Can't add intra-doc-link-resolution checking for tokio-compat feature

[Nemo157]

We currently get failures from tokio-executor:

> RUSTDOCFLAGS=-Dwarnings cargo doc --all --exclude futures-preview --all-features --no-deps
[...]
 Documenting futures-executor-preview v0.3.0-alpha.2 (file:///Users/Nemo157/sources/futures-rs/futures-executor)
error: `[Future::poll]` cannot be resolved, ignoring it...
 --> /Users/Nemo157/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-executor-0.1.2/src/lib.rs:8:52
  |
8 | //! The executor is responsible for ensuring that [`Future::poll`] is called
  |                                                    ^^^^^^^^^^^^^^ cannot be resolved, ignoring
  |
 = note: `-D intra-doc-link-resolution-failure` implied by `-D warnings`
 = help: to escape `[` and `]` characters, just add '\' before them like `\[` or `\]`

error: `[notified]` cannot be resolved, ignoring it...
 --> /Users/Nemo157/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-executor-0.1.2/src/lib.rs:9:27
  |
9 | //! whenever the task is [notified]. Notification happens when the internal
  |                           ^^^^^^^^ cannot be resolved, ignoring
  |
  = help: to escape `[` and `]` characters, just add '\' before them like `\[` or `\]`

error: Could not document `futures-executor-preview`.

Caused by:
  process didn't exit successfully: `rustdoc -Zunstable-options --edition=2018 --crate-name futures_executor futures-executor/src/lib.rs -o /Users/Nemo157/sources/futures-rs/target/doc --cfg 'feature="default"' --cfg 'feature="futures-channel-preview"' --cfg 'feature="futures-core-preview"' --cfg 'feature="futures-util-preview"' --cfg 'feature="lazy_static"' --cfg 'feature="num_cpus"' --cfg 'feature="std"' -L dependency=/Users/Nemo157/sources/futures-rs/target/debug/deps --extern futures_channel=/Users/Nemo157/sources/futures-rs/target/debug/deps/libfutures_channel-9055849c3f27deac.rmeta --extern futures_core=/Users/Nemo157/sources/futures-rs/target/debug/deps/libfutures_core-ca2b0fbec6f42841.rmeta --extern futures_util=/Users/Nemo157/sources/futures-rs/target/debug/deps/libfutures_util-f9f5995bc051d6da.rmeta --extern lazy_static=/Users/Nemo157/sources/futures-rs/target/debug/deps/liblazy_static-c39b9c59668038dc.rmeta --extern num_cpus=/Users/Nemo157/sources/futures-rs/target/debug/deps/libnum_cpus-f47a2c889c4e2dc8.rmeta -Dwarnings` (exit code: 1)
warning: build failed, waiting for other jobs to finish...
[...]

I'm actually really confused about what's happening here, why is it referencing tokio-executor code when documenting futures-executor-preview? Only futures-util-preview depends on tokio-executor, and the warnings that are currently occurring in futures-util-preview don't appear while documenting futures-executor-preview even without -Dwarnings, so somehow direct dependencies are suppressed, but dependencies-of-dependencies aren't? Except these warnings also appear when documenting futures-util-preview so that can't be it 😕

[Nemo157]

Might be rust-lang/rust#51684, fix PR has been opened so hopefully can check this again soon.

[MajorBreakfast]

It might have also something to do with reexports for which Rustdoc seems to be quite broken.