2229: Handle capturing a reference into a repr packed struct #82878
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@bors r+ |
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📌 Commit efe0319f05bbccafe282bd6c6eed5bdff06edf1b has been approved by |
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@bors r- I want to think about this layout call for one second |
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Mar 9, 2021
| let pos = place.projections.iter().enumerate().position(|(i, p)| { | ||
| let ty = place.ty_before_projection(i); | ||
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| match p.kind { |
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There are a lot of matches and ifs here. It'd be nice to have a comment indicating what you are looking for. Something like:
// Return true for fields of packed structs, unless those fields have alignment 1.
RFC 1240 states that it is unsafe to capture references into a
packed-struct. This PR ensures that when a closure captures a precise
path, we aren't violating this safety constraint.
To acheive so we restrict the capture precision to the struct itself.
An interesting edge case:
```rust
struct Foo(String);
let foo: Foo;
let c = || {
println!("{}", foo.0);
let x = foo.0;
}
```
Given how closures get desugared today, foo.0 will be moved into the
closure, making the `println!`, safe. However this can be very subtle
and also will be unsafe if the closure gets inline.
Closes: rust-lang/project-rfc-2229#33
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@nikomatsakis updated |
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@bors r+ delegate+ |
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📌 Commit 612a9b2 has been approved by |
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…akis
2229: Handle capturing a reference into a repr packed struct
RFC 1240 states that it is unsafe to capture references into a
packed-struct. This PR ensures that when a closure captures a precise
path, we aren't violating this safety constraint.
To acheive so we restrict the capture precision to the struct itself.
An interesting edge case where we decided to restrict precision:
```rust
struct Foo(String);
let foo: Foo;
let c = || {
println!("{}", foo.0);
let x = foo.0;
}
```
Given how closures get desugared today, foo.0 will be moved into the
closure, making the `println!`, safe. However this can be very subtle
and also will be unsafe if the closure gets inline.
Closes: rust-lang/project-rfc-2229#33
r? `@nikomatsakis`
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☀️ Test successful - checks-actions |
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RFC 1240 states that it is unsafe to capture references into a
packed-struct. This PR ensures that when a closure captures a precise
path, we aren't violating this safety constraint.
To acheive so we restrict the capture precision to the struct itself.
An interesting edge case where we decided to restrict precision:
Given how closures get desugared today, foo.0 will be moved into the
closure, making the
println!, safe. However this can be very subtleand also will be unsafe if the closure gets inline.
Closes: rust-lang/project-rfc-2229#33
r? @nikomatsakis