typeck: Prohibit RPIT types that inherit lifetimes#62849
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typeck: Prohibit RPIT types that inherit lifetimes Part of #61949. This PR prohibits return position `impl Trait` types that "inherit lifetimes" from the parent scope. The intent is to forbid cases that are challenging until they can be addressed properly. cc @nikomatsakis
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| @@ -0,0 +1,8 @@ | |||
| error: `async fn` return type cannot contain a projection or `Self` that references lifetimes from a parent scope | |||
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I wonder if we should try to give some clue for how to workaround this -- this is basically a rustc bug.
In the case of Self, the suggestion would be to write the Self type explicitly.
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I've dug around for a bit and I've not been able to find a way to determine if the return type was originally Self from here. I'm happy to add a suggestion if anyone knows a way to determine this.
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At minimum we could just -- for this particular issue -- give it an error code and direct them to some chapter in the async book where we explain in more depth (in the extended explanation). But we'd need a link first. Maybe we can just file a follow-up issue on the matter to improve diagnostics.
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Hey! This is a ping from triage, we would like to know if you @davidtwco could give us a few more minutes to update here by fixing the conflicting files so we can move forward. Thanks. @rustbot modify labels to +S-waiting-on-author, -S-waiting-on-review |
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@edmilsonefs thanks, I've resolved the conflict. |
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typeck: Prohibit RPIT types that inherit lifetimes Part of #61949. This PR prohibits return position `impl Trait` types that "inherit lifetimes" from the parent scope. The intent is to forbid cases that are challenging until they can be addressed properly. cc @nikomatsakis
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Rollup of 10 pull requests Successful merges: - #62760 (Deduplicate error messages in `librsctc_mir`) - #62849 (typeck: Prohibit RPIT types that inherit lifetimes) - #63383 (`async fn` lifetime elision tests) - #63421 (Implement Clone, Display for ascii::EscapeDefault) - #63459 (syntax: account for CVarArgs being in the argument list.) - #63475 (Bring back suggestion for splitting `<-` into `< -`) - #63485 (ci: move mirrors to their standalone bucket) - #63486 (Document `From` trait for `BinaryHeap`) - #63488 (improve DiagnosticBuilder docs) - #63493 (Remove unneeded comment in src/libcore/hash/mod.rs) Failed merges: r? @ghost
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…imes, r=nikomatsakis typeck: Prohibit RPIT types that inherit lifetimes Part of rust-lang#61949. This PR prohibits return position `impl Trait` types that "inherit lifetimes" from the parent scope. The intent is to forbid cases that are challenging until they can be addressed properly. cc @nikomatsakis
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…imes, r=nikomatsakis typeck: Prohibit RPIT types that inherit lifetimes Part of rust-lang#61949. This PR prohibits return position `impl Trait` types that "inherit lifetimes" from the parent scope. The intent is to forbid cases that are challenging until they can be addressed properly. cc @nikomatsakis
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⌛ Testing commit 861d1bb with merge ade62304ed223496e69511fa5fb9b83420b7d5c9... |
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…imes, r=nikomatsakis typeck: Prohibit RPIT types that inherit lifetimes Part of rust-lang#61949. This PR prohibits return position `impl Trait` types that "inherit lifetimes" from the parent scope. The intent is to forbid cases that are challenging until they can be addressed properly. cc @nikomatsakis
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@bors retry rolled up. |
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Rollup of 17 pull requests Successful merges: - #62760 (Deduplicate error messages in `librsctc_mir`) - #62849 (typeck: Prohibit RPIT types that inherit lifetimes) - #63383 (`async fn` lifetime elision tests) - #63421 (Implement Clone, Display for ascii::EscapeDefault) - #63459 (syntax: account for CVarArgs being in the argument list.) - #63475 (Bring back suggestion for splitting `<-` into `< -`) - #63485 (ci: move mirrors to their standalone bucket) - #63486 (Document `From` trait for `BinaryHeap`) - #63488 (improve DiagnosticBuilder docs) - #63493 (Remove unneeded comment in src/libcore/hash/mod.rs) - #63499 (handle elision in async fn correctly) - #63501 (use `ParamName` to track in-scope lifetimes instead of Ident) - #63508 (Do not ICE when synthesizing spans falling inside unicode chars) - #63511 (ci: add a check for clock drift) - #63512 (Provide map_ok and map_err method for Poll<Option<Result<T, E>>>) - #63529 (RELEASES.md: ? is one of three Kleene operators) - #63530 (Fix typo in error message.) Failed merges: r? @ghost
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Rollup of 17 pull requests Successful merges: - #62760 (Deduplicate error messages in `librsctc_mir`) - #62849 (typeck: Prohibit RPIT types that inherit lifetimes) - #63383 (`async fn` lifetime elision tests) - #63421 (Implement Clone, Display for ascii::EscapeDefault) - #63459 (syntax: account for CVarArgs being in the argument list.) - #63475 (Bring back suggestion for splitting `<-` into `< -`) - #63485 (ci: move mirrors to their standalone bucket) - #63486 (Document `From` trait for `BinaryHeap`) - #63488 (improve DiagnosticBuilder docs) - #63493 (Remove unneeded comment in src/libcore/hash/mod.rs) - #63499 (handle elision in async fn correctly) - #63501 (use `ParamName` to track in-scope lifetimes instead of Ident) - #63508 (Do not ICE when synthesizing spans falling inside unicode chars) - #63511 (ci: add a check for clock drift) - #63512 (Provide map_ok and map_err method for Poll<Option<Result<T, E>>>) - #63529 (RELEASES.md: ? is one of three Kleene operators) - #63530 (Fix typo in error message.) Failed merges: r? @ghost
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…amertj
Stabilize `async_await` in Rust 1.39.0
Here we stabilize:
- free and inherent `async fn`s,
- the `<expr>.await` expression form,
- and the `async move? { ... }` block form.
