Take 2: Implement object-safety and dynamic dispatch for arbitrary_self_types #54383

mikeyhew · 2018-09-20T09:40:44Z

This replaces #50173. Over the months that that PR was open, we made a lot of changes to the way this was going to be implemented, and the long, meandering comment thread and commit history would have been confusing to people reading it in the future. So I decided to package everything up with new, straighforward commits and open a new PR.

Here are the main points. Please read the commit messages for details.

To simplify codegen, we only support receivers that have the ABI of a pointer. That means they are builtin pointer types, or newtypes thereof.
We introduce a new trait: DispatchFromDyn<T>, similar to CoerceUnsized<T>. DispatchFromDyn has extra requirements that CoerceUnsized does not: when you implement DispatchFromDyn for a struct, there cannot be any extra fields besides the field being coerced and PhantomData fields. This ensures that the struct's ABI is the same as a pointer.
For a method's receiver (e.g. self: Rc<Self>) to be object-safe, it needs to have the following property:
- let DynReceiver be the receiver when Self = dyn Trait
- let ConcreteReceiver be the receiver when Self = T, where T is some unknown Sized type that implements Trait, and is the erased type of the trait object.
- ConcreteReceiver must implement DispatchFromDyn<DynReceiver>

In the case of Rc<Self>, this requires Rc<T>: DispatchFromDyn<Rc<dyn Trait>>

These rules are explained more thoroughly in the doc comment on receiver_is_dispatchable in object_safety.rs.

r? @nikomatsakis and @eddyb

cc @arielb1 @cramertj @withoutboats

Special thanks to @nikomatsakis for getting me un-stuck when implementing the object-safety checks, and @eddyb for helping with the codegen parts.

EDIT 2018-11-01: updated because CoerceSized has been replaced with DispatchFromDyn

rust-highfive · 2018-09-20T10:47:33Z

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.

[00:46:58]    Compiling std v0.0.0 (file:///checkout/src/libstd)
[00:47:16] warning: `[T]` cannot be resolved, ignoring it...
[00:47:16]   --> libcore/ops/unsize.rs:89:9
[00:47:16]    |
[00:47:16] 89 | /// - &[T] is CoerceSized<&[T; N]> for any N
[00:47:16]    |
[00:47:16]    = note: #[warn(intra_doc_link_resolution_failure)] on by default
[00:47:16]    = help: to escape `[` and `]` characters, just add '\' before them like `\[` or `\]`
[00:47:16] 
[00:47:16] 
[00:47:16] warning: `[T]` cannot be resolved, ignoring it...
[00:47:16]   --> libcore/ops/unsize.rs:89:9
[00:47:16]    |
[00:47:16] 89 | /// - &[T] is CoerceSized<&[T; N]> for any N
[00:47:16]    |
[00:47:16]    = help: to escape `[` and `]` characters, just add '\' before them like `\[` or `\]`
[00:47:16] 
[00:47:37]     Checking compiler_builtins v0.0.0 (file:///checkout/src/rustc/compiler_builtins_shim)
---
[00:47:40]     Checking panic_abort v0.0.0 (file:///checkout/src/libpanic_abort)
[00:47:42] warning: `[T]` cannot be resolved, ignoring it...
[00:47:42]   --> /checkout/src/libcore/ops/unsize.rs:89:9
[00:47:42]    |
[00:47:42] 89 | /// - &[T] is CoerceSized<&[T; N]> for any N
[00:47:42]    |
[00:47:42]    = note: #[warn(intra_doc_link_resolution_failure)] on by default
[00:47:42]    = help: to escape `[` and `]` characters, just add '\' before them like `\[` or `\]`
[00:47:42] 
---
[00:47:51] 
[00:47:51] warning: `[T]` cannot be resolved, ignoring it...
[00:47:51]   --> /checkout/src/libcore/ops/unsize.rs:89:9
[00:47:51]    |
[00:47:51] 89 | /// - &[T] is CoerceSized<&[T; N]> for any N
[00:47:51]    |
[00:47:51]    = help: to escape `[` and `]` characters, just add '\' before them like `\[` or `\]`
[00:47:51] 
[00:47:51] warning: `[Weak::upgrade]` cannot be resolved, ignoring it...
---
[00:57:48] ....................................................................................................
[00:57:51] .......................................................i............................................
[00:57:54] ....................................................................................................
[00:57:57] ....................................................................................................
