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document Rust 1.90 changes #580

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6cecf63
document Rust 1.90 changes
tshepang Oct 10, 2025
f669cc9
bump version
tshepang Oct 10, 2025
b874b5d
the restriction was not documented
tshepang Oct 13, 2025
a9fdd2d
remove an obsolete restriction
tshepang Oct 16, 2025
af19a30
restore an adjusted restriction
tshepang Oct 18, 2025
47ce8fd
that equivalent paragraph was actually moved to a new place
tshepang Oct 18, 2025
00c1bfd
add restrictions on constant expressions
tshepang Oct 18, 2025
d261499
lifetime extension here applies to static lifetimes
tshepang Oct 25, 2025
6465ff2
stronger wording
tshepang Oct 25, 2025
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11 changes: 9 additions & 2 deletions src/changelog.rst
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Expand Up @@ -331,8 +331,15 @@ Language changes in Rust 1.83.0

* `Stabilize \`&mut\`, \`*mut\`, \`&Cell\`, and \`*const Cell\` in const. <https://github.com/rust-lang/rust/pull/129195>`_

* Changed paragraphs: :p:`fls_to4e7imq2c0w`, :p:`fls_6g7c1kjrmfnr`, :p:`fls_hkbwa8xx2fwx`
* Removed paragraph: :p:`fls_ox6sgl9n43g2`
* Changed paragraphs:

- :p:`fls_to4e7imq2c0w`

- :p:`fls_6g7c1kjrmfnr`

- :p:`fls_hkbwa8xx2fwx`

- :p:`fls_ox6sgl9n43g2`

* `Allow creating references to statics in \`const\` initializers. <https://github.com/rust-lang/rust/pull/129759>`_

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3 changes: 3 additions & 0 deletions src/values.rst
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Expand Up @@ -95,6 +95,9 @@ The :t:`type specification` of a :t:`constant` shall have ``'static``
The :t:`type` of a :t:`constant` shall implement the :std:`core::marker::Sized`
:t:`trait`.

:dp:`fls_ox6sgl9n43g2`
The type of a :t:`constant` cannot be a :t:`mutable reference type`.
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@traviscross traviscross Oct 18, 2025

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This doesn't cover it.

struct W<T>(T);
const _: W<&mut ()> = W(&mut ()); //~ ERROR
const _: W<&AtomicU8> = W(&AtomicU8::new(0)); //~ ERROR

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@tshepang tshepang Oct 18, 2025

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to be clear, are those additional rules

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@traviscross traviscross Oct 18, 2025 •
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What I'm getting at here specifically is that the final value can't contain any mutable references, not just that it can't be a mutable reference type.

struct W<T>(T);
static mut S: u8 = 0;
const _: W<&mut u8> = W(unsafe { &mut S }); //~ ERROR
//       ^^^^^^^^^^ Not a mutable reference type.

And then, yes, there are additional rules that prohibit mutable borrows of lifetime-extended temporaries even when that doesn't result in a mutable reference being contained in the final value.

struct W<T>(T);
const _: W<&u8> = W(&mut 0); //~ ERROR

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@tshepang tshepang Oct 18, 2025

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at attempt 00c1bfd


:dp:`fls_ndmfqxjpvsqy`
A :t:`constant initializer` is a :t:`construct` that provides the :t:`value` of
its related :t:`constant`.
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