rustc_resolve: improve const generic errors by Unique-Usman · Pull Request #152913 · rust-lang/rust

Unique-Usman · 2026-02-20T14:49:03Z

rustbot · 2026-02-20T14:49:08Z

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Unique-Usman · 2026-02-20T14:49:21Z

r? @estebank

compiler/rustc_resolve/src/late/diagnostics.rs

compiler/rustc_hir_analysis/src/hir_ty_lowering/generics.rs

compiler/rustc_resolve/src/late/diagnostics.rs

tests/ui/const-generics/const-generic-function.stderr

tests/ui/const-generics/const-arg-in-const-arg.min.stderr

compiler/rustc_resolve/src/build_reduced_graph.rs

tests/ui/missing/missing-items/missing-type-parameter2.stderr

estebank · 2026-03-06T17:31:53Z

compiler/rustc_resolve/src/build_reduced_graph.rs

                        .struct_constructors
                        .insert(local_def_id, (ctor_res, ctor_vis.to_def_id(), ret_fields));
                }
+                self.r.struct_generics.insert(local_def_id, generics.clone());


Let's see if we can struct_generics store references. That should keep mem usage to a minimum.

estebank · 2026-03-06T17:32:57Z

compiler/rustc_resolve/src/late.rs

+                if let Some(const_err) = const_err {
+                    err.cancel();
+                    err = const_err;
+                }


This is currently inactive, right? const_err isn't None anywhere right now?

const_err is actually always None except in the case of where we add the error we just introduce see it here -> https://github.com/rust-lang/rust/pull/152913/changes#diff-2c81e6d8048a31a3ce43f30181aaa037e0ad0076e7aee67792ca993f28c75ac3R3440-R3441

it is to prevent the type error from showing up.

tests/ui/const-generics/early/invalid-const-arguments.stderr

rustbot · 2026-03-06T17:35:33Z

HIR ty lowering was modified

cc @fmease

Unique-Usman · 2026-03-10T02:48:12Z

@estebank

estebank · 2026-03-12T04:10:08Z

tests/ui/const-generics/assoc_const_as_type_argument.stderr

@@ -4,18 +4,19 @@ error[E0575]: expected associated type, found associated constant `Trait::ASSOC`
 LL |     bar::<<T as Trait>::ASSOC>();
   |           ^^^^^^^^^^^^^^^^^^^ not a associated type

-error[E0747]: unresolved item provided when a constant was expected
-  --> $DIR/assoc_const_as_type_argument.rs:8:11
+error[E0284]: type annotations needed


It is unfortunate that after silencing E0747 we end up with these inference errors instead...

I think we can split the work into two PRs: one silencing the unnecessary/redundant resolve error ("unresolved item when X was expected") and another for the appropriate const generic suggestions. That would make things easier to review and evolve on isolation.

Yeah, thanks. we can resolve the E0747 error after getting this pr merged. I already update the patch to not silence the E0747 for now.

compiler/rustc_resolve/src/late/diagnostics.rs

estebank · 2026-03-16T21:04:21Z

@bors r+

rust-bors · 2026-03-16T21:04:24Z

📌 Commit 54aebeb has been approved by estebank

It is now in the queue for this repository.

rustc_resolve: improve const generic errors

rust-bors · 2026-03-17T00:54:19Z

💔 Test for f80d097 failed: CI. Failed job:

auto - aarch64-msvc-1 (web logs, enhanced plaintext logs)

Signed-off-by: Usman Akinyemi <usmanakinyemi202@gmail.com>

rustbot · 2026-03-19T06:28:48Z

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.

estebank · 2026-03-19T22:03:15Z

@bors r+

The error seems to be spurious/not related to this PR. It was rebased on top of a more recent main.

rust-bors · 2026-03-19T22:03:18Z

📌 Commit f60b649 has been approved by estebank

It is now in the queue for this repository.

rust-bors · 2026-03-20T04:12:23Z

⌛ Testing commit f60b649 with merge 76be1cc...

Workflow: https://github.com/rust-lang/rust/actions/runs/23328740950

rustc_resolve: improve const generic errors

rustbot assigned JonathanBrouwer Feb 20, 2026

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Unique-Usman marked this pull request as draft February 20, 2026 14:49

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Auto merge of #152913 - Unique-Usman:ua/constnottype, r=estebank

f80d097

rustc_resolve: improve const generic errors

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rustc_resolve: improve const generic errors

f60b649

Signed-off-by: Usman Akinyemi <usmanakinyemi202@gmail.com>

Unique-Usman force-pushed the ua/constnottype branch from 54aebeb to f60b649 Compare March 19, 2026 06:28

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rust-bors bot pushed a commit that referenced this pull request Mar 20, 2026

Auto merge of #152913 - Unique-Usman:ua/constnottype, r=estebank

76be1cc

rustc_resolve: improve const generic errors

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