[00:58:00] ..iiiiiiiii.........................................................................................
[00:58:06] ....................................................................................................
[00:58:10] .....................................................................................i..............
[00:58:12] ....................................................................................................
[00:58:16] ........................................i.i..ii.....................................................
---
[01:03:36] .......................................................................................i............
[01:03:39] ....................................................................................................
[01:03:43] ....................................................................................................
[01:03:45] ....................................................................................................
[01:03:48] ..i.ii.ii.ii.............................i..........................................................
[01:03:48] test result: ok. 6714 passed; 0 failed; 88 ignored; 0 measured; 0 filtered out
[01:03:48] 
[01:03:48]  finished in 421.992
[01:03:48] travis_fold:end:test_ui_nll
---
travis_time:start:test_run-pass
Check compiletest suite=run-pass mode=run-pass (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[01:03:48] 
[01:03:48] running 551 tests
[01:04:03] ........F.................................i.........................................................
[01:04:30] ....................................................................................................
[01:04:40] ....................................................................................................
[01:04:58] ..................i.................................................................................
[01:05:05] ...................................................
[01:05:05] ...................................................
[01:05:05] failures:
[01:05:05] 
[01:05:05] ---- [run-pass] run-pass/arbitrary_self_types_stdlib_pointers.rs stdout ----
[01:05:05] 
[01:05:05] error: compilation failed!
[01:05:05] status: exit code: 1
[01:05:05] command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/run-pass/arbitrary_self_types_stdlib_pointers.rs" "--target=x86_64-unknown-linux-gnu" "-C" "prefer-dynamic" "-o" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/run-pass/arbitrary_self_types_stdlib_pointers/a" "-Crpath" "-O" "-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/run-pass/arbitrary_self_types_stdlib_pointers/auxiliary"
[01:05:05] ------------------------------------------
[01:05:05] 
[01:05:05] ------------------------------------------
[01:05:05] stderr:
[01:05:05] stderr:
[01:05:05] ------------------------------------------
[01:05:05] error[E0282]: type annotations needed
[01:05:05]   --> /checkout/src/test/run-pass/arbitrary_self_types_stdlib_pointers.rs:54:19
[01:05:05]    |
[01:05:05] 54 |     let pin_box = Box::new(4i64).into() as Pin<Box<dyn Trait>>;
[01:05:05]    |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot infer type for `T`
[01:05:05]    = note: type must be known at this point
[01:05:05] 
[01:05:05] error: aborting due to previous error
[01:05:05] 
[01:05:05] 
[01:05:05] For more information about this error, try `rustc --explain E0282`.
[01:05:05] 
[01:05:05] ------------------------------------------
[01:05:05] 
[01:05:05] thread '[run-pass] run-pass/arbitrary_self_types_stdlib_pointers.rs' panicked at 'explicit panic', tools/compiletest/src/runtest.rs:3205:9
[01:05:05] 
[01:05:05] 
[01:05:05] failures:
[01:05:05]     [run-pass] run-pass/arbitrary_self_types_stdlib_pointers.rs
[01:05:05]     [run-pass] run-pass/arbitrary_self_types_stdlib_pointers.rs
[01:05:05] 
[01:05:05] test result: FAILED. 548 passed; 1 failed; 2 ignored; 0 measured; 0 filtered out
[01:05:05] 
[01:05:05] thread 'main' panicked at 'Some tests failed', tools/compiletest/src/main.rs:496:22
[01:05:05] 
[01:05:05] 
[01:05:05] 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/run-pass" "--build-base" "/check

