Rollup merge of #69745 - estebank:predicate-obligations-3, r=nikomats…

…akis,eddyb

Use `PredicateObligation`s instead of `Predicate`s

Keep more information about trait binding failures. Use more specific spans by pointing at bindings that introduce obligations.

Subset of #69709.

r? @eddyb

src/librustc_infer/infer/outlives/verify.rs

@@ -296,7 +296,10 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
         let identity_proj = tcx.mk_projection(assoc_item_def_id, identity_substs);
         self.collect_outlives_from_predicate_list(
             move |ty| ty == identity_proj,
-            traits::elaborate_predicates(tcx, trait_predicates),
+            traits::elaborate_predicates(tcx, trait_predicates)
+                .into_iter()
+                .map(|o| o.predicate)
+                .collect::<Vec<_>>(),
         )
         .map(|b| b.1)
     }

src/librustc_infer/traits/util.rs

@@ -1,8 +1,10 @@
 use smallvec::smallvec;
 
+use crate::traits::{Obligation, ObligationCause, PredicateObligation};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_middle::ty::outlives::Component;
 use rustc_middle::ty::{self, ToPolyTraitRef, ToPredicate, TyCtxt, WithConstness};
+use rustc_span::Span;
 
 pub fn anonymize_predicate<'tcx>(
     tcx: TyCtxt<'tcx>,
@@ -87,7 +89,7 @@ impl<T: AsRef<ty::Predicate<'tcx>>> Extend<T> for PredicateSet<'tcx> {
 /// holds as well. Similarly, if we have `trait Foo: 'static`, and we know that
 /// `T: Foo`, then we know that `T: 'static`.
 pub struct Elaborator<'tcx> {
-    stack: Vec<ty::Predicate<'tcx>>,
+    stack: Vec<PredicateObligation<'tcx>>,
     visited: PredicateSet<'tcx>,
 }
 
@@ -112,35 +114,60 @@ pub fn elaborate_predicates<'tcx>(
 ) -> Elaborator<'tcx> {
     let mut visited = PredicateSet::new(tcx);
     predicates.retain(|pred| visited.insert(pred));
-    Elaborator { stack: predicates, visited }
+    let obligations: Vec<_> =
+        predicates.into_iter().map(|predicate| predicate_obligation(predicate, None)).collect();
+    elaborate_obligations(tcx, obligations)
+}
+
+pub fn elaborate_obligations<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    mut obligations: Vec<PredicateObligation<'tcx>>,
+) -> Elaborator<'tcx> {
+    let mut visited = PredicateSet::new(tcx);
+    obligations.retain(|obligation| visited.insert(&obligation.predicate));
+    Elaborator { stack: obligations, visited }
+}
+
+fn predicate_obligation<'tcx>(
+    predicate: ty::Predicate<'tcx>,
+    span: Option<Span>,
+) -> PredicateObligation<'tcx> {
+    let mut cause = ObligationCause::dummy();
+    if let Some(span) = span {
+        cause.span = span;
+    }
+    Obligation { cause, param_env: ty::ParamEnv::empty(), recursion_depth: 0, predicate }
 }
 
 impl Elaborator<'tcx> {
     pub fn filter_to_traits(self) -> FilterToTraits<Self> {
         FilterToTraits::new(self)
     }
 
-    fn elaborate(&mut self, predicate: &ty::Predicate<'tcx>) {
+    fn elaborate(&mut self, obligation: &PredicateObligation<'tcx>) {
         let tcx = self.visited.tcx;
-        match *predicate {
+        match obligation.predicate {
             ty::Predicate::Trait(ref data, _) => {
                 // Get predicates declared on the trait.
                 let predicates = tcx.super_predicates_of(data.def_id());
 
