Introduce a no-op `PlaceMention` statement for `let _ =`. #102256

cjgillot · 2022-09-25T09:27:36Z

Fixes #54003
Fixes #80059
Split from #101500

This PR introduces a new PlaceMention statement dedicated to matches that neither introduce bindings nor ascribe types. Without this, all traces of the match would vanish from MIR, making it impossible to diagnose unsafety or use in #101500.

This allows to mark let _ = <unsafe union access or dereference> as requiring an unsafe block.
Nominating for lang team, as this introduces an extra error.

rust-highfive · 2022-09-25T09:27:39Z

r? @TaKO8Ki

(rust-highfive has picked a reviewer for you, use r? to override)

rustbot · 2022-09-25T09:27:39Z

This PR changes MIR

cc @oli-obk, @RalfJung, @JakobDegen, @davidtwco, @celinval, @vakaras

lukas-code · 2022-09-25T12:04:13Z

Does this also fix #80059?

cjgillot · 2022-09-25T12:36:22Z

@lukas-code, yes, I added a test.

RalfJung · 2022-09-25T13:40:15Z

This sounds great!

For Miri's rust-lang/miri#2360 it'd be awesome if those FakeRead could stick around in MIR a bit longer than they currently do (i.e., the pass that removes them should not be run with -Zmir-opt-level=0). Then we can also detect UB from incorrect union accesses / derefs for a _ place. (But if it's better to do that in a future PR, that's also fine.)

JakobDegen · 2022-09-25T13:49:56Z

We currently spec FakeRead as being a semantic nop; we could make an exception for the ForWildcard case, but it might be cleaner to have a new StatementKind::PlaceComputation or something like that

cjgillot · 2022-09-25T15:14:21Z

I made this a FakeRead because that's was the easiest. If a dedicated statement is better, I can add one. How should it be named?

cjgillot · 2022-09-25T15:16:59Z

We currently spec FakeRead as being a semantic nop; we could make an exception for the ForWildcard case, but it might be cleaner to have a new StatementKind::PlaceComputation or something like that

@JakobDegen I don't see the issue. FakeRead is an analysis helper for borrowck and unsafeck, and this PR uses it like this.

JakobDegen · 2022-09-25T15:19:20Z

I don't see the issue. FakeRead is an analysis helper for borrowck and unsafeck, and this PR uses it like this.

Sorry, that was in response to Ralf's comment about rust-lang/miri#2360 . For the purposes in this PR what you have is completely fine (in other words, if we wanted to use this to fix the miri issue it would stop being an analysis helper)

est31 · 2022-09-27T01:10:19Z

I've tried the example in #80059 for destructuring assignments to _ (so I removed the let to have fn foo(ptr: *const bool) { _ = *ptr; }), and there are similarly no errors. Does the PR fix the situation there too?

cjgillot · 2022-09-27T19:52:40Z

@est31 it does. Added to the test.

est31 · 2022-09-28T03:05:55Z

@cjgillot thanks! Would it be useful to add it to the test for #54003 as well?

cjgillot · 2022-09-28T11:39:29Z

src/test/ui/binding/issue-53114-safety-checks.rs

@@ -22,7 +22,7 @@ fn let_wild_gets_unsafe_field() {
    let p = P { a: &2, b: &3 };
    let _ = &p.b;  //~ ERROR    reference to packed field
    //~^  WARN will become a hard error
-    let _ = u1.a;  // #53114: should eventually signal error as well
+    let _ = u1.a;  //~ ERROR  [E0133]


@est31 this is the test for #54003.

I meant one with _ = only, without a let.

pnkfelix · 2022-10-06T17:01:29Z

We talked about this in the T-lang meeting.

The main concern, from the language side, was that we had carefully calibrated a boundary for what kinds of things should be considered "syntactic checks" (checking for missing unsafe { ... } is an instance of that), vs "flow analysis" (checking that your variable is initialized is an instance of that).
So that leads to an assumption that unsafeck should "naturally" be performed on something that reflects the structure of the AST, like THIR.

A contributor even spent some time on trying to port the unsafeck to THIR (or perhaps HIR, not sure from comments)
Anyway that work (Port improved unused_unsafe check to -Zthir_unsafeck #99379) was never finished, and the PR was abandoned.

