const-eval: ICE when we hit a non-const fn by RalfJung · Pull Request #163972 · rust-lang/rust

RalfJung · 2026-10-08T07:40:30Z

We made this a "nice" error solely so we can test miri-unleashed better, but it was never meant to be an error that users can actually get -- just a second line of defense in case there is a bug in our const checking logic. This seems to cause some confusion so let's make it an ICE when Miri is not unleashed.

This also uncovered that even if const_precise_live_drops finds a problem, we still run the code that was found to not be const-safe: #163973.

r? @oli-obk
Cc @tmiasko

rustbot · 2026-10-08T07:40:34Z

Some changes occurred to the CTFE machinery

cc @oli-obk, @lcnr

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.

RalfJung · 2026-10-08T07:49:23Z

This also uncovered that apparently const_precise_live_drops is unsound

That turned out to not be the case. const_precise_live_drops does notice that these consts are faulty. However we then still run them anyway, which definitely should not happen. I opened #163973 for that.

oli-obk

@bors r+ rollup

View changes since this review

rust-bors · 2026-10-08T10:30:05Z

📌 Commit f74a200 has been tentatively approved by oli-obk

It will be put into the queue for this repository once PR CI succeeds.

…uwer Rollup of 9 pull requests Successful merges: - #163462 (Fix COFF renaming of decorated (stdcall/fastcall/vectorcall) exports) - #163855 (Include enclosing item's context on const errors) - #163861 (Run LLDB debuginfo tests on `x86_64-mingw`) - #163538 (Add `rustc::missing_generic_type_visitable` lint) - #163617 (mips: make `Complex<T>` ABI match GCC) - #163832 (reject non-async coroutine closures as async callables) - #163958 (only make `RustaceansAreAwesome` satisfy trait clauses) - #163974 (Condense AdtDef lang item checks into one match) - #163979 (Add `bf16` to arm features) Failed merges: - #163972 (const-eval: ICE when we hit a non-const fn)

…uwer Rollup of 12 pull requests Successful merges: - #163462 (Fix COFF renaming of decorated (stdcall/fastcall/vectorcall) exports) - #163855 (Include enclosing item's context on const errors) - #163861 (Run LLDB debuginfo tests on `x86_64-mingw`) - #161201 (Speed up tidy again) - #163538 (Add `rustc::missing_generic_type_visitable` lint) - #163617 (mips: make `Complex<T>` ABI match GCC) - #163772 (comptime fn error: suggest wrapping in const block) - #163832 (reject non-async coroutine closures as async callables) - #163958 (only make `RustaceansAreAwesome` satisfy trait clauses) - #163974 (Condense AdtDef lang item checks into one match) - #163979 (Add `bf16` to arm features) - #163989 (Revert "compiletest: stream output of executor process when --no-capture is set") Failed merges: - #163972 (const-eval: ICE when we hit a non-const fn)

…uwer Rollup of 19 pull requests Successful merges: - #156112 (Distinguish `repr(C)` ZSTs from others in ABI computation) - #157941 (Deny partial `-Z stack-protector` by default in all editions) - #163462 (Fix COFF renaming of decorated (stdcall/fastcall/vectorcall) exports) - #163855 (Include enclosing item's context on const errors) - #163861 (Run LLDB debuginfo tests on `x86_64-mingw`) - #163913 ( Silence redundant failed obligations on the same statement) - #161201 (Speed up tidy again) - #163380 (Tweak "name not found" resolution error when it happens from within a derive expansion) - #163538 (Add `rustc::missing_generic_type_visitable` lint) - #163617 (mips: make `Complex<T>` ABI match GCC) - #163772 (comptime fn error: suggest wrapping in const block) - #163813 (use pre-borrowck typing env for early MIR validation) - #163924 (replace instances of NonNull::new(&mut x).expect("...") with NonNull::from_mut) - #163958 (only make `RustaceansAreAwesome` satisfy trait clauses) - #163960 (vexos: clear .bss from assembly) - #163974 (Condense AdtDef lang item checks into one match) - #163979 (Add `bf16` to arm features) - #163989 (Revert "compiletest: stream output of executor process when --no-capture is set") - #163995 (m68k-unknown-none-elf: Remove code model) Failed merges: - #163832 (reject non-async coroutine closures as async callables) - #163972 (const-eval: ICE when we hit a non-const fn)