The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:2270ea6e
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)

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)

rust-highfive · 2018-09-20T17:49:50Z

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.

[00:40:48]    Compiling std v0.0.0 (file:///checkout/src/libstd)
[00:41:01] warning: `[T]` cannot be resolved, ignoring it...
[00:41:01]   --> libcore/ops/unsize.rs:89:9
[00:41:01]    |
[00:41:01] 89 | /// - &[T] is CoerceSized<&[T; N]> for any N
[00:41:01]    |
[00:41:01]    = note: #[warn(intra_doc_link_resolution_failure)] on by default
[00:41:01]    = help: to escape `[` and `]` characters, just add '\' before them like `\[` or `\]`
[00:41:01] 
[00:41:01] 
[00:41:01] warning: `[T]` cannot be resolved, ignoring it...
[00:41:01]   --> libcore/ops/unsize.rs:89:9
[00:41:01]    |
[00:41:01] 89 | /// - &[T] is CoerceSized<&[T; N]> for any N
[00:41:01]    |
[00:41:01]    = help: to escape `[` and `]` characters, just add '\' before them like `\[` or `\]`
[00:41:01] 
[00:41:19]     Checking compiler_builtins v0.0.0 (file:///checkout/src/rustc/compiler_builtins_shim)
---
[00:41:21]     Checking alloc_jemalloc v0.0.0 (file:///checkout/src/liballoc_jemalloc)
[00:41:23] warning: `[T]` cannot be resolved, ignoring it...
[00:41:23]   --> /checkout/src/libcore/ops/unsize.rs:89:9
[00:41:23]    |
[00:41:23] 89 | /// - &[T] is CoerceSized<&[T; N]> for any N
[00:41:23]    |
[00:41:23]    = note: #[warn(intra_doc_link_resolution_failure)] on by default
[00:41:23]    = help: to escape `[` and `]` characters, just add '\' before them like `\[` or `\]`
[00:41:23] 
---
[00:41:29] 
[00:41:29] warning: `[T]` cannot be resolved, ignoring it...
[00:41:29]   --> /checkout/src/libcore/ops/unsize.rs:89:9
[00:41:29]    |
[00:41:29] 89 | /// - &[T] is CoerceSized<&[T; N]> for any N
[00:41:29]    |
[00:41:29]    = help: to escape `[` and `]` characters, just add '\' before them like `\[` or `\]`
[00:41:29] 
[00:41:29] warning: `[Weak::upgrade]` cannot be resolved, ignoring it...
---
[00:49:23] ....................................................................................................
[00:49:26] ......................................................i.............................................
[00:49:28] ....................................................................................................
[00:49:31] ....................................................................................................
[00:49:33] ..iiiiiiiii.........................................................................................
[00:49:39] ....................................................................................................
[00:49:41] .....................................................................................i..............
[00:49:44] ....................................................................................................
[00:49:46] ........................................i.i..ii.....................................................
---
[01:16:30]   |
[01:16:30] 3 | use std::marker::PhantomData;
[01:16:30]   |
[01:16:30] 
[01:16:30] error[E0378]: the trait `CoerceSized` may only be implemented for structs containing the field being coerced, `PhantomData` fields, and nothing else
[01:16:30]   --> /checkout/obj/build/x86_64-unknown-linux-gnu/test/error-index.md:5599:1
[01:16:30]    |
[01:16:30] 16 | / impl<T, U> CoerceSized<Wrapper<T>> for Wrapper<U>
[01:16:30] 17 | | where
[01:16:30] 18 | |     T: CoerceUnsized<U>,
[01:16:30] 19 | |     U: CoerceSized<T>,
[01:16:30] 20 | | {}
[01:16:30]    |
[01:16:30]    |
[01:16:30]    = note: extra field `_phantom` of type `[type error]` is not allowed
[01:16:30] thread '/checkout/obj/build/x86_64-unknown-linux-gnu/test/error-index.md - Rust_Compiler_Error_Index::E0378 (line 5585)' panicked at 'couldn't compile the test', librustdoc/test.rs:333:13
[01:16:30] 
[01:16:30] 
[01:16:30] failures:
---
[01:16:30] 
[01:16:30] 
[01:16:30] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[01:16:30] Build completed unsuccessfully in 0:34:23
[01:16:30] make: *** [check] Erro5381060 .
2984884 ./obj/build
2365004 ./obj/build/x86_64-unknown-linux-gnu
1192992 ./.git
1067680 ./src
---
162932 ./.git/modules/src/tools/lldb/objects/pack
151412 ./src/tools/clang
149112 ./src/llvm-emscripten/test
148628 ./obj/build/bootstrap/debug/incremental
142256 ./obj/build/x86_64-unknown-linux-gnu/stage1-rustc/x86 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:0655edaa
travis_time:start:0655edaa
$ 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:0729ee22
$ 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)

eddyb · 2018-09-20T18:21:26Z

I see a few problems with CoerceSized:

the name - CoerceUnsized means "coerce, via the unsizing coercion (applied on a field)"; there is no "sizing" coercion, and even if it it made sense, it'd be "re-sized" or something
the conceptualizing, of "getting back the sized type", doesn't really work in current Rust - I believe what we want here is "existential unpacking", involving skolem forms or something like that - but that's much longer term, we don't have the compiler technology in rustc for soundly doing it
the parameter order compared to CoerceUnsized doesn't seem to serve a specific purpose

I'd prefer something like this, instead:

trait CoerceUnsizedDispatchable<T: ?Sized>: CoerceUnsized<T> {}

Making the requirements (also including some other slight renames):

ConcreteReceiver = (typeof self) where Self: Sized;
DynReceiver = (typeof self)[dyn Trait/Self];
ConcreteReceiver: CoerceUnsizedDispatchable<DynReceiver>

nikomatsakis · 2018-09-20T18:29:08Z

@eddyb

I don't really understand why you would say this is not a "sizing" coercion. It seems like exactly what it is to me. Like any coercion, the type changes and so does the in-memory representation (in contrast to a subtyping relationship which -- at least in rustc -- implies that the type changes but not the in-memory representation).

In this case, we are coercing a Rc type to a Rc<S> type
- where U is the unsized type we start with
- and S is the (hidden) sized type that underlies it

You are absolutely correct that the final type (Rc<S>) is not a type that we know statically, but I don't know why that makes it less of a coercion.

Obviously, this all a bikeshed, so I'm willing to go with whatever we settle on. The name CoerceUnsizedDispatchable doesn't exactly "roll off the tongue though".

eddyb · 2018-09-20T20:10:18Z

We discussed this on Discord and we reached some agreement that the current state is not as clear-cut as we'd like it to be eventually (e.g. we can't currently make Rc<T> out of Rc<dyn Trait>, so codegen has to get the internal *mut RcBox<dyn Trait> from Rc and dispatch on that).

