crater: 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?

[rust-log-analyzer]

The job x86_64-gnu-gcc failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

test [crashes] tests/crashes/131373.rs ... ok
test [crashes] tests/crashes/131886.rs ... ok
test [crashes] tests/crashes/132126.rs ... ok
test [crashes] tests/crashes/132960.rs ... ok
2025-11-12T17:46:04.636491Z ERROR compiletest::runtest: fatal error, panic: "crashtest no longer crashes/triggers ICE, hooray! Please give it a meaningful name, add a doc-comment to the start of the test explaining why it exists and move it to tests/ui or wherever you see fit. Adding 'Fixes #<issueNr>' to your PR description ensures that the corresponding ticket is auto-closed upon merge. If you want to see verbose output, set `COMPILETEST_VERBOSE_CRASHES=1`."
test [crashes] tests/crashes/132765.rs ... ok
test [crashes] tests/crashes/133965.rs ... ignored, ignored if rustc wasn't built with debug assertions
test [crashes] tests/crashes/133613.rs ... FAILED
test [crashes] tests/crashes/134061.rs ... ignored, ignored if rustc wasn't built with debug assertions
test [crashes] tests/crashes/134479.rs ... ignored, gcc backend is marked as ignore
---

---- [crashes] tests/crashes/133613.rs stdout ----
------rustc stdout------------------------------

------rustc stderr------------------------------
error[E0658]: return type notation is experimental
##[error] --> /checkout/tests/crashes/133613.rs:6:47
  |
6 |     fn stream(&self) -> impl IntFactory<stream(..): IntFactory<stream(..): Send>>;
  |                                               ^^^^
  |
  = note: see issue #109417 <https://github.com/rust-lang/rust/issues/109417> for more information
  = help: add `#![feature(return_type_notation)]` to the crate attributes to enable
  = note: this compiler was built on 2025-11-12; consider upgrading it if it is out of date

error[E0658]: return type notation is experimental
##[error] --> /checkout/tests/crashes/133613.rs:6:70
  |
6 |     fn stream(&self) -> impl IntFactory<stream(..): IntFactory<stream(..): Send>>;
  |                                                                      ^^^^
  |
  = note: see issue #109417 <https://github.com/rust-lang/rust/issues/109417> for more information
  = help: add `#![feature(return_type_notation)]` to the crate attributes to enable
  = note: this compiler was built on 2025-11-12; consider upgrading it if it is out of date
---
  |
3 | struct Wrapper<'a>();
  |                ^^ unused lifetime parameter
  |
  = help: consider removing `'a`, referring to it in a field, or using a marker such as `PhantomData`

error: aborting due to 4 previous errors

Some errors have detailed explanations: E0392, E0601, E0658.
For more information about an error, try `rustc --explain E0392`.

------------------------------------------

error: crashtest no longer crashes/triggers ICE, hooray! Please give it a meaningful name, add a doc-comment to the start of the test explaining why it exists and move it to tests/ui or wherever you see fit. Adding 'Fixes #<issueNr>' to your PR description ensures that the corresponding ticket is auto-closed upon merge. If you want to see verbose output, set `COMPILETEST_VERBOSE_CRASHES=1`.

thread '[crashes] tests/crashes/133613.rs' panicked at src/tools/compiletest/src/runtest/crashes.rs:17:18:
fatal error
stack backtrace:
   5: __rustc::rust_begin_unwind

For more information how to resolve CI failures of this job, visit this link.

[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-148477-1 is now running

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

[craterbot]

🎉 Experiment pr-148477-1 is completed!
📊 9 regressed and 4 fixed (736518 total)
📊 1769 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-148477-1/retry-regressed-list.txt ↩

[lqd]

There were no new regressions in that last crater run:

• for dependents: there's 1 new dependent of modcholesky
• for root crates themselves: the other entries present there are spurious or unrelated