Inherit function lifetimes for impl-trait #103449

cjgillot · 2022-10-23T19:11:39Z

Blocked on #103448
Specific diff https://github.com/cjgillot/rust/compare/no-late-fn..variance-rpit

This PR attempts to stop duplicating generic parameters between functions and opaque types.

fn foo<'a, 'b, T>() -> impl Sized + 'a {}

// OLD
fn foo<'a, 'b, T>() -> foo::<'static, 'static, T>::opaque::<'a> {}
opaque foo::<T>::opaque<'a>: Sized + 'a;

// OLD post #103448
fn foo<'a, 'b, T>() -> foo::<'static, 'static, T>::opaque::<'a> {}
opaque foo::<'_a, '_b, T>::opaque<'a>: Sized + 'a;

// NEW
fn foo<'a, 'b, T>() -> foo::<'a, 'b, T>::opaque {}
opaque foo::<'a, 'b, T>::opaque: Sized + 'a;

This allows to support Self in impl-trait, since we do not replace lifetimes by 'static any more.

The implementation relies on 2 tweaking rules for opaques in 2 places:

we only relate substs that correspond to captured lifetimes during TypeRelation;
we only list captured lifetimes in choice region computation.

For simplicity, I encoded the "capturedness" of lifetimes as a variance, Bivariant vs Invariant for unused vs captured lifetimes. The variances_of query used to ICE for opaques.

Writing the PR description made me realize that this strategy can be used without #103448 to support Self in RPIT. I'll probably make such a PR during the week.

r? types

rustbot · 2022-10-23T19:11:43Z

Some changes occurred in compiler/rustc_codegen_cranelift

cc @bjorn3

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

Some changes occurred in src/librustdoc/clean/types.rs

cc @camelid

Some changes occurred to the CTFE / Miri engine

cc @rust-lang/miri

compiler-errors · 2022-10-23T19:14:26Z

This allows to support Self in impl-trait, since we do not replace lifetimes by 'static any more.

Can you elaborate on this? I don't have context of what impl Trait currently has issues with.

bors · 2022-10-24T20:25:29Z

☔ The latest upstream changes (presumably #103337) made this pull request unmergeable. Please resolve the merge conflicts.

rustbot · 2022-10-26T20:09:16Z

The Miri subtree was changed

cc @rust-lang/miri

rust-log-analyzer · 2022-10-26T20:24:53Z

The job mingw-check failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

configure: rust.debug-assertions := True
configure: rust.overflow-checks := True
configure: llvm.assertions      := True
configure: dist.missing-tools   := True
configure: build.configure-args := ['--enable-sccache', '--disable-manage-submodu ...
configure: writing `config.toml` in current directory
configure: 
configure: run `python /checkout/x.py --help`
Attempting with retry: make prepare
---
* highest error code: E0790
Found 506 error codes
Found 0 error(s) in error codes
Done!
tidy error: /checkout/compiler/rustc_ast_lowering/src/lib.rs:1467: unexplained "```ignore" doctest; try one:

* make the test actually pass, by adding necessary imports and declarations, or
* use "```text", if the code is not Rust code, or
* use "```compile_fail,Ennnn", if the code is expected to fail at compile time, or
* use "```should_panic", if the code is expected to fail at run time, or
* use "```no_run", if the code should type-check but not necessary linkable/runnable, or
* explain it like "```ignore (cannot-test-this-because-xxxx)", if the annotation cannot be avoided.


tidy error: /checkout/compiler/rustc_ast_lowering/src/lib.rs:1474: unexplained "```ignore" doctest; try one:

* make the test actually pass, by adding necessary imports and declarations, or
* use "```text", if the code is not Rust code, or
* use "```compile_fail,Ennnn", if the code is expected to fail at compile time, or
* use "```should_panic", if the code is expected to fail at run time, or
* use "```no_run", if the code should type-check but not necessary linkable/runnable, or
* explain it like "```ignore (cannot-test-this-because-xxxx)", if the annotation cannot be avoided.

* 387 features
some tidy checks failed
Build completed unsuccessfully in 0:00:11

bors · 2022-10-27T13:52:44Z

☔ The latest upstream changes (presumably #103623) made this pull request unmergeable. Please resolve the merge conflicts.

Support using `Self` or projections inside an RPIT/async fn I reuse the same idea as rust-lang#103449 to use variances to encode whether a lifetime parameter is captured by impl-trait. The current implementation of async and RPIT replace all lifetimes from the parent generics by `'static`. This PR changes the scheme ```rust impl<'a> Foo<'a> { fn foo<'b, T>() -> impl Into<Self> + 'b { ... } } opaque Foo::<'_a>::foo::<'_b, T>::opaque<'b>: Into<Foo<'_a>> + 'b; impl<'a> Foo<'a> { // OLD fn foo<'b, T>() -> Foo::<'static>::foo::<'static, T>::opaque::<'b> { ... } ^^^^^^^ the `Self` becomes `Foo<'static>` // NEW fn foo<'b, T>() -> Foo::<'a>::foo::<'b, T>::opaque::<'b> { ... } ^^ the `Self` stays `Foo<'a>` } ``` There is the same issue with projections. In the example, substitute `Self` by `<T as Trait<'b>>::Assoc` in the sugared version, and `Foo<'_a>` by `<T as Trait<'_b>>::Assoc` in the desugared one. This allows to support `Self` in impl-trait, since we do not replace lifetimes by `'static` any more. The same trick allows to use projections like `T::Assoc` where `Self` is allowed. The feature is gated behind a `impl_trait_projections` feature gate. The implementation relies on 2 tweaking rules for opaques in 2 places: - we only relate substs that correspond to captured lifetimes during TypeRelation; - we only list captured lifetimes in choice region computation. For simplicity, I encoded the "capturedness" of lifetimes as a variance, `Bivariant` vs `Invariant` for unused vs captured lifetimes. The `variances_of` query used to ICE for opaques. Impl-trait that do not reference `Self` or projections will have their variances as: - `o` (invariant) for each parent type or const; - `*` (bivariant) for each parent lifetime --> will not participate in borrowck; - `o` (invariant) for each own lifetime. Impl-trait that does reference `Self` and/or projections will have some parent lifetimes marked as `o` (as the example above), and participate in type relation and borrowck. In the example above, `variances_of(opaque) = ['_a: o, '_b: *, T: o, 'b: o]`. r? types cc `@compiler-errors` , as you asked about the issue with `Self` and projections.

