Point at associated type for some obligations

10 files changed, 93 insertions, 41 deletions

diff --git a/src/librustc/traits/error_reporting.rs b/src/librustc/traits/error_reporting.rs
index daa4a215a23..7ab907701bf 100644
--- a/src/librustc/traits/error_reporting.rs
+++ b/src/librustc/traits/error_reporting.rs
@@ -2199,6 +2199,12 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                     );
                 }
             }
+            ObligationCauseCode::AssocTypeBound(impl_span, orig) => {
+                err.span_label(orig, "associated type defined here");
+                if let Some(sp) = impl_span {
+                    err.span_label(sp, "in this `impl` item");
+                }
+            }
         }
     }
 
diff --git a/src/librustc/traits/mod.rs b/src/librustc/traits/mod.rs
index d96330bf0a9..9640a8a29d1 100644
--- a/src/librustc/traits/mod.rs
+++ b/src/librustc/traits/mod.rs
@@ -268,6 +268,8 @@ pub enum ObligationCauseCode<'tcx> {
 
     /// #[feature(trivial_bounds)] is not enabled
     TrivialBound,
+
+    AssocTypeBound(/*impl*/ Option<Span>, /*original*/ Span),
 }
 
 // `ObligationCauseCode` is used a lot. Make sure it doesn't unintentionally get bigger.
diff --git a/src/librustc/traits/structural_impls.rs b/src/librustc/traits/structural_impls.rs
index dab62a6bcb5..f81d4b3ca30 100644
--- a/src/librustc/traits/structural_impls.rs
+++ b/src/librustc/traits/structural_impls.rs
@@ -544,6 +544,7 @@ impl<'a, 'tcx> Lift<'tcx> for traits::ObligationCauseCode<'a> {
             super::MethodReceiver => Some(super::MethodReceiver),
             super::BlockTailExpression(id) => Some(super::BlockTailExpression(id)),
             super::TrivialBound => Some(super::TrivialBound),
+            super::AssocTypeBound(impl_sp, sp) => Some(super::AssocTypeBound(impl_sp, sp)),
         }
     }
 }
diff --git a/src/librustc/ty/mod.rs b/src/librustc/ty/mod.rs
index d377b7328e8..d81f5e40701 100644
--- a/src/librustc/ty/mod.rs
+++ b/src/librustc/ty/mod.rs
@@ -3139,6 +3139,7 @@ impl<'tcx> TyCtxt<'tcx> {
     }
 }
 
+#[derive(Clone)]
 pub struct AssocItemsIterator<'tcx> {
     tcx: TyCtxt<'tcx>,
     def_ids: &'tcx [DefId],
diff --git a/src/librustc/ty/wf.rs b/src/librustc/ty/wf.rs
index ecb075e30b1..ce92fd82761 100644
--- a/src/librustc/ty/wf.rs
+++ b/src/librustc/ty/wf.rs
@@ -22,11 +22,14 @@ pub fn obligations<'a, 'tcx>(
     ty: Ty<'tcx>,
     span: Span,
 ) -> Option<Vec<traits::PredicateObligation<'tcx>>> {
-    let mut wf = WfPredicates { infcx,
-                                param_env,
-                                body_id,
-                                span,
-                                out: vec![] };
+    let mut wf = WfPredicates {
+        infcx,
+        param_env,
+        body_id,
+        span,
+        out: vec![],
+        item: None,
+    };
     if wf.compute(ty) {
         debug!("wf::obligations({:?}, body_id={:?}) = {:?}", ty, body_id, wf.out);
         let result = wf.normalize();
@@ -47,8 +50,9 @@ pub fn trait_obligations<'a, 'tcx>(
     body_id: hir::HirId,
     trait_ref: &ty::TraitRef<'tcx>,
     span: Span,
+    item: Option<&'tcx hir::Item>,
 ) -> Vec<traits::PredicateObligation<'tcx>> {
-    let mut wf = WfPredicates { infcx, param_env, body_id, span, out: vec![] };
+    let mut wf = WfPredicates { infcx, param_env, body_id, span, out: vec![], item };
     wf.compute_trait_ref(trait_ref, Elaborate::All);
     wf.normalize()
 }
@@ -60,7 +64,7 @@ pub fn predicate_obligations<'a, 'tcx>(
     predicate: &ty::Predicate<'tcx>,
     span: Span,
 ) -> Vec<traits::PredicateObligation<'tcx>> {
-    let mut wf = WfPredicates { infcx, param_env, body_id, span, out: vec![] };
+    let mut wf = WfPredicates { infcx, param_env, body_id, span, out: vec![], item: None };
 