So, there's an architectural question for T-compiler: I believe this PR is adding something useful today, and so I suspect we should land it.

But: Do we think there's any chance we'll resurrect #99379, or otherwise try to do unsafeck on THIR, in the near term? I would like an answer from T-compiler about that before moving forward on this PR.

@rustbot label I-compiler-nominated

cjgillot · 2022-10-06T19:12:42Z

When I originally wrote this commit, I did not intend it to be useful for unsafeck. My focus was #101500, which is "flow analysis".

While I agree with the syntactic/dataflow separation between THIR and MIR, I still think that this PR is useful:

it solves the linked issues now, without having to wait for the better THIR-based unsafeck;
it (possibly) eases the transition to THIR-based unsafeck, by removing a difference in behaviour;
it adds the necessary information to MIR for Perform unused assignment and unused variables lints on MIR. #101500 to happen.

RalfJung · 2022-10-07T13:10:51Z

But: Do we think there's any chance we'll resurrect #99379, or otherwise try to do unsafeck on THIR, in the near term? I would like an answer from T-compiler about that before moving forward on this PR.

If we do, then this PR just means MIR and THIR unsafety checking are more in line with each other, right? I don't quite understand what the concern is here.

RalfJung · 2022-10-07T13:12:00Z

While I agree with the syntactic/dataflow separation between THIR and MIR, I still think that this PR is useful:

I think this PR is crucial since it is a first step towards resolving rust-lang/miri#2360.

RalfJung · 2022-10-07T13:14:19Z

Btw, this will also fix #79735, won't it?

cjgillot · 2022-10-08T20:35:54Z

Btw, this will also fix #79735, won't it?

It should. I'll test it when I get my laptop working again.

A bit more problematic: this PR also introduces an error in this snippet, which currently passes borrow checking.

fn foo(mut n: Option<usize>) {
    let _ = if let Some(ref mut s) = n {
        s
    } else {
        &mut 0
        //~^ ERROR temporary value dropped while borrowed
    };
}

This error already happens for let _a = and match { ... } { _ => {} }. Should the error be kept or worked around?

cjgillot · 2023-03-09T19:03:44Z

Updated coverage info.
@bors r=lcnr

bors · 2023-03-09T19:03:46Z

📌 Commit 684de04 has been approved by lcnr

It is now in the queue for this repository.

bors · 2023-03-09T19:03:47Z

🌲 The tree is currently closed for pull requests below priority 100. This pull request will be tested once the tree is reopened.

bors · 2023-03-10T11:56:02Z

⌛ Testing commit 684de04 with merge d583342...

bors · 2023-03-10T14:38:28Z

☀️ Test successful - checks-actions
Approved by: lcnr
Pushing d583342 to master...

rust-timer · 2023-03-10T15:56:43Z

Finished benchmarking commit (d583342): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.2%	[-2.3%, -2.1%]	2
All ❌✅ (primary)	-	-	0

Cycles

This benchmark run did not return any relevant results for this metric.

…726,RalfJung Evaluate place expression in `PlaceMention` rust-lang#102256 introduces a `PlaceMention(place)` MIR statement which keep trace of `let _ = place` statements from surface rust, but without semantics. This PR proposes to change the behaviour of `let _ =` patterns with respect to the borrow-checker to verify that the bound place is live. Specifically, consider this code: ```rust let _ = { let a = 5; &a }; ``` This passes borrowck without error on stable. Meanwhile, replacing `_` by `_: _` or `_p` errors with "error[E0597]: `a` does not live long enough", [see playground](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=c448d25a7c205dc95a0967fe96bccce8). This PR *does not* change how `_` patterns behave with respect to initializedness: it remains ok to bind a moved-from place to `_`. The relevant test is `tests/ui/borrowck/let_underscore_temporary.rs`. Crater check found no regression. For consistency, this PR changes miri to evaluate the place found in `PlaceMention`, and report eventual dangling pointers found within it. r? `@RalfJung`