The name we settled on was DynDispatchFrom (as in, dispatch on concrete from dynamic), although I just thought of DispatchFromDyn, which might be more intuitive.

Also, I suggested that that these additional checks are performed (for object safety):

layout_of(ConcreteReceiver).abi == Scalar(Pointer)
layout_of(DynReceiver).abi == ScalarPair(Pointer, Pointer)

This way, we don't die in codegen / miri, and we instead, detect it much earlier (this is "temporary", until we can do something closer to existential unpacking).

bors · 2018-09-21T01:20:59Z

☔ The latest upstream changes (presumably #54389) made this pull request unmergeable. Please resolve the merge conflicts.

rust-highfive · 2018-09-21T07:46:07Z

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.

[00:54:26] ....................................................................................................
[00:54:28] ......................................................i.............................................
[00:54:31] ....................................................................................................
[00:54:34] ....................................................................................................
[00:54:37] ..iiiiiiiii.........................................................................................
[00:54:43] ....................................................................................................
[00:54:46] ......................................................................................i.............
[00:54:49] ....................................................................................................
[00:54:52] .........................................i.i..ii....................................................
---
[01:27:28] 
[01:27:28] failures:
[01:27:28] 
[01:27:28] ---- /checkout/obj/build/x86_64-unknown-linux-gnu/test/error-index.md - Rust_Compiler_Error_Index::E0378 (line 5565) stdout ----
[01:27:28] error[E0405]: cannot find trait `CoerceUnsized` in this scope
[01:27:28]   --> /checkout/obj/build/x86_64-unknown-linux-gnu/test/error-index.md:5574:28
[01:27:28]    |
[01:27:28] 11 | impl<T: ?Sized, U: ?Sized> CoerceUnsized<Ptr<U>> for Ptr<T>
[01:27:28]    |                            ^^^^^^^^^^^^^ did you mean `CoerceSized`?
[01:27:28]    |
[01:27:28]    |
[01:27:28] 3  | use std::ops::CoerceUnsized;
[01:27:28] 
[01:27:28] thread '/checkout/obj/build/x86_64-unknown-linux-gnu/test/error-index.md - Rust_Compiler_Error_Index::E0378 (line 5565)' panicked at 'couldn't compile the test', librustdoc/test.rs:333:13
[01:27:28] note: Run with `RUST_BACKTRACE=1` for a backtrace.
[01:27:28] 
[01:27:28] 
[01:27:28] ---- /checkout/obj/build/x86_64-unknown-linux-gnu/test/error-index.md - Rust_Compiler_Error_Index::E0378 (line 5585) stdout ----
[01:27:28] error[E0412]: cannot find type `PhantomData` in this scope
[01:27:28]  --> /checkout/obj/build/x86_64-unknown-linux-gnu/test/error-index.md:5591:15
[01:27:28]   |
[01:27:28] 8 |     _phantom: PhantomData<()>,
[01
travis_time:end:04993b6f:start=1537510713754336308,finish=1537515962628450007,duration=5248874113699

The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
---
travis_time:end:1a9d4020:start=1537515964439982332,finish=1537515964443983046,duration=4000714
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:2caf179e
$ ln -s . checkout && for CORE in obj/cores/core.

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)

mikeyhew · 2018-09-26T16:39:33Z

@eddyb @nikomatsakis so what trait do you want, and what would example impls look like for Rc<T> and Pin?

nikomatsakis

Argh, I appear to keep failing to finish a complete review. Here are a few in-process comments, all tiny.

nikomatsakis · 2018-09-24T21:28:44Z

src/libcore/ops/unsize.rs

+/// - and similarly for &mut T, *const T, *mut T, Box<T>, Rc<T>, Arc<T>
+#[unstable(feature = "coerce_sized", issue = "0")]
+#[cfg_attr(not(stage0), lang = "coerce_sized")]
+pub trait CoerceSized<T> where T: CoerceUnsized<Self> {


So, we need to rename this, per @eddyb's suggestion

nikomatsakis · 2018-09-24T21:50:44Z

src/librustc_codegen_llvm/mir/block.rs

-                            continue;
+                        // descend through newtype wrappers until `op` is a builtin pointer to
+                        // `dyn Trait`, e.g. `*const dyn Trait`, `&mut dyn Trait`
+                        'descend_newtypes: while !op.layout.ty.is_unsafe_ptr()


can we encapsulate this into a helper fn? this say hacky loop appears twice, no?

Sure, if you think it will make the code more readable. I worry it might make it less so, but I'll see what I can do and you can review it

Now that I'm rebasing on #54183, which has conflicts here, I'm starting to realize that this code isn't very easy to understand. So I'm going to try to do the refactor you suggested and add some comments to explain what's going on, since it's very hacky. Essentially we're taking a newtyped pointer, removing all the newtype wrappers to get a *mut dyn Trait, &dyn Trait or similar, taking away the vtable so it's just a thin pointer, but telling the compiler its type is still *mut dyn Trait because it understands that as a special case somewhere else according to @eddyb

nikomatsakis · 2018-09-27T19:02:48Z

@mikeyhew

so what trait do you want, and what would example impls look like for Rc<T> and Pin?

