fix supposedly unreachable `bug!` being reachable by khyperia · Pull Request #162173 · rust-lang/rust

khyperia · 2026-09-02T07:23:31Z

bug! introduced in #161929

wfcheck.rs does a normalize on a type here

rust/compiler/rustc_hir_analysis/src/check/wfcheck.rs

Line 929 in edc52f8

let ty = wfcx.deeply_normalize(span, Some(WellFormedLoc::Ty(def_id)), ty);

which reduces the contained alias within from a nonrigid InherentSelf to a rigid InherentImpl, because we do so upon encountering a too-generic-to-ctfe alias

the very next line, it then register_wf_obligation on the resulting normalized type, that contains an InherentImpl

inside wf, that eventually hits the bug! I added and ICEs

rust/compiler/rustc_trait_selection/src/traits/wf.rs

Line 1104 in a433023

    
           "This ought to be unreachable, the entrypoints of WF should still have InherentSelf-form alias consts."

r? @BoxyUwU

rustbot · 2026-09-02T07:23:35Z

changes to the core type system

cc @lcnr

rustbot · 2026-09-02T07:23:38Z

BoxyUwU is currently at their maximum review capacity.
They may take a while to respond.

BoxyUwU · 2026-09-02T09:44:30Z

                    match alias_const.kind {
-                        ty::AliasConstKind::InherentSelf { .. } => {
+                        ty::AliasConstKind::InherentSelf { .. }
+                        | ty::AliasConstKind::InherentImpl { .. } => {


Suggested change

| ty::AliasConstKind::InherentImpl { .. } => {

// FIXME: This should be unreachable but isn't because we

// normalize in item wfck before computing wf requirements

| ty::AliasConstKind::InherentImpl { .. } => {

View changes since the review

BoxyUwU · 2026-09-02T09:44:50Z


-        if !data.self_ty().has_escaping_bound_vars() {
+        let can_compute_impl_args =
+            matches!(data.kind, ty::AliasTermKind::InherentConstImpl { .. })


comment on why ignoring escaping bound vars is fine with inherent impl form

View changes since the review

BoxyUwU

r=me after nits

View changes since this review

khyperia · 2026-09-02T11:31:25Z

@bors r=BoxyUwU rollup

rust-bors · 2026-09-02T11:31:28Z

📌 Commit e7e2b01 has been approved by BoxyUwU

It is now in the queue for this repository.

@BoxyUwU

fix supposedly unreachable `bug!` being reachable `bug!` introduced in rust-lang#161929 fixes rust-lang#162146 wfcheck.rs does a normalize on a type here https://github.com/rust-lang/rust/blob/edc52f87c28f328c61685a02c47887a5cec7d767/compiler/rustc_hir_analysis/src/check/wfcheck.rs#L929 which reduces the contained alias within from a nonrigid InherentSelf to a rigid InherentImpl, because we do so upon encountering a too-generic-to-ctfe alias the very next line, it then `register_wf_obligation` on the resulting normalized type, that contains an InherentImpl inside wf, that eventually hits the `bug!` I added and ICEs https://github.com/rust-lang/rust/blob/a4330234a776684c36428d001721d0320d24dd77/compiler/rustc_trait_selection/src/traits/wf.rs#L1104 r? @BoxyUwU

@BoxyUwU

fix supposedly unreachable `bug!` being reachable `bug!` introduced in rust-lang#161929 fixes rust-lang#162146 wfcheck.rs does a normalize on a type here https://github.com/rust-lang/rust/blob/edc52f87c28f328c61685a02c47887a5cec7d767/compiler/rustc_hir_analysis/src/check/wfcheck.rs#L929 which reduces the contained alias within from a nonrigid InherentSelf to a rigid InherentImpl, because we do so upon encountering a too-generic-to-ctfe alias the very next line, it then `register_wf_obligation` on the resulting normalized type, that contains an InherentImpl inside wf, that eventually hits the `bug!` I added and ICEs https://github.com/rust-lang/rust/blob/a4330234a776684c36428d001721d0320d24dd77/compiler/rustc_trait_selection/src/traits/wf.rs#L1104 r? @BoxyUwU

@BoxyUwU

fix supposedly unreachable `bug!` being reachable `bug!` introduced in rust-lang#161929 fixes rust-lang#162146 wfcheck.rs does a normalize on a type here https://github.com/rust-lang/rust/blob/edc52f87c28f328c61685a02c47887a5cec7d767/compiler/rustc_hir_analysis/src/check/wfcheck.rs#L929 which reduces the contained alias within from a nonrigid InherentSelf to a rigid InherentImpl, because we do so upon encountering a too-generic-to-ctfe alias the very next line, it then `register_wf_obligation` on the resulting normalized type, that contains an InherentImpl inside wf, that eventually hits the `bug!` I added and ICEs https://github.com/rust-lang/rust/blob/a4330234a776684c36428d001721d0320d24dd77/compiler/rustc_trait_selection/src/traits/wf.rs#L1104 r? @BoxyUwU