Evaluate place expression in `PlaceMention` rust-lang/rust#102256 introduces a `PlaceMention(place)` MIR statement which keep trace of `let _ = place` statements from surface rust, but without semantics. This PR proposes to change the behaviour of `let _ =` patterns with respect to the borrow-checker to verify that the bound place is live. Specifically, consider this code: ```rust let _ = { let a = 5; &a }; ``` This passes borrowck without error on stable. Meanwhile, replacing `_` by `_: _` or `_p` errors with "error[E0597]: `a` does not live long enough", [see playground](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=c448d25a7c205dc95a0967fe96bccce8). This PR *does not* change how `_` patterns behave with respect to initializedness: it remains ok to bind a moved-from place to `_`. The relevant test is `tests/ui/borrowck/let_underscore_temporary.rs`. Crater check found no regression. For consistency, this PR changes miri to evaluate the place found in `PlaceMention`, and report eventual dangling pointers found within it. r? `@RalfJung`

Pkgsrc changes: * Adjust patches and cargo checksums to new versions. * Adjust to not cross-build to 8.0, due to LLVM using c++17, so adjust USE_LANGUAGES. Upstream changes: Version 1.70.0 (2023-06-01) ========================== Language -------- - [Relax ordering rules for `asm!` operands] (rust-lang/rust#105798) - [Properly allow macro expanded `format_args` invocations to uses captures] (rust-lang/rust#106505) - [Lint ambiguous glob re-exports] (rust-lang/rust#107880) - [Perform const and unsafe checking for expressions in `let _ = expr` position.] (rust-lang/rust#102256) Compiler -------- - [Extend -Cdebuginfo with new options and named aliases] (rust-lang/rust#109808) This provides a smaller version of debuginfo for cases that only need line number information (`-Cdebuginfo=line-tables-only`), which may eventually become the default for `-Cdebuginfo=1`. - [Make `unused_allocation` lint against `Box::new` too] (rust-lang/rust#104363) - [Detect uninhabited types early in const eval] (rust-lang/rust#109435) - [Switch to LLD as default linker for {arm,thumb}v4t-none-eabi] (rust-lang/rust#109721) - [Add tier 3 target `loongarch64-unknown-linux-gnu`] (rust-lang/rust#96971) - [Add tier 3 target for `i586-pc-nto-qnx700` (QNX Neutrino RTOS, version 7.0)] (rust-lang/rust#109173), - [Insert alignment checks for pointer dereferences as debug assertions] (rust-lang/rust#98112) This catches undefined behavior at runtime, and may cause existing code to fail. Refer to Rust's [platform support page][platform-support-doc] for more information on Rust's tiered platform support. Libraries --------- - [Document NonZeroXxx layout guarantees] (rust-lang/rust#94786) - [Windows: make `Command` prefer non-verbatim paths] (rust-lang/rust#96391) - [Implement Default for some alloc/core iterators] (rust-lang/rust#99929) - [Fix handling of trailing bare CR in str::lines] (rust-lang/rust#100311) - [allow negative numeric literals in `concat!`] (rust-lang/rust#106844) - [Add documentation about the memory layout of `Cell`] (rust-lang/rust#106921) - [Use `partial_cmp` to implement tuple `lt`/`le`/`ge`/`gt`] (rust-lang/rust#108157) - [Stabilize `atomic_as_ptr`] (rust-lang/rust#108419) - [Stabilize `nonnull_slice_from_raw_parts`] (rust-lang/rust#97506) - [Partial stabilization of `once_cell`] (rust-lang/rust#105587) - [Stabilize `nonzero_min_max`] (rust-lang/rust#106633) - [Flatten/inline format_args!() and (string and int) literal arguments into format_args!()] (rust-lang/rust#106824) - [Stabilize movbe target feature] (rust-lang/rust#107711) - [don't splice from files into pipes in io::copy] (rust-lang/rust#108283) - [Add a builtin unstable `FnPtr` trait that is implemented for all function pointers] (rust-lang/rust#108080) This extends `Debug`, `Pointer`, `Hash`, `PartialEq`, `Eq`, `PartialOrd`, and `Ord` implementations for function pointers with all ABIs. Stabilized APIs --------------- - [`NonZero*::MIN/MAX`] (https://doc.rust-lang.org/stable/std/num/struct.NonZeroI8.html#associatedconstant.MIN) - [`BinaryHeap::retain`] (https://doc.rust-lang.org/stable/std/collections/struct.BinaryHeap.html#method.retain) - [`Default for std::collections::binary_heap::IntoIter`] (https://doc.rust-lang.org/stable/std/collections/binary_heap/struct.IntoIter.html) - [`Default for std::collections::btree_map::{IntoIter, Iter, IterMut}`] (https://doc.rust-lang.org/stable/std/collections/btree_map/struct.IntoIter.html) - [`Default for std::collections::btree_map::{IntoKeys, Keys}`] (https://doc.rust-lang.org/stable/std/collections/btree_map/struct.IntoKeys.html) - [`Default for std::collections::btree_map::{IntoValues, Values}`] (https://doc.rust-lang.org/stable/std/collections/btree_map/struct.IntoKeys.html) - [`Default