Change ManuallyDrop<T> to a lang item. #52711

eddyb · Jul 25, 2018

This PR implements the approach @RalfJung proposes in https://internals.rust-lang.org/t/pre-rfc-unions-drop-types-and-manuallydrop/8025 (lang item struct instead of union).

A followup PR can easily solve #47034 as well, by just adding a few ?Sized to libcore/mem.rs.

r? @nikomatsakis

RalfJung · Jul 25, 2018

ManuallySized<T>

;) Should be ManuallyDrop<T>

rust-highfive · Jul 25, 2018

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.

[01:15:50] travis_fold:end:stage0-linkchecker

[01:15:50] travis_time:end:stage0-linkchecker:start=1532547690616675272,finish=1532547693142869704,duration=2526194432

[01:16:03] reference/destructors.html:217: broken link - std/mem/union.ManuallyDrop.html
[01:16:03] reference/print.html:6644: broken link - std/mem/union.ManuallyDrop.html
[01:16:05] thread 'main' panicked at 'found some broken links', tools/linkchecker/main.rs:49:9
[01:16:05] 
[01:16:05] 
[01:16:05] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/linkchecker" "/checkout/obj/build/x86_64-unknown-linux-gnu/doc"
[01:16:05] expected success, got: exit code: 101
[01:16:05] expected success, got: exit code: 101
[01:16:05] 
[01:16:05] 
[01:16:05] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[01:16:05] Build completed unsuccessfully in 0:30:50
[01:16:05] Makefile:58: recipe for target 'check' failed
[01:16:05] make: *** [check] Error 1

The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:0e0645c0
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
---
travis_time:end:3377eb80:start=1532547710293822346,finish=1532547710303072311,duration=9249965
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:01cea5d2
$ 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 -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:32dd27d6
travis_time:start:32dd27d6
$ 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:0e595516
$ 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)

scottmcm · Jul 25, 2018

scottmcm reviewed Jul 25, 2018

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scottmcm · Jul 25, 2018

src/libcore/mem.rs

-#[derive(Copy)]
-pub union ManuallyDrop<T>{ value: T }
+#[lang = "manually_drop"]
+#[derive(Copy, Clone, Debug, Default, PartialEq, Eq, PartialOrd, Ord, Hash)]


Nice that these can all just be derives, now! 👍

nikomatsakis · Jul 26, 2018

@eddyb

[01:16:03] reference/destructors.html:217: broken link - std/mem/union.ManuallyDrop.html
[01:16:03] reference/print.html:6644: broken link - std/mem/union.ManuallyDrop.html

r=me once travis is happy

RalfJung · Jul 27, 2018

RalfJung reviewed Jul 27, 2018

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RalfJung · Jul 27, 2018

src/librustc/traits/query/dropck_outlives.rs

@@ -243,7 +243,10 @@ pub fn trivial_dropck_outlives<'tcx>(tcx: TyCtxt<'_, '_, 'tcx>, ty: Ty<'tcx>) ->

        ty::TyAdt(def, _) => {
            if def.is_union() {
-                // Unions never run have a dtor.
+                // Unions never have a dtor.
+                true


A union implementing Drop itself is not a concern here?

Good question, cc @arielb1 @pnkfelix @nikomatsakis

Actually, yes, I think it is a concern. :D #52786
(but the bug is already on nightly, so it's not introduced by this PR)

RalfJung · Jul 27, 2018

This makes ManuallyDrop for unsized types insta-stable. Does that require an FCP?

@eddyb said he doesn't have much time to follow up on this, but I think I can take over. I should probably also add at least one test because it seems there are none?

eddyb · Jul 27, 2018

FWIW we would only need an FCP for the second commit, the first one can be landed independently and then union-related changes can be made in parallel with generalized to !Sized.

RalfJung · Jul 27, 2018

So shall we split the PR?

RalfJung · Jul 27, 2018

PR submitted to fix link in reference: rust-lang-nursery/reference#373

rust-highfive · Jul 27, 2018

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.

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RalfJung · Jul 27, 2018

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RalfJung · Jul 27, 2018

Updated reference submodule so the links should be fixed.

rust-highfive · Jul 27, 2018

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.