Closes rust-lang#62149.
Closes rust-lang#50547.
All the blockers are now closed.
<details>
- [x] FCP in rust-lang#62149
- [x] rust-lang#61949; PR in rust-lang#62849.
- [x] rust-lang#62517; PR in rust-lang#63376.
- [x] rust-lang#63225; PR in rust-lang#63501
- [x] rust-lang#63388; PR in rust-lang#63499
- [x] rust-lang#63500; PR in rust-lang#63501
- [x] rust-lang#62121 (comment)
- [x] Some tests for control flow (PR rust-lang#63387):
- `?`
- `return` in `async` blocks
- `break`
- [x] rust-lang#61775 (comment), i.e. tests for rust-lang#60944 with `async fn`s instead). PR in rust-lang#63383
</details>
r? @cramertj
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Stabilize `impl_trait_projections` Closes rust-lang#115659 ## TL;DR: This allows us to mention `Self` and `T::Assoc` in async fn and return-position `impl Trait`, as you would expect you'd be able to. Some examples: ```rust #![feature(return_position_impl_trait_in_trait, async_fn_in_trait)] // (just needed for final tests below) // ---------------------------------------- // struct Wrapper<'a, T>(&'a T); impl Wrapper<'_, ()> { async fn async_fn() -> Self { //^ Previously rejected because it returns `-> Self`, not `-> Wrapper<'_, ()>`. Wrapper(&()) } fn impl_trait() -> impl Iterator<Item = Self> { //^ Previously rejected because it mentions `Self`, not `Wrapper<'_, ()>`. std::iter::once(Wrapper(&())) } } // ---------------------------------------- // trait Trait<'a> { type Assoc; fn new() -> Self::Assoc; } impl Trait<'_> for () { type Assoc = (); fn new() {} } impl<'a, T: Trait<'a>> Wrapper<'a, T> { async fn mk_assoc() -> T::Assoc { //^ Previously rejected because `T::Assoc` doesn't mention `'a` in the HIR, // but ends up resolving to `<T as Trait<'a>>::Assoc`, which does rely on `'a`. // That's the important part -- the elided trait. T::new() } fn a_few_assocs() -> impl Iterator<Item = T::Assoc> { //^ Previously rejected for the same reason [T::new(), T::new(), T::new()].into_iter() } } // ---------------------------------------- // trait InTrait { async fn async_fn() -> Self; fn impl_trait() -> impl Iterator<Item = Self>; } impl InTrait for &() { async fn async_fn() -> Self { &() } //^ Previously rejected just like inherent impls fn impl_trait() -> impl Iterator<Item = Self> { //^ Previously rejected just like inherent impls [&()].into_iter() } } ``` ## Technical: Lifetimes in return-position `impl Trait` (and `async fn`) are duplicated as early-bound generics local to the opaque in order to make sure we are able to substitute any late-bound lifetimes from the function in the opaque's hidden type. (The [dev guide](https://rustc-dev-guide.rust-lang.org/return-position-impl-trait-in-trait.html#aside-opaque-lifetime-duplication) has a small section about why this is necessary -- this was written for RPITITs, but it applies to all RPITs) Prior to rust-lang#103491, all of the early-bound lifetimes not local to the opaque were replaced with `'static` to avoid issues where relating opaques caused their *non-captured* lifetimes to be related. This `'static` replacement led to strange and possibly unsound behaviors (rust-lang#61949 (comment)) (rust-lang#53613) when referencing the `Self` type alias in an impl or indirectly referencing a lifetime parameter via a projection type (via a `T::Assoc` projection without an explicit trait), since lifetime resolution is performed on the HIR, when neither `T::Assoc`-style projections or `Self` in impls are expanded. Therefore an error was implemented in rust-lang#62849 to deny this subtle behavior as a known limitation of the compiler. It was attempted by `@cjgillot` to fix this in rust-lang#91403, which was subsequently unlanded. Then it was re-attempted to much success (🎉) in rust-lang#103491, which is where we currently are in the compiler. The PR above (rust-lang#103491) fixed this issue technically by *not* replacing the opaque's parent lifetimes with `'static`, but instead using variance to properly track which lifetimes are captured and are not. The PR gated any of the "side-effects" of the PR behind a feature gate (`impl_trait_projections`) presumably to avoid having to involve T-lang or T-types in the PR as well. `@cjgillot` can clarify this if I'm misunderstanding what their intention was with the feature gate. Since we're not replacing (possibly *invariant*!) lifetimes with `'static` anymore, there are no more soundness concerns here. Therefore, this PR removes the feature gate. Tests: * `tests/ui/async-await/feature-self-return-type.rs` * `tests/ui/impl-trait/feature-self-return-type.rs` * `tests/ui/async-await/issues/issue-78600.rs` * `tests/ui/impl-trait/capture-lifetime-not-in-hir.rs` --- r? cjgillot on the impl (not much, just removing the feature gate) I'm gonna mark this as FCP for T-lang and T-types.
