check if len of array const arg matches the expected len of the type when lowering to valtree by sjwang05 · Pull Request #158587 · rust-lang/rust

rustbot · 2026-06-29T23:01:45Z

rustbot has assigned @JohnTitor.
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 73 candidates
Random selection from 17 candidates

JohnTitor · 2026-07-03T08:00:04Z

 .map(|elem| self.lower_const_arg(elem, *elem_ty))
 .collect::<Vec<_>>();

+ if let Some(expected_len) = len.try_to_target_usize(tcx)


IMO it should catch more cases if len is normalized, e.g. type const LEN (I haven't checked deeply so it may be caught by somewhere already)
View changes since the review

Thanks, I changed it to call try_normalize_erasing_regions with an empty ParamEnv on the expected len and added a test for it, so now something like fn baz<const A: [u8; <S as Trait>::LEN]>() {} produces the correct error. Something like fn baz<T: Trait, const A: [u8; <T as Trait>::LEN]>() {} still ICEs if too long/produces UB if too short, however, since we can't resolve T to an actual type: trying to do try_evaluate_const with a non-empty ParamEnv led to cycle errors.

Could you open another issue and add an ICE test for that case (if not exists yet)? At least we should track it.

Opened #160553 and added a corresponding test to the crashes/ dir

rustbot · 2026-08-05T08:59:10Z

This PR changes a file inside tests/crashes. If a crash was fixed, please move into the corresponding ui subdir and add 'Fixes #' to the PR description to autoclose the issue upon merge.

rustbot · 2026-08-05T08:59:12Z

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.

sjwang05 · 2026-08-05T09:00:39Z

@rustbot ready

sjwang05 · 2026-08-05T18:22:48Z

Looks like -Copt-level=0 is needed for the crashtest, otherwise inlining followed by SimplifyLocals gets rid of the return value entirely.

...Neat!

JohnTitor

Thanks! @bors r+

rust-bors · 2026-08-08T23:40:19Z

📌 Commit d43f980 has been approved by JohnTitor

It is now in the queue for this repository.

check if len of array const arg matches the expected len of the type when lowering to valtree When creating valtrees for arrays passed as const args in `lower_const_arg_array`, we assume the array has the correct length without actually checking the length of the arg, leading to UB at runtime (rust-lang#155168) or an ICE during CTFE (rust-lang#151079). This PR adds a check comparing the expected length of the type with the actual number of elements, similar to `lower_const_arg_tup`. fixesrust-lang#155168

Rollup of 6 pull requests Successful merges: - #160529 (Upgrade and deduplicate dependencies) - #158517 (Initial implementation of named `Fn` trait parameters) - #158587 (check if len of array const arg matches the expected len of the type when lowering to valtree) - #160748 (Add regression test for cross-crate assoc const private field leak in rustdoc) - #160708 (remove old update mechanism) - #160768 (Fix autodiff_illegal.rs test)

Rollup of 5 pull requests Successful merges: - #158517 (Initial implementation of named `Fn` trait parameters) - #158587 (check if len of array const arg matches the expected len of the type when lowering to valtree) - #160748 (Add regression test for cross-crate assoc const private field leak in rustdoc) - #160708 (remove old update mechanism) - #160768 (Fix autodiff_illegal.rs test)

Rollup merge of #158587 - sjwang05:issue-155168, r=JohnTitor check if len of array const arg matches the expected len of the type when lowering to valtree When creating valtrees for arrays passed as const args in `lower_const_arg_array`, we assume the array has the correct length without actually checking the length of the arg, leading to UB at runtime (#155168) or an ICE during CTFE (#151079). This PR adds a check comparing the expected length of the type with the actual number of elements, similar to `lower_const_arg_tup`. fixes#155168

sjwang05 · 2026-06-29T23:01:40Z

When creating valtrees for arrays passed as const args in lower_const_arg_array, we assume the array has the correct length without actually checking the length of the arg, leading to UB at runtime (#155168) or an ICE during CTFE (#151079). This PR adds a check comparing the expected length of the type with the actual number of elements, similar to lower_const_arg_tup.

fixes#155168

rustbot · 2026-06-29T23:01:43Z

HIR ty lowering was modified

rustbot · 2026-06-29T23:01:45Z

rustbot has assigned @JohnTitor.
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 73 candidates
Random selection from 17 candidates

