Ban multi-trait objects via trait aliases #59445

alexreg · 2019-03-26T18:27:59Z

Obviously, multi-trait objects are not normally supported, so they should not be supported via trait aliases.

This has been factored out from the previous PR #55994 (see point 1).

RELNOTES:

We now allow dyn Send + fmt::Debug with equivalent semantics to dyn fmt::Debug + Send.
That is, the order of the mentioned traits does not matter wrt. principal/not-principal traits.
This is a small change that might deserve a mention in the blog post because it is a language change but most likely not.

See https://github.com/rust-lang/rust/blob/ce2ee305f9165c037ecddddb5792588a15ff6c37/src/test/ui/traits/wf-trait-object-reverse-order.rs.

// @Centril

Centril

Implementation looks mostly good aside from comments below... The diagnostics look great.

However, I think some more tests are needed. In particular, it would be nice to exercise the recursive behavior here including things like dyn A + B where trait A = C + D;, trait B = E + F, trait F = G + 'static; and various other combinations including auto traits, region constraints, where clauses on the trait alias, and so on.

src/librustc/traits/mod.rs

src/librustc/traits/util.rs

src/librustc_typeck/astconv.rs

Centril · 2019-03-30T17:44:17Z

src/librustc_typeck/astconv.rs

@@ -1175,14 +1198,13 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
                } else {
                    self.re_infer(span, None).unwrap_or_else(|| {
                        span_err!(tcx.sess, span, E0228,
-                                  "the lifetime bound for this object type cannot be deduced \
-                                   from context; please supply an explicit bound");
+                            "the lifetime bound for this object type cannot be deduced \


Suggested change

"the lifetime bound for this object type cannot be deduced \

"the lifetime bound for this object type cannot be inferred \

while reading this PR again, I noticed this... we use "infer" elsewhere and so we should prefer that everywhere instead of C++isms like "deduce".

That should be a separate PR I think. You're welcome to make it though, and I can review. ;-)

@alexreg Sure; leaving it here (unresolved) for visibility and as a reminder ;)

@Centril With this PR merging now, just a note for you that this is unresolved, in case you want to create an issue or PR for it yourself.

oli-obk · 2019-05-21T22:17:21Z

is the beta cut already successfull even without #60999 having been merged?

alexreg · 2019-05-21T22:39:33Z

Not 100% sure, but @Centril and I thought that by the time this PR works its way up the queue now, the toolstate problem should have disappeared at least, so it should be no problem.

bors · 2019-05-22T00:44:19Z

⌛ Testing commit ce2ee30 with merge de414067da0f3f6c80530b9ba2a9f98e90c2f484...

bors · 2019-05-22T00:50:08Z

💔 Test failed - checks-travis

rust-highfive · 2019-05-22T00:50:09Z

The job x86_64-gnu-distcheck 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.

[00:03:51]    Compiling textwrap v0.11.0
[00:03:53] error: failed to run custom build command for `rand_chacha v0.1.1`
[00:03:53] process didn't exit successfully: `/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-bootstrap-tools/debug/build/rand_chacha-264db25efa48e2e1/build-script-build` (exit code: 101)
[00:03:53] --- stdout
[00:03:53] cargo:rerun-if-changed=build.rs
[00:03:53] --- stderr
[00:03:53] thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', src/libcore/option.rs:345:21
[00:03:53] note: Run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
[00:03:53] thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', src/libcore/option.rs:345:21
[00:03:53] thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', src/libcore/option.rs:345:21
[00:03:53] note: Run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
[00:03:53] thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Error { kind: Other("could not probe for `std`") }', src/libcore/result.rs:997:5
[00:03:53] 
[00:03:53] warning: build failed, waiting for other jobs to finish...
[00:03:53] error: failed to run custom build command for `rand_pcg v0.1.2`
[00:03:53] process didn't exit successfully: `/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-bootstrap-tools/debug/build/rand_pcg-77510ee48e3cc776/build-script-build` (exit code: 101)
[00:03:53] process didn't exit successfully: `/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-bootstrap-tools/debug/build/rand_pcg-77510ee48e3cc776/build-script-build` (exit code: 101)
[00:03:53] --- stdout
[00:03:53] cargo:rerun-if-changed=build.rs
[00:03:53] --- stderr
[00:03:53] thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', src/libcore/option.rs:345:21
[00:03:53] note: Run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
[00:03:53] thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', src/libcore/option.rs:345:21
[00:03:53] thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', src/libcore/option.rs:345:21
[00:03:53] note: Run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
[00:03:53] thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Error { kind: Other("could not probe for `std`") }', src/libcore/result.rs:997:5
[00:03:53] 
[00:03:53] warning: build failed, waiting for other jobs to finish...
[00:03:53] warning: build failed, waiting for other jobs to finish...
[00:03:56] error: failed to compile `cargo-vendor v0.1.22`, intermediate artifacts can be found at `/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-bootstrap-tools`
[00:03:56] Caused by:
[00:03:56]   build failed
[00:03:56] 
[00:03:56] 
[00:03:56] 
[00:03:56] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "install" "-j" "4" "--locked" "--color" "always" "--force" "--debug" "--vers" "0.1.22" "cargo-vendor"
[00:03:56] 
[00:03:56] 
[00:03:56] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test distcheck
[00:03:56] Build completed unsuccessfully in 0:00:34
---
travis_time:end:2065bca2:start=1558486191740556448,finish=1558486191752078901,duration=11522453
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:07ad57f0
$ 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:1213ecc0
travis_time:start:1213ecc0
$ 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:0298c0e0
$ 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)

