Fixed ICE when using function pointer as const generic parameter #151219

enthropy7 · 2026-01-16T17:09:04Z

added bounds check in prohibit_explicit_late_bound_lifetimes to prevent index out of bounds panic when args.args is empty. also regression test here to ensure function pointers in const generics produce proper error messages instead of ICE.

Fixes #151186
Fixes #137084

rustbot · 2026-01-16T17:09:08Z

HIR ty lowering was modified

cc @fmease

rustbot · 2026-01-16T17:09:11Z

r? @WaffleLapkin

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compiler/rustc_hir_analysis/src/hir_ty_lowering/generics.rs

enthropy7 · 2026-01-16T18:34:18Z

also fixes #137084

tests/ui/const-generics/fn-item-as-const-arg-137084.rs

tests/ui/const-generics/ice-151186-fn-ptr-in-where-clause.rs

fmease · 2026-01-16T18:47:16Z

also fixes #137084

Please mention all issues in the PR description via e.g., Fixes #NNN, so they can be auto-closed on merge & are properly linked (useful for e.g., search queries). Read more about keywords here: https://docs.github.com/en/get-started/writing-on-github/working-with-advanced-formatting/using-keywords-in-issues-and-pull-requests

Moreover, please remove the #NNN from the title, it's not descriptive & nobody can click on it either.

BoxyUwU · 2026-01-16T20:05:43Z

r? BoxyUwU

BoxyUwU · 2026-01-19T11:55:18Z

compiler/rustc_hir_analysis/src/hir_ty_lowering/generics.rs

    }

-    if let Some(span_late) = def.has_late_bound_regions {
+    if let Some(span_late) = def.has_late_bound_regions


this function is somewhat confusing to me 🤔

Can you try doing two things for me:

remove the infer_lifetimes case above, it seems unnecessary if we only emit an error/fcw if there's explicit arguments given

use args.has_lifetime_params() instead of !args.args.is_empty(), I think this is closer to the logic we want, especially for cases like this where there are arguments but they're not lifetimes

I think both of these together would make it a lot easier to read this fn 😅

hi again! thanks for the review! implemented all of your suggestions, now waiting for CI check, tests passed, fn now looking better and more consistent :3

BoxyUwU · 2026-01-19T11:55:30Z

@rustbot author

rustbot · 2026-01-19T11:55:34Z

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

enthropy7 · 2026-01-19T14:58:43Z

@rustbot ready

BoxyUwU · 2026-01-19T16:06:45Z

compiler/rustc_hir_analysis/src/hir_ty_lowering/generics.rs

+        let Some(first_lifetime_arg) =
+            args.args.iter().find(|arg| matches!(arg, GenericArg::Lifetime(_)))
+        else {
+            return ExplicitLateBound::No;
+        };
+        let span = first_lifetime_arg.span();


why change this? if args isnt empty then args.args[0] should work fine

sorry, overcomplicated it, was a little bit confused

BoxyUwU

Thanks, looks good to me. Can you squash all your commits into one? I'll r+ it afterwards

View changes since this review

enthropy7 · 2026-01-21T13:33:38Z

Thanks, looks good to me. Can you squash all your commits into one? I'll r+ it afterwards

View changes since this review

done, thanks for the tips on working at this PR!

WaffleLapkin · 2026-01-21T18:09:53Z

@bors r=BoxyUwU

rust-bors · 2026-01-21T18:09:56Z

📌 Commit 4131674 has been approved by BoxyUwU

It is now in the queue for this repository.

Fixed ICE when using function pointer as const generic parameter added bounds check in prohibit_explicit_late_bound_lifetimes to prevent index out of bounds panic when args.args is empty. also regression test here to ensure function pointers in const generics produce proper error messages instead of ICE. Fixes rust-lang#151186 Fixes rust-lang#137084

@ghost

…uwer Rollup of 5 pull requests Successful merges: - #151010 (std: use `ByteStr`'s `Display` for `OsStr`) - #151156 (Add GCC and the GCC codegen backend to build-manifest and rustup) - #151219 (Fixed ICE when using function pointer as const generic parameter) - #151343 (Port some crate level attrs to the attribute parser) - #151463 (add x86_64-unknown-linux-gnuasan to CI) r? @ghost

Rollup merge of #151219 - enthropy7:main, r=BoxyUwU Fixed ICE when using function pointer as const generic parameter added bounds check in prohibit_explicit_late_bound_lifetimes to prevent index out of bounds panic when args.args is empty. also regression test here to ensure function pointers in const generics produce proper error messages instead of ICE. Fixes #151186 Fixes #137084

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 Jan 16, 2026

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enthropy7 force-pushed the main branch from 36f99c5 to 9dba588 Compare January 16, 2026 17:12

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enthropy7 force-pushed the main branch 4 times, most recently from 2cc5c51 to 1db0e70 Compare January 16, 2026 18:23

Kivooeo reviewed Jan 16, 2026

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compiler/rustc_hir_analysis/src/hir_ty_lowering/generics.rs Outdated Show resolved Hide resolved

enthropy7 force-pushed the main branch from 1db0e70 to 62d26d0 Compare January 16, 2026 18:33

fmease reviewed Jan 16, 2026

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tests/ui/const-generics/fn-item-as-const-arg-137084.rs Outdated Show resolved Hide resolved

tests/ui/const-generics/ice-151186-fn-ptr-in-where-clause.rs Outdated Show resolved Hide resolved

enthropy7 force-pushed the main branch from 62d26d0 to 2971126 Compare January 16, 2026 18:46

enthropy7 changed the title ~~Fixes issue #151186 ICE when using function pointer as const generic parameter~~ Fixes ICE when using function pointer as const generic parameter Jan 16, 2026

enthropy7 force-pushed the main branch 2 times, most recently from d7a40b3 to 87f1829 Compare January 16, 2026 18:52

enthropy7 changed the title ~~Fixes ICE when using function pointer as const generic parameter~~ Fixed ICE when using function pointer as const generic parameter Jan 16, 2026

enthropy7 force-pushed the main branch 2 times, most recently from 5cd5886 to f0865a1 Compare January 16, 2026 19:02

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enthropy7 force-pushed the main branch 2 times, most recently from c9e6735 to ce65294 Compare January 19, 2026 16:15

BoxyUwU approved these changes Jan 21, 2026

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Fix ICE when using function pointer as const generic parameter

4131674

enthropy7 force-pushed the main branch from ce65294 to 4131674 Compare January 21, 2026 13:32

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 Jan 21, 2026

JonathanBrouwer mentioned this pull request Jan 21, 2026

Rollup of 5 pull requests #151471

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JonathanBrouwer mentioned this pull request Jan 21, 2026

Rollup of 6 pull requests #151472

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rust-bors bot merged commit afc1842 into rust-lang:main Jan 22, 2026
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rustbot added this to the 1.95.0 milestone Jan 22, 2026

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Fixed ICE when using function pointer as const generic parameter #151219

Fixed ICE when using function pointer as const generic parameter #151219

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