JohnTitor · 2026-07-03T08:00:04Z

 .map(|elem| self.lower_const_arg(elem, *elem_ty))
 .collect::<Vec<_>>();

+ if let Some(expected_len) = len.try_to_target_usize(tcx)


IMO it should catch more cases if len is normalized, e.g. type const LEN (I haven't checked deeply so it may be caught by somewhere already)
View changes since the review

Thanks, I changed it to call try_normalize_erasing_regions with an empty ParamEnv on the expected len and added a test for it, so now something like fn baz<const A: [u8; <S as Trait>::LEN]>() {} produces the correct error. Something like fn baz<T: Trait, const A: [u8; <T as Trait>::LEN]>() {} still ICEs if too long/produces UB if too short, however, since we can't resolve T to an actual type: trying to do try_evaluate_const with a non-empty ParamEnv led to cycle errors.

Could you open another issue and add an ICE test for that case (if not exists yet)? At least we should track it.

Opened #160553 and added a corresponding test to the crashes/ dir

rustbot · 2026-08-05T08:59:10Z

This PR changes a file inside tests/crashes. If a crash was fixed, please move into the corresponding ui subdir and add 'Fixes #' to the PR description to autoclose the issue upon merge.

rustbot · 2026-08-05T08:59:12Z

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.

sjwang05 · 2026-08-05T09:00:39Z

@rustbot ready

sjwang05 · 2026-08-05T18:22:48Z

Looks like -Copt-level=0 is needed for the crashtest, otherwise inlining followed by SimplifyLocals gets rid of the return value entirely.

...Neat!

JohnTitor

Thanks! @bors r+

rust-bors · 2026-08-08T23:40:19Z

📌 Commit d43f980 has been approved by JohnTitor

It is now in the queue for this repository.

check if len of array const arg matches the expected len of the type when lowering to valtree When creating valtrees for arrays passed as const args in `lower_const_arg_array`, we assume the array has the correct length without actually checking the length of the arg, leading to UB at runtime (rust-lang#155168) or an ICE during CTFE (rust-lang#151079). This PR adds a check comparing the expected length of the type with the actual number of elements, similar to `lower_const_arg_tup`. fixesrust-lang#155168

Rollup of 6 pull requests Successful merges: - #160529 (Upgrade and deduplicate dependencies) - #158517 (Initial implementation of named `Fn` trait parameters) - #158587 (check if len of array const arg matches the expected len of the type when lowering to valtree) - #160748 (Add regression test for cross-crate assoc const private field leak in rustdoc) - #160708 (remove old update mechanism) - #160768 (Fix autodiff_illegal.rs test)

Rollup of 5 pull requests Successful merges: - #158517 (Initial implementation of named `Fn` trait parameters) - #158587 (check if len of array const arg matches the expected len of the type when lowering to valtree) - #160748 (Add regression test for cross-crate assoc const private field leak in rustdoc) - #160708 (remove old update mechanism) - #160768 (Fix autodiff_illegal.rs test)

Rollup merge of #158587 - sjwang05:issue-155168, r=JohnTitor check if len of array const arg matches the expected len of the type when lowering to valtree When creating valtrees for arrays passed as const args in `lower_const_arg_array`, we assume the array has the correct length without actually checking the length of the arg, leading to UB at runtime (#155168) or an ICE during CTFE (#151079). This PR adds a check comparing the expected length of the type with the actual number of elements, similar to `lower_const_arg_tup`. fixes#155168

sjwang05 · 2026-06-29T23:01:40Z

When creating valtrees for arrays passed as const args in lower_const_arg_array, we assume the array has the correct length without actually checking the length of the arg, leading to UB at runtime (#155168) or an ICE during CTFE (#151079). This PR adds a check comparing the expected length of the type with the actual number of elements, similar to lower_const_arg_tup.

fixes#155168

rustbot · 2026-06-29T23:01:43Z

HIR ty lowering was modified

rustbot · 2026-06-29T23:01:45Z

rustbot has assigned @JohnTitor.
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 73 candidates
Random selection from 17 candidates

JohnTitor · 2026-07-03T08:00:04Z

 .map(|elem| self.lower_const_arg(elem, *elem_ty))
 .collect::<Vec<_>>();

+ if let Some(expected_len) = len.try_to_target_usize(tcx)


IMO it should catch more cases if len is normalized, e.g. type const LEN (I haven't checked deeply so it may be caught by somewhere already)
View changes since the review

Thanks, I changed it to call try_normalize_erasing_regions with an empty ParamEnv on the expected len and added a test for it, so now something like fn baz<const A: [u8; <S as Trait>::LEN]>() {} produces the correct error. Something like fn baz<T: Trait, const A: [u8; <T as Trait>::LEN]>() {} still ICEs if too long/produces UB if too short, however, since we can't resolve T to an actual type: trying to do try_evaluate_const with a non-empty ParamEnv led to cycle errors.