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Stabilize `impl_trait_projections` Closes rust-lang#115659 ## TL;DR: This allows us to mention `Self` and `T::Assoc` in async fn and return-position `impl Trait`, as you would expect you'd be able to. Some examples: ```rust #![feature(return_position_impl_trait_in_trait, async_fn_in_trait)] // (just needed for final tests below) // ---------------------------------------- // struct Wrapper<'a, T>(&'a T); impl Wrapper<'_, ()> { async fn async_fn() -> Self { //^ Previously rejected because it returns `-> Self`, not `-> Wrapper<'_, ()>`. Wrapper(&()) } fn impl_trait() -> impl Iterator<Item = Self> { //^ Previously rejected because it mentions `Self`, not `Wrapper<'_, ()>`. std::iter::once(Wrapper(&())) } } // ---------------------------------------- // trait Trait<'a> { type Assoc; fn new() -> Self::Assoc; } impl Trait<'_> for () { type Assoc = (); fn new() {} } impl<'a, T: Trait<'a>> Wrapper<'a, T> { async fn mk_assoc() -> T::Assoc { //^ Previously rejected because `T::Assoc` doesn't mention `'a` in the HIR, // but ends up resolving to `<T as Trait<'a>>::Assoc`, which does rely on `'a`. // That's the important part -- the elided trait. T::new() } fn a_few_assocs() -> impl Iterator<Item = T::Assoc> { //^ Previously rejected for the same reason [T::new(), T::new(), T::new()].into_iter() } } // ---------------------------------------- // trait InTrait { async fn async_fn() -> Self; fn impl_trait() -> impl Iterator<Item = Self>; } impl InTrait for &() { async fn async_fn() -> Self { &() } //^ Previously rejected just like inherent impls fn impl_trait() -> impl Iterator<Item = Self> { //^ Previously rejected just like inherent impls [&()].into_iter() } } ``` ## Technical: Lifetimes in return-position `impl Trait` (and `async fn`) are duplicated as early-bound generics local to the opaque in order to make sure we are able to substitute any late-bound lifetimes from the function in the opaque's hidden type. (The [dev guide](https://rustc-dev-guide.rust-lang.org/return-position-impl-trait-in-trait.html#aside-opaque-lifetime-duplication) has a small section about why this is necessary -- this was written for RPITITs, but it applies to all RPITs) Prior to rust-lang#103491, all of the early-bound lifetimes not local to the opaque were replaced with `'static` to avoid issues where relating opaques caused their *non-captured* lifetimes to be related. This `'static` replacement led to strange and possibly unsound behaviors (rust-lang#61949 (comment)) (rust-lang#53613) when referencing the `Self` type alias in an impl or indirectly referencing a lifetime parameter via a projection type (via a `T::Assoc` projection without an explicit trait), since lifetime resolution is performed on the HIR, when neither `T::Assoc`-style projections or `Self` in impls are expanded. Therefore an error was implemented in rust-lang#62849 to deny this subtle behavior as a known limitation of the compiler. It was attempted by `@cjgillot` to fix this in rust-lang#91403, which was subsequently unlanded. Then it was re-attempted to much success (🎉) in rust-lang#103491, which is where we currently are in the compiler. The PR above (rust-lang#103491) fixed this issue technically by *not* replacing the opaque's parent lifetimes with `'static`, but instead using variance to properly track which lifetimes are captured and are not. The PR gated any of the "side-effects" of the PR behind a feature gate (`impl_trait_projections`) presumably to avoid having to involve T-lang or T-types in the PR as well. `@cjgillot` can clarify this if I'm misunderstanding what their intention was with the feature gate. Since we're not replacing (possibly *invariant*!) lifetimes with `'static` anymore, there are no more soundness concerns here. Therefore, this PR removes the feature gate. Tests: * `tests/ui/async-await/feature-self-return-type.rs` * `tests/ui/impl-trait/feature-self-return-type.rs` * `tests/ui/async-await/issues/issue-78600.rs` * `tests/ui/impl-trait/capture-lifetime-not-in-hir.rs` --- r? cjgillot on the impl (not much, just removing the feature gate) I'm gonna mark this as FCP for T-lang and T-types.
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Part of #61949.
This PR prohibits return position
impl Traittypes that "inheritlifetimes" from the parent scope. The intent is to forbid cases that are
challenging until they can be addressed properly.
cc @nikomatsakis