for std::collections::btree_map::Range`] (https://doc.rust-lang.org/stable/std/collections/btree_map/struct.Range.html) - [`Default for std::collections::btree_set::{IntoIter, Iter}`] (https://doc.rust-lang.org/stable/std/collections/btree_set/struct.IntoIter.html) - [`Default for std::collections::btree_set::Range`] (https://doc.rust-lang.org/stable/std/collections/btree_set/struct.Range.html) - [`Default for std::collections::linked_list::{IntoIter, Iter, IterMut}`] (https://doc.rust-lang.org/stable/alloc/collections/linked_list/struct.IntoIter.html) - [`Default for std::vec::IntoIter`] (https://doc.rust-lang.org/stable/alloc/vec/struct.IntoIter.html#impl-Default-for-IntoIter%3CT,+A%3E) - [`Default for std::iter::Chain`] (https://doc.rust-lang.org/stable/std/iter/struct.Chain.html) - [`Default for std::iter::Cloned`] (https://doc.rust-lang.org/stable/std/iter/struct.Cloned.html) - [`Default for std::iter::Copied`] (https://doc.rust-lang.org/stable/std/iter/struct.Copied.html) - [`Default for std::iter::Enumerate`] (https://doc.rust-lang.org/stable/std/iter/struct.Enumerate.html) - [`Default for std::iter::Flatten`] (https://doc.rust-lang.org/stable/std/iter/struct.Flatten.html) - [`Default for std::iter::Fuse`] (https://doc.rust-lang.org/stable/std/iter/struct.Fuse.html) - [`Default for std::iter::Rev`] (https://doc.rust-lang.org/stable/std/iter/struct.Rev.html) - [`Default for std::slice::Iter`] (https://doc.rust-lang.org/stable/std/slice/struct.Iter.html) - [`Default for std::slice::IterMut`] (https://doc.rust-lang.org/stable/std/slice/struct.IterMut.html) - [`Rc::into_inner`] (https://doc.rust-lang.org/stable/alloc/rc/struct.Rc.html#method.into_inner) - [`Arc::into_inner`] (https://doc.rust-lang.org/stable/alloc/sync/struct.Arc.html#method.into_inner) - [`std::cell::OnceCell`] (https://doc.rust-lang.org/stable/std/cell/struct.OnceCell.html) - [`Option::is_some_and`] (https://doc.rust-lang.org/stable/std/option/enum.Option.html#method.is_some_and) - [`NonNull::slice_from_raw_parts`] (https://doc.rust-lang.org/stable/std/ptr/struct.NonNull.html#method.slice_from_raw_parts) - [`Result::is_ok_and`] (https://doc.rust-lang.org/stable/std/result/enum.Result.html#method.is_ok_and) - [`Result::is_err_and`] (https://doc.rust-lang.org/stable/std/result/enum.Result.html#method.is_err_and) - [`std::sync::atomic::Atomic*::as_ptr`] (https://doc.rust-lang.org/stable/std/sync/atomic/struct.AtomicU8.html#method.as_ptr) - [`std::io::IsTerminal`] (https://doc.rust-lang.org/stable/std/io/trait.IsTerminal.html) - [`std::os::linux::net::SocketAddrExt`] (https://doc.rust-lang.org/stable/std/os/linux/net/trait.SocketAddrExt.html) - [`std::os::unix::net::UnixDatagram::bind_addr`] (https://doc.rust-lang.org/stable/std/os/unix/net/struct.UnixDatagram.html#method.bind_addr) - [`std::os::unix::net::UnixDatagram::connect_addr`] (https://doc.rust-lang.org/stable/std/os/unix/net/struct.UnixDatagram.html#method.connect_addr) - [`std::os::unix::net::UnixDatagram::send_to_addr`] (https://doc.rust-lang.org/stable/std/os/unix/net/struct.UnixDatagram.html#method.send_to_addr) - [`std::os::unix::net::UnixListener::bind_addr`] (https://doc.rust-lang.org/stable/std/os/unix/net/struct.UnixListener.html#method.bind_addr) - [`std::path::Path::as_mut_os_str`] (https://doc.rust-lang.org/stable/std/path/struct.Path.html#method.as_mut_os_str) - [`std::sync::OnceLock`] (https://doc.rust-lang.org/stable/std/sync/struct.OnceLock.html) Cargo ----- - [Add `CARGO_PKG_README`] (rust-lang/cargo#11645) - [Make `sparse` the default protocol for crates.io] (rust-lang/cargo#11791) - [Accurately show status when downgrading dependencies] (rust-lang/cargo#11839) - [Use registry.default for login/logout] (rust-lang/cargo#11949) - [Stabilize `cargo logout`] (rust-lang/cargo#11950) Misc ---- - [Stabilize rustdoc `--test-run-directory`] (rust-lang/rust#103682) Compatibility Notes ------------------- - [Prevent stable `libtest` from supporting `-Zunstable-options`] (rust-lang/rust#109044) - [Perform const and unsafe checking for expressions in `let _ = expr` position.] (rust-lang/rust#102256) - [WebAssembly targets enable `sign-ext` and `mutable-globals` features in codegen] (rust-lang/rust#109807) This may cause incompatibility with older execution environments. - [Insert alignment checks for pointer dereferences as debug assertions] (rust-lang/rust#98112) This catches undefined behavior at runtime, and may cause existing code to fail. Internal Changes ---------------- These changes do not affect any public interfaces of Rust, but they represent significant improvements to the performance or internals of rustc and related tools. - [Upgrade to LLVM 16] (rust-lang/rust#109474) - [Use SipHash-1-3 instead of SipHash-2-4 for StableHasher] (rust-lang/rust#107925)