@BoxyUwU

fix supposedly unreachable `bug!` being reachable `bug!` introduced in rust-lang#161929 fixes rust-lang#162146 wfcheck.rs does a normalize on a type here https://github.com/rust-lang/rust/blob/edc52f87c28f328c61685a02c47887a5cec7d767/compiler/rustc_hir_analysis/src/check/wfcheck.rs#L929 which reduces the contained alias within from a nonrigid InherentSelf to a rigid InherentImpl, because we do so upon encountering a too-generic-to-ctfe alias the very next line, it then `register_wf_obligation` on the resulting normalized type, that contains an InherentImpl inside wf, that eventually hits the `bug!` I added and ICEs https://github.com/rust-lang/rust/blob/a4330234a776684c36428d001721d0320d24dd77/compiler/rustc_trait_selection/src/traits/wf.rs#L1104 r? @BoxyUwU

…uwer Rollup of 23 pull requests Successful merges: - #162164 (Revert "Implement Debug for C-like enums with a concatenated string") - #160564 (volatile: allow accesses to non-AM memory to trap) - #161579 (suggest calling a fn item used as the iterator of a `for` loop) - #162044 (coverage: Resolve spans to file-coordinates in a separate step) - #162120 (Introduce `PerOwnerLoweringState`) - #162151 (Test itanium mangling of `f16` and `f128`) - #162162 (Don't special-case `!` in stability checks anymore) - #162181 (Remove wrong UnusedBraces lint for iterator loop in edition 2024 ) - #162187 (Rename `thir::ExprKind::Use` to `ValueExpr`) - #158401 (mgca: Don't ICE when evaluating ValTrees that contain error constants) - #159873 (fuchsia: Add safestack as a supported sanitizer for x86_64 fuchsia) - #161847 (Preserve visibility in nested macro import suggestions) - #161972 (Improve tests for `#[track_caller]` in async) - #162008 (Render the `box` pattern removal diagnostic more actionable & remove `box` expression recovery) - #162065 (std: don't reference `libc::O_NOFOLLOW` on VxWorks in `set_perm_nofollow`) - #162076 (docs(num): clarify conditions under which error occurs in `impl TryFrom<int> for int`) - #162152 (Revert "retrieve supported GCC targets from the sysroot") - #162153 (Prefer `LLVMGetVersion` for runtime info) - #162168 (fix ICE in project_goals/inherent) - #162171 (Explain LoongArch f16 NaN-boxing in inline asm) - #162173 (fix supposedly unreachable `bug!` being reachable) - #162191 (core: mark float `ClampBounds` methods as `#[inline]`) - #162199 (docs(time): clarify exact seconds for hour and minute)

@BoxyUwU

fix supposedly unreachable `bug!` being reachable `bug!` introduced in rust-lang#161929 fixes rust-lang#162146 wfcheck.rs does a normalize on a type here https://github.com/rust-lang/rust/blob/edc52f87c28f328c61685a02c47887a5cec7d767/compiler/rustc_hir_analysis/src/check/wfcheck.rs#L929 which reduces the contained alias within from a nonrigid InherentSelf to a rigid InherentImpl, because we do so upon encountering a too-generic-to-ctfe alias the very next line, it then `register_wf_obligation` on the resulting normalized type, that contains an InherentImpl inside wf, that eventually hits the `bug!` I added and ICEs https://github.com/rust-lang/rust/blob/a4330234a776684c36428d001721d0320d24dd77/compiler/rustc_trait_selection/src/traits/wf.rs#L1104 r? @BoxyUwU

