Slightly improve mismatched GAT where clause error

compiler/rustc_infer/src/infer/error_reporting/nice_region_error/trait_impl_difference.rs

@@ -2,17 +2,17 @@
 
 use crate::infer::error_reporting::nice_region_error::NiceRegionError;
 use crate::infer::lexical_region_resolve::RegionResolutionError;
-use crate::infer::{SubregionOrigin, Subtype};
-use crate::traits::ObligationCauseCode::CompareImplMethodObligation;
+use crate::infer::Subtype;
+use crate::traits::ObligationCauseCode::{CompareImplMethodObligation, CompareImplTypeObligation};
 use rustc_errors::{ErrorGuaranteed, MultiSpan};
 use rustc_hir as hir;
 use rustc_hir::def::Res;
-use rustc_hir::def_id::{DefId, LocalDefId};
+use rustc_hir::def_id::DefId;
 use rustc_hir::intravisit::Visitor;
 use rustc_middle::hir::nested_filter;
 use rustc_middle::ty::print::RegionHighlightMode;
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeSuperVisitable, TypeVisitor};
-use rustc_span::{Span, Symbol};
+use rustc_span::Span;
 
 use std::ops::ControlFlow;
 
@@ -22,38 +22,23 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
         let error = self.error.as_ref()?;
         debug!("try_report_impl_not_conforming_to_trait {:?}", error);
         if let RegionResolutionError::SubSupConflict(
-                _, var_origin, sub_origin, _sub, sup_origin, _sup, _,
+                _,
+                var_origin,
+                sub_origin,
+                _sub,
+                sup_origin,
+                _sup,
+                _,
             ) = error.clone()
-            && let (&Subtype(ref sup_trace), &Subtype(ref sub_trace)) = (&sup_origin, &sub_origin)
-            && let (
-                sub_expected_found @ Some((sub_expected, sub_found)),
-                sup_expected_found @ Some(_),
-                CompareImplMethodObligation { trait_item_def_id, .. },
-            ) = (sub_trace.values.ty(), sup_trace.values.ty(), sub_trace.cause.code())
+            && let (Subtype(sup_trace), Subtype(sub_trace)) = (&sup_origin, &sub_origin)
+            && let sub_expected_found @ Some((sub_expected, sub_found)) = sub_trace.values.ty()
+            && let sup_expected_found @ Some(_) = sup_trace.values.ty()
+            && let CompareImplMethodObligation { trait_item_def_id, .. }
+                 | CompareImplTypeObligation { trait_item_def_id, .. } = sub_trace.cause.code()
             && sup_expected_found == sub_expected_found
         {
-            let guar = self.emit_err(
-                var_origin.span(),
-                sub_expected,
-                sub_found,
-                *trait_item_def_id,
-            );
-            return Some(guar);
-        }
-        if let RegionResolutionError::ConcreteFailure(origin, _, _)
-            | RegionResolutionError::GenericBoundFailure(origin, _, _) = error.clone()
-            && let SubregionOrigin::CompareImplTypeObligation {
-                span,
-                impl_item_def_id,
-                trait_item_def_id,
-            } = origin
-        {
-            let guar = self.emit_associated_type_err(
-                span,
-                self.infcx.tcx.item_name(impl_item_def_id.to_def_id()),
-                impl_item_def_id,
-                trait_item_def_id,
-            );
+            let guar =
+                self.emit_err(var_origin.span(), sub_expected, sub_found, *trait_item_def_id);
             return Some(guar);
         }
         None
@@ -147,25 +132,6 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
         }
         err.emit()
     }
-
-    fn emit_associated_type_err(
-        &self,
-        span: Span,
-        item_name: Symbol,
-        impl_item_def_id: LocalDefId,
-        trait_item_def_id: DefId,
-    ) -> ErrorGuaranteed {
-        let impl_sp = self.tcx().def_span(impl_item_def_id);
-        let trait_sp = self.tcx().def_span(trait_item_def_id);
-        let mut err = self
-            .tcx()
-            .sess
-            .struct_span_err(span, &format!("`impl` associated type signature for `{}` doesn't match `trait` associated type signature", item_name));
-        err.span_label(impl_sp, "found");
-        err.span_label(trait_sp, "expected");
-
-        err.emit()
-    }
 }
 