Pkgsrc changes: * Adjust patches and cargo checksums to new versions. * Add support for NetBSD/riscv64. Upstream changes: Version 1.70.0 (2023-06-01) ========================== Language -------- - [Relax ordering rules for `asm!` operands] (rust-lang/rust#105798) - [Properly allow macro expanded `format_args` invocations to uses captures] (rust-lang/rust#106505) - [Lint ambiguous glob re-exports] (rust-lang/rust#107880) - [Perform const and unsafe checking for expressions in `let _ = expr` position.] (rust-lang/rust#102256) Compiler -------- - [Extend -Cdebuginfo with new options and named aliases] (rust-lang/rust#109808) This provides a smaller version of debuginfo for cases that only need line number information (`-Cdebuginfo=line-tables-only`), which may eventually become the default for `-Cdebuginfo=1`. - [Make `unused_allocation` lint against `Box::new` too] (rust-lang/rust#104363) - [Detect uninhabited types early in const eval] (rust-lang/rust#109435) - [Switch to LLD as default linker for {arm,thumb}v4t-none-eabi] (rust-lang/rust#109721) - [Add tier 3 target `loongarch64-unknown-linux-gnu`] (rust-lang/rust#96971) - [Add tier 3 target for `i586-pc-nto-qnx700`(QNX Neutrino RTOS, version 7.0)] (rust-lang/rust#109173), - [Insert alignment checks for pointer dereferences as debug assertions] (rust-lang/rust#98112) This catches undefined behavior at runtime, and may cause existing code to fail. Refer to Rust's [platform support page][platform-support-doc] for more information on Rust's tiered platform support. Libraries --------- - [Document NonZeroXxx layout guarantees] (rust-lang/rust#94786) - [Windows: make `Command` prefer non-verbatim paths] (rust-lang/rust#96391) - [Implement Default for some alloc/core iterators] (rust-lang/rust#99929) - [Fix handling of trailing bare CR in str::lines] (rust-lang/rust#100311) - [allow negative numeric literals in `concat!`] (rust-lang/rust#106844) - [Add documentation about the memory layout of `Cell`] (rust-lang/rust#106921) - [Use `partial_cmp` to implement tuple `lt`/`le`/`ge`/`gt`] (rust-lang/rust#108157) - [Stabilize `atomic_as_ptr`] (rust-lang/rust#108419) - [Stabilize `nonnull_slice_from_raw_parts`] (rust-lang/rust#97506) - [Partial stabilization of `once_cell`] (rust-lang/rust#105587) - [Stabilize `nonzero_min_max`] (rust-lang/rust#106633) - [Flatten/inline format_args!() and (string and int) literal arguments into format_args!()] (rust-lang/rust#106824) - [Stabilize movbe target feature] (rust-lang/rust#107711) - [don't splice from files into pipes in io::copy] (rust-lang/rust#108283) - [Add a builtin unstable `FnPtr` trait that is implemented for all function pointers] (rust-lang/rust#108080) This extends `Debug`, `Pointer`, `Hash`, `PartialEq`, `Eq`, `PartialOrd`, and `Ord` implementations for function pointers with all ABIs. Stabilized APIs --------------- - [`NonZero*::MIN/MAX`] (https://doc.rust-lang.org/stable/std/num/struct.NonZeroI8.html#associatedconstant.MIN) - [`BinaryHeap::retain`] (https://doc.rust-lang.org/stable/std/collections/struct.BinaryHeap.html#method.retain) - [`Default for std::collections::binary_heap::IntoIter`] (https://doc.rust-lang.org/stable/std/collections/binary_heap/struct.IntoIter.html) - [`Default for std::collections::btree_map::{IntoIter, Iter, IterMut}`] (https://doc.rust-lang.org/stable/std/collections/btree_map/struct.IntoIter.html) - [`Default for std::collections::btree_map::{IntoKeys, Keys}`] (https://doc.rust-lang.org/stable/std/collections/btree_map/struct.IntoKeys.html) - [`Default for std::collections::btree_map::{IntoValues, Values}`] (https://doc.rust-lang.org/stable/std/collections/btree_map/struct.IntoKeys.html) - [`Default for std::collections::btree_map::Range`] (https://doc.rust-lang.org/stable/std/collections/btree_map/struct.Range.html) - [`Default for std::collections::btree_set::{IntoIter, Iter}`] (https://doc.rust-lang.org/stable/std/collections/btree_set/struct.IntoIter.html) - [`Default for std::collections::btree_set::Range`] (https://doc.rust-lang.org/stable/std/collections/btree_set/struct.Range.html) - [`Default for std::collections::linked_list::{IntoIter, Iter, IterMut}`] (https://doc.rust-lang.org/stable/alloc/collections/linked_list/struct.IntoIter.html) - [`Default