-                let predicates = predicates
-                    .predicates
-                    .iter()
-                    .map(|(pred, _)| pred.subst_supertrait(tcx, &data.to_poly_trait_ref()));
-                debug!("super_predicates: data={:?} predicates={:?}", data, predicates.clone());
+                let obligations = predicates.predicates.iter().map(|(pred, span)| {
+                    predicate_obligation(
+                        pred.subst_supertrait(tcx, &data.to_poly_trait_ref()),
+                        Some(*span),
+                    )
+                });
+                debug!("super_predicates: data={:?} predicates={:?}", data, &obligations);
 
                 // Only keep those bounds that we haven't already seen.
                 // This is necessary to prevent infinite recursion in some
                 // cases. One common case is when people define
                 // `trait Sized: Sized { }` rather than `trait Sized { }`.
                 let visited = &mut self.visited;
-                let predicates = predicates.filter(|pred| visited.insert(pred));
+                let obligations =
+                    obligations.filter(|obligation| visited.insert(&obligation.predicate));
 
-                self.stack.extend(predicates);
+                self.stack.extend(obligations);
             }
             ty::Predicate::WellFormed(..) => {
                 // Currently, we do not elaborate WF predicates,
@@ -221,25 +248,26 @@ impl Elaborator<'tcx> {
                                 None
                             }
                         })
-                        .filter(|p| visited.insert(p)),
+                        .filter(|p| visited.insert(p))
+                        .map(|p| predicate_obligation(p, None)),
                 );
             }
         }
     }
 }
 
 impl Iterator for Elaborator<'tcx> {
-    type Item = ty::Predicate<'tcx>;
+    type Item = PredicateObligation<'tcx>;
 
     fn size_hint(&self) -> (usize, Option<usize>) {
         (self.stack.len(), None)
     }
 
-    fn next(&mut self) -> Option<ty::Predicate<'tcx>> {
+    fn next(&mut self) -> Option<Self::Item> {
         // Extract next item from top-most stack frame, if any.
-        if let Some(pred) = self.stack.pop() {
-            self.elaborate(&pred);
-            Some(pred)
+        if let Some(obligation) = self.stack.pop() {
+            self.elaborate(&obligation);
+            Some(obligation)
         } else {
             None
         }
@@ -282,12 +310,12 @@ impl<I> FilterToTraits<I> {
     }
 }
 
-impl<'tcx, I: Iterator<Item = ty::Predicate<'tcx>>> Iterator for FilterToTraits<I> {
+impl<'tcx, I: Iterator<Item = PredicateObligation<'tcx>>> Iterator for FilterToTraits<I> {
     type Item = ty::PolyTraitRef<'tcx>;
 
     fn next(&mut self) -> Option<ty::PolyTraitRef<'tcx>> {
-        while let Some(pred) = self.base_iterator.next() {
-            if let ty::Predicate::Trait(data, _) = pred {
+        while let Some(obligation) = self.base_iterator.next() {
+            if let ty::Predicate::Trait(data, _) = obligation.predicate {
                 return Some(data.to_poly_trait_ref());
             }
         }

src/librustc_mir/transform/const_prop.rs

@@ -126,7 +126,7 @@ impl<'tcx> MirPass<'tcx> for ConstProp {
             .collect();
         if !traits::normalize_and_test_predicates(
             tcx,
-            traits::elaborate_predicates(tcx, predicates).collect(),
+            traits::elaborate_predicates(tcx, predicates).map(|o| o.predicate).collect(),
         ) {
             trace!("ConstProp skipped for {:?}: found unsatisfiable predicates", source.def_id());
             return;

src/librustc_trait_selection/opaque_types.rs

@@ -1255,8 +1255,8 @@ crate fn required_region_bounds(
     assert!(!erased_self_ty.has_escaping_bound_vars());
 
     traits::elaborate_predicates(tcx, predicates)
-        .filter_map(|predicate| {
-            match predicate {
+        .filter_map(|obligation| {
+            match obligation.predicate {
                 ty::Predicate::Projection(..)
                 | ty::Predicate::Trait(..)
                 | ty::Predicate::Subtype(..)