[01:12:44] travis_fold:end:stage0-linkchecker

[01:12:44] travis_time:end:stage0-linkchecker:start=1532696023062930756,finish=1532696025506231937,duration=2443301181

[01:12:56] reference/items/implementations.html:268: broken link fragment `#lint-check-attributes.html` pointing to `reference/attributes.html`
[01:12:56] reference/expressions/block-expr.html:205: broken link fragment `#lint-check-attributes.html` pointing to `reference/attributes.html`
[01:12:56] reference/print.html:2292: broken link fragment `#lint-check-attributes.html` pointing to `reference/attributes.html`
[01:12:56] reference/print.html:3485: broken link fragment `#lint-check-attributes.html` pointing to `reference/attributes.html`
[01:12:56] reference/print.html:3845: broken link fragment `#lint-check-attributes.html` pointing to `reference/attributes.html`
[01:12:56] reference/statements.html:227: broken link fragment `#lint-check-attributes.html` pointing to `reference/attributes.html`
[01:12:58] thread 'main' panicked at 'found some broken links', tools/linkchecker/main.rs:49:9
[01:12:58] 
[01:12:58] 
[01:12:58] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/linkchecker" "/checkout/obj/build/x86_64-unknown-linux-gnu/doc"
[01:12:58] expected success, got: exit code: 101
[01:12:58] expected success, got: exit code: 101
[01:12:58] 
[01:12:58] 
[01:12:58] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[01:12:58] Build completed unsuccessfully in 0:30:31
[01:12:58] make: *** [check] Error 1
[01:12:58] Makefile:58: recipe for target 'check' failed

The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:15946a16
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
---
travis_time:end:03414e70:start=1532696041014582096,finish=1532696041023499098,duration=8917002
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:0cac76c6
$ 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 -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:2f984988
travis_time:start:2f984988
$ 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:03449c0e
$ 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)

RalfJung · Jul 27, 2018

Dang, unrelated updates in the reference contain broken links.

Reported as rust-lang-nursery/reference#374

EDIT: Fix submitted: rust-lang-nursery/reference#375

RalfJung · Jul 27, 2018

r=me once travis is happy

@bors r=nikomatsakis

bors · Jul 27, 2018

📌 Commit 4e6aea1 has been approved by nikomatsakis

bors · Jul 28, 2018

⌛️ Testing commit 4e6aea1 with merge 26e73da...

bors · Jul 28, 2018

☀️ Test successful - status-appveyor, status-travis
Approved by: nikomatsakis
Pushing 26e73da to master...

Change ManuallyDrop from an union to a struct and make it a lang item.

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eddyb changed the title ~~Change ManuallySized<T> to a lang item and relax it to allow T: ?Sized.~~ Change ManuallyDrop<T> to a lang item and relax it to allow T: ?Sized. Jul 25, 2018

eddyb force-pushed the eddyb:unsized-manuallydrop branch from f1bf3af to 591eeff Jul 27, 2018

eddyb changed the title ~~Change ManuallyDrop<T> to a lang item and relax it to allow T: ?Sized.~~ Change ManuallyDrop<T> to a lang item. Jul 27, 2018

add smoke test for ManuallyDrop

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RalfJung referenced this pull request Jul 27, 2018
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fix link to ManuallyDrop #373

update reference to fix links

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uodate reference again to hopefully fix all link issues

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update ManuallyDrop RFC to reflect how the implementation now looks rust-lang/rfcs#2510

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Add empty dropped variant to ManuallyDrop #49056

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unsized ManuallyDrop #53033

pnkfelix referenced this pull request Oct 9, 2018
Closed
error: internal compiler error: Accessing `(*_310)` with the kind `Write(Move)` shouldn't be possible #54597

bluss referenced this pull request Dec 3, 2018
Open
Possible UB from use of uninitialized `[&T; N]` #126

RalfJung referenced this pull request Dec 3, 2018
Closed
Implement a stop-gap “MaybeUninit” using ManuallyDrop #97

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eddyb commented Jul 25, 2018 • edited

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eddyb changed the title Change ManuallySized<T> to a lang item and relax it to allow T: ?Sized. Change ManuallyDrop<T> to a lang item and relax it to allow T: ?Sized. Jul 25, 2018

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eddyb force-pushed the eddyb:unsized-manuallydrop branch from f1bf3af to 591eeff Jul 27, 2018

eddyb changed the title Change ManuallyDrop<T> to a lang item and relax it to allow T: ?Sized. Change ManuallyDrop<T> to a lang item. Jul 27, 2018

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eddyb commented Jul 25, 2018 •

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