I think the name we settled on was DispatchFromDyn. I think this implies that we swap the order of the arguments, and I also believe @eddyb said something about removing the T: CoerceUnsized requirement. So if the current definition is:

pub trait CoerceSized<T> where T: CoerceUnsized<Self> {..}

impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceSized<Rc<T>> for Rc<U> {}

Then we might have:

pub trait DispatchFromDyn<T> { }

impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Rc<U>> for Rc<T> {}

Does that sound about right, @eddyb?

I'm not sure what the implications are of removing the CoerceUnsized requirement, though. Are there any?

nikomatsakis · 2018-09-27T19:03:45Z

And of course @eddyb mentioned adding these "layout checks" for object safety:

layout_of(ConcreteReceiver).abi == Scalar(Pointer)
layout_of(DynReceiver).abi == ScalarPair(Pointer, Pointer)

src/librustc/traits/object_safety.rs

nikomatsakis · 2018-09-27T19:16:09Z

src/librustc/traits/object_safety.rs

+    ///
+    ///     forall (U: ?Sized) {
+    ///         if (Self: Unsize<U>) {
+    ///             Receiver[Self => U]: CoerceSized<Receiver>


Receiver: DynDispatchFrom<Receiver[Self => U]>

mikeyhew · 2018-09-27T23:13:26Z

I'm not sure what the implications are of removing the CoerceUnsized requirement, though. Are there any?

No, because I ended up reimplementing all of the CoerceUnsized checks for CoerceSized here: https://github.com/rust-lang/rust/pull/54383/files#diff-aaae39ee387dc6a0aea969d3799e2bfa

eddyb · 2018-09-28T07:35:07Z

All of @nikomatsakis' comments seem good, I'll take a look at the PR after all the changes have been made.

bors · 2018-09-29T15:09:10Z

☔ The latest upstream changes (presumably #54660) made this pull request unmergeable. Please resolve the merge conflicts.

rust-highfive · 2018-10-04T04:44:09Z

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.

[00:49:17] ...............................................................................................i.... 2200/4549
[00:49:21] .................................................................................................... 2300/4549
[00:49:25] .................................................................................................... 2400/4549
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[00:49:45] ..........................i......................................................................... 3000/4549
[00:49:47] ......................................................................................i.i..ii....... 3100/4549
---
travis_time:start:test_run-pass
Check compiletest suite=run-pass mode=run-pass (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[00:50:34] 
[00:50:34] running 2874 tests
[00:50:45] ...........F........................................................................................ 100/2874
[00:51:03] .................................................................................................... 300/2874
[00:51:13] .................................................................................................... 400/2874
[00:51:21] .................................................................................................... 500/2874
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---
[00:55:30] .................................................................................................... 2500/2874
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[00:56:13] .................................................................................................... 2800/2874
56:23] To update references, rerun the tests and pass the `--bless` flag
[00:56:23] To only update this specific test, also pass `--test-args arbitrary_self_types_pointers_and_wrappers.rs`
[00:56:23] error: 1 errors occurred comparing output.
[00:56:23] status: exit code: 0
[00:56:23] status: exit code: 0
[00:56:23] command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/run-pass/arbitrary_self_types_pointers_and_wrappers.rs" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "-Zui-testing" "-C" "prefer-dynamic" "-o" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/run-pass/arbitrary_self_types_pointers_and_wrappers/a" "-Crpath" "-O" "-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/run-pass/arbitrary_self_types_pointers_and_wrappers/auxiliary"
[00:56:23] ------------------------------------------
[00:56:23] 
[00:56:23] ------------------------------------------
[00:56:23] stderr:
[00:56:23] stderr:
[00:56:23] ------------------------------------------
[00:56:23] {"message":"unused import: `fmt::Debug`","code":{"code":"unused_imports","explanation":null},"level":"warning","spans":[{"file_name":"/checkout/src/test/run-pass/arbitrary_self_types_pointers_and_wrappers.rs","byte_start":645,"byte_end":655,"line_start":16,"line_end":16,"column_start":5,"column_end":15,"is_primary":true,"text":[{"text":"    fmt::Debug,","highlight_start":5,"highlight_end":15}],"label":null,"suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"#[warn(unused/bootstrap-3ivyub3ic2113/s-f5eakr5kqq-ffhwli-8vudgacockuw
134192 ./obj/build/x86_64-unknown-linux-gnu/stage1-rustc/x86_64-unknown-linux-gnu/release
131276 ./obj/build/x86_64-unknown-linux-gnu/stage1-rustc/x86_64-unknown-linux-gnu/release/deps
130808 ./obj/build/x86_64-unknown-linux-gnu/stage0-bootstrap-tools/x86_64-unknown-linux-gnu
130804 ./obj/build/x86_64-unknown-linux-gnu/stage0-bootstrap-tools/x86_64-unknown-linux-gnu/release

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)

mikeyhew · 2018-10-04T08:01:05Z

OK, CoerceSized is now called DispatchFromDyn. @eddyb I guess it's your turn to review.

