Implement #[cfg(accessible(::path::to::thing)]

[pickfire]

Works towards #64797

[rust-highfive]

r? @petrochenkov

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[rust-highfive]

The job x86_64-gnu-llvm-6.0 of your PR failed (pretty log, raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

2019-11-12T00:50:47.5249375Z ##[command]git remote add origin https://github.com/rust-lang/rust
2019-11-12T00:50:47.5265307Z ##[command]git config gc.auto 0
2019-11-12T00:50:47.5277615Z ##[command]git config --get-all http.https://github.com/rust-lang/rust.extraheader
2019-11-12T00:50:47.5280347Z ##[command]git config --get-all http.proxy
2019-11-12T00:50:47.5283340Z ##[command]git -c http.extraheader="AUTHORIZATION: basic ***" fetch --force --tags --prune --progress --no-recurse-submodules --depth=2 origin +refs/heads/*:refs/remotes/origin/* +refs/pull/66319/merge:refs/remotes/pull/66319/merge
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---
2019-11-12T02:00:16.7627720Z failures:
2019-11-12T02:00:16.7662985Z 
2019-11-12T02:00:16.7663524Z ---- [ui] ui/feature-gates/feature-gate-cfg_accessible.rs stdout ----
2019-11-12T02:00:16.7663592Z normalized stderr:
2019-11-12T02:00:16.7663870Z error[E0537]: invalid predicate `accessible`
2019-11-12T02:00:16.7664211Z   --> $DIR/feature-gate-cfg_accessible.rs:1:7
2019-11-12T02:00:16.7664265Z    |
2019-11-12T02:00:16.7664335Z LL | #[cfg(accessible(::std::mem::ManuallyDrop))]
2019-11-12T02:00:16.7664438Z 
2019-11-12T02:00:16.7664438Z 
2019-11-12T02:00:16.7664491Z error[E0601]: `main` function not found in crate `feature_gate_cfg_accessible`
2019-11-12T02:00:16.7664784Z   --> $DIR/feature-gate-cfg_accessible.rs:1:1
2019-11-12T02:00:16.7664840Z    |
2019-11-12T02:00:16.7664890Z LL | / #[cfg(accessible(::std::mem::ManuallyDrop))]
2019-11-12T02:00:16.7664956Z LL | | fn main() {}
2019-11-12T02:00:16.7665268Z    | |____________^ consider adding a `main` function to `$DIR/feature-gate-cfg_accessible.rs`
2019-11-12T02:00:16.7665358Z error: aborting due to 2 previous errors
2019-11-12T02:00:16.7665405Z 
2019-11-12T02:00:16.7665455Z Some errors have detailed explanations: E0537, E0601.
2019-11-12T02:00:16.7665752Z For more information about an error, try `rustc --explain E0537`.
2019-11-12T02:00:16.7665752Z For more information about an error, try `rustc --explain E0537`.
2019-11-12T02:00:16.7665790Z 
2019-11-12T02:00:16.7665837Z 
2019-11-12T02:00:16.7665865Z 
2019-11-12T02:00:16.7665913Z The actual stderr differed from the expected stderr.
2019-11-12T02:00:16.7666468Z Actual stderr saved to /checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/feature-gates/feature-gate-cfg_accessible/feature-gate-cfg_accessible.stderr
2019-11-12T02:00:16.7687584Z To update references, rerun the tests and pass the `--bless` flag
2019-11-12T02:00:16.7687983Z To only update this specific test, also pass `--test-args feature-gates/feature-gate-cfg_accessible.rs`
2019-11-12T02:00:16.7688106Z error: 1 errors occurred comparing output.
2019-11-12T02:00:16.7688158Z status: exit code: 1
2019-11-12T02:00:16.7688158Z status: exit code: 1
2019-11-12T02:00:16.7689118Z command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/feature-gates/feature-gate-cfg_accessible.rs" "-Zthreads=1" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "-Zui-testing" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/feature-gates/feature-gate-cfg_accessible" "-Crpath" "-O" "-Cdebuginfo=0" "-Zunstable-options" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/feature-gates/feature-gate-cfg_accessible/auxiliary" "-A" "unused"
2019-11-12T02:00:16.7689544Z ------------------------------------------
2019-11-12T02:00:16.7689586Z 
2019-11-12T02:00:16.7689863Z ------------------------------------------
2019-11-12T02:00:16.7689917Z stderr:
2019-11-12T02:00:16.7689917Z stderr:
2019-11-12T02:00:16.7690194Z ------------------------------------------
2019-11-12T02:00:16.7690254Z error[E0537]: invalid predicate `accessible`
2019-11-12T02:00:16.7690570Z   --> /checkout/src/test/ui/feature-gates/feature-gate-cfg_accessible.rs:1:7
2019-11-12T02:00:16.7690639Z    |
2019-11-12T02:00:16.7690709Z LL | #[cfg(accessible(::std::mem::ManuallyDrop))] //~^ ERROR: currently unstable
2019-11-12T02:00:16.7690803Z 
2019-11-12T02:00:16.7690803Z 
2019-11-12T02:00:16.7690871Z error[E0601]: `main` function not found in crate `feature_gate_cfg_accessible`
2019-11-12T02:00:16.7691209Z   --> /checkout/src/test/ui/feature-gates/feature-gate-cfg_accessible.rs:1:1