Could you open another issue and add an ICE test for that case (if not exists yet)? At least we should track it.

Opened #160553 and added a corresponding test to the crashes/ dir

rustbot · 2026-08-05T08:59:10Z

This PR changes a file inside tests/crashes. If a crash was fixed, please move into the corresponding ui subdir and add 'Fixes #' to the PR description to autoclose the issue upon merge.

rustbot · 2026-08-05T08:59:12Z

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.

sjwang05 · 2026-08-05T09:00:39Z

@rustbot ready

sjwang05 · 2026-08-05T18:22:48Z

Looks like -Copt-level=0 is needed for the crashtest, otherwise inlining followed by SimplifyLocals gets rid of the return value entirely.

...Neat!

JohnTitor

Thanks! @bors r+

rust-bors · 2026-08-08T23:40:19Z

📌 Commit d43f980 has been approved by JohnTitor

It is now in the queue for this repository.

check if len of array const arg matches the expected len of the type when lowering to valtree When creating valtrees for arrays passed as const args in `lower_const_arg_array`, we assume the array has the correct length without actually checking the length of the arg, leading to UB at runtime (rust-lang#155168) or an ICE during CTFE (rust-lang#151079). This PR adds a check comparing the expected length of the type with the actual number of elements, similar to `lower_const_arg_tup`. fixesrust-lang#155168

Rollup of 6 pull requests Successful merges: - #160529 (Upgrade and deduplicate dependencies) - #158517 (Initial implementation of named `Fn` trait parameters) - #158587 (check if len of array const arg matches the expected len of the type when lowering to valtree) - #160748 (Add regression test for cross-crate assoc const private field leak in rustdoc) - #160708 (remove old update mechanism) - #160768 (Fix autodiff_illegal.rs test)

Rollup of 5 pull requests Successful merges: - #158517 (Initial implementation of named `Fn` trait parameters) - #158587 (check if len of array const arg matches the expected len of the type when lowering to valtree) - #160748 (Add regression test for cross-crate assoc const private field leak in rustdoc) - #160708 (remove old update mechanism) - #160768 (Fix autodiff_illegal.rs test)

Rollup merge of #158587 - sjwang05:issue-155168, r=JohnTitor check if len of array const arg matches the expected len of the type when lowering to valtree When creating valtrees for arrays passed as const args in `lower_const_arg_array`, we assume the array has the correct length without actually checking the length of the arg, leading to UB at runtime (#155168) or an ICE during CTFE (#151079). This PR adds a check comparing the expected length of the type with the actual number of elements, similar to `lower_const_arg_tup`. fixes#155168

sjwang05 · 2026-06-29T23:01:40Z

When creating valtrees for arrays passed as const args in lower_const_arg_array, we assume the array has the correct length without actually checking the length of the arg, leading to UB at runtime (#155168) or an ICE during CTFE (#151079). This PR adds a check comparing the expected length of the type with the actual number of elements, similar to lower_const_arg_tup.

fixes#155168

rustbot · 2026-06-29T23:01:43Z

HIR ty lowering was modified

rustbot · 2026-06-29T23:01:45Z

rustbot has assigned @JohnTitor.
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 73 candidates
Random selection from 17 candidates

JohnTitor · 2026-07-03T08:00:04Z

 .map(|elem| self.lower_const_arg(elem, *elem_ty))
 .collect::<Vec<_>>();

+ if let Some(expected_len) = len.try_to_target_usize(tcx)


IMO it should catch more cases if len is normalized, e.g. type const LEN (I haven't checked deeply so it may be caught by somewhere already)
View changes since the review

Thanks, I changed it to call try_normalize_erasing_regions with an empty ParamEnv on the expected len and added a test for it, so now something like fn baz<const A: [u8; <S as Trait>::LEN]>() {} produces the correct error. Something like fn baz<T: Trait, const A: [u8; <T as Trait>::LEN]>() {} still ICEs if too long/produces UB if too short, however, since we can't resolve T to an actual type: trying to do try_evaluate_const with a non-empty ParamEnv led to cycle errors.

