fix(mgca): Allow specifying generic args (of enum) on enum itself in unit & tuple variant constructions in (direct) const args by JayanAXHF · Pull Request #155198 · rust-lang/rust

JayanAXHF · 2026-04-12T13:23:51Z

Basically, we check if there are three segments and if the first one is a DefKind::Enum, and then use the correct segment for Enum::<...>::Variant syntax for both DefKind::Ctor(_, CtorKind::Const | CtorKind::Fn)

PS: i'm not sure if the common logic from these two branches could be extracted

r? fmease

rustbot · 2026-04-12T13:23:56Z

HIR ty lowering was modified

cc @fmease

JayanAXHF · 2026-04-13T13:15:59Z

Fixed that @fmease

fmease

Thanks for working on this! I got some thoughts, apologies for the many comments; most of them are really minor that can be fixed super quickly.

View changes since this review

fmease · 2026-04-13T13:34:21Z

- .prohibit_generic_args(leading_segments.iter(), GenericsArgsErrExtend::None);
-
+ // Check if this is the Enum::<...>::Variant form
+ let use_enum_segment = if path.segments.len() == 2


The path should be allowed to have more than two segments. Right now, you're only allowing Enum::<...>::Variant but not e.g., very::long::path::to::Enum::<...>::Variant. So it should be >= 2 rather than == 2.
Once you implement that you also need to make sure to reject arguments on all segments before the enum segment since module::<...>::Enum::<...>::Variant should be forbidden.

JayanAXHF · 2026-04-14T14:21:49Z

@rustbot ready

fmease

I'm so sorry for the delay! Some final comments

View changes since this review

fmease · 2026-05-08T00:10:21Z

- let _ = self
- .prohibit_generic_args(leading_segments.iter(), GenericsArgsErrExtend::None);
-
+ let generics = self.probe_generic_path_segments(


I'm glad my suggestion to use probe_generic_path_segments is working out.
However, calling that function isn't sufficient, you still need (manually) prohibit generic args on all path segments that aren't generic using prohibit_generic_args, I know this API is a bit awkward. See the preexisting callers of probe_generic_path_segments for how they do it.
(I guess it could be nice if we'd have one function that does the "probing" and the "prohibiting" at once for convenience but I don't think we can do that yet w/o refactoring some things first, so that has to wait for another time)

I don't think we can do that yet w/o refactoring some things first
I believe we can. Currently, how this is done is
let generic_segments = self.probe_generic_path_segments(path.segments, opt_self_ty, kind, did, span);let indices:FxHashSet<_> = generic_segments.iter().map(|GenericPathSegment(_, index)| index).collect();let _ = self.prohibit_generic_args( path.segments.iter().enumerate().filter_map(|(index, seg)| {if !indices.contains(&index){Some(seg)}else{None}}),GenericsArgsErrExtend::DefVariant(&path.segments),);
I believe this could just be turned into a function

Ah, in that case, go for it! Unless you'd to leave it to a follow-up PR; this way we can merge this PR faster :)

Let's go for a follow-up PR. I'll create an issue so i don't forget if that's okay

JayanAXHF · 2026-05-20T11:18:04Z

apologies for the delay, will look into this on the weekend

rustbot · 2026-05-25T13:40:39Z

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.

JayanAXHF · 2026-05-25T13:41:15Z

Made the changes @fmease

@rustbot ready

fmease

Apologies for the delay, two final nits and one other note.

View changes since this review

fmease · 2026-06-08T18:32:07Z

- let _ = self
- .prohibit_generic_args(leading_segments.iter(), GenericsArgsErrExtend::None);
-
+ let generics = self.probe_generic_path_segments(


Ah, in that case, go for it! Unless you'd to leave it to a follow-up PR; this way we can merge this PR faster :)

…unit & tuple variant constructions in (direct) const args

fmease · 2026-06-10T21:47:07Z

Thanks for your work and your patience! :)

I've --bless'ed the failing test since that was all it needed. and I took the liberty to squash your commits. @bors r+ rollup

rust-bors · 2026-06-10T21:47:10Z

📌 Commit 7fe4408 has been approved by fmease

It is now in the queue for this repository.

