Rollup merge of #100888 - spastorino:coherence-negative-impls-implied-bounds, r=lcnr

Coherence negative impls implied bounds

Fixes #93875

This PR is rebased on top of #100789 and it would need to include that one which is already r+ed.

r? ``@nikomatsakis``

cc ``@lcnr`` (which I've talked about 3222f420d9, I guess after you finish your reordering of modules and work with OutlivesEnvironmentEnv this commit can just be reverted).

compiler/rustc_trait_selection/src/lib.rs

@@ -20,6 +20,7 @@
 #![feature(let_else)]
 #![feature(if_let_guard)]
 #![feature(never_type)]
+#![feature(type_alias_impl_trait)]
 #![recursion_limit = "512"] // For rustdoc
 
 #[macro_use]

compiler/rustc_trait_selection/src/traits/coherence.rs

@@ -6,16 +6,18 @@
 
 use crate::infer::outlives::env::OutlivesEnvironment;
 use crate::infer::{CombinedSnapshot, InferOk};
+use crate::traits::outlives_bounds::InferCtxtExt as _;
 use crate::traits::select::IntercrateAmbiguityCause;
 use crate::traits::util::impl_subject_and_oblig;
 use crate::traits::SkipLeakCheck;
 use crate::traits::{
-    self, Normalized, Obligation, ObligationCause, PredicateObligation, PredicateObligations,
+    self, Normalized, Obligation, ObligationCause, ObligationCtxt, PredicateObligation,
-    SelectionContext,
+    PredicateObligations, SelectionContext,
 };
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_errors::Diagnostic;
-use rustc_hir::def_id::{DefId, LOCAL_CRATE};
+use rustc_hir::def_id::{DefId, CRATE_DEF_ID, LOCAL_CRATE};
+use rustc_hir::CRATE_HIR_ID;
 use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
 use rustc_infer::traits::util;
 use rustc_middle::traits::specialization_graph::OverlapMode;
@@ -322,7 +324,7 @@ fn negative_impl<'cx, 'tcx>(
         let (subject2, obligations) =
             impl_subject_and_oblig(selcx, impl_env, impl2_def_id, impl2_substs);
 
-        !equate(&infcx, impl_env, subject1, subject2, obligations)
+        !equate(&infcx, impl_env, subject1, subject2, obligations, impl1_def_id)
     })
 }
 
@@ -332,6 +334,7 @@ fn equate<'cx, 'tcx>(
     subject1: ImplSubject<'tcx>,
     subject2: ImplSubject<'tcx>,
     obligations: impl Iterator<Item = PredicateObligation<'tcx>>,
+    body_def_id: DefId,
 ) -> bool {
     // do the impls unify? If not, not disjoint.
     let Ok(InferOk { obligations: more_obligations, .. }) =
@@ -342,8 +345,10 @@ fn equate<'cx, 'tcx>(
     };
 
     let selcx = &mut SelectionContext::new(&infcx);
-    let opt_failing_obligation =
+    let opt_failing_obligation = obligations
-        obligations.into_iter().chain(more_obligations).find(|o| negative_impl_exists(selcx, o));
+        .into_iter()
+        .chain(more_obligations)
+        .find(|o| negative_impl_exists(selcx, o, body_def_id));
 
     if let Some(failing_obligation) = opt_failing_obligation {
         debug!("overlap: obligation unsatisfiable {:?}", failing_obligation);
@@ -358,14 +363,15 @@ fn equate<'cx, 'tcx>(
 fn negative_impl_exists<'cx, 'tcx>(
     selcx: &SelectionContext<'cx, 'tcx>,
     o: &PredicateObligation<'tcx>,
+    body_def_id: DefId,
 ) -> bool {
-    if resolve_negative_obligation(selcx.infcx().fork(), o) {
+    if resolve_negative_obligation(selcx.infcx().fork(), o, body_def_id) {
         return true;
     }
 