Could you open another issue and add an ICE test for that case (if not exists yet)? At least we should track it.

Opened #160553 and added a corresponding test to the crashes/ dir

rustbot · 2026-08-05T08:59:10Z

This PR changes a file inside tests/crashes. If a crash was fixed, please move into the corresponding ui subdir and add 'Fixes #' to the PR description to autoclose the issue upon merge.

rustbot · 2026-08-05T08:59:12Z

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.

sjwang05 · 2026-08-05T09:00:39Z

@rustbot ready

sjwang05 · 2026-08-05T18:22:48Z

Looks like -Copt-level=0 is needed for the crashtest, otherwise inlining followed by SimplifyLocals gets rid of the return value entirely.

...Neat!

JohnTitor

Thanks! @bors r+

rust-bors · 2026-08-08T23:40:19Z

📌 Commit d43f980 has been approved by JohnTitor

It is now in the queue for this repository.

check if len of array const arg matches the expected len of the type when lowering to valtree When creating valtrees for arrays passed as const args in `lower_const_arg_array`, we assume the array has the correct length without actually checking the length of the arg, leading to UB at runtime (rust-lang#155168) or an ICE during CTFE (rust-lang#151079). This PR adds a check comparing the expected length of the type with the actual number of elements, similar to `lower_const_arg_tup`. fixesrust-lang#155168

Rollup of 6 pull requests Successful merges: - #160529 (Upgrade and deduplicate dependencies) - #158517 (Initial implementation of named `Fn` trait parameters) - #158587 (check if len of array const arg matches the expected len of the type when lowering to valtree) - #160748 (Add regression test for cross-crate assoc const private field leak in rustdoc) - #160708 (remove old update mechanism) - #160768 (Fix autodiff_illegal.rs test)

Rollup of 5 pull requests Successful merges: - #158517 (Initial implementation of named `Fn` trait parameters) - #158587 (check if len of array const arg matches the expected len of the type when lowering to valtree) - #160748 (Add regression test for cross-crate assoc const private field leak in rustdoc) - #160708 (remove old update mechanism) - #160768 (Fix autodiff_illegal.rs test)

Rollup merge of #158587 - sjwang05:issue-155168, r=JohnTitor check if len of array const arg matches the expected len of the type when lowering to valtree When creating valtrees for arrays passed as const args in `lower_const_arg_array`, we assume the array has the correct length without actually checking the length of the arg, leading to UB at runtime (#155168) or an ICE during CTFE (#151079). This PR adds a check comparing the expected length of the type with the actual number of elements, similar to `lower_const_arg_tup`. fixes#155168

sjwang05 · 2026-06-29T23:01:40Z

When creating valtrees for arrays passed as const args in lower_const_arg_array, we assume the array has the correct length without actually checking the length of the arg, leading to UB at runtime (#155168) or an ICE during CTFE (#151079). This PR adds a check comparing the expected length of the type with the actual number of elements, similar to lower_const_arg_tup.

fixes#155168

rustbot · 2026-06-29T23:01:43Z

HIR ty lowering was modified

rustbot · 2026-06-29T23:01:45Z

rustbot has assigned @JohnTitor.
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 73 candidates
Random selection from 17 candidates

JohnTitor · 2026-07-03T08:00:04Z

 .map(|elem| self.lower_const_arg(elem, *elem_ty))
 .collect::<Vec<_>>();

+ if let Some(expected_len) = len.try_to_target_usize(tcx)


IMO it should catch more cases if len is normalized, e.g. type const LEN (I haven't checked deeply so it may be caught by somewhere already)
View changes since the review

Thanks, I changed it to call try_normalize_erasing_regions with an empty ParamEnv on the expected len and added a test for it, so now something like fn baz<const A: [u8; <S as Trait>::LEN]>() {} produces the correct error. Something like fn baz<T: Trait, const A: [u8; <T as Trait>::LEN]>() {} still ICEs if too long/produces UB if too short, however, since we can't resolve T to an actual type: trying to do try_evaluate_const with a non-empty ParamEnv led to cycle errors.

