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Auto merge of #124811 - matthiaskrgr:rollup-4zpov13, r=matthiaskrgr
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Rollup of 4 pull requests

Successful merges:

 - #124520 (Document that `create_dir_all` calls `mkdir`/`CreateDirW` multiple times)
 - #124724 (Prefer lower vtable candidates in select in new solver)
 - #124771 (Don't consider candidates with no failing where clauses when refining obligation causes in new solver)
 - #124808 (Use `super_fold` in `RegionsToStatic` visitor)

r? `@ghost`
`@rustbot` modify labels: rollup
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bors committed May 6, 2024
2 parents fc47cf3 + ad73b16 commit 3111015
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Showing 12 changed files with 137 additions and 15 deletions.
2 changes: 1 addition & 1 deletion compiler/rustc_next_trait_solver/src/canonicalizer.rs
Original file line number Diff line number Diff line change
Expand Up @@ -455,7 +455,7 @@ impl<I: Interner> TypeFolder<I> for RegionsToStatic<I> {
I::Binder<T>: TypeSuperFoldable<I>,
{
self.binder.shift_in(1);
let t = t.fold_with(self);
let t = t.super_fold_with(self);
self.binder.shift_out(1);
t
}
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18 changes: 13 additions & 5 deletions compiler/rustc_trait_selection/src/solve/eval_ctxt/select.rs
Original file line number Diff line number Diff line change
Expand Up @@ -58,6 +58,12 @@ impl<'tcx> inspect::ProofTreeVisitor<'tcx> for Select {
)));
}

// Don't winnow until `Certainty::Yes` -- we don't need to winnow until
// codegen, and only on the good path.
if matches!(goal.result().unwrap(), Certainty::Maybe(..)) {
return ControlFlow::Break(Ok(None));
}

// We need to winnow. See comments on `candidate_should_be_dropped_in_favor_of`.
let mut i = 0;
while i < candidates.len() {
Expand Down Expand Up @@ -86,7 +92,7 @@ fn candidate_should_be_dropped_in_favor_of<'tcx>(
other: &inspect::InspectCandidate<'_, 'tcx>,
) -> bool {
// Don't winnow until `Certainty::Yes` -- we don't need to winnow until
// codegen, technically.
// codegen, and only on the good path.
if matches!(other.result().unwrap(), Certainty::Maybe(..)) {
return false;
}
Expand All @@ -105,12 +111,14 @@ fn candidate_should_be_dropped_in_favor_of<'tcx>(
bug!("should not have assembled a CoherenceUnknowable candidate")
}

// In the old trait solver, we arbitrarily choose lower vtable candidates
// over higher ones.
(
CandidateSource::BuiltinImpl(BuiltinImplSource::Object { vtable_base: a }),
CandidateSource::BuiltinImpl(BuiltinImplSource::Object { vtable_base: b }),
) => a >= b,
// Prefer dyn candidates over non-dyn candidates. This is necessary to
// handle the unsoundness between `impl<T: ?Sized> Any for T` and `dyn Any: Any`.
(
CandidateSource::BuiltinImpl(BuiltinImplSource::Object { .. }),
CandidateSource::BuiltinImpl(BuiltinImplSource::Object { .. }),
) => false,
(
CandidateSource::Impl(_) | CandidateSource::ParamEnv(_) | CandidateSource::AliasBound,
CandidateSource::BuiltinImpl(BuiltinImplSource::Object { .. }),
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48 changes: 42 additions & 6 deletions compiler/rustc_trait_selection/src/solve/fulfill.rs
Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,7 @@ use rustc_middle::ty::{self, TyCtxt};
use rustc_span::symbol::sym;

use super::eval_ctxt::GenerateProofTree;
use super::inspect::{ProofTreeInferCtxtExt, ProofTreeVisitor};
use super::inspect::{InspectCandidate, InspectGoal, ProofTreeInferCtxtExt, ProofTreeVisitor};
use super::{Certainty, InferCtxtEvalExt};

/// A trait engine using the new trait solver.
Expand Down Expand Up @@ -304,6 +304,46 @@ impl<'tcx> BestObligation<'tcx> {
self.obligation = old_obligation;
res
}

/// Filter out the candidates that aren't either error or ambiguous (depending
/// on what we are looking for), and also throw out candidates that have no
/// failing WC (or higher-ranked obligations, for which there should only be
/// one candidate anyways -- but I digress). This most likely means that the
/// goal just didn't unify at all, e.g. a param candidate with an alias in it.
fn non_trivial_candidates<'a>(
&self,
goal: &'a InspectGoal<'a, 'tcx>,
) -> Vec<InspectCandidate<'a, 'tcx>> {
let mut candidates = goal
.candidates()
.into_iter()
.filter(|candidate| match self.consider_ambiguities {
true => matches!(candidate.result(), Ok(Certainty::Maybe(_))),
false => matches!(candidate.result(), Err(_)),
})
.collect::<Vec<_>>();

