cargo doc --examples ignores dev dependencies

[asomers]

Problem

With --examples, cargo doc is supposed to document your examples too. However, the examples may need dev dependencies in order to compile, and cargo doc does not include those, leading to errors about unresolved imports.

Steps

1. git clone git@github.com:asomers/mockall.git
2. cd mockall
3. cargo doc --examples

...
error[E0432]: unresolved import `mockall_double`
 --> mockall/examples/ffi.rs:8:5
  |
8 | use mockall_double::double;
  |     ^^^^^^^^^^^^^^ use of undeclared crate or module `mockall_double`
  |
help: there is a crate or module with a similar name
  |
8 | use mockall_derive::double;
  |     ~~~~~~~~~~~~~~
...

Possible Solution(s)

cargo doc --examples should resolve dev-dependencies, just like cargo check --examples does.

Notes

No response

Version

> cargo version --verbose
cargo 1.60.0-nightly (95bb3c92b 2022-01-18)
release: 1.60.0-nightly
commit-hash: 95bb3c92bf516017e812e7f1c14c2dea3845b30e
commit-date: 2022-01-18
host: x86_64-unknown-freebsd
libgit2: 1.3.0 (sys:0.13.23 vendored)
libcurl: 7.80.0-DEV (sys:0.4.51+curl-7.80.0 vendored ssl:OpenSSL/1.1.1l)
os: FreeBSD 14.0-CURRENT [64-bit]

[ehuss]

For fixing: This line needs to consider other dependency kinds based on the target type. Here is how it is done for regular builds. Perhaps those can be shared?

[Rustin170506]

@rustbot claim

[jyn514]

Duplicate of #9198.