     // (*) ok to skip binders, because wf code is prepared for it
     match *predicate {
@@ -107,6 +111,7 @@ struct WfPredicates<'a, 'tcx> {
     body_id: hir::HirId,
     span: Span,
     out: Vec<traits::PredicateObligation<'tcx>>,
+    item: Option<&'tcx hir::Item>,
 }
 
 /// Controls whether we "elaborate" supertraits and so forth on the WF
@@ -157,33 +162,54 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> {
                 .collect()
     }
 
-    /// Pushes the obligations required for `trait_ref` to be WF into
-    /// `self.out`.
+    /// Pushes the obligations required for `trait_ref` to be WF into `self.out`.
     fn compute_trait_ref(&mut self, trait_ref: &ty::TraitRef<'tcx>, elaborate: Elaborate) {
         let obligations = self.nominal_obligations(trait_ref.def_id, trait_ref.substs);
-
+        let assoc_items = self.infcx.tcx.associated_items(trait_ref.def_id);
         let cause = self.cause(traits::MiscObligation);
         let param_env = self.param_env;
 
         if let Elaborate::All = elaborate {
             let predicates = obligations.iter()
-                                        .map(|obligation| obligation.predicate.clone())
-                                        .collect();
+                .map(|obligation| obligation.predicate.clone())
+                .collect();
             let implied_obligations = traits::elaborate_predicates(self.infcx.tcx, predicates);
+            let item_span: Option<Span> = self.item.map(|i| i.span);
+            let item = &self.item;
             let implied_obligations = implied_obligations.map(|pred| {
-                traits::Obligation::new(cause.clone(), param_env, pred)
+                let mut cause = cause.clone();
+                if let ty::Predicate::Trait(proj) = &pred {
+                    if let (
+                        ty::Projection(ty::ProjectionTy { item_def_id, .. }),
+                        Some(hir::ItemKind::Impl(.., bounds)),
+                     ) = (&proj.skip_binder().self_ty().kind, item.map(|i| &i.kind)) {
+                        if let Some((bound, assoc_item)) = assoc_items.clone()
+                            .filter(|i| i.def_id == *item_def_id)
+                            .next()
+                            .and_then(|assoc_item| bounds.iter()
+                                    .filter(|b| b.ident == assoc_item.ident)
+                                    .next()
+                                    .map(|bound| (bound, assoc_item)))
+                        {
+                            cause.span = bound.span;
+                            cause.code = traits::AssocTypeBound(item_span, assoc_item.ident.span);
+                        }
+                    }
+                }
+                traits::Obligation::new(cause, param_env, pred)
             });
             self.out.extend(implied_obligations);
         }
 
         self.out.extend(obligations);
 
-        self.out.extend(
-            trait_ref.substs.types()
-                            .filter(|ty| !ty.has_escaping_bound_vars())
-                            .map(|ty| traits::Obligation::new(cause.clone(),
-                                                              param_env,
-                                                              ty::Predicate::WellFormed(ty))));
+        self.out.extend(trait_ref.substs.types()
+            .filter(|ty| !ty.has_escaping_bound_vars())
+            .map(|ty| traits::Obligation::new(
+                cause.clone(),
+                param_env,
+                ty::Predicate::WellFormed(ty),
+            )));
     }
 
     /// Pushes the obligations required for `trait_ref::Item` to be WF
diff --git a/src/librustc_typeck/check/wfcheck.rs b/src/librustc_typeck/check/wfcheck.rs
index 18b103960c7..b4b8d4566d5 100644
--- a/src/librustc_typeck/check/wfcheck.rs
+++ b/src/librustc_typeck/check/wfcheck.rs
@@ -430,7 +430,7 @@ fn check_item_type(
 
 fn check_impl<'tcx>(
     tcx: TyCtxt<'tcx>,
-    item: &hir::Item,
+    item: &'tcx hir::Item,
     ast_self_ty: &hir::Ty,
     ast_trait_ref: &Option<hir::TraitRef>,
 ) {
@@ -445,15 +445,18 @@ fn check_impl<'tcx>(
                 // therefore don't need to be WF (the trait's `Self: Trait` predicate
                 // won't hold).
                 let trait_ref = fcx.tcx.impl_trait_ref(item_def_id).unwrap();
-                let trait_ref =
-                    fcx.normalize_associated_types_in(
-                        ast_trait_ref.path.span, &trait_ref);
-                let obligations =
-                    ty::wf::trait_obligations(fcx,
-                                              fcx.param_env,
-                                              fcx.body_id,
-                                              &trait_ref,
-                                              ast_trait_ref.path.span);
+                let trait_ref = fcx.normalize_associated_types_in(
+                    ast_trait_ref.path.span,
+                    &trait_ref,
+                );
+                let obligations = ty::wf::trait_obligations(
+                    fcx,
+                    fcx.param_env,
+                    fcx.body_id,
+                    &trait_ref,
+                    ast_trait_ref.path.span,
+                    Some(item),
+                );
                 for obligation in obligations {
                     fcx.register_predicate(obligation);
                 }
diff --git a/src/test/ui/issues/issue-43784-associated-type.rs b/src/test/ui/issues/issue-43784-associated-type.rs
index fb58ad6600f..92083d88f1b 100644
--- a/src/test/ui/issues/issue-43784-associated-type.rs
+++ b/src/test/ui/issues/issue-43784-associated-type.rs
@@ -10,8 +10,8 @@ impl<T> Partial<T> for T::Assoc where
 {
 }
 
