> cargo new foo && cd foo
     Created binary (application) `foo` package
> cargo add --dev serde
    Updating 'https://github.com/rust-lang/crates.io-index' index
      Adding serde v1.0.123 to dev-dependencies
> mkdir examples
> echo 'use serde; fn main() {}' > examples/bar.rs
> mkdir benches
> echo 'use serde; fn main() {}' > benches/bar.rs

> cargo build --bench bar --example bar
   Compiling serde v1.0.123
   Compiling foo v0.1.0 (/tmp/tmp.zlGcSI2CHo/foo)
warning: unused import: `serde`
 --> examples/bar.rs:1:5
  |
1 | use serde; fn main() {}
  |     ^^^^^
  |
  = note: `#[warn(unused_imports)]` on by default

warning: unused import: `serde`
 --> benches/bar.rs:1:5
  |
1 | use serde; fn main() {}
  |     ^^^^^
  |
  = note: `#[warn(unused_imports)]` on by default

warning: 1 warning emitted

warning: 1 warning emitted

    Finished dev [unoptimized + debuginfo] target(s) in 4.60s

> cargo rustdoc --example bar
 Documenting foo v0.1.0 (/tmp/tmp.zlGcSI2CHo/foo)
error[E0432]: unresolved import `serde`
 --> examples/bar.rs:1:5
  |
1 | use serde; fn main() {}
  |     ^^^^^ no external crate `serde`

error: Compilation failed, aborting rustdoc

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0432`.
error: could not document `foo`

Caused by:
  process didn't exit successfully: `rustdoc --edition=2018 --crate-type bin --crate-name bar examples/bar.rs -o /tmp/tmp.zlGcSI2CHo/foo/target/doc --error-format=json --json=diagnostic-rendered-ansi -L dependency=/tmp/tmp.zlGcSI2CHo/foo/target/debug/deps --crate-version 0.1.0` (exit code: 1)


> cargo rustdoc --bench bar
 Documenting foo v0.1.0 (/tmp/tmp.zlGcSI2CHo/foo)
error[E0432]: unresolved import `serde`
 --> benches/bar.rs:1:5
  |
1 | use serde; fn main() {}
  |     ^^^^^ no external crate `serde`

error: Compilation failed, aborting rustdoc

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0432`.
error: could not document `foo`

Caused by:
  process didn't exit successfully: `rustdoc --edition=2018 --crate-type bin --crate-name bar benches/bar.rs -o /tmp/tmp.zlGcSI2CHo/foo/target/doc --error-format=json --json=diagnostic-rendered-ansi -L dependency=/tmp/tmp.zlGcSI2CHo/foo/target/debug/deps --crate-version 0.1.0` (exit code: 1)