diff options
| -rw-r--r-- | compiler/rustc_middle/src/ty/sty.rs | 9 | ||||
| -rw-r--r-- | compiler/rustc_trait_selection/src/traits/coherence.rs | 30 |
2 files changed, 38 insertions, 1 deletions
diff --git a/compiler/rustc_middle/src/ty/sty.rs b/compiler/rustc_middle/src/ty/sty.rs index c1fa84dcb25..04cc4db0bcf 100644 --- a/compiler/rustc_middle/src/ty/sty.rs +++ b/compiler/rustc_middle/src/ty/sty.rs @@ -1845,6 +1845,15 @@ impl<'tcx> TyS<'tcx> { ) } + /// Get the mutability of the reference or `None` when not a reference + #[inline] + pub fn ref_mutability(&self) -> Option<hir::Mutability> { + match self.kind() { + Ref(_, _, mutability) => Some(*mutability), + _ => None, + } + } + #[inline] pub fn is_unsafe_ptr(&self) -> bool { matches!(self.kind(), RawPtr(_)) diff --git a/compiler/rustc_trait_selection/src/traits/coherence.rs b/compiler/rustc_trait_selection/src/traits/coherence.rs index 99b96f60964..e8ae1f44a36 100644 --- a/compiler/rustc_trait_selection/src/traits/coherence.rs +++ b/compiler/rustc_trait_selection/src/traits/coherence.rs @@ -11,7 +11,7 @@ use crate::traits::{self, Normalized, Obligation, ObligationCause, SelectionCont use rustc_hir::def_id::{DefId, LOCAL_CRATE}; use rustc_middle::ty::fold::TypeFoldable; use rustc_middle::ty::subst::Subst; -use rustc_middle::ty::{self, Ty, TyCtxt}; +use rustc_middle::ty::{self, fast_reject, Ty, TyCtxt}; use rustc_span::symbol::sym; use rustc_span::DUMMY_SP; use std::iter; @@ -67,6 +67,34 @@ where impl2_def_id={:?})", impl1_def_id, impl2_def_id, ); + // Before doing expensive operations like entering an inference context, do + // a quick check via fast_reject to tell if the impl headers could possibly + // unify. + let impl1_ref = tcx.impl_trait_ref(impl1_def_id); + let impl2_ref = tcx.impl_trait_ref(impl2_def_id); + + // Check if any of the input types definitely do not unify. + if impl1_ref + .iter() + .flat_map(|tref| tref.substs.types()) + .zip(impl2_ref.iter().flat_map(|tref| tref.substs.types())) + .any(|(ty1, ty2)| { + let t1 = fast_reject::simplify_type(tcx, ty1, false); + let t2 = fast_reject::simplify_type(tcx, ty2, false); + if let (Some(t1), Some(t2)) = (t1, t2) { + // Simplified successfully + // Types cannot unify if they differ in their reference mutability or simplify to different types + t1 != t2 || ty1.ref_mutability() != ty2.ref_mutability() + } else { + // Types might unify + false + } + }) + { + // Some types involved are definitely different, so the impls couldn't possibly overlap. + debug!("overlapping_impls: fast_reject early-exit"); + return no_overlap(); + } let overlaps = tcx.infer_ctxt().enter(|infcx| { let selcx = &mut SelectionContext::intercrate(&infcx); |