Mem uninit doc ptr drop

[Firstyear]

Extend the mem::uninitialized documentation to account for partially initialized arrays and how to correctly handle these. These are used in some datastructures (trees for example) or in FFI.

r? @Manishearth

[rust-highfive]

The job x86_64-gnu-llvm-6.0 of your PR failed on Travis (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.

travis_time:end:05454486:start=1545187482086206592,finish=1545187541815966755,duration=59729760163
$ git checkout -qf FETCH_HEAD
travis_fold:end:git.checkout

Encrypted environment variables have been removed for security reasons.
See https://docs.travis-ci.com/user/pull-requests/#pull-requests-and-security-restrictions
$ export SCCACHE_BUCKET=rust-lang-ci-sccache2
$ export SCCACHE_REGION=us-west-1
Setting environment variables from .travis.yml
$ export IMAGE=x86_64-gnu-llvm-6.0
---

[00:03:41] travis_fold:start:tidy
travis_time:start:tidy
tidy check
[00:03:41] tidy error: /checkout/src/libcore/mem.rs:617: line longer than 100 chars
[00:03:43] some tidy checks failed
[00:03:43] 
[00:03:43] 
[00:03:43] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/tidy" "/checkout/src" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "--no-vendor" "--quiet"
[00:03:43] 
[00:03:43] 
[00:03:43] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test src/tools/tidy
[00:03:43] Build completed unsuccessfully in 0:00:45
[00:03:43] Build completed unsuccessfully in 0:00:45
[00:03:43] Makefile:79: recipe for target 'tidy' failed
[00:03:43] make: *** [tidy] Error 1
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:12dd683e
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Wed Dec 19 02:49:33 UTC 2018
---
travis_time:end:023f3028:start=1545187773701690394,finish=1545187773706967821,duration=5277427
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:025e00de
$ ln -s . checkout && for CORE in obj/cores/core.*; do EXE=$(echo $CORE | sed 's|obj/cores/core\.[0-9]*\.!checkout!\(.*\)|\1|;y|!|/|'); if [ -f "$EXE" ]; then printf travis_fold":start:crashlog\n\033[31;1m%s\033[0m\n" "$CORE"; gdb --batch -q -c "$CORE" "$EXE" -iex 'set auto-load off' -iex 'dir src/' -iex 'set sysroot .' -ex bt -ex q; echo travis_fold":"end:crashlog; fi; done || true
travis_fold:end:after_failure.4
travis_fold:start:after_failure.5
travis_time:start:0123c684
travis_time:start:0123c684
$ cat ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers || true
cat: ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers: No such file or directory
travis_fold:end:after_failure.5
travis_fold:start:after_failure.6
travis_time:start:20dc2772
$ dmesg | grep -i kill

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[Firstyear]

I've updated based on your feedback @Manishearth, I think the travis build failure is not related to this work.

[Manishearth]

It's related: [00:03:41] tidy error: /checkout/src/libcore/mem.rs:617: line longer than 100 chars

[Firstyear]

I apologise, I really didn't see that error. I was staring at the log for quite a while :( Fixed and pushing.

[Manishearth]

@bors r+

thanks!

[bors]

📌 Commit b2d8040 has been approved by Manishearth

[emilyalbini]

@bors rollup