ignore implied bounds with placeholders

[aliemjay]

given the following code:

trait Trait {
    type Ty<'a> where Self: 'a;
}

impl<T> Trait for T {
    type Ty<'a> = () where Self: 'a;
}

struct Foo<T: Trait>(T)
where
    for<'x> T::Ty<'x>: Sized;

when computing the implied bounds from Foo<X> we incorrectly get the bound X: !x from the normalization of for<'x> <X as Trait>::Ty::<'x>: Sized. This is a a known bug! we shouldn't use the constraints that arise from normalization as implied bounds. See #109628.

Ignore these bounds for now. This should prevent later ICEs.

Fixes #112250
Fixes #107409

[rustbot]

r? @WaffleLapkin

(rustbot has picked a reviewer for you, use r? to override)

[aliemjay]

cc @lcnr (because it involves #109628)
r? types

[lcnr]

❤️

r=me after nits

[lcnr]

can you move that into the TypeOp?

[aliemjay]

Moving this into the TypeOp has no benefit as we would have to duplicate the logic in QueryTypeOp::{perform_query,perform_locally_in_new_solver} as well. It is also more difficult to handle canonicalized query responses - there is no easy way to detect placeholders for example.

Doing it in the query itself is difficult as we need to do OpportunisticRegionResolution before checking for placeholders. Using TypeVisitableExt::has_placeholders to check for erroneus placeholders there does not play well with #109388 as it would yield many false positives.

[Dylan-DPC]

@aliemjay any updates on this? thanks

[bors]

☔ The latest upstream changes (presumably #117228) made this pull request unmergeable. Please resolve the merge conflicts.

[chrysn]

I think I have a case similar to #112250 in code at https://gitlab.com/chrysn/coap-message-demos branch embedded-nal-coap-clientserver when run as cargo +nightly run --example std_embedded_nal_coap --features example-std_embedded_nal_coap. Before I start minimizing this for hours I'd like to try this PR, but the code widely depends on newly stabilized features. Would you consider updating?

[aliemjay]

@rustbot review

[lcnr]

@bors r+

[bors]

📌 Commit af79fd1 has been approved by lcnr

It is now in the queue for this repository.

[bors]

⌛ Testing commit af79fd1 with merge 4d7f952...

[bors]

☀️ Test successful - checks-actions
Approved by: lcnr
Pushing 4d7f952 to master...

[rust-timer]

Finished benchmarking commit (4d7f952): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.4%	[-2.4%, -2.4%]	1
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	1.5%	[1.1%, 1.8%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-1.0%	[-1.0%, -1.0%]	1
Improvements ✅ (secondary)	-2.0%	[-3.4%, -1.0%]	6
All ❌✅ (primary)	0.6%	[-1.0%, 1.8%]	3

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

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

Binary size

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

Bootstrap: 676.982s -> 676.352s (-0.09%)
Artifact size: 313.61 MiB -> 313.63 MiB (0.00%)

[lqd]

(deep-vector is currently being noisy)