I'm guessing CI will fail on error-index.md again. If it does, hopefully someone can tell me how to run that test locally, so I don't have to work off CI.

I'm getting a failing LLVM assertion on one of the thin-lto tests, but I'm guessing it's a stage 1 thing because I had it before and it didn't show up in CI

src/librustc_typeck/coherence/builtin.rs

mikeyhew · 2018-10-04T08:18:59Z

And of course @eddyb mentioned adding these "layout checks" for object safety:

layout_of(ConcreteReceiver).abi == Scalar(Pointer)
layout_of(DynReceiver).abi == ScalarPair(Pointer, Pointer)

Oh, I just remembered this. Will add them later, don't let me forget

mikeyhew · 2018-10-04T08:21:52Z

src/test/ui/traits/trait-item-privacy.stderr

@@ -100,30 +100,6 @@ error[E0624]: associated constant `A` is private
 LL |     C::A; //~ ERROR associated constant `A` is private
   |     ^^^^



Someone ought to take a look at this, I'm not sure why some errors are going away but see the commit message on 6db1879

seems plausible, I'm not too worried about this

rust-highfive · 2018-10-04T08:57:52Z

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.

[00:45:56] .................................................................................................i.. 2200/4552
[00:46:01] .................................................................................................... 2300/4552
[00:46:04] .................................................................................................... 2400/4552
[00:46:07] .................................................................................................... 2500/4552
[00:46:11] .........iiiiiiiii.................................................................................. 2600/4552
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[00:46:23] ............................i....................................................................... 3000/4552
[00:46:25] ........................................................................................i.i..ii..... 3100/4552
---
travis_time:start:test_codegen
Check compiletest suite=codegen mode=codegen (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[00:58:09] 
[00:58:09] running 107 tests
[00:58:12] i..ii...iii....i...i.........i..iii...........i.....i....ii...i.i.ii..............i...ii..ii.i....ii 100/107
[00:58:12] test result: ok. 77 passed; 0 failed; 30 ignored; 0 measured; 0 filtered out
[00:58:12] 
[00:58:12]  finished in 3.193
[00:58:12] travis_fold:end:test_codegen
---
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[01:11:25] ..................................................................................i................. 2100/2166
[01:11:30] .....................................i............................
[01:11:30] failures:
[01:11:30] 
[01:11:30] 
[01:11:30] ---- ops/unsize.rs - ops::unsize::DispatchFromDyn (line 86) stdout ----
[01:11:30] error[E0405]: cannot find trait `DispatchFromDyn` in this scope
[01:11:30]  --> ops/unsize.rs:87:28
[01:11:30]   |
[01:11:30] 4 | impl<T: ?Sized, U: ?Sized> DispatchFromDyn<Rc<U>> for Rc<T>
[01:11:30] help: possible candidate is found in another module, you can import it into scope
[01:11:30]   |
[01:11:30]   |
[01:11:30] 3 | use std::ops::DispatchFromDyn;
[01:11:30] 
[01:11:30] error[E0412]: cannot find type `Rc` in this scope
[01:11:30]  --> ops/unsize.rs:87:44
[01:11:30]   |
[01:11:30]   |
[01:11:30] 4 | impl<T: ?Sized, U: ?Sized> DispatchFromDyn<Rc<U>> for Rc<T>
[01:11:30]   |                                            ^^ not found in this scope
[01:11:30]   |
[01:11:30] 3 | use std::rc::Rc;
[01:11:30]   |
[01:11:30] 
[01:11:30] 
[01:11:30] error[E0412]: cannot find type `Rc` in this scope
[01:11:30]  --> ops/unsize.rs:87:55
[01:11:30]   |
[01:11:30] 4 | impl<T: ?Sized, U: ?Sized> DispatchFromDyn<Rc<U>> for Rc<T>
[01:11:30]   |                                                       ^^ not found in this scope
[01:11:30]   |
[01:11:30] 3 | use std::rc::Rc;
[01:11:30]   |
[01:11:30] 
[01:11:30] 
[01:11:30] error[E0405]: cannot find trait `Unsize` in this scope
[01:11:30]  --> ops/unsize.rs:89:8
[01:11:30]   |
[01:11:30] 6 |     T: Unsize<U>,
[01:11:30] help: possible candidate is found in another module, you can import it into scope
[01:11:30]   |
[01:11:30] 3 | use std::marker::Unsize;
[01:11:30]   |
[01:11:30]   |
[01:11:30] 
[01:11:30] thread 'ops/unsize.rs - ops::unsize::DispatchFromDyn (line 86)' panicked at 'couldn't compile the test', librustdoc/test.rs:333:13
[01:11:30] 
[01:11:30] 
[01:11:30] failures:
[01:11:30] failures:
[01:11:30]     ops/unsize.rs - ops::unsize::DispatchFromDyn (line 86)
[01:11:30] test result: FAILED. 2162 passed; 1 failed; 3 ignored; 0 measured; 0 filtered out
[01:11:30] 
[01:11:30] error: test failed, to rerun pass '--doc'
[01:11:30] 
[01:11:30] 
[01:11:30] 
[01:11:30] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "test" "--target" "x86_64-unknown-linux-gnu" "-j" "4" "--release" "--locked" "--color" "always" "--features" "panic-unwind jemalloc backtrace" "--manifest-path" "/checkout/src/libstd/Cargo.toml" "-p" "core" "--" "--quiet"
[01:11:30] 
[01:11:30] 
[01:11:30] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[01:11:30] Build completed unsuccessfully in 0:29:55
[01:11:30] Build completed unsuccessfully in 0:29:55
[01:11:30] Makefile:58: recipe for target 'check' failed
[01:11:30] make: *** [check] Error 1

