Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @alexcrichton (or someone else) soon.

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One of the use cases is flycheck/flycheck-rust#68. Let me know, if it's not an ideal solution!

@alexcrichton hi Alex! Does it look like smth we can merge? Thanks!

Looks good to me, thanks! Could this also be renamed to required-features in the JSON?

@alexcrichton Sure! I've pushed additional commit -- is it ok, or should I squash both commits together?
Field attribute is now longer than 80 chars, but it seems cargo codebase already has attributes like this. Happy to fix it though.

Thanks for you time!

@bors: r+

Looks good to me, thanks!

📌 Commit 349d264 has been approved by alexcrichton

@bors: retry

@bors: r+

💡 This pull request was already approved, no need to approve it again.

📌 Commit 349d264 has been approved by alexcrichton

@bors: r+

📌 Commit 9c38505 has been approved by alexcrichton

⌛ Testing commit 9c38505 with merge 0dc7f69d0f1065b4a901b195acaa50795900d438...

💔 Test failed - status-appveyor

failures:
---- build_script::switch_features_rerun stdout ----
running `C:\projects\cargo\target\debug\cargo.exe run -v --features=foo`
running `C:\projects\cargo\target\debug\cargo.exe run -v`
running `C:\projects\cargo\target\debug\cargo.exe run -v --features=foo`
thread 'build_script::switch_features_rerun' panicked at '
Expected: execs
    but: exited with exit code: 101
--- stdout
--- stderr
       Fresh foo v0.0.1 (file:///C:/projects/cargo/target/cit/t353/foo)
error: failed to link or copy `C:\projects\cargo\target\cit\t353\foo\target\debug\deps\foo-86673955dda3b155.exe` to `C:\projects\cargo\target\cit\t353\foo\target\debug\foo.exe`
Caused by:
  Access is denied. (os error 5)
', tests\testsuite\support\hamcrest.rs:13:9
note: Run with `RUST_BACKTRACE=1` for a backtrace.

hm, environment error?

@bors: retry

ah yeah, that's likely spurious

Looks like it would need the same treatment as changing_bin_features_caches_targets. It's unfortunate, and a little awkward. Personally I would prefer to add retry logic to cargo itself, since there is likely other tests that are vulnerable, and will likely be new ones in the future.

⌛ Testing commit 9c38505 with merge c0ec76f...

☀️ Test successful - status-appveyor, status-travis
Approved by: alexcrichton
Pushing c0ec76f to master...

@alexcrichton any idea when this feature will be available in nightly?

I've updated today and cargo is still from 0ec7281b9 2018-08-20.

@little-arhat update PR posted at rust-lang/rust#53935, once it gets through it should be in the next nightly.