… r=fmease fix(mgca): Allow specifying generic args (of enum) on enum itself in unit & tuple variant constructions in (direct) const args Closesrust-lang#154915 Basically, we check if there are three segments and if the first one is a `DefKind::Enum`, and then use the correct segment for `Enum::<...>::Variant` syntax for both `DefKind::Ctor(_, CtorKind::Const | CtorKind::Fn)` PS: i'm not sure if the common logic from these two branches could be extracted r? fmease

Rollup of 31 pull requests Successful merges: - #141030 (Expand free alias types during variance computation) - #154853 (mgca: Register `ConstArgHasType` when normalizing projection consts) - #155527 (Replace printables table with `unicode_data.rs` tables) - #156629 (Stabilize `core::range::{legacy, RangeFull, RangeTo}`) - #157280 (traits: Allow escaping self types in ExistentialTraitRef::with_self_ty) - #157282 (Fix post-monomorphization error note race in the parallel frontend) - #157352 (Make the retained dep graph deterministic under the parallel frontend) - #157601 (Emit error for unused target expression in glob and list delegations) - #157611 (Update `browser-ui-test` version to `0.24.0`) - #157620 (Add a strategy FnMut to inject behavior into the flush cycle) - #157645 (Windows TLS - Only register the `atexit` hook when `cleanup` can be unloaded) - #157646 (Keep rename-imported main alive in dead-code analysis under `--test`) - #157647 (Start using comptime for reflection intrinsics and their wrapper functions) - #157719 (resolve: Partially revert "Remove a special case for dummy imports") - #155153 (Ensure Send/Sync is not implemented for std::env::Vars{,Os}) - #155198 (fix(mgca): Allow specifying generic args (of enum) on enum itself in unit & tuple variant constructions in (direct) const args) - #155323 (refactor `TypeRelativePath::AssocItem` to use `AliasTerm`) - #156497 (fix-155516: Don't suggest wrong unwrap expect) - #156583 (Support defaults for static EIIs) - #157013 (Ensure inferred let pattern types are well-formed) - #157196 (Only suggest reborrowing a moved value where the reborrow is valid) - #157230 (borrowck: avoid ICE describing fields on generic params) - #157288 (platform support: add SNaN erratum to MIPS targets) - #157330 (remove `IsTypeConst` from `hir::TraitItemKind`) - #157350 (compiletest: ignore SVG `y` offset in by-lines comparison) - #157355 (Add `or_try_*` variants for `HashMap` and `BTreeMap` Entry APIs) - #157577 (Fix parser error recovery treating 'dyn' as a strict keyword in Rust 2015 when used in `dyn + dyn`) - #157670 (Rename `errors.rs` file to `diagnostics.rs` (4/N)) - #157691 (Move symbol hiding code to a new file) - #157700 (Rename `errors.rs` file to `diagnostics.rs` (5/N)) - #157703 (Fix doc link to Instant sub in saturating caveat) Failed merges: - #157699 (Arg splat experiment - hir FnDecl impl)

Rollup merge of #155198 - JayanAXHF:mgca/const-generic-args, r=fmease fix(mgca): Allow specifying generic args (of enum) on enum itself in unit & tuple variant constructions in (direct) const args Closes#154915 Basically, we check if there are three segments and if the first one is a `DefKind::Enum`, and then use the correct segment for `Enum::<...>::Variant` syntax for both `DefKind::Ctor(_, CtorKind::Const | CtorKind::Fn)` PS: i'm not sure if the common logic from these two branches could be extracted r? fmease