     // Try to prove a negative obligation exists for super predicates
     for o in util::elaborate_predicates(selcx.tcx(), iter::once(o.predicate)) {
-        if resolve_negative_obligation(selcx.infcx().fork(), &o) {
+        if resolve_negative_obligation(selcx.infcx().fork(), &o, body_def_id) {
             return true;
         }
     }
@@ -377,6 +383,7 @@ fn negative_impl_exists<'cx, 'tcx>(
 fn resolve_negative_obligation<'cx, 'tcx>(
     infcx: InferCtxt<'cx, 'tcx>,
     o: &PredicateObligation<'tcx>,
+    body_def_id: DefId,
 ) -> bool {
     let tcx = infcx.tcx;
 
@@ -385,12 +392,24 @@ fn resolve_negative_obligation<'cx, 'tcx>(
     };
 
     let param_env = o.param_env;
-    let errors = super::fully_solve_obligation(&infcx, o);
+    if !super::fully_solve_obligation(&infcx, o).is_empty() {
-    if !errors.is_empty() {
         return false;
     }
 
-    let outlives_env = OutlivesEnvironment::new(param_env);
+    let (body_id, body_def_id) = if let Some(body_def_id) = body_def_id.as_local() {
+        (tcx.hir().local_def_id_to_hir_id(body_def_id), body_def_id)
+    } else {
+        (CRATE_HIR_ID, CRATE_DEF_ID)
+    };
+
+    let ocx = ObligationCtxt::new(&infcx);
+    let wf_tys = ocx.assumed_wf_types(param_env, DUMMY_SP, body_def_id);
+    let outlives_env = OutlivesEnvironment::with_bounds(
+        param_env,
+        Some(&infcx),
+        infcx.implied_bounds_tys(param_env, body_id, wf_tys),
+    );
+
     infcx.process_registered_region_obligations(outlives_env.region_bound_pairs(), param_env);
 
     infcx.resolve_regions(&outlives_env).is_empty()

compiler/rustc_trait_selection/src/traits/mod.rs

@@ -13,6 +13,7 @@ mod fulfill;
 pub mod misc;
 mod object_safety;
 mod on_unimplemented;
+pub mod outlives_bounds;
 mod project;
 pub mod query;
 pub(crate) mod relationships;

compiler/rustc_trait_selection/src/traits/outlives_bounds.rs

@@ -1,11 +1,11 @@
+use crate::infer::InferCtxt;
+use crate::traits::query::type_op::{self, TypeOp, TypeOpOutput};
+use crate::traits::query::NoSolution;
+use crate::traits::{ObligationCause, TraitEngine, TraitEngineExt};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_hir as hir;
 use rustc_hir::HirId;
 use rustc_middle::ty::{self, ParamEnv, Ty};
-use rustc_trait_selection::infer::InferCtxt;
-use rustc_trait_selection::traits::query::type_op::{self, TypeOp, TypeOpOutput};
-use rustc_trait_selection::traits::query::NoSolution;
-use rustc_trait_selection::traits::{ObligationCause, TraitEngine, TraitEngineExt};
 
 pub use rustc_middle::traits::query::OutlivesBound;
 

compiler/rustc_typeck/src/check/compare_method.rs

@@ -1,6 +1,5 @@
 use super::potentially_plural_count;
 use crate::errors::LifetimesOrBoundsMismatchOnTrait;
-use crate::outlives::outlives_bounds::InferCtxtExt as _;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticId, ErrorGuaranteed};
 use rustc_hir as hir;
@@ -17,6 +16,7 @@ use rustc_middle::ty::{self, DefIdTree};
 use rustc_middle::ty::{GenericParamDefKind, ToPredicate, TyCtxt};
 use rustc_span::Span;
 use rustc_trait_selection::traits::error_reporting::InferCtxtExt;
+use rustc_trait_selection::traits::outlives_bounds::InferCtxtExt as _;
 use rustc_trait_selection::traits::{
     self, ObligationCause, ObligationCauseCode, ObligationCtxt, Reveal,
 };

