify package tarball

Version

rustdoc 1.94.0-nightly (22c74ba91 2026-01-15)

Additional Details

Start with the reproduction package's Cargo.toml and examples/demo.rs, then run cargo package followed by cargo +nightly docs-rs in the packaged directory. Trace how rustdoc scrape examples handles the dev-dependency feature during the packaged build. Done means the packaged docs-rs simulation succeeds with serde's derive feature enabled, while the direct package build remains successful.