don't normalize where-clauses when checking well-formedness

[lqd]

WfCheck checks where-clauses after normalization, and we'd like to see what would break if it didn't for rust-lang/trait-system-refactor-initiative#255

r? ghost

[lqd]

@bors try

[rust-bors]

☀️ Try build successful (CI)
Build commit: f3d95de (f3d95de532264a1215023baa665c0028aecf74b1, parent: 90b65889799733f21ebdf59d96411aa531c5900a)

[lqd]

@craterbot check

[craterbot]

👌 Experiment pr-148477 created and queued.
🤖 Automatically detected try build f3d95de
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[craterbot]

🚧 Experiment pr-148477 is now running

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[craterbot]

🎉 Experiment pr-148477 is completed!
📊 7 regressed and 7 fixed (730342 total)
📊 1888 spurious results on the retry-regessed-list.txt, consider a retry¹ if this is a significant amount.
📰 Open the summary report.

⚠️ If you notice any spurious failure please add them to the denylist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

Footnotes

1. re-run the experiment with crates=https://crater-reports.s3.amazonaws.com/pr-148477/retry-regressed-list.txt ↩

[bors]

☔ The latest upstream changes (presumably #139558) made this pull request unmergeable. Please resolve the merge conflicts.

[lcnr]

Affected projects:

2 dependencies of modcholesky, same as rust-lang/trait-system-refactor-initiative#255

pub struct View<A>(A);
pub trait Data {
    type Elem;
}
impl<'a, A> Data for View<&'a A> {
    type Elem = A;
}

pub fn repro<'a, T>()
where
    <View<&'a T> as Data>::Elem: Sized,
{

https://github.com/vilicvane/unipipe/tree/9019a4b03df6ed222975b2774d686d5803860568

pub struct LifetimeTestPipe2<'a, T> {
    prefix: &'a str,
    transformer: &'a dyn Fn(&T) -> String,
    buffer: Vec<String>,
}

impl<'a, T> unipipe::UniPipe for LifetimeTestPipe2<'a, T> {
    type Input = T;
    type Output = String;

    fn next(&mut self, input: Option<Self::Input>) -> impl Into<Output<Self::Output>> {
        // ...
    }
}
#[unipipe::unipipe(iterator, try_iterator)]
impl<'a, T> LifetimeTestPipe2<'a, T> {
    pub fn new(prefix: &'a str, transformer: &'a dyn Fn(&T) -> String) -> Self {
        Self {
            prefix,
            transformer,
            buffer: Vec::new(),
        }
    }
}

expands to something containing

pub trait LifetimeTestPipe2UniPipeIteratorExt<'a, T>:
    Iterator<Item = <LifetimeTestPipe2<'a, T> as ::unipipe::UniPipe>::Input> + Sized
{
    // ...
}
impl<'a, T, TIterator> LifetimeTestPipe2UniPipeIteratorExt<'a, T> for TIterator where
    TIterator: Iterator<Item = <LifetimeTestPipe2<'a, T> as ::unipipe::UniPipe>::Input>
{
}

pub trait LifetimeTestPipe2UniPipeTryIteratorExt<'a, T, TError>:
    Iterator<Item = Result<<LifetimeTestPipe2<'a, T> as ::unipipe::UniPipe>::Input, TError>> + Sized
{
    // ...
}
impl<'a, T, TError, TIterator> LifetimeTestPipe2UniPipeTryIteratorExt<'a, T, TError> for TIterator where
    TIterator:
        Iterator<Item = Result<<LifetimeTestPipe2<'a, T> as ::unipipe::UniPipe>::Input, TError>>
{
}

That one is annoying. The macros can't really know the implied bounds of LifetimeTestPipe2, so I avoiding these errors is really challenging :<

[lcnr]

I think we should also stop normalizing in check_associated_type_bounds before checking that the where-clauses are wf.

rust/compiler/rustc_hir_analysis/src/check/wfcheck.rs

Lines 1154 to 1163 in a7b3715

	let wf_obligations = bounds.iter_identity_copied().flat_map(|(bound, bound_span)| {
	let normalized_bound = wfcx.normalize(span, None, bound);
	traits::wf::clause_obligations(
	wfcx.infcx,
	wfcx.param_env,
	wfcx.body_def_id,
	normalized_bound,
	bound_span,
	)
	});

[lqd]

And probably these

rust/compiler/rustc_hir_analysis/src/check/wfcheck.rs

Line 1490 in cf33ee0

let pred = wfcx.normalize(sp, None, pred);

from the default args as well, right?

