Suggest the `[const] Destruct` bound for type parameters in const functions when missing by jakubadamw · Pull Request #155013 · rust-lang/rust

jakubadamw · 2026-04-08T21:23:12Z

When a const function drops a value whose type is a type parameter without a [const] Destruct bound, suggest adding it so that the destructor can be evaluated at compile-time.

Closes #103270.

Example:

const fn f(_x: impl std::fmt::Debug) {}

Before:

error[E0493]: destructor of `impl std::fmt::Debug` cannot be evaluated at compile-time
  --> $DIR/min_const_fn.rs:1:11
   |
LL | const fn f(_x: impl std::fmt::Debug) {}
   |                  ^^                         - value is dropped here
   |                  |
   |                  the destructor for this type cannot be evaluated in constant functions

After:

error[E0493]: destructor of `impl std::fmt::Debug` cannot be evaluated at compile-time
  --> $DIR/min_const_fn.rs:1:11
   |
LL | const fn f(_x: impl std::fmt::Debug) {}
   |                  ^^                         - value is dropped here
   |                  |
   |                  the destructor for this type cannot be evaluated in constant functions
   |
help: consider restricting opaque type `impl std::fmt::Debug` with unstable trait `Destruct`
   |
LL | const fn f(_x: impl std::fmt::Debug + [const] Destruct) {}
   |                                           ++++++++++++++++++

No new tests as the existing ones had their results updated with the new suggestion.

rustbot · 2026-04-08T21:23:16Z

Some changes occurred to constck

cc @fee1-dead

Some changes occurred to the CTFE machinery

cc @RalfJung, @oli-obk, @lcnr

rustbot · 2026-04-08T21:23:18Z

r? @wesleywiser

rustbot has assigned @wesleywiser.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

Why was this reviewer chosen?

The reviewer was selected based on:

Owners of files modified in this PR: compiler
compiler expanded to 69 candidates
Random selection from 12 candidates

Kivooeo · 2026-04-08T23:38:46Z

thanks for the contribution, but this is experimental syntax which means syntax may change in future, so I think it should be held until stabilization

wesleywiser

I think we would probably only want to offer this suggestion if the user is on a nightly compiler.

View changes since this review

rustbot · 2026-04-24T20:12:54Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

jakubadamw · 2026-07-13T00:06:40Z

@wesleywiser, thank you, I made the suggestion trigger on nightly only. 🙂

…ctions When a const function drops a value whose type is a type parameter, suggest adding a `[const] Destruct` bound so the destructor can be evaluated at compile-time.

The suggested bound requires the unstable `const_destruct` feature, so it is not actionable on a stable compiler. Add a run-make test that verifies the suggestion is only emitted on nightly.

rustbot · 2026-07-13T09:09:24Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

oli-obk

r? @oli-obk

@bors r+ rollup

View changes since this review

rust-bors · 2026-07-14T11:10:00Z

📌 Commit 2f961b8 has been approved by oli-obk

It is now in the queue for this repository.

Suggest the `[const] Destruct` bound for type parameters in const functions when missing When a const function drops a value whose type is a type parameter without a `[const] Destruct` bound, suggest adding it so that the destructor can be evaluated at compile-time. Closes rust-lang#103270. Example: ```rust const fn f(_x: impl std::fmt::Debug) {} ``` Before: ``` error[E0493]: destructor of `impl std::fmt::Debug` cannot be evaluated at compile-time --> $DIR/min_const_fn.rs:1:11 | LL | const fn f(_x: impl std::fmt::Debug) {} | ^^ - value is dropped here | | | the destructor for this type cannot be evaluated in constant functions ``` After: ``` error[E0493]: destructor of `impl std::fmt::Debug` cannot be evaluated at compile-time --> $DIR/min_const_fn.rs:1:11 | LL | const fn f(_x: impl std::fmt::Debug) {} | ^^ - value is dropped here | | | the destructor for this type cannot be evaluated in constant functions | help: consider restricting opaque type `impl std::fmt::Debug` with unstable trait `Destruct` | LL | const fn f(_x: impl std::fmt::Debug + [const] Destruct) {} | ++++++++++++++++++ ``` No new tests as the existing ones had their results updated with the new suggestion.