 struct TypeParamSpanVisitor<'tcx> {

compiler/rustc_typeck/src/check/compare_method.rs

@@ -1212,15 +1212,6 @@ fn compare_type_predicate_entailment<'tcx>(
     // `ObligationCause` (and the `FnCtxt`). This is what
     // `regionck_item` expects.
     let impl_ty_hir_id = tcx.hir().local_def_id_to_hir_id(impl_ty.def_id.expect_local());
-    let cause = ObligationCause::new(
-        impl_ty_span,
-        impl_ty_hir_id,
-        ObligationCauseCode::CompareImplTypeObligation {
-            impl_item_def_id: impl_ty.def_id.expect_local(),
-            trait_item_def_id: trait_ty.def_id,
-        },
-    );
-
     debug!("compare_type_predicate_entailment: trait_to_impl_substs={:?}", trait_to_impl_substs);
 
     // The predicates declared by the impl definition, the trait and the
@@ -1239,7 +1230,7 @@ fn compare_type_predicate_entailment<'tcx>(
         Reveal::UserFacing,
         hir::Constness::NotConst,
     );
-    let param_env = traits::normalize_param_env_or_error(tcx, param_env, normalize_cause.clone());
+    let param_env = traits::normalize_param_env_or_error(tcx, param_env, normalize_cause);
     tcx.infer_ctxt().enter(|infcx| {
         let ocx = ObligationCtxt::new(&infcx);
 
@@ -1247,12 +1238,24 @@ fn compare_type_predicate_entailment<'tcx>(
 
         let mut selcx = traits::SelectionContext::new(&infcx);
 
-        for predicate in impl_ty_own_bounds.predicates {
+        assert_eq!(impl_ty_own_bounds.predicates.len(), impl_ty_own_bounds.spans.len());
+        for (span, predicate) in
+            std::iter::zip(impl_ty_own_bounds.spans, impl_ty_own_bounds.predicates)
+        {
+            let cause = ObligationCause::misc(span, impl_ty_hir_id);
             let traits::Normalized { value: predicate, obligations } =
-                traits::normalize(&mut selcx, param_env, normalize_cause.clone(), predicate);
+                traits::normalize(&mut selcx, param_env, cause, predicate);
 
+            let cause = ObligationCause::new(
+                span,
+                impl_ty_hir_id,
+                ObligationCauseCode::CompareImplTypeObligation {
+                    impl_item_def_id: impl_ty.def_id.expect_local(),
+                    trait_item_def_id: trait_ty.def_id,
+                },
+            );
             ocx.register_obligations(obligations);
-            ocx.register_obligation(traits::Obligation::new(cause.clone(), param_env, predicate));
+            ocx.register_obligation(traits::Obligation::new(cause, param_env, predicate));
         }
 
         // Check that all obligations are satisfied by the implementation's

src/test/ui/generic-associated-types/generic-associated-types-where.stderr

@@ -11,13 +11,13 @@ LL |     type Assoc2<T: std::fmt::Display> = Vec<T>;
    |                  +++++++++++++++++++
 
 error[E0276]: impl has stricter requirements than trait
-  --> $DIR/generic-associated-types-where.rs:22:5
+  --> $DIR/generic-associated-types-where.rs:22:38
    |
 LL |     type Assoc3<T>;
    |     -------------- definition of `Assoc3` from trait
 ...
 LL |     type Assoc3<T> = Vec<T> where T: Iterator;
-   |     ^^^^^^^^^^^^^^ impl has extra requirement `T: Iterator`
+   |                                      ^^^^^^^^ impl has extra requirement `T: Iterator`
 