…uwer Rollup of 19 pull requests Successful merges: - rust-lang/rust#156112 (Distinguish `repr(C)` ZSTs from others in ABI computation) - rust-lang/rust#157941 (Deny partial `-Z stack-protector` by default in all editions) - rust-lang/rust#163462 (Fix COFF renaming of decorated (stdcall/fastcall/vectorcall) exports) - rust-lang/rust#163855 (Include enclosing item's context on const errors) - rust-lang/rust#163861 (Run LLDB debuginfo tests on `x86_64-mingw`) - rust-lang/rust#163913 ( Silence redundant failed obligations on the same statement) - rust-lang/rust#161201 (Speed up tidy again) - rust-lang/rust#163380 (Tweak "name not found" resolution error when it happens from within a derive expansion) - rust-lang/rust#163538 (Add `rustc::missing_generic_type_visitable` lint) - rust-lang/rust#163617 (mips: make `Complex<T>` ABI match GCC) - rust-lang/rust#163772 (comptime fn error: suggest wrapping in const block) - rust-lang/rust#163813 (use pre-borrowck typing env for early MIR validation) - rust-lang/rust#163924 (replace instances of NonNull::new(&mut x).expect("...") with NonNull::from_mut) - rust-lang/rust#163958 (only make `RustaceansAreAwesome` satisfy trait clauses) - rust-lang/rust#163960 (vexos: clear .bss from assembly) - rust-lang/rust#163974 (Condense AdtDef lang item checks into one match) - rust-lang/rust#163979 (Add `bf16` to arm features) - rust-lang/rust#163989 (Revert "compiletest: stream output of executor process when --no-capture is set") - rust-lang/rust#163995 (m68k-unknown-none-elf: Remove code model) Failed merges: - rust-lang/rust#163832 (reject non-async coroutine closures as async callables) - rust-lang/rust#163972 (const-eval: ICE when we hit a non-const fn)

@oli-obk

const-eval: ICE when we hit a non-const fn We made this a "nice" error solely so we can test miri-unleashed better, but it was never meant to be an error that users can actually get -- just a second line of defense in case there is a bug in our const checking logic. This seems to [cause some confusion](rust-lang#161627 (comment)) so let's make it an ICE when Miri is not unleashed. This also uncovered that even if `const_precise_live_drops` finds a problem, we still run the code that was found to not be const-safe: rust-lang#163973. r? @oli-obk Cc @tmiasko

@oli-obk

const-eval: ICE when we hit a non-const fn We made this a "nice" error solely so we can test miri-unleashed better, but it was never meant to be an error that users can actually get -- just a second line of defense in case there is a bug in our const checking logic. This seems to [cause some confusion](rust-lang#161627 (comment)) so let's make it an ICE when Miri is not unleashed. This also uncovered that even if `const_precise_live_drops` finds a problem, we still run the code that was found to not be const-safe: rust-lang#163973. r? @oli-obk Cc @tmiasko

…uwer Rollup of 14 pull requests Successful merges: - #162652 (Syntactically reject leading parenthesized precise capturing lists in bare trait object types (`(use<…>)+`)) - #163337 (MIR move elimination [3/6]: PreciseLiveness) - #163954 (fix(bootstrap/darwin): fix rpath for distributed LLD) - #163193 (cfi: mangle `f128` as `e` rather than `g` on platforms without `_Float128`) - #163634 (move overflow lint computation into decorator) - #163666 (Updates the expect message library/core/src/time.rs) - #163727 (rigid aliases to non-rigid for fully normalized check) - #163745 (replace `fully_monomorphized` with `cx.typing_env()`) - #163912 (Fix debug assert failure in `note_obligation_cause_code_inner`) - #163972 (const-eval: ICE when we hit a non-const fn) - #164000 (When mentioning that closure doesn't implement trait, point at closure) - #164007 ([rustdoc] Prefer local paths over remote ones when foreign item is locally reexported) - #164017 (cg_llvm: Avoid some explicit casts to `*const c_char`) - #164025 (Less `CanonicalVarValues`)

JonathanBrouwer · 2026-10-09T13:21:24Z

💔 I suspect this PR failed tests as part of a rollup
@bors r-

After fixing the problem, consider running a try job for the failed job before re-approving.

Link to failure: #164027 (comment)

rust-bors · 2026-10-09T13:21:33Z

This pull request was unapproved.

This PR was contained in a rollup (#164027), which was unapproved.

View changes since this unapproval

RalfJung · 2026-10-09T13:42:34Z

So apparently path remapping is broken on aarch64 and we have to do it by hand in the regexes? Is that a known problem?