-impl<T> Complete for T { //~ ERROR the trait bound `T: std::marker::Copy` is not satisfied
-    type Assoc = T;
+impl<T> Complete for T {
+    type Assoc = T; //~ ERROR the trait bound `T: std::marker::Copy` is not satisfied
 }
 
 fn main() {}
diff --git a/src/test/ui/issues/issue-43784-associated-type.stderr b/src/test/ui/issues/issue-43784-associated-type.stderr
index e91e53499ce..cfab66302cd 100644
--- a/src/test/ui/issues/issue-43784-associated-type.stderr
+++ b/src/test/ui/issues/issue-43784-associated-type.stderr
@@ -1,10 +1,17 @@
 error[E0277]: the trait bound `T: std::marker::Copy` is not satisfied
-  --> $DIR/issue-43784-associated-type.rs:13:9
+  --> $DIR/issue-43784-associated-type.rs:14:5
    |
-LL | impl<T> Complete for T {
-   |      -  ^^^^^^^^ the trait `std::marker::Copy` is not implemented for `T`
-   |      |
-   |      help: consider restricting this bound: `T: std::marker::Copy`
+LL |       type Assoc: Partial<Self>;
+   |            ----- associated type defined here
+...
+LL | / impl<T> Complete for T {
+   | |      - help: consider restricting this bound: `T: std::marker::Copy`
+LL | |     type Assoc = T;
+   | |     ^^^^^^^^^^^^^^^ the trait `std::marker::Copy` is not implemented for `T`
+LL | | }
+   | |_- in this `impl` item
+   |
+   = help: consider adding a `where T: std::marker::Copy` bound
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/traits/cycle-cache-err-60010.rs b/src/test/ui/traits/cycle-cache-err-60010.rs
index 45aa1b3c522..cbddef082be 100644
--- a/src/test/ui/traits/cycle-cache-err-60010.rs
+++ b/src/test/ui/traits/cycle-cache-err-60010.rs
@@ -27,8 +27,8 @@ struct SalsaStorage {
     _parse: <ParseQuery as Query<RootDatabase>>::Data, //~ ERROR overflow
 }
 
-impl Database for RootDatabase { //~ ERROR overflow
-    type Storage = SalsaStorage;
+impl Database for RootDatabase {
+    type Storage = SalsaStorage; //~ ERROR overflow
 }
 impl HasQueryGroup for RootDatabase {}
 impl<DB> Query<DB> for ParseQuery
diff --git a/src/test/ui/traits/cycle-cache-err-60010.stderr b/src/test/ui/traits/cycle-cache-err-60010.stderr
index 9192f7ba2e3..a7b8dd05527 100644
--- a/src/test/ui/traits/cycle-cache-err-60010.stderr
+++ b/src/test/ui/traits/cycle-cache-err-60010.stderr
@@ -7,10 +7,16 @@ LL |     _parse: <ParseQuery as Query<RootDatabase>>::Data,
    = note: required because of the requirements on the impl of `Query<RootDatabase>` for `ParseQuery`
 
 error[E0275]: overflow evaluating the requirement `RootDatabase: SourceDatabase`
-  --> $DIR/cycle-cache-err-60010.rs:30:6
+  --> $DIR/cycle-cache-err-60010.rs:31:5
    |
-LL | impl Database for RootDatabase {
-   |      ^^^^^^^^
+LL |       type Storage;
+   |            ------- associated type defined here
+...
+LL | / impl Database for RootDatabase {
+LL | |     type Storage = SalsaStorage;
+   | |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL | | }
+   | |_- in this `impl` item
    |
    = note: required because of the requirements on the impl of `Query<RootDatabase>` for `ParseQuery`
    = note: required because it appears within the type `SalsaStorage`