mati865 · 2019-05-22T08:14:37Z

#61027 already broke Clippy so for sure tools don't block it anymore.

Centril · 2019-05-22T08:19:44Z

@bors retry

bors · 2019-05-22T08:22:28Z

⌛ Testing commit ce2ee30 with merge 37ff5d3...

@Centril

…=oli-obk Ban multi-trait objects via trait aliases Obviously, multi-trait objects are not normally supported, so they should not be supported via trait aliases. This has been factored out from the previous PR #55994 (see point 1). r? @Centril CC @nikomatsakis ------------------ ### RELNOTES: We now allow `dyn Send + fmt::Debug` with equivalent semantics to `dyn fmt::Debug + Send`. That is, the order of the mentioned traits does not matter wrt. principal/not-principal traits. This is a small change that might deserve a mention in the blog post because it is a language change but most likely not. See https://github.com/rust-lang/rust/blob/ce2ee305f9165c037ecddddb5792588a15ff6c37/src/test/ui/traits/wf-trait-object-reverse-order.rs. // @Centril

bors · 2019-05-22T11:08:13Z

☀️ Test successful - checks-travis, status-appveyor
Approved by: oli-obk
Pushing 37ff5d3 to master...

Pkgsrc changes: * NetBSD/sparc64 disabling of "packed" removed ("packed" removed upstream) * Adapt src_libstd_build.rs patch, update sed'ing of .cargo-checksum.json Build verified on NetBSD 8.0/amd64. Upstream changes: Version 1.36.0 (2019-07-04) ========================== Language -------- - [Non-Lexical Lifetimes are now enabled on the 2015 edition.][59114] - [The order of traits in trait objects no longer affects the semantics of that object.][59445] e.g. `dyn Send + fmt::Debug` is now equivalent to `dyn fmt::Debug + Send`, where this was previously not the case. Libraries --------- - [`HashMap`'s implementation has been replaced with `hashbrown::HashMap` implem entation.][58623] - [`TryFromSliceError` now implements `From<Infallible>`.][60318] - [`mem::needs_drop` is now available as a const fn.][60364] - [`alloc::Layout::from_size_align_unchecked` is now available as a const fn.][6 0370] - [`String` now implements `BorrowMut<str>`.][60404] - [`io::Cursor` now implements `Default`.][60234] - [Both `NonNull::{dangling, cast}` are now const fns.][60244] - [The `alloc` crate is now stable.][59675] `alloc` allows you to use a subset of `std` (e.g. `Vec`, `Box`, `Arc`) in `#![no_std]` environments if the environment has access to heap memory allocation. - [`String` now implements `From<&String>`.][59825] - [You can now pass multiple arguments to the `dbg!` macro.][59826] `dbg!` will return a tuple of each argument when there is multiple arguments. - [`Result::{is_err, is_ok}` are now `#[must_use]` and will produce a warning if not used.][59648] Stabilized APIs --------------- - [`VecDeque::rotate_left`] - [`VecDeque::rotate_right`] - [`Iterator::copied`] - [`io::IoSlice`] - [`io::IoSliceMut`] - [`Read::read_vectored`] - [`Write::write_vectored`] - [`str::as_mut_ptr`] - [`mem::MaybeUninit`] - [`pointer::align_offset`] - [`future::Future`] - [`task::Context`] - [`task::RawWaker`] - [`task::RawWakerVTable`] - [`task::Waker`] - [`task::Poll`] Cargo ----- - [Cargo will now produce an error if you attempt to use the name of a required dependency as a feature.][cargo/6860] - [You can now pass the `--offline` flag to run cargo without accessing the netw ork.][cargo/6934] You can find further change's in [Cargo's 1.36.0 release notes][cargo-1-36-0]. Clippy ------ There have been numerous additions and fixes to clippy, see [Clippy's 1.36.0 rel ease notes][clippy-1-36-0] for more details. Misc ---- Compatibility Notes ------------------- - [`std::arch::x86::_rdtsc` returns `u64` instead of `i64`][stdsimd/559] - [`std::arch::x86_64::_mm_shuffle_ps` takes an `i32` instead of `u32` for `mask `][stdsimd/522] - With the stabilisation of `mem::MaybeUninit`, `mem::uninitialized` use is no longer recommended, and will be deprecated in 1.38.0. [60318]: rust-lang/rust#60318 [60364]: rust-lang/rust#60364 [60370]: rust-lang/rust#60370 [60404]: rust-lang/rust#60404 [60234]: rust-lang/rust#60234 [60244]: rust-lang/rust#60244 [58623]: rust-lang/rust#58623 [59648]: rust-lang/rust#59648 [59675]: rust-lang/rust#59675 [59825]: rust-lang/rust#59825 [59826]: rust-lang/rust#59826 [59445]: rust-lang/rust#59445 [59114]: rust-lang/rust#59114 [cargo/6860]: rust-lang/cargo#6860 [cargo/6934]: rust-lang/cargo#6934 [`VecDeque::rotate_left`]: https://doc.rust-lang.org/std/collections/struct.VecDeque.html#method.rotate_left [`VecDeque::rotate_right`]: https://doc.rust-lang.org/std/collections/struct.VecDeque.html#method.rotate_right [`Iterator::copied`]: https://doc.rust-lang.org/std/iter/trait.Iterator.html#tymethod.copied [`io::IoSlice`]: https://doc.rust-lang.org/std/io/struct.IoSlice.html [`io::IoSliceMut`]: https://doc.rust-lang.org/std/io/struct.IoSliceMut.html [`Read::read_vectored`]: https://doc.rust-lang.org/std/io/trait.Read.html#method.read_vectored [`Write::write_vectored`]: https://doc.rust-lang.org/std/io/trait.Write.html#method.write_vectored [`str::as_mut_ptr`]: https://doc.rust-lang.org/std/primitive.str.html#method.as_mut_ptr [`mem::MaybeUninit`]: https://doc.rust-lang.org/std/mem/union.MaybeUninit.html [`pointer::align_offset`]: https://doc.rust-lang.org/std/primitive.pointer.html#method.align_offset [`future::Future`]: https://doc.rust-lang.org/std/future/trait.Future.html [`task::Context`]: https://doc.rust-lang.org/beta/std/task/struct.Context.html [`task::RawWaker`]: https://doc.rust-lang.org/beta/std/task/struct.RawWaker.html [`task::RawWakerVTable`]: https://doc.rust-lang.org/beta/std/task/struct.RawWakerVTable.html [`task::Waker`]: https://doc.rust-lang.org/beta/std/task/struct.Waker.html [`task::Poll`]: https://doc.rust-lang.org/beta/std/task/enum.Poll.html [clippy-1-36-0]: https://github.com/rust-lang/rust-clippy/blob/master/CHANGELOG.md#rust-136 [cargo-1-36-0]: https://github.com/rust-lang/cargo/blob/master/CHANGELOG.md#cargo-136-2019-07-04 [stdsimd/522]: rust-lang/stdarch#522 [stdsimd/559]: rust-lang/stdarch#559

rust-highfive assigned Centril Mar 26, 2019

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Mar 26, 2019