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Auto merge of #135618 - lcnr:coherence-unknown, r=compiler-errors
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add cache to `AmbiguityCausesVisitor`

fixes #135457, alternative to #135524.

cc https://rust-lang.zulipchat.com/#narrow/channel/364551-t-types.2Ftrait-system-refactor/topic/new-solver.20hang.20.23135457

r? `@compiler-errors`
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@bors
bors committed Jan 18, 2025
2 parents 6067b36 + 0910173 commit 8e59cf9
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Showing 5 changed files with 115 additions and 28 deletions.
69 changes: 45 additions & 24 deletions compiler/rustc_trait_selection/src/traits/coherence.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,7 @@
use std::fmt::Debug;

use rustc_data_structures::fx::FxIndexSet;
use rustc_data_structures::fx::{FxHashSet, FxIndexSet};
use rustc_errors::{Diag, EmissionGuarantee};
use rustc_hir::def::DefKind;
use rustc_hir::def_id::DefId;
Expand Down Expand Up @@ -116,28 +116,39 @@ pub fn overlapping_impls(
return None;
}

let _overlap_with_bad_diagnostics = overlap(
tcx,
TrackAmbiguityCauses::No,
skip_leak_check,
impl1_def_id,
impl2_def_id,
overlap_mode,
)?;

// In the case where we detect an error, run the check again, but
// this time tracking intercrate ambiguity causes for better
// diagnostics. (These take time and can lead to false errors.)
let overlap = overlap(
tcx,
TrackAmbiguityCauses::Yes,
skip_leak_check,
impl1_def_id,
impl2_def_id,
overlap_mode,
)
.unwrap();
Some(overlap)
if tcx.next_trait_solver_in_coherence() {
overlap(
tcx,
TrackAmbiguityCauses::Yes,
skip_leak_check,
impl1_def_id,
impl2_def_id,
overlap_mode,
)
} else {
let _overlap_with_bad_diagnostics = overlap(
tcx,
TrackAmbiguityCauses::No,
skip_leak_check,
impl1_def_id,
impl2_def_id,
overlap_mode,
)?;

// In the case where we detect an error, run the check again, but
// this time tracking intercrate ambiguity causes for better
// diagnostics. (These take time and can lead to false errors.)
let overlap = overlap(
tcx,
TrackAmbiguityCauses::Yes,
skip_leak_check,
impl1_def_id,
impl2_def_id,
overlap_mode,
)
.unwrap();
Some(overlap)
}
}

fn fresh_impl_header<'tcx>(infcx: &InferCtxt<'tcx>, impl_def_id: DefId) -> ty::ImplHeader<'tcx> {
Expand Down Expand Up @@ -615,6 +626,7 @@ fn compute_intercrate_ambiguity_causes<'tcx>(
}

struct AmbiguityCausesVisitor<'a, 'tcx> {
cache: FxHashSet<Goal<'tcx, ty::Predicate<'tcx>>>,
causes: &'a mut FxIndexSet<IntercrateAmbiguityCause<'tcx>>,
}

Expand All @@ -624,6 +636,10 @@ impl<'a, 'tcx> ProofTreeVisitor<'tcx> for AmbiguityCausesVisitor<'a, 'tcx> {
}

fn visit_goal(&mut self, goal: &InspectGoal<'_, 'tcx>) {
if !self.cache.insert(goal.goal()) {
return;
}

