Tracking Issue for RFC 3606: Drop temporaries in tail expressions before local variables #123739
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A-edition-2024
Area: The 2024 edition
B-RFC-approved
Blocker: Approved by a merged RFC but not yet implemented.
C-tracking-issue
Category: A tracking issue for an RFC or an unstable feature.
F-shorter_tail_lifetimes
`#![feature(shorter_tail_lifetimes)]`
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Status: Needs documentation.
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traviscross
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(assigning self as lang team liason to ensure things progress here for 2024 edition) |
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Jun 14, 2024
…fetime, r=estebank,davidtwco Place tail expression behind terminating scope This PR implements rust-lang#123739 so that we can do further experiments in nightly. A little rewrite has been applied to `for await` lowering. It was previously `unsafe { Pin::unchecked_new(into_async_iter(..)) }`. Under the edition 2024 rule, however, `into_async_iter` gets dropped at the end of the `unsafe` block. This presumably the first Edition 2024 migration rule goes by hoisting `into_async_iter(..)` into `match` one level above, so it now looks like the following. ```rust match into_async_iter($iter_expr) { ref mut iter => match unsafe { Pin::unchecked_new(iter) } { ... } } ```
jieyouxu
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Jun 19, 2024
…fetime, r=estebank,davidtwco Place tail expression behind terminating scope This PR implements rust-lang#123739 so that we can do further experiments in nightly. A little rewrite has been applied to `for await` lowering. It was previously `unsafe { Pin::unchecked_new(into_async_iter(..)) }`. Under the edition 2024 rule, however, `into_async_iter` gets dropped at the end of the `unsafe` block. This presumably the first Edition 2024 migration rule goes by hoisting `into_async_iter(..)` into `match` one level above, so it now looks like the following. ```rust match into_async_iter($iter_expr) { ref mut iter => match unsafe { Pin::unchecked_new(iter) } { ... } } ```
jieyouxu
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Jun 19, 2024
…fetime, r=estebank,davidtwco Place tail expression behind terminating scope This PR implements rust-lang#123739 so that we can do further experiments in nightly. A little rewrite has been applied to `for await` lowering. It was previously `unsafe { Pin::unchecked_new(into_async_iter(..)) }`. Under the edition 2024 rule, however, `into_async_iter` gets dropped at the end of the `unsafe` block. This presumably the first Edition 2024 migration rule goes by hoisting `into_async_iter(..)` into `match` one level above, so it now looks like the following. ```rust match into_async_iter($iter_expr) { ref mut iter => match unsafe { Pin::unchecked_new(iter) } { ... } } ```
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Jun 19, 2024
Rollup merge of rust-lang#125293 - dingxiangfei2009:tail-expr-temp-lifetime, r=estebank,davidtwco Place tail expression behind terminating scope This PR implements rust-lang#123739 so that we can do further experiments in nightly. A little rewrite has been applied to `for await` lowering. It was previously `unsafe { Pin::unchecked_new(into_async_iter(..)) }`. Under the edition 2024 rule, however, `into_async_iter` gets dropped at the end of the `unsafe` block. This presumably the first Edition 2024 migration rule goes by hoisting `into_async_iter(..)` into `match` one level above, so it now looks like the following. ```rust match into_async_iter($iter_expr) { ref mut iter => match unsafe { Pin::unchecked_new(iter) } { ... } } ```
matthiaskrgr
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Aug 20, 2024
…op-order, r=jieyouxu Lint on tail expr drop order change in Edition 2024 This lint warns users to consider extra discretion on the effect of a transposed drop order arising from Edition 2024, which involves temporaries in tail expression location with significant drop implementation. cc `@traviscross` Tracking: - rust-lang#123739
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Aug 21, 2024
Rollup merge of rust-lang#128662 - dingxiangfei2009:lint-tail-expr-drop-order, r=jieyouxu Lint on tail expr drop order change in Edition 2024 This lint warns users to consider extra discretion on the effect of a transposed drop order arising from Edition 2024, which involves temporaries in tail expression location with significant drop implementation. cc `@traviscross` Tracking: - rust-lang#123739
This was referenced Aug 26, 2024
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bors
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Oct 8, 2024
…t-2, r=<try> Reduce false positives of tail-expr-drop-order from consumed values (attempt #2) r? `@nikomatsakis` Tracked by rust-lang#123739. Related to rust-lang#129864 but not replacing, yet. Related to rust-lang#130836. This is an implementation of the approach suggested in the [Zulip stream](https://rust-lang.zulipchat.com/#narrow/stream/213817-t-lang/topic/temporary.20drop.20order.20changes). A new MIR statement `BackwardsIncompatibleDrop` is added to the MIR syntax. The lint now works by inspecting possibly live move paths before at the `BackwardsIncompatibleDrop` location and the actual drop under the current edition, which should be one before Edition 2024 in practice.
