Fix ICE when Self is used in enum discriminant of a generic enum by GokhanKabar · Pull Request #153815 · rust-lang/rust

GokhanKabar · 2026-03-13T09:16:42Z

Fixes #153756
Let discriminant AnonConst inherit parent generics via Node::Variant in generics_of, and emit a proper error instead of span_bug! for the TooGeneric case in wfcheck.

rustbot · 2026-03-13T09:16:48Z

r? @petrochenkov

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tests/ui/enum-discriminant/generic-self-in-discr-ice.rs

petrochenkov · 2026-03-13T13:39:41Z

There's probably a way to implement this better.
r? types

BoxyUwU · 2026-03-13T14:50:47Z

r? BoxyUwU

BoxyUwU · 2026-03-17T12:32:23Z

Yeah this isn't quite what we want 🤔 The general structure here is supposed to be that name resolution rejects uses of generic parameters, and the things it can't do we reject during HIR ty lowering.

Name resolution can't/doesn't reject uses of Self which alias a generic type, nor can it reject generic parameters introduce by type dependent name resolution (e.g. <Self>::Assoc turning into <u8 as Trait<T>>::Assoc). So we have special cases for those in HIR ty lowering.

Instead of adding a new place where we check for illegal generic parameters can you look into why the existing checks in HIR ty lowering aren't working correctly for discriminant exprs. I expect that what happened is that the refactoring in #150519 was overly fit to const generics rather than all anon consts and so stopped validating stuff that it should.

https://github.com/rust-lang/rust/pull/150519/changes#diff-ce4273e1e949bf3052de7a08466c4dad785890b24091122954541b615b0ba199R2161

rustbot · 2026-03-17T14:31:05Z

HIR ty lowering was modified

cc @fmease

compiler/rustc_hir_analysis/src/check/wfcheck.rs

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

compiler/rustc_hir_analysis/src/check/wfcheck.rs

rustbot · 2026-04-03T15:24:34Z

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.

BoxyUwU · 2026-04-07T12:15:19Z

tests/ui/enum-discriminant/generic-self-in-discr-inline-const.rs

@@ -0,0 +1,15 @@
+//@ check-fail
+// Test that `Self` is rejected even when nested inside an inline const
+// or closure within an enum discriminant. Regression test for issue #154281.


can you add the test for the closure case ✨

BoxyUwU · 2026-04-14T14:32:05Z

@bors squash

* Fix ICE when Self is used in enum discriminant of a generic enum Move the validation into the existing `check_param_uses_if_mcg` machinery in HIR ty lowering instead of adding a new check in wfcheck. After the `AnonConstKind` refactoring, `ForbidMCGParamUsesFolder` was only gated on `AnonConstKind::MCG`, causing discriminant anon consts (`NonTypeSystem`) to bypass it entirely. Add `anon_const_forbids_generic_params()` which returns the appropriate `ForbidParamContext` for both MCG and enum discriminant contexts. Wire it into `check_param_uses_if_mcg` so that `Self` aliasing a generic type is caught before reaching `const_eval_poly`. Convert the `TooGeneric` span_bug into a proper diagnostic as a fallback for anything slipping through type-dependent path resolution. * Address review comments - Rename `ForbidMCGParamUsesFolder` to `ForbidParamUsesFolder` - Rename `MinConstGenerics` variant to `ConstArgument` with updated doc - Simplify doc comment on `anon_const_forbids_generic_params` - Make match on `AnonConstKind` exhaustive - Move `anon_const_def_id` inside the `if let` in `check_param_uses_if_mcg` - Remove now-unreachable `TooGeneric` span_err in wfcheck * Revert TooGeneric arm back to span_bug! as requested by reviewer * Use generics_of to determine if NonTypeSystem anon consts allow generic params * Also check InlineConst and Closure defs nested in enum discriminants * Simplify logic for determining anonymous constant parent in generic contexts * add test

rust-bors · 2026-04-14T14:32:32Z

🔨 7 commits were squashed into aacac7e.

BoxyUwU · 2026-04-14T14:32:59Z

@bors r+

sorry for the long turnaround on reviews :) thank you for working on this

rust-bors · 2026-04-14T14:33:03Z

📌 Commit aacac7e has been approved by BoxyUwU

It is now in the queue for this repository.

