correct spans in parem_env to deduplicate errors

compiler/rustc_trait_selection/src/traits/mod.rs

@@ -217,12 +217,12 @@ pub fn type_known_to_meet_bound_modulo_regions<'a, 'tcx>(
 #[instrument(level = "debug", skip(tcx, elaborated_env))]
 fn do_normalize_predicates<'tcx>(
     tcx: TyCtxt<'tcx>,
-    cause: ObligationCause<'tcx>,
+    span: Span,
+    mut causes: impl Iterator<Item = ObligationCause<'tcx>> + Debug,
     elaborated_env: ty::ParamEnv<'tcx>,
     predicates: Vec<ty::Predicate<'tcx>>,
     outlives: bool,
 ) -> Result<Vec<ty::Predicate<'tcx>>, ErrorGuaranteed> {
-    let span = cause.span;
     // FIXME. We should really... do something with these region
     // obligations. But this call just continues the older
     // behavior (i.e., doesn't cause any new bugs), and it would
@@ -241,9 +241,10 @@ fn do_normalize_predicates<'tcx>(
             if outlives
                 != matches!(predicate.kind().skip_binder(), ty::PredicateKind::TypeOutlives(..))
             {
+                causes.next().unwrap();
                 Ok(predicate)
             } else {
-                fully_normalize(&infcx, cause.clone(), elaborated_env, predicate)
+                fully_normalize(&infcx, causes.next().unwrap(), elaborated_env, predicate)
             }
         }) {
             Ok(predicates) => predicates,
@@ -304,6 +305,7 @@ fn do_normalize_predicates<'tcx>(
 
 // FIXME: this is gonna need to be removed ...
 /// Normalizes the parameter environment, reporting errors if they occur.
+#[inline]
 #[instrument(level = "debug", skip(tcx))]
 pub fn normalize_param_env_or_error<'tcx>(
     tcx: TyCtxt<'tcx>,
@@ -331,6 +333,23 @@ pub fn normalize_param_env_or_error<'tcx>(
 
     debug!("normalize_param_env_or_error: elaborated-predicates={:?}", predicates);
 
+    normalize_param_env_with_causes(
+        tcx,
+        unnormalized_env,
+        cause.span,
+        std::iter::repeat(cause),
+        predicates,
+    )
+}
+
+#[instrument(level = "debug", skip(tcx))]
+pub fn normalize_param_env_with_causes<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    unnormalized_env: ty::ParamEnv<'tcx>,
+    span: Span,
+    causes: impl Iterator<Item = ObligationCause<'tcx>> + Clone + Debug,
+    predicates: Vec<ty::Predicate<'tcx>>,
+) -> ty::ParamEnv<'tcx> {
     let elaborated_env = ty::ParamEnv::new(
         tcx.intern_predicates(&predicates),
         unnormalized_env.reveal(),
@@ -358,7 +377,8 @@ pub fn normalize_param_env_or_error<'tcx>(
 
     let Ok(predicates) = do_normalize_predicates(
         tcx,
-        cause.clone(),
+        span.clone(),
+        causes.clone(),
         elaborated_env,
         predicates,
         false,
@@ -378,7 +398,8 @@ pub fn normalize_param_env_or_error<'tcx>(
     );
     let Ok(predicates) = do_normalize_predicates(
         tcx,
-        cause,
+        span,
+        causes,
         outlives_env,
         predicates,
         true

compiler/rustc_ty_utils/src/ty.rs

@@ -1,6 +1,8 @@
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
+use rustc_infer::traits::util::elaborate_obligations;
+use rustc_infer::traits::Obligation;
 use rustc_middle::ty::{self, Binder, Predicate, PredicateKind, ToPredicate, Ty, TyCtxt};
 use rustc_trait_selection::traits;
 
@@ -110,7 +112,7 @@ fn param_env(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ParamEnv<'_> {
     }
     // Compute the bounds on Self and the type parameters.
 
-    let ty::InstantiatedPredicates { mut predicates, .. } =
+    let ty::InstantiatedPredicates { mut predicates, spans } =
         tcx.predicates_of(def_id).instantiate_identity(tcx);
 
     // Finally, we have to normalize the bounds in the environment, in
@@ -132,6 +134,7 @@ fn param_env(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ParamEnv<'_> {
 
     let local_did = def_id.as_local();
     let hir_id = local_did.map(|def_id| tcx.hir().local_def_id_to_hir_id(def_id));
+    let mut is_fn = false;
 
     let constness = match hir_id {
         Some(hir_id) => match tcx.hir().get(hir_id) {
@@ -181,8 +184,11 @@ fn param_env(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ParamEnv<'_> {
                 kind:
                     hir::ItemKind::Fn(hir::FnSig { header: hir::FnHeader { constness, .. }, .. }, ..),
                 ..
-            })
-            | hir::Node::TraitItem(hir::TraitItem {
+            }) => {
+                is_fn = true;
+                *constness
+            }
+            hir::Node::TraitItem(hir::TraitItem {
                 kind:
                     hir::TraitItemKind::Fn(
                         hir::FnSig { header: hir::FnHeader { constness, .. }, .. },
@@ -214,8 +220,36 @@ fn param_env(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ParamEnv<'_> {
         _ => hir::CRATE_HIR_ID,
     };
 
-    let cause = traits::ObligationCause::misc(tcx.def_span(def_id), body_id);
-    traits::normalize_param_env_or_error(tcx, unnormalized_env, cause)
+    let span = tcx.def_span(def_id);
+
+    if is_fn {
+        let mut spans = spans.into_iter();
+        let obligations: Vec<_> = predicates
+            .into_iter()
+            .map(|predicate| {
+                let cause = traits::ObligationCause::misc(spans.next().unwrap_or(span), body_id);
+                Obligation::new(cause, ty::ParamEnv::empty(), predicate)
+            })
+            .collect();
+
+        let (predicates, causes): (Vec<_>, Vec<_>) = elaborate_obligations(tcx, obligations)
+            .map(|obligation| (obligation.predicate, obligation.cause))
+            .unzip();
+
+        traits::normalize_param_env_with_causes(
+            tcx,
+            unnormalized_env,
+            span,
+            causes.into_iter(),
+            predicates,
+        )
+    } else {
+        traits::normalize_param_env_or_error(
+            tcx,
+            unnormalized_env,
+            traits::ObligationCause::misc(span, body_id),
+        )
+    }
 }
 
 /// Elaborate the environment.

src/test/ui/associated-types/issue-102185.rs

@@ -0,0 +1,17 @@
+// compile-flags: -Zdeduplicate-diagnostics=yes
+
+fn f<T>(_: impl A<X = T>) {}
+                //~^ ERROR the trait bound `T: B` is not satisfied [E0277]
+trait A: C<Z = <<Self as A>::X as B>::Y> {
+    type X: B;
+}
+
+trait B {
+    type Y;
+}
+
+trait C {
+    type Z;
+}
+
+fn main() {}

src/test/ui/associated-types/issue-102185.stderr

@@ -0,0 +1,14 @@
+error[E0277]: the trait bound `T: B` is not satisfied
+  --> $DIR/issue-102185.rs:3:17
+   |
+LL | fn f<T>(_: impl A<X = T>) {}
+   |                 ^^^^^^^^ the trait `B` is not implemented for `T`
+   |
+help: consider restricting type parameter `T`
+   |
+LL | fn f<T: B>(_: impl A<X = T>) {}
+   |       +++
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.