bors
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Oct 12, 2024
…t-2, r=<try> Reduce false positives of tail-expr-drop-order from consumed values (attempt #2) r? `@nikomatsakis` Tracked by rust-lang#123739. Related to rust-lang#129864 but not replacing, yet. Related to rust-lang#130836. This is an implementation of the approach suggested in the [Zulip stream](https://rust-lang.zulipchat.com/#narrow/stream/213817-t-lang/topic/temporary.20drop.20order.20changes). A new MIR statement `BackwardsIncompatibleDrop` is added to the MIR syntax. The lint now works by inspecting possibly live move paths before at the `BackwardsIncompatibleDrop` location and the actual drop under the current edition, which should be one before Edition 2024 in practice.
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Oct 23, 2024
…-tail-lifetimes, r=lcnr Stabilize shorter-tail-lifetimes Close rust-lang#131445 Tracked by rust-lang#123739 We found a test case `tests/ui/drop/drop_order.rs` that had not been covered by the change. The test fixture is fixed now with the correct expectation.
matthiaskrgr
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Oct 24, 2024
…-tail-lifetimes, r=lcnr Stabilize shorter-tail-lifetimes Close rust-lang#131445 Tracked by rust-lang#123739 We found a test case `tests/ui/drop/drop_order.rs` that had not been covered by the change. The test fixture is fixed now with the correct expectation.
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Oct 24, 2024
Rollup merge of rust-lang#131983 - dingxiangfei2009:stabilize-shorter-tail-lifetimes, r=lcnr Stabilize shorter-tail-lifetimes Close rust-lang#131445 Tracked by rust-lang#123739 We found a test case `tests/ui/drop/drop_order.rs` that had not been covered by the change. The test fixture is fixed now with the correct expectation.
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hlinnaka
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Nov 3, 2024
Compiling with nightly rust compiler, I'm getting a lot of errors like this:
error: `if let` assigns a shorter lifetime since Edition 2024
--> proxy/src/auth/backend/jwt.rs:226:16
|
226 | if let Some(permit) = self.try_acquire_permit() {
| ^^^^^^^^^^^^^^^^^^^-------------------------
| |
| this value has a significant drop implementation which may observe a major change in drop order and requires your discretion
|
= warning: this changes meaning in Rust 2024
= note: for more information, see issue #124085 <rust-lang/rust#124085>
help: the value is now dropped here in Edition 2024
--> proxy/src/auth/backend/jwt.rs:241:13
|
241 | } else {
| ^
note: the lint level is defined here
--> proxy/src/lib.rs:8:5
|
8 | rust_2024_compatibility
| ^^^^^^^^^^^^^^^^^^^^^^^
= note: `#[deny(if_let_rescope)]` implied by `#[deny(rust_2024_compatibility)]`
and this:
error: these values and local bindings have significant drop implementation that will have a different drop order from that of Edition 2021
--> proxy/src/auth/backend/jwt.rs:376:18
|
369 | let client = Client::builder()
| ------ these values have significant drop implementation and will observe changes in drop order under Edition 2024
...
376 | map: DashMap::default(),
| ^^^^^^^^^^^^^^^^^^
|
= warning: this changes meaning in Rust 2024
= note: for more information, see issue #123739 <rust-lang/rust#123739>
= note: `#[deny(tail_expr_drop_order)]` implied by `#[deny(rust_2024_compatibility)]`
They are caused by the `rust_2024_compatibility` lint option.
When we actually switch to the 2024 edition, it makes sense to go
through all these and check that the drop order changes don't break
anything, but in the meanwhile, there's no easy way to avoid these
errors. Disable it, to allow compiling with nightly again.