Could you open another issue and add an ICE test for that case (if not exists yet)? At least we should track it.

Opened #160553 and added a corresponding test to the crashes/ dir

rustbot · 2026-08-05T08:59:10Z

This PR changes a file inside tests/crashes. If a crash was fixed, please move into the corresponding ui subdir and add 'Fixes #' to the PR description to autoclose the issue upon merge.

rustbot · 2026-08-05T08:59:12Z

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.

sjwang05 · 2026-08-05T09:00:39Z

@rustbot ready

sjwang05 · 2026-08-05T18:22:48Z

Looks like -Copt-level=0 is needed for the crashtest, otherwise inlining followed by SimplifyLocals gets rid of the return value entirely.

...Neat!

JohnTitor

Thanks! @bors r+

rust-bors · 2026-08-08T23:40:19Z

📌 Commit d43f980 has been approved by JohnTitor

It is now in the queue for this repository.

check if len of array const arg matches the expected len of the type when lowering to valtree When creating valtrees for arrays passed as const args in `lower_const_arg_array`, we assume the array has the correct length without actually checking the length of the arg, leading to UB at runtime (rust-lang#155168) or an ICE during CTFE (rust-lang#151079). This PR adds a check comparing the expected length of the type with the actual number of elements, similar to `lower_const_arg_tup`. fixesrust-lang#155168

Rollup of 6 pull requests Successful merges: - #160529 (Upgrade and deduplicate dependencies) - #158517 (Initial implementation of named `Fn` trait parameters) - #158587 (check if len of array const arg matches the expected len of the type when lowering to valtree) - #160748 (Add regression test for cross-crate assoc const private field leak in rustdoc) - #160708 (remove old update mechanism) - #160768 (Fix autodiff_illegal.rs test)

Rollup of 5 pull requests Successful merges: - #158517 (Initial implementation of named `Fn` trait parameters) - #158587 (check if len of array const arg matches the expected len of the type when lowering to valtree) - #160748 (Add regression test for cross-crate assoc const private field leak in rustdoc) - #160708 (remove old update mechanism) - #160768 (Fix autodiff_illegal.rs test)

Rollup merge of #158587 - sjwang05:issue-155168, r=JohnTitor check if len of array const arg matches the expected len of the type when lowering to valtree When creating valtrees for arrays passed as const args in `lower_const_arg_array`, we assume the array has the correct length without actually checking the length of the arg, leading to UB at runtime (#155168) or an ICE during CTFE (#151079). This PR adds a check comparing the expected length of the type with the actual number of elements, similar to `lower_const_arg_tup`. fixes#155168

sjwang05 · 2026-06-29T23:01:40Z

When creating valtrees for arrays passed as const args in lower_const_arg_array, we assume the array has the correct length without actually checking the length of the arg, leading to UB at runtime (#155168) or an ICE during CTFE (#151079). This PR adds a check comparing the expected length of the type with the actual number of elements, similar to lower_const_arg_tup.

fixes#155168

rustbot · 2026-06-29T23:01:43Z

HIR ty lowering was modified

rustbot · 2026-06-29T23:01:45Z

rustbot has assigned @JohnTitor.
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 73 candidates
Random selection from 17 candidates

JohnTitor · 2026-07-03T08:00:04Z

 .map(|elem| self.lower_const_arg(elem, *elem_ty))
 .collect::<Vec<_>>();

+ if let Some(expected_len) = len.try_to_target_usize(tcx)


IMO it should catch more cases if len is normalized, e.g. type const LEN (I haven't checked deeply so it may be caught by somewhere already)
View changes since the review

Thanks, I changed it to call try_normalize_erasing_regions with an empty ParamEnv on the expected len and added a test for it, so now something like fn baz<const A: [u8; <S as Trait>::LEN]>() {} produces the correct error. Something like fn baz<T: Trait, const A: [u8; <T as Trait>::LEN]>() {} still ICEs if too long/produces UB if too short, however, since we can't resolve T to an actual type: trying to do try_evaluate_const with a non-empty ParamEnv led to cycle errors.

Could you open another issue and add an ICE test for that case (if not exists yet)? At least we should track it.

