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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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15 changes: 15 additions & 0 deletions src/changelog.rst
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Expand Up @@ -18,6 +18,21 @@ with the change that has been applied due to it.
just the language changes that had an impact to the FLS. See the `release
notes`_ for a full list of changes.

Language changes in Rust 1.90.0
-------------------------------

- `Split up the unknown_or_malformed_diagnostic_attributes lint <https://github.com/rust-lang/rust/pull/140717>`_

- No change: lints are not part of the FLS

- `Allow constants whose final value has references to mutable/external memory, but reject such constants as patterns <https://github.com/rust-lang/rust/pull/140942>`_

- New paragraph: :p:`fls_wJ9f906BlBvg`
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@traviscross traviscross Oct 12, 2025

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Do I read things correctly that we don't need to relax the legality rules for constants in 7.1 because they already did not state the restriction against references to mutable places? (Should the changelog say that?)

Similarly, there's no legality rule in 7.1 restricting against mutable references in the final value of a constant. Is that leaning instead on the rule in chapter 6, fls_ox6sgl9n43g2, that:

It is a static error to create a :t:mutable reference in a :t:constant context.

?

Note, however, that rule is wrong:

const _: () = { _ = &mut 0; () }; // OK

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@traviscross traviscross Oct 12, 2025

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Similarly, are we missing the rule against shared references to interior mutable lifetime-extended temporaries in the final value of a constant?

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@PLeVasseur PLeVasseur Oct 13, 2025

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@traviscross -- by:

Similarly, are we missing the rule against shared references to interior mutable lifetime-extended temporaries in the final value of a constant?

You refer here to this portion of the Reference, inside the Note?

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@traviscross traviscross Oct 13, 2025

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Yes; normatively it's stated in https://doc.rust-lang.org/nightly/reference/const_eval.html#r-const-eval.const-expr.borrows.

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@tshepang tshepang Oct 13, 2025

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Do I read things correctly that we don't need to relax the legality rules for constants in 7.1 because they already did not state the restriction against references to mutable places? (Should the changelog say that?)

oh, indeed, the changelog can say that

Similarly, there's no legality rule in 7.1 restricting against mutable references in the final value of a constant. Is that leaning instead on the rule in chapter 6, fls_ox6sgl9n43g2, that:

It is a static error to create a :t:mutable reference in a :t:constant context.

?

Note, however, that rule is wrong:

const _: () = { _ = &mut 0; () }; // OK

let me submit a change fixing this

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@tshepang tshepang Oct 16, 2025 •
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b874b5d and a9fdd2d


- `Allow volatile access to non-Rust memory, including address 0 <https://github.com/rust-lang/rust/pull/141260>`_

- No change: lints are not part of the FLS

Language changes in Rust 1.89.0
-------------------------------

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6 changes: 6 additions & 0 deletions src/patterns.rst
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Expand Up @@ -370,6 +370,12 @@ When a :t:`path pattern` refers to an :t:`associated constant` or a
:t:`constant`, the :t:`type` of the :t:`associated constant` or :t:`constant`
shall be :t:`structurally equal`.

:dp:`fls_wJ9f906BlBvg`
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@PLeVasseur PLeVasseur Oct 13, 2025

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Adding some traceability here to the Reference PR portion which means the FLS need be updated.

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@tshepang tshepang Oct 13, 2025

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what is meant by "need be updated"

When a :t:`path pattern` refers to an :t:`associated constant` or a
:t:`constant`, the :t:`constant` must not contain any references to
:t:`[mutable static]s`, :t:`[static]s` with :t:`interior mutability`,
or :t:`[external static]s`.

:dp:`fls_hF19K8sWU8FF`
When the type of the :t:`path pattern` is of an :t:`enum type` or
:t:`struct type`, then the :t:`enum type` or :t:`struct type` shall be subject
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2 changes: 1 addition & 1 deletion version.rst
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@@ -1,4 +1,4 @@
.. SPDX-License-Identifier: MIT OR Apache-2.0
SPDX-FileCopyrightText: The Ferrocene Developers
SPDX-FileCopyrightText: The Rust Project Developers
.. |spec_version| replace:: 1.88.0
.. |spec_version| replace:: 1.90.0