hlinnaka
added a commit
to neondatabase/neon
that referenced
this issue
Nov 3, 2024
Compiling with nightly rust compiler, I'm getting a lot of errors like this:
error: `if let` assigns a shorter lifetime since Edition 2024
--> proxy/src/auth/backend/jwt.rs:226:16
|
226 | if let Some(permit) = self.try_acquire_permit() {
| ^^^^^^^^^^^^^^^^^^^-------------------------
| |
| this value has a significant drop implementation which may observe a major change in drop order and requires your discretion
|
= warning: this changes meaning in Rust 2024
= note: for more information, see issue #124085 <rust-lang/rust#124085>
help: the value is now dropped here in Edition 2024
--> proxy/src/auth/backend/jwt.rs:241:13
|
241 | } else {
| ^
note: the lint level is defined here
--> proxy/src/lib.rs:8:5
|
8 | rust_2024_compatibility
| ^^^^^^^^^^^^^^^^^^^^^^^
= note: `#[deny(if_let_rescope)]` implied by `#[deny(rust_2024_compatibility)]`
and this:
error: these values and local bindings have significant drop implementation that will have a different drop order from that of Edition 2021
--> proxy/src/auth/backend/jwt.rs:376:18
|
369 | let client = Client::builder()
| ------ these values have significant drop implementation and will observe changes in drop order under Edition 2024
...
376 | map: DashMap::default(),
| ^^^^^^^^^^^^^^^^^^
|
= warning: this changes meaning in Rust 2024
= note: for more information, see issue #123739 <rust-lang/rust#123739>
= note: `#[deny(tail_expr_drop_order)]` implied by `#[deny(rust_2024_compatibility)]`
They are caused by the `rust_2024_compatibility` lint option.
When we actually switch to the 2024 edition, it makes sense to go
through all these and check that the drop order changes don't break
anything, but in the meanwhile, there's no easy way to avoid these
errors. Disable it, to allow compiling with nightly again.
hlinnaka
added a commit
to neondatabase/neon
that referenced
this issue
Nov 4, 2024
Compiling with nightly rust compiler, I'm getting a lot of errors like this:
error: `if let` assigns a shorter lifetime since Edition 2024
--> proxy/src/auth/backend/jwt.rs:226:16
|
226 | if let Some(permit) = self.try_acquire_permit() {
| ^^^^^^^^^^^^^^^^^^^-------------------------
| |
| this value has a significant drop implementation which may observe a major change in drop order and requires your discretion
|
= warning: this changes meaning in Rust 2024
= note: for more information, see issue #124085 <rust-lang/rust#124085>
help: the value is now dropped here in Edition 2024
--> proxy/src/auth/backend/jwt.rs:241:13
|
241 | } else {
| ^
note: the lint level is defined here
--> proxy/src/lib.rs:8:5
|
8 | rust_2024_compatibility
| ^^^^^^^^^^^^^^^^^^^^^^^
= note: `#[deny(if_let_rescope)]` implied by `#[deny(rust_2024_compatibility)]`
and this:
error: these values and local bindings have significant drop implementation that will have a different drop order from that of Edition 2021
--> proxy/src/auth/backend/jwt.rs:376:18
|
369 | let client = Client::builder()
| ------ these values have significant drop implementation and will observe changes in drop order under Edition 2024
...
376 | map: DashMap::default(),
| ^^^^^^^^^^^^^^^^^^
|
= warning: this changes meaning in Rust 2024
= note: for more information, see issue #123739 <rust-lang/rust#123739>
= note: `#[deny(tail_expr_drop_order)]` implied by `#[deny(rust_2024_compatibility)]`
They are caused by the `rust_2024_compatibility` lint option.
When we actually switch to the 2024 edition, it makes sense to go
through all these and check that the drop order changes don't break
anything, but in the meanwhile, there's no easy way to avoid these
errors. Disable it, to allow compiling with nightly again.
conradludgate
pushed a commit
to neondatabase/neon
that referenced
this issue
Nov 4, 2024
Compiling with nightly rust compiler, I'm getting a lot of errors like this:
error: `if let` assigns a shorter lifetime since Edition 2024
--> proxy/src/auth/backend/jwt.rs:226:16
|
226 | if let Some(permit) = self.try_acquire_permit() {
| ^^^^^^^^^^^^^^^^^^^-------------------------
| |
| this value has a significant drop implementation which may observe a major change in drop order and requires your discretion
|
= warning: this changes meaning in Rust 2024
= note: for more information, see issue #124085 <rust-lang/rust#124085>
help: the value is now dropped here in Edition 2024
--> proxy/src/auth/backend/jwt.rs:241:13
|
241 | } else {
| ^
note: the lint level is defined here
--> proxy/src/lib.rs:8:5
|
8 | rust_2024_compatibility
| ^^^^^^^^^^^^^^^^^^^^^^^
= note: `#[deny(if_let_rescope)]` implied by `#[deny(rust_2024_compatibility)]`
and this:
error: these values and local bindings have significant drop implementation that will have a different drop order from that of Edition 2021
--> proxy/src/auth/backend/jwt.rs:376:18
|
369 | let client = Client::builder()
| ------ these values have significant drop implementation and will observe changes in drop order under Edition 2024
...