…uwer Rollup of 22 pull requests Successful merges: - #156047 (Fix trait method resolution on an adjusted never type) - #157824 (Comptime inherent impls) - #158235 (Store `DefId` instead of `EiiDecl` in `EiiImplResolution::Known`) - #158723 (Support EII on Windows MSVC) - #158993 (rerun in original typing mode if we meet any opaques in post analysis) - #159160 (Make `HasTokens` a sub-trait of `HasAttrs`.) - #159183 (Introduce InstanceKind::LlvmIntrinsic) - #159251 (Bump rustc-perf submodule) - #155013 (Suggest the `[const] Destruct` bound for type parameters in const functions when missing) - #159155 (unstable book: Document `diagnostic_on_unknown` feature) - #159235 (Add regression test for #95719) - #159243 (inline Once wait and wait_force) - #159255 (Replace shortened type with `_` instead of `...` as placeholder) - #159259 (Add regression test for #144033) - #159265 (bootstrap: skip intrinsic-test when rustfmt is unavailable) - #159269 (disable range-len-try-from.rs on s390x) - #159272 (slice: make swap delegate to swap_unchecked) - #159274 (bootstrap: Rename `std_crates_for_run_make` to `std_crates_for_make_run`) - #159275 (remove obsolete comment) - #159277 (Construct `tokens` for attrs made by `mk_attr_word` and other variants) - #159283 (Remove obsolete verbose flag from deref/ref suggestions) - #159290 (rustc-dev-guide subtree update)

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. labels Apr 8, 2026

rustbot assigned wesleywiser Apr 8, 2026

jakubadamw changed the title ~~Suggest the [const] Destruct bound for type parameters in const functions~~ Suggest the [const] Destruct bound for type parameters in const functions when missing Apr 8, 2026

wesleywiser requested changes Apr 24, 2026

View reviewed changes

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Apr 24, 2026

fee1-dead self-assigned this Apr 25, 2026

This comment has been minimized.

Sign in to view

jakubadamw force-pushed the issue-103270 branch from 2f950f9 to 517b3e6 Compare July 13, 2026 00:03

rustbot added the A-run-make Area: port run-make Makefiles to rmake.rs label Jul 13, 2026

This comment has been minimized.

Sign in to view

jakubadamw requested a review from wesleywiser July 13, 2026 00:05

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jul 13, 2026

This comment has been minimized.

Sign in to view

jakubadamw added 3 commits July 13, 2026 10:08

Suggest the [const] Destruct bound for type parameters in const fun…

7abc537

…ctions When a const function drops a value whose type is a type parameter, suggest adding a `[const] Destruct` bound so the destructor can be evaluated at compile-time.

Bless tests affected by the [const] Destruct suggestion

4fca6bd

Only offer the [const] Destruct suggestion on a nightly compiler

2f961b8

The suggested bound requires the unstable `const_destruct` feature, so it is not actionable on a stable compiler. Add a run-make test that verifies the suggestion is only emitted on nightly.

jakubadamw force-pushed the issue-103270 branch from 517b3e6 to 2f961b8 Compare July 13, 2026 09:09

oli-obk approved these changes Jul 14, 2026

View reviewed changes

rustbot assigned oli-obk and unassigned wesleywiser Jul 14, 2026

rustbot unassigned fee1-dead Jul 14, 2026

rust-bors Bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 14, 2026

JonathanBrouwer mentioned this pull request Jul 14, 2026

Rollup of 17 pull requests #159281

Closed

JonathanBrouwer mentioned this pull request Jul 14, 2026

Rollup of 21 pull requests #159292

Closed

JonathanBrouwer mentioned this pull request Jul 14, 2026

Rollup of 22 pull requests #159293

Open

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

Uh oh!

Suggest the `[const] Destruct` bound for type parameters in const functions when missing#155013

Suggest the `[const] Destruct` bound for type parameters in const functions when missing#155013
jakubadamw wants to merge 3 commits into
rust-lang:mainfrom
jakubadamw:issue-103270

jakubadamw commented Apr 8, 2026 •

edited by rustbot

Loading

Uh oh!

rustbot commented Apr 8, 2026

Uh oh!

rustbot commented Apr 8, 2026

Uh oh!

Kivooeo commented Apr 8, 2026

Uh oh!

wesleywiser left a comment •

edited by rustbot

Loading

Uh oh!

rustbot commented Apr 24, 2026

Uh oh!

This comment has been minimized.

This comment has been minimized.

jakubadamw commented Jul 13, 2026

Uh oh!

This comment has been minimized.

rustbot commented Jul 13, 2026

Uh oh!

oli-obk left a comment •

edited by rustbot

Loading

Uh oh!

rust-bors Bot commented Jul 14, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

7 participants

Uh oh!

Uh oh!

Conversation

jakubadamw commented Apr 8, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

rustbot commented Apr 8, 2026

Uh oh!

rustbot commented Apr 8, 2026

Uh oh!

Kivooeo commented Apr 8, 2026

Uh oh!

wesleywiser left a comment • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

rustbot commented Apr 24, 2026

Uh oh!

This comment has been minimized.

This comment has been minimized.

jakubadamw commented Jul 13, 2026

Uh oh!

This comment has been minimized.

rustbot commented Jul 13, 2026

Uh oh!

oli-obk left a comment • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

rust-bors Bot commented Jul 14, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

7 participants

jakubadamw commented Apr 8, 2026 •

edited by rustbot

Loading

wesleywiser left a comment •

edited by rustbot

Loading

oli-obk left a comment •

edited by rustbot

Loading