Begin experimental support for pin reborrowing #130526

eholk · 2024-09-18T19:40:20Z

This commit adds basic support for reborrowing Pin types in argument position. At the moment it only supports reborrowing Pin<&mut T> as Pin<&mut T> by inserting a call to Pin::as_mut(), and only in argument position (not as the receiver in a method call).

This PR makes the following example compile:

#![feature(pin_ergonomics)]

fn foo(_: Pin<&mut Foo>) {
}

fn bar(mut x: Pin<&mut Foo>) {
    foo(x);
    foo(x);
}

Previously, you would have had to write bar as:

fn bar(mut x: Pin<&mut Foo>) {
    foo(x.as_mut());
    foo(x);
}

Tracking:

Tracking issue for pin ergonomics #130494

r? @compiler-errors

This commit adds basic support for reborrowing `Pin` types in argument position. At the moment it only supports reborrowing `Pin<&mut T>` as `Pin<&mut T>` by inserting a call to `Pin::as_mut()`, and only in argument position (not as the receiver in a method call).

compiler-errors

Left some thoughts. Specifically, aside from the nits, there's a problem with the desugaring that makes it not as general as when the feature gate is disabled due to the specific lowering to a call of Pin::as_mut. I think that should be changed.

tests/ui/async-await/pin-reborrow-arg.rs

tests/ui/async-await/pin-reborrow-self.rs

compiler/rustc_hir_typeck/src/coercion.rs

compiler/rustc_hir_typeck/src/expr_use_visitor.rs

compiler/rustc_mir_build/src/thir/cx/expr.rs

compiler-errors · 2024-09-18T20:07:30Z

Thanks for making this pretty bite-sized though. I was somewhat afraid you were going to put up a huge pin ergonomics PR; I'm happy to review this work, but if possible, I'd like to have more PRs that are smaller than fewer PRs that are larger (I know I am a huge hypocrite for doing that exact thing, so if it's not possible, then I understand lol).

eholk · 2024-09-18T21:52:23Z

Thanks for making this pretty bite-sized though. I was somewhat afraid you were going to put up a huge pin ergonomics PR; I'm happy to review this work, but if possible, I'd like to have more PRs that are smaller than fewer PRs that are larger (I know I am a huge hypocrite for doing that exact thing, so if it's not possible, then I understand lol).

Thanks for the comments! I'm a fan of going for the smallest atomic change I can do, but sometimes the smallest atomic change is quite large. The nice thing about the pin ergonomics experiment is that it's around 4-6 independent features and half of them should be pretty small.

Generating a call to `as_mut()` let to more restrictive borrows than what reborrowing usually gives us. Instead, we change the desugaring to reborrow the pin internals directly which makes things more expressive.

eholk · 2024-09-19T23:29:38Z

It went ahead and added support for reborrowing Pin<&mut T> and Pin<&T> as Pin<&T>, along with adding a test to make sure you can't reborrow Pin<&T> as Pin<&mut T>.

compiler-errors · 2024-09-20T17:06:03Z

@bors r+ rollup

bors · 2024-09-20T17:06:06Z

📌 Commit a18800f has been approved by compiler-errors

It is now in the queue for this repository.

…llaumeGomez Rollup of 7 pull requests Successful merges: - rust-lang#128209 (Remove macOS 10.10 dynamic linker bug workaround) - rust-lang#130526 (Begin experimental support for pin reborrowing) - rust-lang#130611 (Address diagnostics regression for `const_char_encode_utf8`.) - rust-lang#130614 (Add arm64e-apple-tvos target) - rust-lang#130617 (bail if there are too many non-region infer vars in the query response) - rust-lang#130619 (Fix scraped examples height) - rust-lang#130624 (Add `Vec::as_non_null`) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of rust-lang#130526 - eholk:pin-reborrow, r=compiler-errors Begin experimental support for pin reborrowing This commit adds basic support for reborrowing `Pin` types in argument position. At the moment it only supports reborrowing `Pin<&mut T>` as `Pin<&mut T>` by inserting a call to `Pin::as_mut()`, and only in argument position (not as the receiver in a method call). This PR makes the following example compile: ```rust #![feature(pin_ergonomics)] fn foo(_: Pin<&mut Foo>) { } fn bar(mut x: Pin<&mut Foo>) { foo(x); foo(x); } ``` Previously, you would have had to write `bar` as: ```rust fn bar(mut x: Pin<&mut Foo>) { foo(x.as_mut()); foo(x); } ``` Tracking: - rust-lang#130494 r? `@compiler-errors`

…errors Add support for reborrowing pinned method receivers This builds on rust-lang#130526 to add pinned reborrowing for method receivers. This enables the folllowing examples to work: ```rust #![feature(pin_ergonomics)] #![allow(incomplete_features)] use std::pin::Pin; pub struct Foo; impl Foo { fn foo(self: Pin<&mut Self>) { } fn baz(self: Pin<&Self>) { } } pub fn bar(x: Pin<&mut Foo>) { x.foo(); x.foo(); x.baz(); // Pin<&mut Foo> is downgraded to Pin<&Foo> } pub fn baaz(x: Pin<&Foo>) { x.baz(); x.baz(); } ``` This PR includes the original one, which is currently in the commit queue, but the only code changes are in the latest commit (d3c53aa). rust-lang#130494 r? `@compiler-errors`