376 | map: DashMap::default(),
| ^^^^^^^^^^^^^^^^^^
|
= warning: this changes meaning in Rust 2024
= note: for more information, see issue #123739 <rust-lang/rust#123739>
= note: `#[deny(tail_expr_drop_order)]` implied by `#[deny(rust_2024_compatibility)]`
They are caused by the `rust_2024_compatibility` lint option.
When we actually switch to the 2024 edition, it makes sense to go
through all these and check that the drop order changes don't break
anything, but in the meanwhile, there's no easy way to avoid these
errors. Disable it, to allow compiling with nightly again.
github-merge-queue bot
pushed a commit
to neondatabase/neon
that referenced
this issue
Nov 8, 2024
Compiling with nightly rust compiler, I'm getting a lot of errors like
this:
error: `if let` assigns a shorter lifetime since Edition 2024
--> proxy/src/auth/backend/jwt.rs:226:16
|
226 | if let Some(permit) = self.try_acquire_permit() {
| ^^^^^^^^^^^^^^^^^^^-------------------------
| |
| this value has a significant drop implementation which may observe a
major change in drop order and requires your discretion
|
= warning: this changes meaning in Rust 2024
= note: for more information, see issue #124085
<rust-lang/rust#124085>
help: the value is now dropped here in Edition 2024
--> proxy/src/auth/backend/jwt.rs:241:13
|
241 | } else {
| ^
note: the lint level is defined here
--> proxy/src/lib.rs:8:5
|
8 | rust_2024_compatibility
| ^^^^^^^^^^^^^^^^^^^^^^^
= note: `#[deny(if_let_rescope)]` implied by
`#[deny(rust_2024_compatibility)]`
and this:
error: these values and local bindings have significant drop
implementation that will have a different drop order from that of
Edition 2021
--> proxy/src/auth/backend/jwt.rs:376:18
|
369 | let client = Client::builder()
| ------ these values have significant drop implementation and will
observe changes in drop order under Edition 2024
...
376 | map: DashMap::default(),
| ^^^^^^^^^^^^^^^^^^
|
= warning: this changes meaning in Rust 2024
= note: for more information, see issue #123739
<rust-lang/rust#123739>
= note: `#[deny(tail_expr_drop_order)]` implied by
`#[deny(rust_2024_compatibility)]`
They are caused by the `rust_2024_compatibility` lint option.
When we actually switch to the 2024 edition, it makes sense to go
through all these and check that the drop order changes don't break
anything, but in the meanwhile, there's no easy way to avoid these
errors. Disable it, to allow compiling with nightly again.
Co-authored-by: Arpad Müller <[email protected]>
github-merge-queue bot
pushed a commit
to neondatabase/neon
that referenced
this issue
Nov 8, 2024
Compiling with nightly rust compiler, I'm getting a lot of errors like
this:
error: `if let` assigns a shorter lifetime since Edition 2024
--> proxy/src/auth/backend/jwt.rs:226:16
|
226 | if let Some(permit) = self.try_acquire_permit() {
| ^^^^^^^^^^^^^^^^^^^-------------------------
| |
| this value has a significant drop implementation which may observe a
major change in drop order and requires your discretion
|
= warning: this changes meaning in Rust 2024
= note: for more information, see issue #124085
<rust-lang/rust#124085>
help: the value is now dropped here in Edition 2024
--> proxy/src/auth/backend/jwt.rs:241:13
|
241 | } else {
| ^
note: the lint level is defined here
--> proxy/src/lib.rs:8:5
|
8 | rust_2024_compatibility
| ^^^^^^^^^^^^^^^^^^^^^^^
= note: `#[deny(if_let_rescope)]` implied by
`#[deny(rust_2024_compatibility)]`
and this:
error: these values and local bindings have significant drop
implementation that will have a different drop order from that of
Edition 2021
--> proxy/src/auth/backend/jwt.rs:376:18
|
369 | let client = Client::builder()
| ------ these values have significant drop implementation and will
observe changes in drop order under Edition 2024
...
376 | map: DashMap::default(),
| ^^^^^^^^^^^^^^^^^^
|
= warning: this changes meaning in Rust 2024
= note: for more information, see issue #123739
<rust-lang/rust#123739>
= note: `#[deny(tail_expr_drop_order)]` implied by
`#[deny(rust_2024_compatibility)]`
They are caused by the `rust_2024_compatibility` lint option.