for std::vec::IntoIter`] (https://doc.rust-lang.org/stable/alloc/vec/struct.IntoIter.html#impl-Default-for-IntoIter%3CT,+A%3E) - [`Default for std::iter::Chain`] (https://doc.rust-lang.org/stable/std/iter/struct.Chain.html) - [`Default for std::iter::Cloned`] (https://doc.rust-lang.org/stable/std/iter/struct.Cloned.html) - [`Default for std::iter::Copied`] (https://doc.rust-lang.org/stable/std/iter/struct.Copied.html) - [`Default for std::iter::Enumerate`] (https://doc.rust-lang.org/stable/std/iter/struct.Enumerate.html) - [`Default for std::iter::Flatten`] (https://doc.rust-lang.org/stable/std/iter/struct.Flatten.html) - [`Default for std::iter::Fuse`] (https://doc.rust-lang.org/stable/std/iter/struct.Fuse.html) - [`Default for std::iter::Rev`] (https://doc.rust-lang.org/stable/std/iter/struct.Rev.html) - [`Default for std::slice::Iter`] (https://doc.rust-lang.org/stable/std/slice/struct.Iter.html) - [`Default for std::slice::IterMut`] (https://doc.rust-lang.org/stable/std/slice/struct.IterMut.html) - [`Rc::into_inner`] (https://doc.rust-lang.org/stable/alloc/rc/struct.Rc.html#method.into_inner) - [`Arc::into_inner`] (https://doc.rust-lang.org/stable/alloc/sync/struct.Arc.html#method.into_inner) - [`std::cell::OnceCell`] (https://doc.rust-lang.org/stable/std/cell/struct.OnceCell.html) - [`Option::is_some_and`] (https://doc.rust-lang.org/stable/std/option/enum.Option.html#method.is_some_and) - [`NonNull::slice_from_raw_parts`] (https://doc.rust-lang.org/stable/std/ptr/struct.NonNull.html#method.slice_from_raw_parts) - [`Result::is_ok_and`] (https://doc.rust-lang.org/stable/std/result/enum.Result.html#method.is_ok_and) - [`Result::is_err_and`] (https://doc.rust-lang.org/stable/std/result/enum.Result.html#method.is_err_and) - [`std::sync::atomic::Atomic*::as_ptr`] (https://doc.rust-lang.org/stable/std/sync/atomic/struct.AtomicU8.html#method.as_ptr) - [`std::io::IsTerminal`] (https://doc.rust-lang.org/stable/std/io/trait.IsTerminal.html) - [`std::os::linux::net::SocketAddrExt`] (https://doc.rust-lang.org/stable/std/os/linux/net/trait.SocketAddrExt.html) - [`std::os::unix::net::UnixDatagram::bind_addr`] (https://doc.rust-lang.org/stable/std/os/unix/net/struct.UnixDatagram.html#method.bind_addr) - [`std::os::unix::net::UnixDatagram::connect_addr`] (https://doc.rust-lang.org/stable/std/os/unix/net/struct.UnixDatagram.html#method.connect_addr) - [`std::os::unix::net::UnixDatagram::send_to_addr`] (https://doc.rust-lang.org/stable/std/os/unix/net/struct.UnixDatagram.html#method.send_to_addr) - [`std::os::unix::net::UnixListener::bind_addr`] (https://doc.rust-lang.org/stable/std/os/unix/net/struct.UnixListener.html#method.bind_addr) - [`std::path::Path::as_mut_os_str`] (https://doc.rust-lang.org/stable/std/path/struct.Path.html#method.as_mut_os_str) - [`std::sync::OnceLock`] (https://doc.rust-lang.org/stable/std/sync/struct.OnceLock.html) Cargo ----- - [Add `CARGO_PKG_README`] (rust-lang/cargo#11645) - [Make `sparse` the default protocol for crates.io] (rust-lang/cargo#11791) - [Accurately show status when downgrading dependencies] (rust-lang/cargo#11839) - [Use registry.default for login/logout] (rust-lang/cargo#11949) - [Stabilize `cargo logout`] (rust-lang/cargo#11950) Misc ---- - [Stabilize rustdoc `--test-run-directory`] (rust-lang/rust#103682) Compatibility Notes ------------------- - [Prevent stable `libtest` from supporting `-Zunstable-options`] (rust-lang/rust#109044) - [Perform const and unsafe checking for expressions in `let _ = expr` position.] (rust-lang/rust#102256) - [WebAssembly targets enable `sign-ext` and `mutable-globals` features in codegen] (rust-lang/rust#109807) This may cause incompatibility with older execution environments. - [Insert alignment checks for pointer dereferences as debug assertions] (rust-lang/rust#98112) This catches undefined behavior at runtime, and may cause existing code to fail. Internal Changes ---------------- These changes do not affect any public interfaces of Rust, but they represent significant improvements to the performance or internals of rustc and related tools. - [Upgrade to LLVM 16] (rust-lang/rust#109474) - [Use SipHash-1-3 instead of SipHash-2-4 for StableHasher] (rust-lang/rust#107925)