The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:05be68ce
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
---
travis_time:end:05816295:start=1538643468589890657,finish=1538643468594941308,duration=5050651
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:080e3e78
$ 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\

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)

tests were failing because I didn't wrap code snippets like in backticks. fixed that now, so hopefully tests will pass on travis

Rename `CoerceSized` to `DispatchFromDyn`, and reverse the direction so that, for example, you write ``` impl<T: Unsize, U> DispatchFromDyn<*const U> for *const T {} ``` instead of ``` impl<T: Unsize, U> DispatchFromDyn<*const T> for *const U {} ``` this way the trait is really just a subset of `CoerceUnsized`. The checks in object_safety.rs are updated for the new trait, and some documentation and method names in there are updated for the new trait name — e.g. `receiver_is_coercible` is now called `receiver_is_dispatchable`. Since the trait now works in the opposite direction, some code had to updated here for that too. I did not update the error messages for invalid `CoerceSized` (now `DispatchFromDyn`) implementations, except to find/replace `CoerceSized` with `DispatchFromDyn`. Will ask for suggestions in the PR thread.

If object-safety checks succeed for a receiver type, make sure the receiver’s abi is a) a Scalar, when Self = () b) a ScalarPair, when Self = dyn Trait

Added to `DispatchFromDyn` and `CoerceUnsized` error messages

also updated the doc on `receiver_is_dispatchable` to reflect current state of the implementation

…candidates I don't really understand what it's for, but see the comment here: rust-lang#50173 (comment) where arielb1 said > Does this check do anything these days? I think `$0: Trait` is always considered ambiguous and nikomatsakis agreed we may be able to get rid of it

disallow `#[repr(C)] and `#[repr(packed)]` on structs implementing DispatchFromDyn because they will change the ABI from Scalar/ScalarPair to Aggregrate, resulting in an ICE during object-safety checks or codegen

mikeyhew · 2018-11-01T22:28:24Z

@kennytm

Could you update the PR description e.g. s/CoerceSized/DispatchFromDyn/g?

Done.

mikeyhew · 2018-11-01T22:31:03Z

This is ready to go.

mikeyhew · 2018-11-02T22:55:23Z

@nikomatsakis can you r+ this?

cramertj · 2018-11-03T00:01:20Z

@bors r=nikomatsakis

(based on the approval below this comment)

bors · 2018-11-03T00:01:22Z

📌 Commit 192e7c4 has been approved by nikomatsakis

bors · 2018-11-03T02:37:36Z

⌛ Testing commit 192e7c4 with merge 3fc70e8...

@nikomatsakis

…omatsakis Take 2: Implement object-safety and dynamic dispatch for arbitrary_self_types This replaces #50173. Over the months that that PR was open, we made a lot of changes to the way this was going to be implemented, and the long, meandering comment thread and commit history would have been confusing to people reading it in the future. So I decided to package everything up with new, straighforward commits and open a new PR. Here are the main points. Please read the commit messages for details. - To simplify codegen, we only support receivers that have the ABI of a pointer. That means they are builtin pointer types, or newtypes thereof. - We introduce a new trait: `DispatchFromDyn<T>`, similar to `CoerceUnsized<T>`. `DispatchFromDyn` has extra requirements that `CoerceUnsized` does not: when you implement `DispatchFromDyn` for a struct, there cannot be any extra fields besides the field being coerced and `PhantomData` fields. This ensures that the struct's ABI is the same as a pointer. - For a method's receiver (e.g. `self: Rc<Self>`) to be object-safe, it needs to have the following property: - let `DynReceiver` be the receiver when `Self = dyn Trait` - let `ConcreteReceiver` be the receiver when `Self = T`, where `T` is some unknown `Sized` type that implements `Trait`, and is the erased type of the trait object. - `ConcreteReceiver` must implement `DispatchFromDyn<DynReceiver>` In the case of `Rc<Self>`, this requires `Rc<T>: DispatchFromDyn<Rc<dyn Trait>>` These rules are explained more thoroughly in the doc comment on `receiver_is_dispatchable` in object_safety.rs. r? @nikomatsakis and @eddyb cc @arielb1 @cramertj @withoutboats Special thanks to @nikomatsakis for getting me un-stuck when implementing the object-safety checks, and @eddyb for helping with the codegen parts. EDIT 2018-11-01: updated because CoerceSized has been replaced with DispatchFromDyn