…r-errors Add support for reborrowing pinned method receivers This builds on rust-lang#130526 to add pinned reborrowing for method receivers. This enables the folllowing examples to work: ```rust #![feature(pin_ergonomics)] #![allow(incomplete_features)] use std::pin::Pin; pub struct Foo; impl Foo { fn foo(self: Pin<&mut Self>) { } fn baz(self: Pin<&Self>) { } } pub fn bar(x: Pin<&mut Foo>) { x.foo(); x.foo(); x.baz(); // Pin<&mut Foo> is downgraded to Pin<&Foo> } pub fn baaz(x: Pin<&Foo>) { x.baz(); x.baz(); } ``` This PR includes the original one, which is currently in the commit queue, but the only code changes are in the latest commit (d3c53aa). rust-lang#130494 r? `@compiler-errors`

Rollup merge of rust-lang#130633 - eholk:pin-reborrow-self, r=compiler-errors Add support for reborrowing pinned method receivers This builds on rust-lang#130526 to add pinned reborrowing for method receivers. This enables the folllowing examples to work: ```rust #![feature(pin_ergonomics)] #![allow(incomplete_features)] use std::pin::Pin; pub struct Foo; impl Foo { fn foo(self: Pin<&mut Self>) { } fn baz(self: Pin<&Self>) { } } pub fn bar(x: Pin<&mut Foo>) { x.foo(); x.foo(); x.baz(); // Pin<&mut Foo> is downgraded to Pin<&Foo> } pub fn baaz(x: Pin<&Foo>) { x.baz(); x.baz(); } ``` This PR includes the original one, which is currently in the commit queue, but the only code changes are in the latest commit (d3c53aa). rust-lang#130494 r? `@compiler-errors`

…er-errors Add `&pin (mut|const) T` type position sugar This adds parser support for `&pin mut T` and `&pin const T` references. These are desugared to `Pin<&mut T>` and `Pin<&T>` in the AST lowering phases. This PR currently includes rust-lang#130526 since that one is in the commit queue. Only the most recent commits (bd45002 and following) are new. Tracking: - rust-lang#130494 r? `@compiler-errors`

Rollup merge of rust-lang#130635 - eholk:pin-reborrow-sugar, r=compiler-errors Add `&pin (mut|const) T` type position sugar This adds parser support for `&pin mut T` and `&pin const T` references. These are desugared to `Pin<&mut T>` and `Pin<&T>` in the AST lowering phases. This PR currently includes rust-lang#130526 since that one is in the commit queue. Only the most recent commits (bd45002 and following) are new. Tracking: - rust-lang#130494 r? `@compiler-errors`

…er-errors Add `&pin (mut|const) T` type position sugar This adds parser support for `&pin mut T` and `&pin const T` references. These are desugared to `Pin<&mut T>` and `Pin<&T>` in the AST lowering phases. This PR currently includes rust-lang#130526 since that one is in the commit queue. Only the most recent commits (bd45002 and following) are new. Tracking: - rust-lang#130494 r? `@compiler-errors`

rustbot assigned compiler-errors Sep 18, 2024

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Sep 18, 2024

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eholk mentioned this pull request Sep 18, 2024

[pin_ergonomics] Allow reborrowing Pin<&mut T> without the value being in a mutable place #130535

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a73c8b1

jieyouxu added the F-pin_ergonomics `#![feature(pin_ergonomics)]` label Sep 19, 2024

eholk added 2 commits September 19, 2024 15:34

Allow shortening reborrows

b2b76fb

Generating a call to `as_mut()` let to more restrictive borrows than what reborrowing usually gives us. Instead, we change the desugaring to reborrow the pin internals directly which makes things more expressive.

Add a test case to make sure we don't reborrow twice

92a5d21

eholk force-pushed the pin-reborrow branch from ac5e0dc to 92a5d21 Compare September 19, 2024 22:41

pin_ergonomics: allow reborrowing as Pin<&T>

a18800f

traviscross mentioned this pull request Sep 19, 2024

Tracking issue for pin ergonomics #130494

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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-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Sep 20, 2024

GuillaumeGomez mentioned this pull request Sep 20, 2024

Rollup of 7 pull requests #130631

Merged

eholk mentioned this pull request Sep 20, 2024

Add support for reborrowing pinned method receivers #130633

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eholk mentioned this pull request Sep 20, 2024

Add &pin (mut|const) T type position sugar #130635

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bors merged commit fe5f734 into rust-lang:master Sep 20, 2024
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Begin experimental support for pin reborrowing #130526

Begin experimental support for pin reborrowing #130526

eholk commented Sep 18, 2024 •

edited by traviscross

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Begin experimental support for pin reborrowing #130526

Begin experimental support for pin reborrowing #130526

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