let infcx = goal.infcx();
for cand in goal.candidates() {
cand.visit_nested_in_probe(self);
Expand Down Expand Up @@ -748,5 +764,10 @@ fn search_ambiguity_causes<'tcx>(
goal: Goal<'tcx, ty::Predicate<'tcx>>,
causes: &mut FxIndexSet<IntercrateAmbiguityCause<'tcx>>,
) {
infcx.probe(|_| infcx.visit_proof_tree(goal, &mut AmbiguityCausesVisitor { causes }));
infcx.probe(|_| {
infcx.visit_proof_tree(goal, &mut AmbiguityCausesVisitor {
cache: Default::default(),
causes,
})
});
}
2 changes: 0 additions & 2 deletions tests/ui/coherence/occurs-check/associated-type.next.stderr
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Original file line number Diff line number Diff line change
@@ -1,7 +1,5 @@
WARN rustc_infer::infer::relate::generalize may incompletely handle alias type: AliasTy { args: [*const ?1t, '^0.Named(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), "'a")], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit), .. }
WARN rustc_infer::infer::relate::generalize may incompletely handle alias type: AliasTy { args: [*const ?1t, '^0.Named(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), "'a")], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit), .. }
WARN rustc_infer::infer::relate::generalize may incompletely handle alias type: AliasTy { args: [*const ?1t, '^0.Named(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), "'a")], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit), .. }
WARN rustc_infer::infer::relate::generalize may incompletely handle alias type: AliasTy { args: [*const ?1t, '^0.Named(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), "'a")], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit), .. }
error[E0119]: conflicting implementations of trait `Overlap<for<'a> fn(&'a (), ())>` for type `for<'a> fn(&'a (), ())`
--> $DIR/associated-type.rs:32:1
|
Expand Down
2 changes: 0 additions & 2 deletions tests/ui/coherence/occurs-check/associated-type.old.stderr
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Original file line number Diff line number Diff line change
@@ -1,7 +1,5 @@
WARN rustc_infer::infer::relate::generalize may incompletely handle alias type: AliasTy { args: [*const ?1t, '^0.Named(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), "'a")], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit), .. }
WARN rustc_infer::infer::relate::generalize may incompletely handle alias type: AliasTy { args: [*const ?1t, '^0.Named(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), "'a")], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit), .. }
WARN rustc_infer::infer::relate::generalize may incompletely handle alias type: AliasTy { args: [*const ?1t, '^0.Named(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), "'a")], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit), .. }
WARN rustc_infer::infer::relate::generalize may incompletely handle alias type: AliasTy { args: [*const ?1t, '^0.Named(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), "'a")], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit), .. }
error[E0119]: conflicting implementations of trait `Overlap<for<'a> fn(&'a (), ())>` for type `for<'a> fn(&'a (), ())`
--> $DIR/associated-type.rs:32:1
|
Expand Down
56 changes: 56 additions & 0 deletions tests/ui/traits/next-solver/coherence/ambiguity-causes-visitor-hang.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,56 @@
// Computing the ambiguity causes for the overlap ended up
// causing an exponential blowup when recursing into the normalization
// goals for `<Box<?t> as RecursiveSuper>::Assoc`. This test
// takes multiple minutes when doing so and less than a second
// otherwise.

//@ compile-flags: -Znext-solver=coherence

trait RecursiveSuper:
Super<
A0 = Self::Assoc,
A1 = Self::Assoc,
A2 = Self::Assoc,
A3 = Self::Assoc,
A4 = Self::Assoc,
A5 = Self::Assoc,
A6 = Self::Assoc,
A7 = Self::Assoc,
A8 = Self::Assoc,
A9 = Self::Assoc,
A10 = Self::Assoc,
A11 = Self::Assoc,
A12 = Self::Assoc,
A13 = Self::Assoc,
A14 = Self::Assoc,
A15 = Self::Assoc,
>
{
type Assoc;
}

trait Super {
type A0;
type A1;
type A2;
type A3;
type A4;
type A5;
type A6;
type A7;
type A8;
type A9;
type A10;
type A11;
type A12;
type A13;
type A14;
type A15;
}

trait Overlap {}
impl<T: RecursiveSuper> Overlap for T {}
impl<T> Overlap for Box<T> {}
//~^ ERROR conflicting implementations of trait `Overlap` for type `Box<_>`

fn main() {}
14 changes: 14 additions & 0 deletions tests/ui/traits/next-solver/coherence/ambiguity-causes-visitor-hang.stderr
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Original file line number Diff line number Diff line change
@@ -0,0 +1,14 @@
error[E0119]: conflicting implementations of trait `Overlap` for type `Box<_>`
--> $DIR/ambiguity-causes-visitor-hang.rs:53:1
|
LL | impl<T: RecursiveSuper> Overlap for T {}
| ------------------------------------- first implementation here
LL | impl<T> Overlap for Box<T> {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `Box<_>`
|
= note: downstream crates may implement trait `Super` for type `std::boxed::Box<_>`
= note: downstream crates may implement trait `RecursiveSuper` for type `std::boxed::Box<_>`

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0119`.

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