src/librustc_trait_selection/traits/auto_trait.rs

@@ -366,7 +366,8 @@ impl AutoTraitFinder<'tcx> {
 
             computed_preds.extend(user_computed_preds.iter().cloned());
             let normalized_preds =
-                elaborate_predicates(tcx, computed_preds.iter().cloned().collect());
+                elaborate_predicates(tcx, computed_preds.iter().cloned().collect())
+                    .map(|o| o.predicate);
             new_env =
                 ty::ParamEnv::new(tcx.mk_predicates(normalized_preds), param_env.reveal, None);
         }

src/librustc_trait_selection/traits/error_reporting/mod.rs

@@ -976,8 +976,8 @@ impl<'a, 'tcx> InferCtxtPrivExt<'tcx> for InferCtxt<'a, 'tcx> {
             }
         };
 
-        for implication in super::elaborate_predicates(self.tcx, vec![*cond]) {
-            if let ty::Predicate::Trait(implication, _) = implication {
+        for obligation in super::elaborate_predicates(self.tcx, vec![*cond]) {
+            if let ty::Predicate::Trait(implication, _) = obligation.predicate {
                 let error = error.to_poly_trait_ref();
                 let implication = implication.to_poly_trait_ref();
                 // FIXME: I'm just not taking associated types at all here.
@@ -1387,7 +1387,9 @@ impl<'a, 'tcx> InferCtxtPrivExt<'tcx> for InferCtxt<'a, 'tcx> {
                     (self.tcx.sess.source_map().span_to_snippet(span), &obligation.cause.code)
                 {
                     let generics = self.tcx.generics_of(*def_id);
-                    if !generics.params.is_empty() && !snippet.ends_with('>') {
+                    if generics.params.iter().filter(|p| p.name.as_str() != "Self").next().is_some()
+                        && !snippet.ends_with('>')
+                    {
                         // FIXME: To avoid spurious suggestions in functions where type arguments
                         // where already supplied, we check the snippet to make sure it doesn't
                         // end with a turbofish. Ideally we would have access to a `PathSegment`
@@ -1405,7 +1407,7 @@ impl<'a, 'tcx> InferCtxtPrivExt<'tcx> for InferCtxt<'a, 'tcx> {
                         //    |                        `Tt::const_val::<[i8; 123]>::<T>`
                         // ...
                         // LL |     const fn const_val<T: Sized>() -> usize {
-                        //    |              --------- - required by this bound in `Tt::const_val`
+                        //    |                        - required by this bound in `Tt::const_val`
                         //    |
                         //    = note: cannot satisfy `_: Tt`
 

src/librustc_trait_selection/traits/error_reporting/on_unimplemented.rs

@@ -142,7 +142,9 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             }
         }
 
-        if let ObligationCauseCode::ItemObligation(item) = obligation.cause.code {
+        if let ObligationCauseCode::ItemObligation(item)
+        | ObligationCauseCode::BindingObligation(item, _) = obligation.cause.code
+        {
             // FIXME: maybe also have some way of handling methods
             // from other traits? That would require name resolution,
             // which we might want to be some sort of hygienic.