Rollup of 31 pull requests Successful merges: - rust-lang#141030 (Expand free alias types during variance computation) - rust-lang#154853 (mgca: Register `ConstArgHasType` when normalizing projection consts) - rust-lang#155527 (Replace printables table with `unicode_data.rs` tables) - rust-lang#156629 (Stabilize `core::range::{legacy, RangeFull, RangeTo}`) - rust-lang#157280 (traits: Allow escaping self types in ExistentialTraitRef::with_self_ty) - rust-lang#157282 (Fix post-monomorphization error note race in the parallel frontend) - rust-lang#157352 (Make the retained dep graph deterministic under the parallel frontend) - rust-lang#157601 (Emit error for unused target expression in glob and list delegations) - rust-lang#157611 (Update `browser-ui-test` version to `0.24.0`) - rust-lang#157620 (Add a strategy FnMut to inject behavior into the flush cycle) - rust-lang#157645 (Windows TLS - Only register the `atexit` hook when `cleanup` can be unloaded) - rust-lang#157646 (Keep rename-imported main alive in dead-code analysis under `--test`) - rust-lang#157647 (Start using comptime for reflection intrinsics and their wrapper functions) - rust-lang#157719 (resolve: Partially revert "Remove a special case for dummy imports") - rust-lang#155153 (Ensure Send/Sync is not implemented for std::env::Vars{,Os}) - rust-lang#155198 (fix(mgca): Allow specifying generic args (of enum) on enum itself in unit & tuple variant constructions in (direct) const args) - rust-lang#155323 (refactor `TypeRelativePath::AssocItem` to use `AliasTerm`) - rust-lang#156497 (fix-155516: Don't suggest wrong unwrap expect) - rust-lang#156583 (Support defaults for static EIIs) - rust-lang#157013 (Ensure inferred let pattern types are well-formed) - rust-lang#157196 (Only suggest reborrowing a moved value where the reborrow is valid) - rust-lang#157230 (borrowck: avoid ICE describing fields on generic params) - rust-lang#157288 (platform support: add SNaN erratum to MIPS targets) - rust-lang#157330 (remove `IsTypeConst` from `hir::TraitItemKind`) - rust-lang#157350 (compiletest: ignore SVG `y` offset in by-lines comparison) - rust-lang#157355 (Add `or_try_*` variants for `HashMap` and `BTreeMap` Entry APIs) - rust-lang#157577 (Fix parser error recovery treating 'dyn' as a strict keyword in Rust 2015 when used in `dyn + dyn`) - rust-lang#157670 (Rename `errors.rs` file to `diagnostics.rs` (4/N)) - rust-lang#157691 (Move symbol hiding code to a new file) - rust-lang#157700 (Rename `errors.rs` file to `diagnostics.rs` (5/N)) - rust-lang#157703 (Fix doc link to Instant sub in saturating caveat) Failed merges: - rust-lang#157699 (Arg splat experiment - hir FnDecl impl)

JonathanBrouwer · 2026-06-13T10:49:04Z

@rust-timer build 4858221

rust-timer · 2026-06-13T13:20:57Z

Finished benchmarking commit (4858221): comparison URL.

Overall result: no relevant changes - no action needed

Benchmarking means the PR may be perf-sensitive. Consider adding rollup=never if this change is not fit for rolling up.

@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

This perf run didn't have relevant results for this metric.

Max RSS (memory usage)

Results (primary -0.0%)

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

	mean	range	count
Regressions ❌ (primary)	2.9%	[2.9%, 2.9%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.0%	[-3.0%, -3.0%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.0%	[-3.0%, 2.9%]	2

Cycles

Results (secondary -2.8%)

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)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.8%	[-2.8%, -2.8%]	1
All ❌✅ (primary)	-	-	0

Binary size

This perf run didn't have relevant results for this metric.