Support using `Self` or projections inside an RPIT/async fn I reuse the same idea as rust-lang/rust#103449 to use variances to encode whether a lifetime parameter is captured by impl-trait. The current implementation of async and RPIT replace all lifetimes from the parent generics by `'static`. This PR changes the scheme ```rust impl<'a> Foo<'a> { fn foo<'b, T>() -> impl Into<Self> + 'b { ... } } opaque Foo::<'_a>::foo::<'_b, T>::opaque<'b>: Into<Foo<'_a>> + 'b; impl<'a> Foo<'a> { // OLD fn foo<'b, T>() -> Foo::<'static>::foo::<'static, T>::opaque::<'b> { ... } ^^^^^^^ the `Self` becomes `Foo<'static>` // NEW fn foo<'b, T>() -> Foo::<'a>::foo::<'b, T>::opaque::<'b> { ... } ^^ the `Self` stays `Foo<'a>` } ``` There is the same issue with projections. In the example, substitute `Self` by `<T as Trait<'b>>::Assoc` in the sugared version, and `Foo<'_a>` by `<T as Trait<'_b>>::Assoc` in the desugared one. This allows to support `Self` in impl-trait, since we do not replace lifetimes by `'static` any more. The same trick allows to use projections like `T::Assoc` where `Self` is allowed. The feature is gated behind a `impl_trait_projections` feature gate. The implementation relies on 2 tweaking rules for opaques in 2 places: - we only relate substs that correspond to captured lifetimes during TypeRelation; - we only list captured lifetimes in choice region computation. For simplicity, I encoded the "capturedness" of lifetimes as a variance, `Bivariant` vs `Invariant` for unused vs captured lifetimes. The `variances_of` query used to ICE for opaques. Impl-trait that do not reference `Self` or projections will have their variances as: - `o` (invariant) for each parent type or const; - `*` (bivariant) for each parent lifetime --> will not participate in borrowck; - `o` (invariant) for each own lifetime. Impl-trait that does reference `Self` and/or projections will have some parent lifetimes marked as `o` (as the example above), and participate in type relation and borrowck. In the example above, `variances_of(opaque) = ['_a: o, '_b: *, T: o, 'b: o]`. r? types cc `@compiler-errors` , as you asked about the issue with `Self` and projections.

cjgillot added the S-blocked Status: Blocked on something else such as an RFC or other implementation work. label Oct 23, 2022

rust-highfive assigned compiler-errors Oct 23, 2022

rustbot added T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-rustdoc Relevant to the rustdoc team, which will review and decide on the PR/issue. labels Oct 23, 2022

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Oct 23, 2022

cjgillot mentioned this pull request Oct 23, 2022

Account for late-bound lifetimes in generics #103448

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cjgillot mentioned this pull request Oct 24, 2022

Support using Self or projections inside an RPIT/async fn #103491

Merged

cjgillot added 19 commits October 26, 2022 17:11

Make verbose print of regions a bit more compact.

20ecbf5

Do not print single ::<'_> for fn items.

6a874c5

Make late_bound_lifetime_arguments a hard error.

29adf97

Validate fn-sig and erased lifetimes in MIR validator.

8529bda

Remember late_bound in GenericParamDefKind.

d7cc37c

Make fn late-bound lifetimes part of the generics.

1db0925

Bless ui tests.

2e30f43

Adapt clippy.

bf1127d

Make fn_sig return a simple FnSig.

8d067f1

FIXME Remove chalk assertion.

cd44af1

Bless mir-opt.

99c916d

Bless codegen tests.

9c9243f

Bless incremental tests.

4ed91e2

Remove has_late_bound_regions from Generics.

2f416e8

Bless rustdoc.

4a173a6

Pacify tidy.

0b021ff

Bless cgu tests.

4cdb3d5

Adapt miri.

7b5fc97

Bless pretty.

1ee46c8

cjgillot added 6 commits October 26, 2022 17:38

Compute variance for opaques too.

388b9d2

Inherit generics for impl-trait.

c91a899

Bless ui tests.

082217a

Use variances for defining use diag.

6dc78b0

Also collect lifetimes for TAIT.

d616fb3

Stop recording lifetimes for async.

f14b283

cjgillot force-pushed the variance-rpit branch from 6ae15c5 to f14b283 Compare October 26, 2022 20:09

compiler-errors removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Nov 7, 2022

spastorino mentioned this pull request May 1, 2023

RPITIT refactor (lower RPITIT as GAT) rust-lang/types-team#90

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cjgillot closed this Oct 12, 2023

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