Introduce ptr::hash for references

[dwijnand]

The RHS is what I used, which wasn't as convenient as ptr::eq, so I wondered: should ptr::hash exist?

My first Rust PR, so I'm going to need some guidance. :)

[rust-highfive]

r? @aidanhs

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[Centril]

Code looks good imo; assigning over to someone on T-libs for review.

r? @sfackler

[dwijnand]

CC @alexcrichton this would've made that interning code in Cargo look more symmetric :)

[alexcrichton]

This seems like it's fine to me to add, but to align with ptr::eq should this perhaps take a raw pointer as well?

[dwijnand]

My hesitation on a raw pointer was to avoid having to make a decision on whether a null pointer should be hashed or not. But I guess if ptr::eq is happy to compare any raw pointer then I guess ptr::hash can hash any raw pointer, and the user can guard against passing it null pointers if need be.

[rust-highfive]

The job x86_64-gnu-llvm-5.0 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:03752b1b:start=1543909813110345578,finish=1543909868985148801,duration=55874803223
$ 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-5.0
---
184272 ./obj/build/cache/2018-10-30
153272 ./src/tools/clang
150332 ./obj/build/bootstrap/debug/incremental
134740 ./obj/build/bootstrap/debug/incremental/bootstrap-1plb86h2refwc
134736 ./obj/build/bootstrap/debug/incremental/bootstrap-1plb86h2refwc/s-f79qgjj7ni-1l6t9lv-4qyniat88vxc
134060 ./.git/modules/src
115340 ./src/llvm/test/CodeGen
107892 ./obj/build/x86_64-unknown-linux-gnu/stage0/lib/rustlib/x86_64-unknown-linux-gnu/codegen-backends
107416 ./src/tools/lldb
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$ 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
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$ 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
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travis_time:start:12bf5050
$ dmesg | grep -i kill

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)

[sinkuu]

As now it's taking a pointer, "behind a reference" may need to be removed.

[bors]

⌛ Testing commit ad76569 with merge 786b54f...

[bors]

💔 Test failed - status-travis

[rust-highfive]

The job dist-aarch64-linux 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.

Building stage2 tool cargo (aarch64-unknown-linux-gnu)
[01:08:28]  Downloading crates ...
[01:08:48] warning: spurious network error (2 tries remaining): [6] Couldn't resolve host name (Could not resolve host: crates.io)
[01:09:08] warning: spurious network error (1 tries remaining): [6] Couldn't resolve host name (Could not resolve host: crates.io)
[01:09:28] error: failed to download from `https://crates.io/api/v1/crates/openssl-src/111.0.1+1.1.1/download`
[01:09:28] Caused by:
[01:09:28]   [6] Couldn't resolve host name (Could not resolve host: crates.io)
[01:09:28] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "build" "--target" "aarch64-unknown-linux-gnu" "-j" "4" "--release" "--locked" "--color" "always" "--manifest-path" "/checkout/src/tools/cargo/Cargo.toml" "--features" "rustc-workspace-hack/all-static" "--message-format" "json"
[01:09:28] expected success, got: exit code: 101
---
travis_time:end:1057ba42:start=1544077771498342503,finish=1544077771506399975,duration=8057472
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travis_time:start:132101c7
$ 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
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$ 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:0da61ed0
$ dmesg | grep -i kill

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)

[kennytm]

@bors retry rollup travis-ci/travis-ci#9696

[dwijnand]

As now it's taking a pointer, "behind a reference" may need to be removed.

@sinkuu you're right, well spotted. But I'm holding back on pushing a commit as I don't want to mess up any rollup efforts. I'm happy to push a fix either in this PR or a follow-up when it's best to.

[dwijnand]

Followed up in #56602.