Opened #160553 and added a corresponding test to the crashes/ dir

rustbot · 2026-08-05T08:59:10Z

This PR changes a file inside tests/crashes. If a crash was fixed, please move into the corresponding ui subdir and add 'Fixes #' to the PR description to autoclose the issue upon merge.

rustbot · 2026-08-05T08:59:12Z

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.

sjwang05 · 2026-08-05T09:00:39Z

@rustbot ready

sjwang05 · 2026-08-05T18:22:48Z

Looks like -Copt-level=0 is needed for the crashtest, otherwise inlining followed by SimplifyLocals gets rid of the return value entirely.

...Neat!

JohnTitor

Thanks! @bors r+

rust-bors · 2026-08-08T23:40:19Z

📌 Commit d43f980 has been approved by JohnTitor

It is now in the queue for this repository.

check if len of array const arg matches the expected len of the type when lowering to valtree When creating valtrees for arrays passed as const args in `lower_const_arg_array`, we assume the array has the correct length without actually checking the length of the arg, leading to UB at runtime (rust-lang#155168) or an ICE during CTFE (rust-lang#151079). This PR adds a check comparing the expected length of the type with the actual number of elements, similar to `lower_const_arg_tup`. fixesrust-lang#155168

Rollup of 6 pull requests Successful merges: - #160529 (Upgrade and deduplicate dependencies) - #158517 (Initial implementation of named `Fn` trait parameters) - #158587 (check if len of array const arg matches the expected len of the type when lowering to valtree) - #160748 (Add regression test for cross-crate assoc const private field leak in rustdoc) - #160708 (remove old update mechanism) - #160768 (Fix autodiff_illegal.rs test)

Rollup of 5 pull requests Successful merges: - #158517 (Initial implementation of named `Fn` trait parameters) - #158587 (check if len of array const arg matches the expected len of the type when lowering to valtree) - #160748 (Add regression test for cross-crate assoc const private field leak in rustdoc) - #160708 (remove old update mechanism) - #160768 (Fix autodiff_illegal.rs test)

Rollup merge of #158587 - sjwang05:issue-155168, r=JohnTitor check if len of array const arg matches the expected len of the type when lowering to valtree When creating valtrees for arrays passed as const args in `lower_const_arg_array`, we assume the array has the correct length without actually checking the length of the arg, leading to UB at runtime (#155168) or an ICE during CTFE (#151079). This PR adds a check comparing the expected length of the type with the actual number of elements, similar to `lower_const_arg_tup`. fixes#155168

sjwang05 · 2026-06-29T23:01:40Z

When creating valtrees for arrays passed as const args in lower_const_arg_array, we assume the array has the correct length without actually checking the length of the arg, leading to UB at runtime (#155168) or an ICE during CTFE (#151079). This PR adds a check comparing the expected length of the type with the actual number of elements, similar to lower_const_arg_tup.

fixes#155168

rustbot · 2026-06-29T23:01:43Z

HIR ty lowering was modified

rustbot · 2026-06-29T23:01:45Z

rustbot has assigned @JohnTitor.
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 73 candidates
Random selection from 17 candidates

JohnTitor · 2026-07-03T08:00:04Z

 .map(|elem| self.lower_const_arg(elem, *elem_ty))
 .collect::<Vec<_>>();

+ if let Some(expected_len) = len.try_to_target_usize(tcx)


IMO it should catch more cases if len is normalized, e.g. type const LEN (I haven't checked deeply so it may be caught by somewhere already)
View changes since the review

Thanks, I changed it to call try_normalize_erasing_regions with an empty ParamEnv on the expected len and added a test for it, so now something like fn baz<const A: [u8; <S as Trait>::LEN]>() {} produces the correct error. Something like fn baz<T: Trait, const A: [u8; <T as Trait>::LEN]>() {} still ICEs if too long/produces UB if too short, however, since we can't resolve T to an actual type: trying to do try_evaluate_const with a non-empty ParamEnv led to cycle errors.

Could you open another issue and add an ICE test for that case (if not exists yet)? At least we should track it.

Opened #160553 and added a corresponding test to the crashes/ dir

rustbot · 2026-08-05T08:59:10Z

This PR changes a file inside tests/crashes. If a crash was fixed, please move into the corresponding ui subdir and add 'Fixes #' to the PR description to autoclose the issue upon merge.

rustbot · 2026-08-05T08:59:12Z

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.

sjwang05 · 2026-08-05T09:00:39Z

@rustbot ready

sjwang05 · 2026-08-05T18:22:48Z

Looks like -Copt-level=0 is needed for the crashtest, otherwise inlining followed by SimplifyLocals gets rid of the return value entirely.