Bootstrap: 517.006s -> 518.123s (0.22%)
Artifact size: 401.43 MiB -> 400.92 MiB (-0.13%)

Rollup of 31 pull requests Successful merges: - rust-lang/rust#141030 (Expand free alias types during variance computation) - rust-lang/rust#154853 (mgca: Register `ConstArgHasType` when normalizing projection consts) - rust-lang/rust#155527 (Replace printables table with `unicode_data.rs` tables) - rust-lang/rust#156629 (Stabilize `core::range::{legacy, RangeFull, RangeTo}`) - rust-lang/rust#157280 (traits: Allow escaping self types in ExistentialTraitRef::with_self_ty) - rust-lang/rust#157282 (Fix post-monomorphization error note race in the parallel frontend) - rust-lang/rust#157352 (Make the retained dep graph deterministic under the parallel frontend) - rust-lang/rust#157601 (Emit error for unused target expression in glob and list delegations) - rust-lang/rust#157611 (Update `browser-ui-test` version to `0.24.0`) - rust-lang/rust#157620 (Add a strategy FnMut to inject behavior into the flush cycle) - rust-lang/rust#157645 (Windows TLS - Only register the `atexit` hook when `cleanup` can be unloaded) - rust-lang/rust#157646 (Keep rename-imported main alive in dead-code analysis under `--test`) - rust-lang/rust#157647 (Start using comptime for reflection intrinsics and their wrapper functions) - rust-lang/rust#157719 (resolve: Partially revert "Remove a special case for dummy imports") - rust-lang/rust#155153 (Ensure Send/Sync is not implemented for std::env::Vars{,Os}) - rust-lang/rust#155198 (fix(mgca): Allow specifying generic args (of enum) on enum itself in unit & tuple variant constructions in (direct) const args) - rust-lang/rust#155323 (refactor `TypeRelativePath::AssocItem` to use `AliasTerm`) - rust-lang/rust#156497 (fix-155516: Don't suggest wrong unwrap expect) - rust-lang/rust#156583 (Support defaults for static EIIs) - rust-lang/rust#157013 (Ensure inferred let pattern types are well-formed) - rust-lang/rust#157196 (Only suggest reborrowing a moved value where the reborrow is valid) - rust-lang/rust#157230 (borrowck: avoid ICE describing fields on generic params) - rust-lang/rust#157288 (platform support: add SNaN erratum to MIPS targets) - rust-lang/rust#157330 (remove `IsTypeConst` from `hir::TraitItemKind`) - rust-lang/rust#157350 (compiletest: ignore SVG `y` offset in by-lines comparison) - rust-lang/rust#157355 (Add `or_try_*` variants for `HashMap` and `BTreeMap` Entry APIs) - rust-lang/rust#157577 (Fix parser error recovery treating 'dyn' as a strict keyword in Rust 2015 when used in `dyn + dyn`) - rust-lang/rust#157670 (Rename `errors.rs` file to `diagnostics.rs` (4/N)) - rust-lang/rust#157691 (Move symbol hiding code to a new file) - rust-lang/rust#157700 (Rename `errors.rs` file to `diagnostics.rs` (5/N)) - rust-lang/rust#157703 (Fix doc link to Instant sub in saturating caveat) Failed merges: - rust-lang/rust#157699 (Arg splat experiment - hir FnDecl impl)

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fix(mgca): Allow specifying generic args (of enum) on enum itself in …
7fe4408
…unit & tuple variant constructions in (direct) const args

fmease force-pushed the mgca/const-generic-args branch from 9d936c2 to 7fe4408Compare June 10, 2026 21:43

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jhpratt mentioned this pull request Jun 11, 2026
Rollup of 28 pull requests #157735
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jhpratt mentioned this pull request Jun 11, 2026
Rollup of 31 pull requests #157739
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rust-borsBot merged commit 644c882 into rust-lang:mainJun 11, 2026
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fmease mentioned this pull request Jun 16, 2026
Tracking Issue for Generic Constant Arguments MVP #132980
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