…RalfJung Allow partially moved values in match This PR attempts to unify the behaviour between `let _ = PLACE`, `let _: TY = PLACE;` and `match PLACE { _ => {} }`. The logical conclusion is that the `match` version should not check for uninitialised places nor check that borrows are still live. The `match PLACE {}` case is handled by keeping a `FakeRead` in the unreachable fallback case to verify that `PLACE` has a legal value. Schematically, `match PLACE { arms }` in surface rust becomes in MIR: ```rust PlaceMention(PLACE) match PLACE { // Decision tree for the explicit arms arms, // An extra fallback arm _ => { FakeRead(ForMatchedPlace, PLACE); unreachable } } ``` `match *borrow { _ => {} }` continues to check that `*borrow` is live, but does not read the value. `match *borrow {}` both checks that `*borrow` is live, and fake-reads the value. Continuation of ~rust-lang#102256 ~rust-lang#104844 Fixes rust-lang#99180 rust-lang#53114

Allow partially moved values in match This PR attempts to unify the behaviour between `let _ = PLACE`, `let _: TY = PLACE;` and `match PLACE { _ => {} }`. The logical conclusion is that the `match` version should not check for uninitialised places nor check that borrows are still live. The `match PLACE {}` case is handled by keeping a `FakeRead` in the unreachable fallback case to verify that `PLACE` has a legal value. Schematically, `match PLACE { arms }` in surface rust becomes in MIR: ```rust PlaceMention(PLACE) match PLACE { // Decision tree for the explicit arms arms, // An extra fallback arm _ => { FakeRead(ForMatchedPlace, PLACE); unreachable } } ``` `match *borrow { _ => {} }` continues to check that `*borrow` is live, but does not read the value. `match *borrow {}` both checks that `*borrow` is live, and fake-reads the value. Continuation of ~rust-lang/rust#102256 ~rust-lang/rust#104844 Fixes rust-lang/rust#99180 rust-lang/rust#53114