...Neat!

JohnTitor

Thanks! @bors r+

rust-bors · 2026-08-08T23:40:19Z

📌 Commit d43f980 has been approved by JohnTitor

It is now in the queue for this repository.

check if len of array const arg matches the expected len of the type when lowering to valtree When creating valtrees for arrays passed as const args in `lower_const_arg_array`, we assume the array has the correct length without actually checking the length of the arg, leading to UB at runtime (rust-lang#155168) or an ICE during CTFE (rust-lang#151079). This PR adds a check comparing the expected length of the type with the actual number of elements, similar to `lower_const_arg_tup`. fixesrust-lang#155168

Rollup of 6 pull requests Successful merges: - #160529 (Upgrade and deduplicate dependencies) - #158517 (Initial implementation of named `Fn` trait parameters) - #158587 (check if len of array const arg matches the expected len of the type when lowering to valtree) - #160748 (Add regression test for cross-crate assoc const private field leak in rustdoc) - #160708 (remove old update mechanism) - #160768 (Fix autodiff_illegal.rs test)

Rollup of 5 pull requests Successful merges: - #158517 (Initial implementation of named `Fn` trait parameters) - #158587 (check if len of array const arg matches the expected len of the type when lowering to valtree) - #160748 (Add regression test for cross-crate assoc const private field leak in rustdoc) - #160708 (remove old update mechanism) - #160768 (Fix autodiff_illegal.rs test)

Rollup merge of #158587 - sjwang05:issue-155168, r=JohnTitor check if len of array const arg matches the expected len of the type when lowering to valtree When creating valtrees for arrays passed as const args in `lower_const_arg_array`, we assume the array has the correct length without actually checking the length of the arg, leading to UB at runtime (#155168) or an ICE during CTFE (#151079). This PR adds a check comparing the expected length of the type with the actual number of elements, similar to `lower_const_arg_tup`. fixes#155168

sjwang05 · 2026-06-29T23:01:40Z

When creating valtrees for arrays passed as const args in lower_const_arg_array, we assume the array has the correct length without actually checking the length of the arg, leading to UB at runtime (#155168) or an ICE during CTFE (#151079). This PR adds a check comparing the expected length of the type with the actual number of elements, similar to lower_const_arg_tup.

fixes#155168

rustbot · 2026-06-29T23:01:43Z

HIR ty lowering was modified

rustbot · 2026-06-29T23:01:45Z

rustbot has assigned @JohnTitor.
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 73 candidates
Random selection from 17 candidates

JohnTitor · 2026-07-03T08:00:04Z

 .map(|elem| self.lower_const_arg(elem, *elem_ty))
 .collect::<Vec<_>>();

+ if let Some(expected_len) = len.try_to_target_usize(tcx)


IMO it should catch more cases if len is normalized, e.g. type const LEN (I haven't checked deeply so it may be caught by somewhere already)
View changes since the review

Thanks, I changed it to call try_normalize_erasing_regions with an empty ParamEnv on the expected len and added a test for it, so now something like fn baz<const A: [u8; <S as Trait>::LEN]>() {} produces the correct error. Something like fn baz<T: Trait, const A: [u8; <T as Trait>::LEN]>() {} still ICEs if too long/produces UB if too short, however, since we can't resolve T to an actual type: trying to do try_evaluate_const with a non-empty ParamEnv led to cycle errors.

Could you open another issue and add an ICE test for that case (if not exists yet)? At least we should track it.

Opened #160553 and added a corresponding test to the crashes/ dir

rustbot · 2026-08-05T08:59:10Z

This PR changes a file inside tests/crashes. If a crash was fixed, please move into the corresponding ui subdir and add 'Fixes #' to the PR description to autoclose the issue upon merge.

rustbot · 2026-08-05T08:59:12Z

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.

sjwang05 · 2026-08-05T09:00:39Z

@rustbot ready

sjwang05 · 2026-08-05T18:22:48Z

Looks like -Copt-level=0 is needed for the crashtest, otherwise inlining followed by SimplifyLocals gets rid of the return value entirely.

...Neat!

JohnTitor

Thanks! @bors r+