When we actually switch to the 2024 edition, it makes sense to go
through all these and check that the drop order changes don't break
anything, but in the meanwhile, there's no easy way to avoid these
errors. Disable it, to allow compiling with nightly again.
Co-authored-by: Arpad Müller <[email protected]>
conradludgate
pushed a commit
to neondatabase/neon
that referenced
this issue
Nov 8, 2024
Compiling with nightly rust compiler, I'm getting a lot of errors like
this:
error: `if let` assigns a shorter lifetime since Edition 2024
--> proxy/src/auth/backend/jwt.rs:226:16
|
226 | if let Some(permit) = self.try_acquire_permit() {
| ^^^^^^^^^^^^^^^^^^^-------------------------
| |
| this value has a significant drop implementation which may observe a
major change in drop order and requires your discretion
|
= warning: this changes meaning in Rust 2024
= note: for more information, see issue #124085
<rust-lang/rust#124085>
help: the value is now dropped here in Edition 2024
--> proxy/src/auth/backend/jwt.rs:241:13
|
241 | } else {
| ^
note: the lint level is defined here
--> proxy/src/lib.rs:8:5
|
8 | rust_2024_compatibility
| ^^^^^^^^^^^^^^^^^^^^^^^
= note: `#[deny(if_let_rescope)]` implied by
`#[deny(rust_2024_compatibility)]`
and this:
error: these values and local bindings have significant drop
implementation that will have a different drop order from that of
Edition 2021
--> proxy/src/auth/backend/jwt.rs:376:18
|
369 | let client = Client::builder()
| ------ these values have significant drop implementation and will
observe changes in drop order under Edition 2024
...
376 | map: DashMap::default(),
| ^^^^^^^^^^^^^^^^^^
|
= warning: this changes meaning in Rust 2024
= note: for more information, see issue #123739
<rust-lang/rust#123739>
= note: `#[deny(tail_expr_drop_order)]` implied by
`#[deny(rust_2024_compatibility)]`
They are caused by the `rust_2024_compatibility` lint option.
When we actually switch to the 2024 edition, it makes sense to go
through all these and check that the drop order changes don't break
anything, but in the meanwhile, there's no easy way to avoid these
errors. Disable it, to allow compiling with nightly again.
Co-authored-by: Arpad Müller <[email protected]>
matthiaskrgr
added a commit
to matthiaskrgr/rust
that referenced
this issue
Nov 11, 2024
…in-let-block-works, r=jieyouxu Ensure that tail expr receive lifetime extension cc `@jieyouxu` `@traviscross` It just came to me that we should add a test to make sure that we honor the contract from the temporary lifetime rule rust-lang#121346. We should continue to implement this rule in Edition 2021 onward and shorter tail expression lifetime should not override it. This is a small PR to improve our assurance and establish a stronger contract. Tracked by rust-lang#123739
rust-timer
added a commit
to rust-lang-ci/rust
that referenced
this issue
Nov 11, 2024
Rollup merge of rust-lang#129627 - dingxiangfei2009:ensure-tail-expr-in-let-block-works, r=jieyouxu Ensure that tail expr receive lifetime extension cc `@jieyouxu` `@traviscross` It just came to me that we should add a test to make sure that we honor the contract from the temporary lifetime rule rust-lang#121346. We should continue to implement this rule in Edition 2021 onward and shorter tail expression lifetime should not override it. This is a small PR to improve our assurance and establish a stronger contract. Tracked by rust-lang#123739
mati865
pushed a commit
to mati865/rust
that referenced
this issue
Nov 12, 2024
…in-let-block-works, r=jieyouxu Ensure that tail expr receive lifetime extension cc `@jieyouxu` `@traviscross` It just came to me that we should add a test to make sure that we honor the contract from the temporary lifetime rule rust-lang#121346. We should continue to implement this rule in Edition 2021 onward and shorter tail expression lifetime should not override it. This is a small PR to improve our assurance and establish a stronger contract. Tracked by rust-lang#123739
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This is a tracking issue for the RFC 3606: Drop temporaries in tail expressions before local variables
The feature gate for the issue is
#![feature(shorter_tail_lifetimes)].About tracking issues
Tracking issues are used to record the overall progress of implementation. They are also used as hubs connecting to other relevant issues, e.g., bugs or open design questions. A tracking issue is however not meant for large scale discussion, questions, or bug reports about a feature. Instead, open a dedicated issue for the specific matter and add the relevant feature gate label.
Steps
shorter_tail_lifetime#131445Unresolved Questions
warn-by-defaultabout these cases in older editions, or only warn when upgrading to Rust 2024?Related
cc @nikomatsakis @m-ou-se
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