compiler/rustc_typeck/src/check/wfcheck.rs

@@ -1,5 +1,4 @@
 use crate::constrained_generic_params::{identify_constrained_generic_params, Parameter};
-use crate::outlives::outlives_bounds::InferCtxtExt as _;
 use rustc_ast as ast;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder, ErrorGuaranteed};
@@ -22,6 +21,7 @@ use rustc_span::symbol::{sym, Ident, Symbol};
 use rustc_span::{Span, DUMMY_SP};
 use rustc_trait_selection::autoderef::Autoderef;
 use rustc_trait_selection::traits::error_reporting::InferCtxtExt;
+use rustc_trait_selection::traits::outlives_bounds::InferCtxtExt as _;
 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _;
 use rustc_trait_selection::traits::{
     self, ObligationCause, ObligationCauseCode, ObligationCtxt, WellFormedLoc,

compiler/rustc_typeck/src/impl_wf_check/min_specialization.rs

@@ -67,7 +67,6 @@
 
 use crate::constrained_generic_params as cgp;
 use crate::errors::SubstsOnOverriddenImpl;
-use crate::outlives::outlives_bounds::InferCtxtExt as _;
 
 use rustc_data_structures::fx::FxHashSet;
 use rustc_hir::def_id::{DefId, LocalDefId};
@@ -79,6 +78,7 @@ use rustc_middle::ty::trait_def::TraitSpecializationKind;
 use rustc_middle::ty::{self, TyCtxt, TypeVisitable};
 use rustc_span::Span;
 use rustc_trait_selection::traits::error_reporting::InferCtxtExt;
+use rustc_trait_selection::traits::outlives_bounds::InferCtxtExt as _;
 use rustc_trait_selection::traits::{self, translate_substs, wf, ObligationCtxt};
 
 pub(super) fn check_min_specialization(tcx: TyCtxt<'_>, impl_def_id: LocalDefId) {

compiler/rustc_typeck/src/outlives/mod.rs

@@ -9,7 +9,6 @@ use rustc_span::Span;
 
 mod explicit;
 mod implicit_infer;
-pub(crate) mod outlives_bounds;
 /// Code to write unit test for outlives.
 pub mod test;
 mod utils;

src/test/ui/coherence/coherence-negative-outlives-lifetimes.rs

@@ -1,9 +1,9 @@
 // revisions: stock with_negative_coherence
+//[with_negative_coherence] check-pass
+
 #![feature(negative_impls)]
 #![cfg_attr(with_negative_coherence, feature(with_negative_coherence))]
 
-// FIXME: this should compile
-
 trait MyPredicate<'a> {}
 
 impl<'a, T> !MyPredicate<'a> for &'a T where T: 'a {}
@@ -12,6 +12,6 @@ trait MyTrait<'a> {}
 
 impl<'a, T: MyPredicate<'a>> MyTrait<'a> for T {}
 impl<'a, T> MyTrait<'a> for &'a T {}
-//~^ ERROR: conflicting implementations of trait `MyTrait<'_>` for type `&_`
+//[stock]~^ ERROR: conflicting implementations of trait `MyTrait<'_>` for type `&_`
 
 fn main() {}

src/test/ui/coherence/coherence-negative-outlives-lifetimes.with_negative_coherence.stderr

@@ -1,11 +0,0 @@
-error[E0119]: conflicting implementations of trait `MyTrait<'_>` for type `&_`
-  --> $DIR/coherence-negative-outlives-lifetimes.rs:14:1
-   |
-LL | impl<'a, T: MyPredicate<'a>> MyTrait<'a> for T {}
-   | ---------------------------------------------- first implementation here
-LL | impl<'a, T> MyTrait<'a> for &'a T {}
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `&_`
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0119`.