bors · 2018-11-03T05:19:04Z

☀️ Test successful - status-appveyor, status-travis
Approved by: nikomatsakis
Pushing 3fc70e8 to master...

rust-highfive assigned nikomatsakis Sep 20, 2018

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Sep 20, 2018

mikeyhew mentioned this pull request Sep 20, 2018

Implement object-safety for arbitrary_self_types #50173

Closed

mikeyhew force-pushed the custom-receivers-object-safety branch from 9e50ace to 474f7f2 Compare September 20, 2018 16:25

mikeyhew force-pushed the custom-receivers-object-safety branch from 474f7f2 to d1a31d0 Compare September 21, 2018 06:16

nikomatsakis reviewed Sep 27, 2018

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nikomatsakis added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Oct 3, 2018

mikeyhew force-pushed the custom-receivers-object-safety branch from d1a31d0 to 166fc50 Compare October 4, 2018 03:45

mikeyhew commented Oct 4, 2018

View reviewed changes

src/librustc_typeck/coherence/builtin.rs Show resolved Hide resolved

mikeyhew commented Oct 4, 2018

View reviewed changes

Nemo157 mentioned this pull request Oct 4, 2018

Tracking issue for RFC 2033: Experimentally add coroutines to Rust #43122

Open

mikeyhew added 10 commits November 1, 2018 18:16

fix docs on trait

c29641e

tests were failing because I didn't wrap code snippets like in backticks. fixed that now, so hopefully tests will pass on travis

update DispatchFromDyn doctest

48d7f8d

fix error-index test

3c56d8d

Replace UncoeribleReceiver error message with UndispatchableReceiver

74ef46c

Add layout sanity checks in object safety

6f2a161

If object-safety checks succeed for a receiver type, make sure the receiver’s abi is a) a Scalar, when Self = () b) a ScalarPair, when Self = dyn Trait

Put backticks around field names, types and paths in error messages

b5b25f8

Added to `DispatchFromDyn` and `CoerceUnsized` error messages

add U: Trait to the param env during DispatchFromDyn check

eb997d7

also updated the doc on `receiver_is_dispatchable` to reflect current state of the implementation

Add a check for reprs that could change the ABI

a468da9

disallow `#[repr(C)] and `#[repr(packed)]` on structs implementing DispatchFromDyn because they will change the ABI from Scalar/ScalarPair to Aggregrate, resulting in an ICE during object-safety checks or codegen

Add comments explaining how codegen works for dyn Trait methods

192e7c4

mikeyhew force-pushed the custom-receivers-object-safety branch from 1b36350 to 192e7c4 Compare November 1, 2018 22:30

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Nov 3, 2018

bors merged commit 192e7c4 into rust-lang:master Nov 3, 2018

bors mentioned this pull request Nov 3, 2018

rustc_codegen_llvm: traitification of LLVM-specific CodegenCx and Builder methods #55627

Merged

mikeyhew mentioned this pull request Nov 3, 2018

Tracking issue for RFC 3519: arbitrary_self_types #44874

Open

9 tasks

Nemo157 mentioned this pull request Nov 25, 2018

Future is now object safe rust-lang/futures-rs#1348

Merged

realcr mentioned this pull request Nov 27, 2018

Remove usage of FutureObj freedomlayer/offset#134

Merged

nikomatsakis mentioned this pull request Jan 3, 2019

error: internal compiler error: src/librustc/ty/relate.rs:753: impossible case reached: can't relate: (T,) with Lifetime('_#1r) #57156

Closed

glandium mentioned this pull request Jan 24, 2019

Associate an allocator to boxes #50882

Closed

RalfJung mentioned this pull request Nov 7, 2019

Implement arbitrary-self dynamic method receivers rust-lang/miri#1038

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Take 2: Implement object-safety and dynamic dispatch for arbitrary_self_types #54383

Take 2: Implement object-safety and dynamic dispatch for arbitrary_self_types #54383

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bors commented Nov 3, 2018

		@@ -100,30 +100,6 @@ error[E0624]: associated constant `A` is private
		LL \| C::A; //~ ERROR associated constant `A` is private
		\| ^^^^

Take 2: Implement object-safety and dynamic dispatch for arbitrary_self_types #54383

Take 2: Implement object-safety and dynamic dispatch for arbitrary_self_types #54383

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