Suggest to add move keyword for generator capture

[csmoe]

Closes#64382
r? @estebank

[estebank]

r=me when you're ready

[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.

2019-10-07T08:38:27.6728705Z ##[command]git remote add origin https://github.com/rust-lang/rust
2019-10-07T08:38:27.6908979Z ##[command]git config gc.auto 0
2019-10-07T08:38:28.2052449Z ##[command]git config --get-all http.https://github.com/rust-lang/rust.extraheader
2019-10-07T08:38:28.2059012Z ##[command]git config --get-all http.proxy
2019-10-07T08:38:28.2064616Z ##[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/65166/merge:refs/remotes/pull/65166/merge
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---
2019-10-07T09:50:04.5364260Z ---- [ui] ui/async-await/async-borrowck-escaping-block-error.rs stdout ----
2019-10-07T09:50:04.5364301Z 2019-10-07T09:50:04.5364377Z error: fixed code is still producing diagnostics
2019-10-07T09:50:04.5364614Z status: exit code: 0
2019-10-07T09:50:04.5365409Z command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/async-await/async-borrowck-escaping-block-error.fixed" "-Zthreads=1" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "-Zui-testing" "-C" "prefer-dynamic" "-o" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/async-await/async-borrowck-escaping-block-error/a" "-Crpath" "-O" "-Cdebuginfo=0" "-Zunstable-options" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "--edition=2018" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/async-await/async-borrowck-escaping-block-error/auxiliary"
2019-10-07T09:50:04.5365962Z ------------------------------------------
2019-10-07T09:50:04.5366014Z 2019-10-07T09:50:04.5366204Z ------------------------------------------
2019-10-07T09:50:04.5366244Z stderr:
2019-10-07T09:50:04.5366244Z stderr:
2019-10-07T09:50:04.5366444Z ------------------------------------------
2019-10-07T09:50:04.5366486Z warning: function is never used: `foo`
2019-10-07T09:50:04.5366709Z --> /checkout/src/test/ui/async-await/async-borrowck-escaping-block-error.fixed:5:1
2019-10-07T09:50:04.5366772Z |
2019-10-07T09:50:04.5366977Z LL | fn foo() -> Box<impl std::future::Future<Output = u32>> {
2019-10-07T09:50:04.5367081Z |
2019-10-07T09:50:04.5367230Z = note: `#[warn(dead_code)]` on by default
2019-10-07T09:50:04.5367271Z 2019-10-07T09:50:04.5367317Z warning: the feature `async_await` has been stable since 1.39.0 and no longer requires an attribute to enable
---
2019-10-07T09:50:04.5406119Z thread 'main' panicked at 'Some tests failed', src/tools/compiletest/src/main.rs:537:22
2019-10-07T09:50:04.5406199Z note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
2019-10-07T09:50:04.5424374Z 2019-10-07T09:50:04.5424488Z 2019-10-07T09:50:04.5425930Z 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"
2019-10-07T09:50:04.5426174Z 2019-10-07T09:50:04.5426200Z 2019-10-07T09:50:04.5438090Z failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
2019-10-07T09:50:04.5438193Z Build completed unsuccessfully in 1:04:34
2019-10-07T09:50:04.5438193Z Build completed unsuccessfully in 1:04:34
2019-10-07T09:50:04.5494988Z == clock drift check ==
2019-10-07T09:50:04.5533037Z local time: Mon Oct 7 09:50:04 UTC 2019
2019-10-07T09:50:04.8307318Z network time: Mon, 07 Oct 2019 09:50:04 GMT
2019-10-07T09:50:04.8307577Z == end clock drift check ==
2019-10-07T09:50:06.0143602Z ##[error]Bash exited with code '1'.
2019-10-07T09:50:06.0193806Z ##[section]Starting: Checkout
2019-10-07T09:50:06.0195845Z ==============================================================================
2019-10-07T09:50:06.0195896Z Task : Get sources
2019-10-07T09:50:06.0195943Z 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)

[estebank]

I'll go ahead and mark this PR as ready for review so it doesn't come up as a draft.

@bors r+

[bors]

📌 Commit d1d2565 has been approved by estebank