RalfJung · 2026-10-09T13:45:43Z

@bors try jobs=dist-aarch64-linux
@bors r+

const-eval: ICE when we hit a non-const fn try-job: dist-aarch64-linux

rust-bors · 2026-10-09T13:45:51Z

📌 Commit e3941d6 has been tentatively approved by RalfJung

It will be put into the queue for this repository once PR CI succeeds.

fmease · 2026-10-09T14:03:29Z

@bors r=oli-obk

rust-bors · 2026-10-09T14:03:32Z

📌 Commit e3941d6 has been tentatively approved by oli-obk

It will be put into the queue for this repository once PR CI succeeds.

rust-bors · 2026-10-09T15:08:15Z

☀️ Try build successful (CI)
Build commit: df4f668 (df4f6687e7d167fe2c8aed11e41411fd6bf3e020)
Base parent: 76c9095 (76c90957b7e422c4b9c45192b0197214d7de5a54)

@oli-obk

const-eval: ICE when we hit a non-const fn We made this a "nice" error solely so we can test miri-unleashed better, but it was never meant to be an error that users can actually get -- just a second line of defense in case there is a bug in our const checking logic. This seems to [cause some confusion](rust-lang#161627 (comment)) so let's make it an ICE when Miri is not unleashed. This also uncovered that even if `const_precise_live_drops` finds a problem, we still run the code that was found to not be const-safe: rust-lang#163973. r? @oli-obk Cc @tmiasko

@oli-obk

const-eval: ICE when we hit a non-const fn We made this a "nice" error solely so we can test miri-unleashed better, but it was never meant to be an error that users can actually get -- just a second line of defense in case there is a bug in our const checking logic. This seems to [cause some confusion](rust-lang#161627 (comment)) so let's make it an ICE when Miri is not unleashed. This also uncovered that even if `const_precise_live_drops` finds a problem, we still run the code that was found to not be const-safe: rust-lang#163973. r? @oli-obk Cc @tmiasko

@oli-obk

const-eval: ICE when we hit a non-const fn We made this a "nice" error solely so we can test miri-unleashed better, but it was never meant to be an error that users can actually get -- just a second line of defense in case there is a bug in our const checking logic. This seems to [cause some confusion](rust-lang#161627 (comment)) so let's make it an ICE when Miri is not unleashed. This also uncovered that even if `const_precise_live_drops` finds a problem, we still run the code that was found to not be const-safe: rust-lang#163973. r? @oli-obk Cc @tmiasko

…uwer Rollup of 24 pull requests Successful merges: - #161998 ( Support type-relative assoc item paths in generic param defaults & const param types) - #162106 (Helpful suggestions for incorrect address-of mutability (2)) - #162652 (Syntactically reject leading parenthesized precise capturing lists in bare trait object types (`(use<…>)+`)) - #163337 (MIR move elimination [3/6]: PreciseLiveness) - #163938 (-Zassumptions-on-binders: rewrite alias outlives constraints more goodly) - #163939 (Better debug impls for some assumptions on binders types) - #163954 (fix(bootstrap/darwin): fix rpath for distributed LLD) - #163956 (Pass the unremapped path to the `rustc` invocation for doctests) - #164042 (Allow testing cg-gcc on any target) - #162443 (Do not retain `Normalization` goal errors in nested goals for `BestObligationVisitor:: non_trivial_candidates `) - #162908 (Fix - const parameters rejected when identical) - #163193 (cfi: mangle `f128` as `e` rather than `g` on platforms without `_Float128`) - #163634 (move overflow lint computation into decorator) - #163666 (Updates the expect message library/core/src/time.rs) - #163727 (rigid aliases to non-rigid for fully normalized check) - #163745 (replace `fully_monomorphized` with `cx.typing_env()`) - #163912 (Fix debug assert failure in `note_obligation_cause_code_inner`) - #163950 (don't treat inherited opaques as defining) - #163972 (const-eval: ICE when we hit a non-const fn) - #164000 (When mentioning that closure doesn't implement trait, point at closure) - #164007 ([rustdoc] Prefer local paths over remote ones when foreign item is locally reexported) - #164008 (properly ignore the current goal's usages) - #164017 (cg_llvm: Avoid some explicit casts to `*const c_char`) - #164025 (Less `CanonicalVarValues`)

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Improve live drop precision #161627

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const-eval: ICE when we hit a non-const fn

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Auto merge of #163972 - RalfJung:non-const-eval, r=<try>

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const-eval: ICE when we hit a non-const fn try-job: dist-aarch64-linux

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