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Make const BorrowMut require const Borrow and make const Fn require const FnMut #147939

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Make const BorrowMut require const Borrow and make const Fn require const FnMut #147939

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@theemathas theemathas commented Oct 21, 2025

This makes it consistent with other const traits in the standard library with supertraits.

I am currently unsure if const FnMut should require const FnOnce or not. See zulip discussion.

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Remove an attempted error annotation
e548d77 
This file previously contained an error annotation with incorrect syntax.
Remove this annotation, as per the dev guide, since this is marked as known-bug.
https://rustc-dev-guide.rust-lang.org/tests/ui.html#known-bugs
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Make const BorrowMut require const Borrow
a2d1d14
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Make const Fn require const FnMut
28819e0
@rustbot 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 Oct 21, 2025
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rustbot commented Oct 21, 2025

r? @lcnr

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oli-obk
oli-obk reviewed Oct 21, 2025
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tests/ui/traits/const-traits/const_closure-const_trait_impl-ice-113381.rs

fn main() {
(const || (()).foo())();
// ^ ERROR: cannot call non-const method `<() as Foo>::foo` in constant functions
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We sometimes leave these in to keep some context for when someone fixes the test. Fine here tho

lcnr
lcnr reviewed Oct 23, 2025
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we should also dedup super traits for constness goals, like we already do for traits.

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lcnr commented Oct 23, 2025

idk if that should be part of this PR, regardless

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@rustbot rustbot assigned oli-obk and unassigned lcnr Oct 23, 2025
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rustbot commented Oct 23, 2025

oli-obk is not on the review rotation at the moment.
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@theemathas theemathas mentioned this pull request Oct 29, 2025
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