cjgillot added the I-lang-nominated Nominated for discussion during a lang team meeting. label Sep 25, 2022

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rustbot added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Sep 25, 2022

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Sep 25, 2022

RalfJung mentioned this pull request Sep 25, 2022

Miri misses UB in place expressions when there are "_" patterns rust-lang/miri#2360

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cjgillot force-pushed the let-under branch 2 times, most recently from dcbbb69 to 6fe81fe Compare September 27, 2022 17:50

cjgillot commented Sep 28, 2022

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rustbot added the I-compiler-nominated Nominated for discussion during a compiler team meeting. label Oct 6, 2022

cjgillot force-pushed the let-under branch from de55ec0 to d51a47f Compare October 8, 2022 16:53

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cjgillot force-pushed the let-under branch from d51a47f to e8dd47b Compare October 9, 2022 09:38

cjgillot force-pushed the let-under branch from 5beb6ea to 684de04 Compare March 9, 2023 17:52

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 Mar 9, 2023

bors mentioned this pull request Mar 10, 2023

Rollup of 9 pull requests #108977

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bors added the merged-by-bors This PR was explicitly merged by bors. label Mar 10, 2023

bors merged commit d583342 into rust-lang:master Mar 10, 2023

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cjgillot deleted the let-under branch March 10, 2023 14:49

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Remove box_syntax #108471

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Remove box expressions from HIR #108958

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scottmcm mentioned this pull request Mar 22, 2023

warning for UB ! exprs is too light #56190

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RalfJung mentioned this pull request Apr 24, 2023

MIR building optimizes away some place expressions around "_" patterns even with -Zmir-opt-level=0 #99180

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lcnr mentioned this pull request May 4, 2023

1.70.0 release notes #111006

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pravic mentioned this pull request May 29, 2023

Github rejects rendering of RELEASES.md #112058

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RalfJung mentioned this pull request Oct 30, 2023

"!" is the only type that is unsafe to raw-ptr-deref into a "_" pattern #79735

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Introduce a no-op `PlaceMention` statement for `let _ =`. #102256

Introduce a no-op `PlaceMention` statement for `let _ =`. #102256

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Introduce a no-op PlaceMention statement for let _ =. #102256

Introduce a no-op PlaceMention statement for let _ =. #102256

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Introduce a no-op `PlaceMention` statement for `let _ =`. #102256

Introduce a no-op `PlaceMention` statement for `let _ =`. #102256

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