src/librustc_trait_selection/traits/error_reporting/suggestions.rs

@@ -948,7 +948,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
     ///   --> $DIR/issue-64130-2-send.rs:21:5
     ///    |
     /// LL | fn is_send<T: Send>(t: T) { }
-    ///    |    -------    ---- required by this bound in `is_send`
+    ///    |               ---- required by this bound in `is_send`
     /// ...
     /// LL |     is_send(bar());
     ///    |     ^^^^^^^ future returned by `bar` is not send
@@ -1345,7 +1345,6 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             ObligationCauseCode::ItemObligation(item_def_id) => {
                 let item_name = tcx.def_path_str(item_def_id);
                 let msg = format!("required by `{}`", item_name);
-
                 if let Some(sp) = tcx.hir().span_if_local(item_def_id) {
                     let sp = tcx.sess.source_map().guess_head_span(sp);
                     err.span_label(sp, &msg);
@@ -1357,7 +1356,15 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                 let item_name = tcx.def_path_str(item_def_id);
                 let msg = format!("required by this bound in `{}`", item_name);
                 if let Some(ident) = tcx.opt_item_name(item_def_id) {
-                    err.span_label(ident.span, "");
+                    let sm = self.tcx.sess.source_map();
+                    let same_line =
+                        match (sm.lookup_line(ident.span.hi()), sm.lookup_line(span.lo())) {
+                            (Ok(l), Ok(r)) => l.line == r.line,
+                            _ => true,
+                        };
+                    if !ident.span.overlaps(span) && !same_line {
+                        err.span_label(ident.span, "");
+                    }
                 }
                 if span != DUMMY_SP {
                     err.span_label(span, &msg);

src/librustc_trait_selection/traits/mod.rs

@@ -297,7 +297,9 @@ pub fn normalize_param_env_or_error<'tcx>(
     );
 
     let mut predicates: Vec<_> =
-        util::elaborate_predicates(tcx, unnormalized_env.caller_bounds.to_vec()).collect();
+        util::elaborate_predicates(tcx, unnormalized_env.caller_bounds.to_vec())
+            .map(|obligation| obligation.predicate)
+            .collect();
 
     debug!("normalize_param_env_or_error: elaborated-predicates={:?}", predicates);
 

src/librustc_trait_selection/traits/object_safety.rs

@@ -298,7 +298,7 @@ fn generics_require_sized_self(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
     // Search for a predicate like `Self : Sized` amongst the trait bounds.
     let predicates = tcx.predicates_of(def_id);
     let predicates = predicates.instantiate_identity(tcx).predicates;
-    elaborate_predicates(tcx, predicates).any(|predicate| match predicate {
+    elaborate_predicates(tcx, predicates).any(|obligation| match obligation.predicate {
         ty::Predicate::Trait(ref trait_pred, _) => {
             trait_pred.def_id() == sized_def_id && trait_pred.skip_binder().self_ty().is_param(0)
         }

src/librustc_trait_selection/traits/project.rs

@@ -900,7 +900,7 @@ fn assemble_candidates_from_trait_def<'cx, 'tcx>(
     // If so, extract what we know from the trait and try to come up with a good answer.
     let trait_predicates = tcx.predicates_of(def_id);
     let bounds = trait_predicates.instantiate(tcx, substs);
-    let bounds = elaborate_predicates(tcx, bounds.predicates);
+    let bounds = elaborate_predicates(tcx, bounds.predicates).map(|o| o.predicate);
     assemble_candidates_from_predicates(
         selcx,
         obligation,
@@ -1162,7 +1162,7 @@ fn confirm_object_candidate<'cx, 'tcx>(
 
         // select only those projections that are actually projecting an
         // item with the correct name
-        let env_predicates = env_predicates.filter_map(|p| match p {
+        let env_predicates = env_predicates.filter_map(|o| match o.predicate {
             ty::Predicate::Projection(data) => {
                 if data.projection_def_id() == obligation.predicate.item_def_id {
                     Some(data)

src/librustc_trait_selection/traits/wf.rs

@@ -312,19 +312,18 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> {
         let item = self.item;
 