Rollup of 23 pull requests Successful merges: - #157808 (sanitizers: Implement support for the sanitize ignorelist) - #160564 (volatile: allow accesses to non-AM memory to trap) - #161579 (suggest calling a fn item used as the iterator of a `for` loop) - #162044 (coverage: Resolve spans to file-coordinates in a separate step) - #162120 (Introduce `PerOwnerLoweringState`) - #162151 (Test itanium mangling of `f16` and `f128`) - #162162 (Don't special-case `!` in stability checks anymore) - #162181 (Remove wrong UnusedBraces lint for iterator loop in edition 2024 ) - #162187 (Rename `thir::ExprKind::Use` to `ValueExpr`) - #158401 (mgca: Don't ICE when evaluating ValTrees that contain error constants) - #159873 (fuchsia: Add safestack as a supported sanitizer for x86_64 fuchsia) - #161847 (Preserve visibility in nested macro import suggestions) - #161972 (Improve tests for `#[track_caller]` in async) - #162008 (Render the `box` pattern removal diagnostic more actionable & remove `box` expression recovery) - #162065 (std: don't reference `libc::O_NOFOLLOW` on VxWorks in `set_perm_nofollow`) - #162076 (docs(num): clarify conditions under which error occurs in `impl TryFrom<int> for int`) - #162152 (Revert "retrieve supported GCC targets from the sysroot") - #162153 (Prefer `LLVMGetVersion` for runtime info) - #162168 (fix ICE in project_goals/inherent) - #162171 (Explain LoongArch f16 NaN-boxing in inline asm) - #162173 (fix supposedly unreachable `bug!` being reachable) - #162191 (core: mark float `ClampBounds` methods as `#[inline]`) - #162199 (docs(time): clarify exact seconds for hour and minute)

@BoxyUwU

fix supposedly unreachable `bug!` being reachable `bug!` introduced in rust-lang#161929 fixes rust-lang#162146 wfcheck.rs does a normalize on a type here https://github.com/rust-lang/rust/blob/edc52f87c28f328c61685a02c47887a5cec7d767/compiler/rustc_hir_analysis/src/check/wfcheck.rs#L929 which reduces the contained alias within from a nonrigid InherentSelf to a rigid InherentImpl, because we do so upon encountering a too-generic-to-ctfe alias the very next line, it then `register_wf_obligation` on the resulting normalized type, that contains an InherentImpl inside wf, that eventually hits the `bug!` I added and ICEs https://github.com/rust-lang/rust/blob/a4330234a776684c36428d001721d0320d24dd77/compiler/rustc_trait_selection/src/traits/wf.rs#L1104 r? @BoxyUwU

Rollup of 29 pull requests Successful merges: - #161694 (add `Complex` ABI run-make test) - #162014 (Move more `rustdoc-html` tests using `--test` into the right folder) - #162164 (Revert "Implement Debug for C-like enums with a concatenated string") - #160564 (volatile: allow accesses to non-AM memory to trap) - #161579 (suggest calling a fn item used as the iterator of a `for` loop) - #162044 (coverage: Resolve spans to file-coordinates in a separate step) - #162120 (Introduce `PerOwnerLoweringState`) - #162132 (std: improve safety documentation in UNIX stack overflow code) - #162151 (Test itanium mangling of `f16` and `f128`) - #162162 (Don't special-case `!` in stability checks anymore) - #162181 (Remove wrong UnusedBraces lint for iterator loop in edition 2024 ) - #162187 (Rename `thir::ExprKind::Use` to `ValueExpr`) - #158401 (mgca: Don't ICE when evaluating ValTrees that contain error constants) - #159873 (fuchsia: Add safestack as a supported sanitizer for x86_64 fuchsia) - #161847 (Preserve visibility in nested macro import suggestions) - #161951 (Windows: add fallback if `canonicalize` fails) - #161972 (Improve tests for `#[track_caller]` in async) - #162008 (Render the `box` pattern removal diagnostic more actionable & remove `box` expression recovery) - #162065 (std: don't reference `libc::O_NOFOLLOW` on VxWorks in `set_perm_nofollow`) - #162076 (docs(num): clarify conditions under which error occurs in `impl TryFrom<int> for int`) - #162152 (Revert "retrieve supported GCC targets from the sysroot") - #162153 (Prefer `LLVMGetVersion` for runtime info) - #162168 (fix ICE in project_goals/inherent) - #162171 (Explain LoongArch f16 NaN-boxing in inline asm) - #162173 (fix supposedly unreachable `bug!` being reachable) - #162180 (remove outdated next-solver FIXMEs) - #162191 (core: mark float `ClampBounds` methods as `#[inline]`) - #162195 (docs(time): clarify exact seconds for week and day) - #162199 (docs(time): clarify exact seconds for hour and minute)

@BoxyUwU

fix supposedly unreachable `bug!` being reachable `bug!` introduced in rust-lang#161929 fixes rust-lang#162146 wfcheck.rs does a normalize on a type here https://github.com/rust-lang/rust/blob/edc52f87c28f328c61685a02c47887a5cec7d767/compiler/rustc_hir_analysis/src/check/wfcheck.rs#L929 which reduces the contained alias within from a nonrigid InherentSelf to a rigid InherentImpl, because we do so upon encountering a too-generic-to-ctfe alias the very next line, it then `register_wf_obligation` on the resulting normalized type, that contains an InherentImpl inside wf, that eventually hits the `bug!` I added and ICEs https://github.com/rust-lang/rust/blob/a4330234a776684c36428d001721d0320d24dd77/compiler/rustc_trait_selection/src/traits/wf.rs#L1104 r? @BoxyUwU