[lcnr]

wrt to normalizing obligations for default params before proving them 😅

we do need to normalize obligations before proving them in the old solver and this already doesn't normalize WellFormed obligations.

rust/compiler/rustc_trait_selection/src/traits/normalize.rs

Line 485 in 5dbf406

if p.allow_normalization() && needs_normalization(self.selcx.infcx, &p) {

rust/compiler/rustc_middle/src/ty/predicate.rs

Lines 125 to 127 in 5dbf406

	PredicateKind::Clause(ClauseKind::WellFormed(_)) | PredicateKind::AliasRelate(..) => {
	false
	}

The only "issue" is when normalizing obligations (or types - which we currently sometimes do intentionally because of implied bounds stuff) before checking that the obligation is well-formed, and this only happens before calling clause_obligations. In a sense calling clause_obligations (and proving its nested obligations) is the same as a emitting a ClauseKind::WellFormed(some_where_clause) goal if we were to support that

[lcnr]

@bors try

[rust-bors]

☀️ Try build successful (CI)
Build commit: 04ea1e1 (04ea1e1f1a12cfa912c228ca278237d92d0bb6df, parent: 5dbf4069dc98bbbca98dd600a65f50c258fbfd56)

[lcnr]

@craterbot check

[craterbot]

👌 Experiment pr-148477-1 created and queued.
🤖 Automatically detected try build 04ea1e1
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[craterbot]

🎉 Experiment pr-148477-2 is completed!
📊 3 regressed and 0 fixed (1730 total)
📊 109 spurious results on the retry-regessed-list.txt, consider a retry¹ if this is a significant amount.
📰 Open the summary report.

⚠️ If you notice any spurious failure please add them to the denylist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

Footnotes

1. re-run the experiment with crates=https://crater-reports.s3.amazonaws.com/pr-148477-2/retry-regressed-list.txt ↩

[craterbot]

🎉 Experiment pr-148477-3 is completed!
📊 3 regressed and 0 fixed (112 total)
📊 32 spurious results on the retry-regessed-list.txt, consider a retry¹ if this is a significant amount.
📰 Open the summary report.

⚠️ If you notice any spurious failure please add them to the denylist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

Footnotes

1. re-run the experiment with crates=https://crater-reports.s3.amazonaws.com/pr-148477-3/retry-regressed-list.txt ↩

[lqd]

1769 spurious results on that crater run feels kinda high to me, would it be possible to rerun that a couple times until its like <100 or sth. i dont expect it to really change the calculus here but if it did find like One extra regression then we can open a PR

The same 3 regressions were in the new runs above, and the spurious results are down to 32.

[BoxyUwU]

@bors r=lcnr,BoxyUwU

[bors]

📌 Commit 99f7e78 has been approved by lcnr,BoxyUwU

It is now in the queue for this repository.

[bors]

⌛ Testing commit 99f7e78 with merge 2a3a62d...

[bors]

☀️ Test successful - checks-actions
Approved by: lcnr,BoxyUwU
Pushing 2a3a62d 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 c4dc70e (parent) -> 2a3a62d (this PR)

Test differences

Show 6 test diffs

Stage 1

• [ui] tests/ui/wf/wf-where-clauses-pre-normalization.rs: [missing] -> pass (J1)

Stage 2

• [ui] tests/ui/wf/wf-where-clauses-pre-normalization.rs: [missing] -> pass (J0)
• [crashes] tests/crashes/133613.rs: pass -> ignore (ignored if rustc wasn't built with debug assertions) (J2)

Additionally, 3 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
• J2: dist-i586-gnu-i586-i686-musl, test-various, x86_64-gnu-gcc

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard 2a3a62d26e9e5badb806ac6a43bb307ff472b514 --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. dist-apple-various: 3421.5s -> 4885.1s (+42.8%)
2. dist-x86_64-apple: 7406.1s -> 8403.1s (+13.5%)
3. dist-aarch64-llvm-mingw: 5521.4s -> 6184.9s (+12.0%)
4. x86_64-gnu-gcc: 3201.3s -> 2842.0s (-11.2%)
5. x86_64-gnu-aux: 7028.4s -> 6381.7s (-9.2%)
6. pr-check-2: 2389.4s -> 2183.4s (-8.6%)
7. aarch64-gnu-llvm-20-2: 2448.5s -> 2244.3s (-8.3%)
8. pr-check-1: 1555.6s -> 1682.8s (+8.2%)
9. tidy: 169.9s -> 156.9s (-7.6%)
10. dist-aarch64-msvc: 6356.7s -> 5892.7s (-7.3%)

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 (2a3a62d): 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 0.2%, secondary 0.7%)

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

	mean	range	count
Regressions ❌ (primary)	2.3%	[2.3%, 2.3%]	1
Regressions ❌ (secondary)	0.7%	[0.6%, 0.7%]	2
Improvements ✅ (primary)	-1.8%	[-1.8%, -1.8%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.2%	[-1.8%, 2.3%]	2

Cycles

Results (secondary 5.2%)

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)	5.2%	[5.2%, 5.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

Results (primary 0.0%, 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)	0.0%	[0.0%, 0.0%]	11
Regressions ❌ (secondary)	0.1%	[0.0%, 0.1%]	5
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.0%	[0.0%, 0.0%]	11

Bootstrap: 473.76s -> 472.42s (-0.28%)
Artifact size: 389.30 MiB -> 389.33 MiB (0.01%)