constify const Fn*: Destruct by bend-n · Pull Request #153874 · rust-lang/rust

bend-n · 2026-03-14T15:16:28Z

makes closures const destruct where their upvars are. i think this makes sense
and is how this should be implemented.

rustbot · 2026-03-14T15:16:33Z

oli-obk is not on the review rotation at the moment.
They may take a while to respond.

oli-obk · 2026-03-14T15:57:44Z

+#[test]
+fn extra_const_array_ops() {
+    let x: [u8; 4] =
+        const { std::array::from_fn(const |i| i + 4).map(const |x| x * 2).map(const |x| x as _) };


Also add a test with upvars (both trivial ones and ones with const Drop impls

And a UI test that fails if an upvar is not const Destruct

oli-obk · 2026-03-16T14:44:10Z

lgtm. Pls squash the commits as the test commit doesn't test "before this PR" behaviour but is just tied to the second commit

r=me

@bors delegate+

rust-bors · 2026-03-16T14:44:13Z

✌️ @bend-n, you can now approve this pull request!

If @oli-obk told you to "r=me" after making some further change, then please make that change and post @bors r=oli-obk.

bend-n · 2026-03-16T15:17:10Z

@bors r=oli-obk

rust-bors · 2026-03-16T17:19:57Z

⌛ Testing commit 04b3bca with merge 629890a...

Workflow: https://github.com/rust-lang/rust/actions/runs/23156680213

@oli-obk

constify const Fn*: Destruct makes closures const destruct where their upvars are. i think this makes sense and is how this should be implemented. r? @oli-obk

rust-bors · 2026-03-16T23:25:45Z

💥 Test timed out after 21600s

theemathas · 2026-03-17T03:40:28Z


-        // Coroutines and closures could implement `[const] Drop`,
+        // Closures are [const] Destruct when all of their upvars (captures) are [const] Destruct.
+        ty::Closure(def, args) if cx.closure_is_const(def) => {


The old and next solvers in this PR seem to treat non-const closures differently. Please test if this code has the same behavior on the old solver and the next solver:

#![feature(const_trait_impl, const_destruct)] use std::marker::Destruct; const fn foo(x: i32) -> impl const Destruct { move || { std::hint::black_box(x); } }

bend-n · 2026-03-17T16:22:01Z

@bors retry

@oli-obk

… r=oli-obk constify const Fn*: Destruct makes closures const destruct where their upvars are. i think this makes sense and is how this should be implemented. r? @oli-obk

rust-bors · 2026-03-17T16:43:07Z

⚠️ A new commit 5ff4862d1f014b3491095d98d280fbd15f2838d5 was pushed.

This pull request was unapproved.

This PR was contained in a rollup (#154007), which was closed.

bend-n · 2026-03-17T16:46:32Z

@rustbot ready

oli-obk · 2026-03-24T15:56:08Z

@bors r+

rust-bors · 2026-03-24T15:56:11Z

📌 Commit b90abe6 has been approved by oli-obk

It is now in the queue for this repository.

…uwer Rollup of 5 pull requests Successful merges: - #152710 (Unalign `PackedFingerprint` on all hosts, not just x86 and x86-64) - #153874 (constify const Fn*: Destruct) - #154097 (improve validation error messages: show surrounding type) - #154277 (use `minicore` more in testing inline assembly) - #154293 (Use verbose span suggestion for type const)

…uwer Rollup of 5 pull requests Successful merges: - rust-lang/rust#152710 (Unalign `PackedFingerprint` on all hosts, not just x86 and x86-64) - rust-lang/rust#153874 (constify const Fn*: Destruct) - rust-lang/rust#154097 (improve validation error messages: show surrounding type) - rust-lang/rust#154277 (use `minicore` more in testing inline assembly) - rust-lang/rust#154293 (Use verbose span suggestion for type const)

rustbot assigned oli-obk Mar 14, 2026