@BoxyUwU

fix supposedly unreachable `bug!` being reachable `bug!` introduced in rust-lang#161929 fixes rust-lang#162146 wfcheck.rs does a normalize on a type here https://github.com/rust-lang/rust/blob/edc52f87c28f328c61685a02c47887a5cec7d767/compiler/rustc_hir_analysis/src/check/wfcheck.rs#L929 which reduces the contained alias within from a nonrigid InherentSelf to a rigid InherentImpl, because we do so upon encountering a too-generic-to-ctfe alias the very next line, it then `register_wf_obligation` on the resulting normalized type, that contains an InherentImpl inside wf, that eventually hits the `bug!` I added and ICEs https://github.com/rust-lang/rust/blob/a4330234a776684c36428d001721d0320d24dd77/compiler/rustc_trait_selection/src/traits/wf.rs#L1104 r? @BoxyUwU

…uwer Rollup of 12 pull requests Successful merges: - #161227 (implement `Add` and `Sub` for `Complex`) - #161280 (make target feature ABI check a hard error on ARM) - #161893 (Add custom allocator support to `(try_)map` on `UniqueArc` and `UniqueRc`) - #162154 (fix[154166]: closure debug capture print) - #161951 (Windows: add fallback if `canonicalize` fails) - #162173 (fix supposedly unreachable `bug!` being reachable) - #162180 (remove outdated next-solver handling) - #162191 (core: mark float `ClampBounds` methods as `#[inline]`) - #162195 (docs(time): clarify exact seconds for week and day) - #162199 (docs(time): clarify exact seconds for hour and minute) - #162222 (coverage: Small cleanups in `extract_hir_info`) - #162230 (Pass -Z merge-functions=disabled in tests/codegen-llvm/intrinsics/unchecked_math.rs)

@BoxyUwU

Rollup merge of #162173 - khyperia:fix-unreachable, r=BoxyUwU fix supposedly unreachable `bug!` being reachable `bug!` introduced in #161929 fixes #162146 wfcheck.rs does a normalize on a type here https://github.com/rust-lang/rust/blob/edc52f87c28f328c61685a02c47887a5cec7d767/compiler/rustc_hir_analysis/src/check/wfcheck.rs#L929 which reduces the contained alias within from a nonrigid InherentSelf to a rigid InherentImpl, because we do so upon encountering a too-generic-to-ctfe alias the very next line, it then `register_wf_obligation` on the resulting normalized type, that contains an InherentImpl inside wf, that eventually hits the `bug!` I added and ICEs https://github.com/rust-lang/rust/blob/a4330234a776684c36428d001721d0320d24dd77/compiler/rustc_trait_selection/src/traits/wf.rs#L1104 r? @BoxyUwU

lcnr · 2026-09-10T10:41:13Z

+                        // FIXME: This should be unreachable but isn't because we normalize in item
+                        // wfck before computing wf requirements


isn't this more generally true? as in

"FIXME(#100041): This should be unreachable, except that we sometimes compute the WF requirements for normalized types"

This is not just a thing in WF checking I think. It may also affect e.g. #100041 (comment) 🤔

For MIR typeck we fetch WF obligations for both normalized and unnormalized types

probably, that makes sense to me at least! boop @BoxyUwU who wrote this (I just copied it into my PR here)

ah right there are other type system bugs

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 Sep 2, 2026

rustbot assigned BoxyUwU Sep 2, 2026

khyperia mentioned this pull request Sep 2, 2026

explicitly track inherent const generic args kind #161929

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fix supposedly unreachable bug! being reachable

e7e2b01

khyperia force-pushed the fix-unreachable branch from 6c03318 to e7e2b01 Compare September 2, 2026 10:05

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Rollup of 18 pull requests #162189

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Rollup of 20 pull requests #162198

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Rollup of 23 pull requests #162206

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Rollup of 23 pull requests #162211

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Rollup of 23 pull requests #162216

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Rollup of 29 pull requests #162221

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Full Const Generics rust-lang/goals#100

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Rollup of 12 pull requests #162249

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khyperia deleted the fix-unreachable branch September 4, 2026 06:19

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fix supposedly unreachable `bug!` being reachable - #162173

fix supposedly unreachable `bug!` being reachable#162173
rust-bors[bot] merged 1 commit into
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		// FIXME: This should be unreachable but isn't because we normalize in item
		// wfck before computing wf requirements

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