…eric-self, r=BoxyUwU Fix ICE when Self is used in enum discriminant of a generic enum Fixes rust-lang#153756 Let discriminant AnonConst inherit parent generics via Node::Variant in generics_of, and emit a proper error instead of span_bug! for the TooGeneric case in wfcheck.

…uwer Rollup of 9 pull requests Successful merges: - #153536 (Add `const_param_ty_unchecked` gate) - #153815 (Fix ICE when Self is used in enum discriminant of a generic enum) - #154882 (Gate tuple const params behind `min_adt_const_params` feature) - #155293 (fix arch names in cfg pretty printer) - #154765 (Clarify ascii whitespace exclusion of vertical tab in the doc) - #155172 (Some small nits for supertrait_item_shadowing, and additional testing) - #155279 (Test/lexer unicode pattern white space) - #155280 (Tests for precise-capture through RPIT and TAIT) - #155304 (remove PointeeParser)

rust-bors · 2026-04-15T05:15:25Z

☀️ Test successful - CI
Approved by: BoxyUwU
Duration: 3h 16m 22s
Pushing bd1e7c7 to main...

github-actions · 2026-04-15T05:18:13Z

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing a5c825c (parent) -> bd1e7c7 (this PR)

Test differences

Show 8 test diffs

Stage 1

[ui] tests/ui/enum-discriminant/generic-self-in-discr-ice.rs: [missing] -> pass (J1)
[ui] tests/ui/enum-discriminant/generic-self-in-discr-inline-const.rs: [missing] -> pass (J1)

Stage 2

[ui] tests/ui/enum-discriminant/generic-self-in-discr-ice.rs: [missing] -> pass (J0)
[ui] tests/ui/enum-discriminant/generic-self-in-discr-inline-const.rs: [missing] -> pass (J0)

Additionally, 4 doctest diffs were found. These are ignored, as they are noisy.

Job group index

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard bd1e7c79485d6a4113bb11dd98cb8b415cd4a55e --output-dir test-dashboard

And then open test-dashboard/index.html in your browser to see an overview of all executed tests.

Job duration changes

dist-aarch64-linux: 1h 45m -> 2h 31m (+44.5%)
dist-s390x-linux: 1h 11m -> 1h 30m (+26.2%)
dist-various-1: 1h 12m -> 54m 31s (-25.3%)
dist-ohos-x86_64: 1h 1m -> 1h 16m (+25.1%)
x86_64-msvc-ext2: 1h 53m -> 1h 24m (-25.0%)
x86_64-gnu-tools: 1h 5m -> 49m 19s (-24.6%)
dist-powerpc64le-linux-musl: 1h 17m -> 1h 36m (+24.2%)
x86_64-gnu-gcc: 1h 8m -> 52m 19s (-24.1%)
x86_64-mingw-2: 2h 45m -> 2h 5m (-24.0%)
aarch64-apple: 4h 7m -> 3h 10m (-23.2%)

How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
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rust-timer · 2026-04-15T05:57:15Z

Finished benchmarking commit (bd1e7c7): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.3%	[-0.3%, -0.2%]	3
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (secondary 2.0%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	4.9%	[2.9%, 6.8%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.8%	[-3.8%, -3.8%]	1
All ❌✅ (primary)	-	-	0

Cycles

Results (primary -0.7%, secondary 3.6%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	2.5%	[2.5%, 2.5%]	1
Regressions ❌ (secondary)	3.6%	[3.6%, 3.6%]	1
Improvements ✅ (primary)	-3.8%	[-3.8%, -3.8%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.7%	[-3.8%, 2.5%]	2

Binary size

Results (primary 0.1%, secondary 0.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.1%	[0.0%, 0.1%]	15
Regressions ❌ (secondary)	0.1%	[0.0%, 0.1%]	20
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.1%	[0.0%, 0.1%]	15

Bootstrap: 489.296s -> 495.503s (1.27%)
Artifact size: 394.04 MiB -> 394.22 MiB (0.05%)

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JonathanBrouwer mentioned this pull request Apr 14, 2026

Rollup of 6 pull requests #155297

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