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Only traverse attrs once while checking for coherence override attributes #93343

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merged 1 commit into from
Jan 28, 2022
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Only traverse attrs once while checking for coherence override attributes #93343

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43 changes: 25 additions & 18 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 @@ -13,6 +13,7 @@ use crate::traits::{
self, FulfillmentContext, Normalized, Obligation, ObligationCause, PredicateObligation,
PredicateObligations, SelectionContext,
};
use rustc_ast::Attribute;
use rustc_hir::def_id::{DefId, LOCAL_CRATE};
use rustc_middle::ty::fast_reject::{self, SimplifyParams, StripReferences};
use rustc_middle::ty::fold::TypeFoldable;
Expand Down Expand Up @@ -160,24 +161,30 @@ impl OverlapMode {
}

fn overlap_mode<'tcx>(tcx: TyCtxt<'tcx>, impl1_def_id: DefId, impl2_def_id: DefId) -> OverlapMode {
if tcx.has_attr(impl1_def_id, sym::rustc_strict_coherence)
!= tcx.has_attr(impl2_def_id, sym::rustc_strict_coherence)
{
bug!("Use strict coherence on both impls",);
}

if tcx.has_attr(impl1_def_id, sym::rustc_with_negative_coherence)
!= tcx.has_attr(impl2_def_id, sym::rustc_with_negative_coherence)
{
bug!("Use with negative coherence on both impls",);
}

if tcx.has_attr(impl1_def_id, sym::rustc_strict_coherence) {
OverlapMode::Strict
} else if tcx.has_attr(impl1_def_id, sym::rustc_with_negative_coherence) {
OverlapMode::WithNegative
} else {
OverlapMode::Stable
// Find the possible coherence mode override opt-in attributes for each `DefId`
let find_coherence_attr = |attr: &Attribute| {
let name = attr.name_or_empty();
match name {
sym::rustc_with_negative_coherence | sym::rustc_strict_coherence => Some(name),
_ => None,
}
};
let impl1_coherence_mode = tcx.get_attrs(impl1_def_id).iter().find_map(find_coherence_attr);
let impl2_coherence_mode = tcx.get_attrs(impl2_def_id).iter().find_map(find_coherence_attr);

// If there are any (that currently happens in tests), they need to match. Otherwise, the
// default 1.0 rules are used.
match (impl1_coherence_mode, impl2_coherence_mode) {
(None, None) => OverlapMode::Stable,
(Some(sym::rustc_with_negative_coherence), Some(sym::rustc_with_negative_coherence)) => {
OverlapMode::WithNegative
}
(Some(sym::rustc_strict_coherence), Some(sym::rustc_strict_coherence)) => {
OverlapMode::Strict
}
(Some(mode), _) | (_, Some(mode)) => {
bug!("Use the same coherence mode on both impls: {}", mode)
}
}
}

Expand Down