avoid recreating field_const vec

[Kivooeo]

r? BoxyUwU

fixes #150354
fixes #150355

[rustbot]

Some changes occurred in rustc_ty_utils::consts.rs

cc @BoxyUwU

[rustbot]

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

[Kivooeo]

@rustbot ready

[BoxyUwU]

In theory we ought to make the same change to the match arms for handling arays/slices/tuples. They're currently doing the same ty::Const::new_value(ct.to_value()) thing which they shouldn't be. I don't think it's possible to write a test case where this matters yet though (we would need mgca to have support for hir::ConstArgKind::Array/Tuple which it doesn't yet).

I feel like a more involved refactor could be nice. Specifically:

• Stop handling Array/Slice/Tuple in destructure_const
• Have all callers of destructure_const handle array/slice/tuples themselves by using the branches of the ValTree.
• Rename destructure_const and ty::DestructuredConst to destructure_adt_const and ty::DestructuredAdtConst

Would you be interested in doing that? Can either do so in this PR or a future PR if you like. I'm happy to just merge this PR without the proposed refactoring if you prefer.

View changes since this review

[Kivooeo]

Would you be interested in doing that?

sure, I'd be happy to look into this refactor in the follow up PRs

[BoxyUwU]

thx

View changes since this review

[Kivooeo]

seems like it should be very fine now

[BoxyUwU]

r=me once CI passes

View changes since this review

[Kivooeo]

@bors r=BoxyUwU rollup

[bors]

📌 Commit 517411f has been approved by BoxyUwU

It is now in the queue for this repository.

[bors]

⌛ Testing commit 517411f with merge 82dd3cb...

[bors]

☀️ Test successful - checks-actions
Approved by: BoxyUwU
Pushing 82dd3cb to main...

[github-actions]

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 8da80d3 (parent) -> 82dd3cb (this PR)

Test differences

Show 4 test diffs

Stage 1

• [ui] tests/ui/const-generics/mgca/printing_valtrees_supports_non_values.rs: [missing] -> pass (J1)

Stage 2

• [ui] tests/ui/const-generics/mgca/printing_valtrees_supports_non_values.rs: [missing] -> pass (J0)

Additionally, 2 doctest diffs were found. These are ignored, as they are noisy.

Job group index

• J0: aarch64-apple, aarch64-gnu, aarch64-gnu-llvm-20-1, aarch64-msvc-1, arm-android, armhf-gnu, dist-i586-gnu-i586-i686-musl, i686-gnu-1, i686-gnu-nopt-1, i686-msvc-1, test-various, x86_64-gnu, x86_64-gnu-debug, x86_64-gnu-gcc, x86_64-gnu-llvm-20, x86_64-gnu-llvm-20-2, x86_64-gnu-llvm-21-2, x86_64-gnu-nopt, x86_64-gnu-stable, x86_64-mingw-1, x86_64-msvc-1
• J1: x86_64-gnu-llvm-20-3, x86_64-gnu-llvm-21-3

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard 82dd3cb008233bfe50ba6b8d6618e6bbd6054eb1 --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

1. x86_64-msvc-1: 9054.6s -> 8128.2s (-10.2%)
2. dist-riscv64-linux: 4897.8s -> 5292.2s (+8.1%)
3. x86_64-gnu-llvm-20-1: 3959.7s -> 4277.9s (+8.0%)
4. dist-aarch64-apple: 6421.4s -> 6876.4s (+7.1%)
5. aarch64-apple: 10141.0s -> 9429.5s (-7.0%)
6. dist-i686-msvc: 8381.3s -> 7872.6s (-6.1%)
7. dist-x86_64-apple: 6418.6s -> 6765.6s (+5.4%)
8. dist-x86_64-musl: 7309.7s -> 7701.8s (+5.4%)
9. dist-ohos-aarch64: 4427.7s -> 4190.7s (-5.4%)
10. aarch64-gnu-llvm-20-1: 3270.7s -> 3442.8s (+5.3%)

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
mostly for t-infra members, for simpler debugging of potential CI slow-downs.

[rust-timer]

Finished benchmarking commit (82dd3cb): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results (primary -6.8%)

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)	-6.8%	[-6.8%, -6.8%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-6.8%	[-6.8%, -6.8%]	1

Cycles

Results (primary 2.8%, secondary 4.7%)

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

	mean	range	count
Regressions ❌ (primary)	2.8%	[1.4%, 4.5%]	13
Regressions ❌ (secondary)	4.7%	[2.8%, 7.5%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.8%	[1.4%, 4.5%]	13

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 483.256s -> 492.292s (1.87%)
Artifact size: 392.46 MiB -> 392.38 MiB (-0.02%)