// If we have >1 candidate, one may still be due to "boring" reasons, like
// an alias-relate that failed to hold when deeply evaluated. We really
// don't care about reasons like this.
if candidates.len() > 1 {
candidates.retain(|candidate| {
goal.infcx().probe(|_| {
candidate.instantiate_nested_goals(self.span()).iter().any(|nested_goal| {
matches!(
nested_goal.source(),
GoalSource::ImplWhereBound | GoalSource::InstantiateHigherRanked
) && match self.consider_ambiguities {
true => matches!(nested_goal.result(), Ok(Certainty::Maybe(_))),
false => matches!(nested_goal.result(), Err(_)),
}
})
})
});
}

candidates
}
}

impl<'tcx> ProofTreeVisitor<'tcx> for BestObligation<'tcx> {
Expand All @@ -314,11 +354,7 @@ impl<'tcx> ProofTreeVisitor<'tcx> for BestObligation<'tcx> {
}

fn visit_goal(&mut self, goal: &super::inspect::InspectGoal<'_, 'tcx>) -> Self::Result {
// FIXME: Throw out candidates that have no failing WC and >0 failing misc goal.
// This most likely means that the goal just didn't unify at all, e.g. a param
// candidate with an alias in it.
let candidates = goal.candidates();

let candidates = self.non_trivial_candidates(goal);
let [candidate] = candidates.as_slice() else {
return ControlFlow::Break(self.obligation.clone());
};
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10 changes: 7 additions & 3 deletions library/std/src/fs.rs
Original file line number Diff line number Diff line change
Expand Up @@ -2258,7 +2258,7 @@ pub fn canonicalize<P: AsRef<Path>>(path: P) -> io::Result<PathBuf> {
/// # Platform-specific behavior
///
/// This function currently corresponds to the `mkdir` function on Unix
/// and the `CreateDirectory` function on Windows.
/// and the `CreateDirectoryW` function on Windows.
/// Note that, this [may change in the future][changes].
///
/// [changes]: io#platform-specific-behavior
Expand Down Expand Up @@ -2298,10 +2298,14 @@ pub fn create_dir<P: AsRef<Path>>(path: P) -> io::Result<()> {
/// Recursively create a directory and all of its parent components if they
/// are missing.
///
/// If this function returns an error, some of the parent components might have
/// been created already.
///
/// # Platform-specific behavior
///
/// This function currently corresponds to the `mkdir` function on Unix
/// and the `CreateDirectory` function on Windows.
/// This function currently corresponds to multiple calls to the `mkdir`
/// function on Unix and the `CreateDirectoryW` function on Windows.
///
/// Note that, this [may change in the future][changes].
///
/// [changes]: io#platform-specific-behavior
Expand Down
Original file line number Diff line number Diff line change
@@ -0,0 +1,8 @@
//@ compile-flags: -Znext-solver=coherence

#[derive(Debug)]
struct X<const FN: fn() = { || {} }>;
//~^ ERROR using function pointers as const generic parameters is forbidden
//~| ERROR using function pointers as const generic parameters is forbidden

fn main() {}
Original file line number Diff line number Diff line change
@@ -0,0 +1,19 @@
error: using function pointers as const generic parameters is forbidden
--> $DIR/const-region-infer-to-static-in-binder.rs:4:20
|
LL | struct X<const FN: fn() = { || {} }>;
| ^^^^
|
= note: the only supported types are integers, `bool` and `char`

error: using function pointers as const generic parameters is forbidden
--> $DIR/const-region-infer-to-static-in-binder.rs:4:20
|
LL | struct X<const FN: fn() = { || {} }>;
| ^^^^
|
= note: the only supported types are integers, `bool` and `char`
= note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error: aborting due to 2 previous errors

Original file line number Diff line number Diff line change
@@ -0,0 +1,22 @@
trait Foo {}
trait Bar {}

impl<T> Foo for T where T: Bar {}
fn needs_foo(_: impl Foo) {}

trait Mirror {
type Mirror;
}
impl<T> Mirror for T {
type Mirror = T;
}

// Make sure the `Alias: Foo` bound doesn't "shadow" the impl, since the
// impl is really the only candidate we care about here for the purpose
// of error reporting.
fn hello<T>() where <T as Mirror>::Mirror: Foo {
needs_foo(());
//~^ ERROR the trait bound `(): Foo` is not satisfied
}

fn main() {}
Original file line number Diff line number Diff line change
@@ -0,0 +1,22 @@
error[E0277]: the trait bound `(): Foo` is not satisfied
--> $DIR/where-clause-doesnt-apply.rs:18:15
|
LL | needs_foo(());
| --------- ^^ the trait `Bar` is not implemented for `()`, which is required by `(): Foo`
| |
| required by a bound introduced by this call
|
note: required for `()` to implement `Foo`
--> $DIR/where-clause-doesnt-apply.rs:4:9
|
LL | impl<T> Foo for T where T: Bar {}
| ^^^ ^ --- unsatisfied trait bound introduced here
note: required by a bound in `needs_foo`
--> $DIR/where-clause-doesnt-apply.rs:5:22
|
LL | fn needs_foo(_: impl Foo) {}
| ^^^ required by this bound in `needs_foo`

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0277`.
3 changes: 3 additions & 0 deletions tests/ui/traits/normalize-supertrait.rs
Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,9 @@
// comparing the supertrait `Derived<()>` to the expected trait.

//@ build-pass
//@ revisions: current next
//@ ignore-compare-mode-next-solver (explicit revisions)
//@[next] compile-flags: -Znext-solver

trait Proj {
type S;
Expand Down

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