         if let Elaborate::All = elaborate {
-            let predicates = obligations.iter().map(|obligation| obligation.predicate).collect();
-            let implied_obligations = traits::elaborate_predicates(tcx, predicates);
-            let implied_obligations = implied_obligations.map(|pred| {
+            let implied_obligations = traits::util::elaborate_obligations(tcx, obligations.clone());
+            let implied_obligations = implied_obligations.map(|obligation| {
                 let mut cause = cause.clone();
                 extend_cause_with_original_assoc_item_obligation(
                     tcx,
                     trait_ref,
                     item,
                     &mut cause,
-                    &pred,
+                    &obligation.predicate,
                     tcx.associated_items(trait_ref.def_id).in_definition_order().copied(),
                 );
-                traits::Obligation::new(cause, param_env, pred)
+                traits::Obligation::new(cause, param_env, obligation.predicate)
             });
             self.out.extend(implied_obligations);
         }
@@ -613,11 +612,14 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> {
         substs: SubstsRef<'tcx>,
     ) -> Vec<traits::PredicateObligation<'tcx>> {
         let predicates = self.infcx.tcx.predicates_of(def_id).instantiate(self.infcx.tcx, substs);
-        let cause = self.cause(traits::ItemObligation(def_id));
         predicates
             .predicates
             .into_iter()
-            .map(|pred| traits::Obligation::new(cause.clone(), self.param_env, pred))
+            .zip(predicates.spans.into_iter())
+            .map(|(pred, span)| {
+                let cause = self.cause(traits::BindingObligation(def_id, span));
+                traits::Obligation::new(cause, self.param_env, pred)
+            })
             .filter(|pred| !pred.has_escaping_bound_vars())
             .collect()
     }

src/librustc_typeck/astconv.rs

@@ -1601,12 +1601,12 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         for (base_trait_ref, span, constness) in regular_traits_refs_spans {
             assert_eq!(constness, Constness::NotConst);
 
-            for trait_ref in traits::elaborate_trait_ref(tcx, base_trait_ref) {
+            for obligation in traits::elaborate_trait_ref(tcx, base_trait_ref) {
                 debug!(
                     "conv_object_ty_poly_trait_ref: observing object predicate `{:?}`",
-                    trait_ref
+                    obligation.predicate
                 );
-                match trait_ref {
+                match obligation.predicate {
                     ty::Predicate::Trait(pred, _) => {
                         associated_types.entry(span).or_default().extend(
                             tcx.associated_items(pred.def_id())

src/librustc_typeck/check/method/confirm.rs

@@ -573,13 +573,15 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
         };
 
         traits::elaborate_predicates(self.tcx, predicates.predicates.clone())
-            .filter_map(|predicate| match predicate {
+            .filter_map(|obligation| match obligation.predicate {
                 ty::Predicate::Trait(trait_pred, _) if trait_pred.def_id() == sized_def_id => {
                     let span = predicates
                         .predicates
                         .iter()
                         .zip(predicates.spans.iter())
-                        .filter_map(|(p, span)| if *p == predicate { Some(*span) } else { None })
+                        .filter_map(
+                            |(p, span)| if *p == obligation.predicate { Some(*span) } else { None },
+                        )
                         .next()
                         .unwrap_or(rustc_span::DUMMY_SP);
                     Some((trait_pred, span))

src/librustc_typeck/check/wfcheck.rs

@@ -1229,7 +1229,8 @@ fn check_false_global_bounds(fcx: &FnCtxt<'_, '_>, span: Span, id: hir::HirId) {
     // Check elaborated bounds.
     let implied_obligations = traits::elaborate_predicates(fcx.tcx, predicates);
 
-    for pred in implied_obligations {
+    for obligation in implied_obligations {
+        let pred = obligation.predicate;
         // Match the existing behavior.
         if pred.is_global() && !pred.has_late_bound_regions() {
             let pred = fcx.normalize_associated_types_in(span, &pred);

src/librustc_typeck/collect.rs

@@ -1650,7 +1650,7 @@ fn predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicates<'_> {
         // prove that the trait applies to the types that were
         // used, and adding the predicate into this list ensures
         // that this is done.
-        let span = tcx.def_span(def_id);
+        let span = tcx.sess.source_map().guess_head_span(tcx.def_span(def_id));
         result.predicates =
             tcx.arena.alloc_from_iter(result.predicates.iter().copied().chain(std::iter::once((
                 ty::TraitRef::identity(tcx, def_id).without_const().to_predicate(),