2019-11-12T02:00:16.7691266Z    |
2019-11-12T02:00:16.7691333Z LL | / #[cfg(accessible(::std::mem::ManuallyDrop))] //~^ ERROR: currently unstable
2019-11-12T02:00:16.7691389Z LL | | fn main() {}
2019-11-12T02:00:16.7691756Z    | |____________^ consider adding a `main` function to `/checkout/src/test/ui/feature-gates/feature-gate-cfg_accessible.rs`
2019-11-12T02:00:16.7691864Z error: aborting due to 2 previous errors
2019-11-12T02:00:16.7691899Z 
2019-11-12T02:00:16.7691950Z Some errors have detailed explanations: E0537, E0601.
2019-11-12T02:00:16.7692415Z For more information about an error, try `rustc --explain E0537`.
---
2019-11-12T02:00:16.7700850Z thread 'main' panicked at 'Some tests failed', src/tools/compiletest/src/main.rs:537:22
2019-11-12T02:00:16.7700948Z note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
2019-11-12T02:00:16.7722460Z 
2019-11-12T02:00:16.7722540Z 
2019-11-12T02:00:16.7725892Z command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/compiletest" "--compile-lib-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib" "--run-lib-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/x86_64-unknown-linux-gnu/lib" "--rustc-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "--src-base" "/checkout/src/test/ui" "--build-base" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui" "--stage-id" "stage2-x86_64-unknown-linux-gnu" "--mode" "ui" "--target" "x86_64-unknown-linux-gnu" "--host" "x86_64-unknown-linux-gnu" "--llvm-filecheck" "/usr/lib/llvm-6.0/bin/FileCheck" "--host-rustcflags" "-Crpath -O -Cdebuginfo=0 -Zunstable-options  -Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "--target-rustcflags" "-Crpath -O -Cdebuginfo=0 -Zunstable-options  -Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "--docck-python" "/usr/bin/python2.7" "--lldb-python" "/usr/bin/python2.7" "--gdb" "/usr/bin/gdb" "--quiet" "--llvm-version" "6.0.0\n" "--system-llvm" "--cc" "" "--cxx" "" "--cflags" "" "--llvm-components" "" "--llvm-cxxflags" "" "--adb-path" "adb" "--adb-test-dir" "/data/tmp/work" "--android-cross-path" "" "--color" "always"
2019-11-12T02:00:16.7726324Z 
2019-11-12T02:00:16.7726368Z 
2019-11-12T02:00:16.7726897Z failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
2019-11-12T02:00:16.7726962Z Build completed unsuccessfully in 1:02:59
2019-11-12T02:00:16.7726962Z Build completed unsuccessfully in 1:02:59
2019-11-12T02:00:16.7777111Z == clock drift check ==
2019-11-12T02:00:16.7808978Z   local time: Tue Nov 12 02:00:16 UTC 2019
2019-11-12T02:00:17.0435283Z   network time: Tue, 12 Nov 2019 02:00:17 GMT
2019-11-12T02:00:17.0440824Z == end clock drift check ==
2019-11-12T02:00:17.9292040Z 
2019-11-12T02:00:17.9400461Z ##[error]Bash exited with code '1'.
2019-11-12T02:00:17.9455693Z ##[section]Starting: Checkout
2019-11-12T02:00:17.9457614Z ==============================================================================
2019-11-12T02:00:17.9457675Z Task         : Get sources
2019-11-12T02:00:17.9457741Z Description  : Get sources from a repository. Supports Git, TfsVC, and SVN repositories.

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[petrochenkov]

I'd strongly suggest to implement cfg(version) (#64796) first because it has an orders of magnitude higher usefulness/complexity ratio (and is also a better task for a first compiler PR).

[pickfire]

@petrochenkov I thought cfg(version) was harder that's why I was checking out on this first. Thanks for pointing that out, IIRC someone is already working on that.

[bors]

☔ The latest upstream changes (presumably #66507) made this pull request unmergeable. Please resolve the merge conflicts.

[JohnCSimon]

Ping from triage:
@pickfire - I see this is a draft PR, but can you post your status?

[pickfire]

@JohnCSimon I am current working on version which is similar to this but I am kinda stuck on this not knowing how to proceed next.

[JohnCSimon]

@pickfire
Ping from triage - it's after the holidays - can you post your status on this PR, please? Thanks

[petrochenkov]

This is not a beginner-friendly feature to implement and I have some implementation in progress (#64797 (comment)), so I'll close this PR and let @pickfire focus on cfg(version).

[pickfire]

Holidays?

@JohnCSimon I am not currently working on this, been trying out on cfg(version) but still kinda stuck (I hope someone can give some guidance) and busy as of now. Sorry, I did not explicitly ping here regarding that.