 error: aborting due to 2 previous errors
 

src/test/ui/generic-associated-types/impl_bounds.rs

@@ -13,9 +13,9 @@ struct Fooy<T>(T);
 
 impl<T> Foo for Fooy<T> {
     type A<'a> = (&'a ()) where Self: 'static;
-    //~^ ERROR `impl` associated type
+    //~^ ERROR the parameter type `T` may not live long enoug
     type B<'a, 'b> = (&'a(), &'b ()) where 'b: 'a;
-    //~^ ERROR `impl` associated type
+    //~^ ERROR impl has stricter requirements than trait
     //~| ERROR lifetime bound not satisfied
     type C = String where Self: Copy;
     //~^ ERROR the trait bound `T: Copy` is not satisfied

src/test/ui/generic-associated-types/impl_bounds.stderr

@@ -1,20 +1,22 @@
-error: `impl` associated type signature for `A` doesn't match `trait` associated type signature
-  --> $DIR/impl_bounds.rs:15:5
+error[E0310]: the parameter type `T` may not live long enough
+  --> $DIR/impl_bounds.rs:15:39
    |
-LL |     type A<'a> where Self: 'a;
-   |     ---------- expected
-...
 LL |     type A<'a> = (&'a ()) where Self: 'static;
-   |     ^^^^^^^^^^ found
+   |                                       ^^^^^^^ ...so that the definition in impl matches the definition from the trait
+   |
+help: consider adding an explicit lifetime bound...
+   |
+LL | impl<T: 'static> Foo for Fooy<T> {
+   |       +++++++++
 
-error: `impl` associated type signature for `B` doesn't match `trait` associated type signature
-  --> $DIR/impl_bounds.rs:17:5
+error[E0276]: impl has stricter requirements than trait
+  --> $DIR/impl_bounds.rs:17:48
    |
 LL |     type B<'a, 'b> where 'a: 'b;
-   |     -------------- expected
+   |     -------------- definition of `B` from trait
 ...
 LL |     type B<'a, 'b> = (&'a(), &'b ()) where 'b: 'a;
-   |     ^^^^^^^^^^^^^^ found
+   |                                                ^^ impl has extra requirement `'b: 'a`
 
 error[E0478]: lifetime bound not satisfied
   --> $DIR/impl_bounds.rs:17:22
@@ -37,10 +39,10 @@ LL |     type B<'a, 'b> = (&'a(), &'b ()) where 'b: 'a;
    |                ^^
 
 error[E0277]: the trait bound `T: Copy` is not satisfied
-  --> $DIR/impl_bounds.rs:20:5
+  --> $DIR/impl_bounds.rs:20:33
    |
 LL |     type C = String where Self: Copy;
-   |     ^^^^^^ the trait `Copy` is not implemented for `T`
+   |                                 ^^^^ the trait `Copy` is not implemented for `T`
    |
 note: required because of the requirements on the impl of `Copy` for `Fooy<T>`
   --> $DIR/impl_bounds.rs:11:10
@@ -88,5 +90,5 @@ LL | impl<T: std::marker::Copy> Foo for Fooy<T> {
 
 error: aborting due to 5 previous errors
 
-Some errors have detailed explanations: E0277, E0478.
-For more information about an error, try `rustc --explain E0277`.
+Some errors have detailed explanations: E0276, E0277, E0310, E0478.
+For more information about an error, try `rustc --explain E0276`.

src/test/ui/generic-associated-types/issue-47206-where-clause.stderr

@@ -1,11 +1,11 @@
 error[E0276]: impl has stricter requirements than trait
-  --> $DIR/issue-47206-where-clause.rs:12:5
+  --> $DIR/issue-47206-where-clause.rs:12:38
    |
 LL |     type Assoc3<T>;
    |     -------------- definition of `Assoc3` from trait
 ...
 LL |     type Assoc3<T> = Vec<T> where T: Iterator;
-   |     ^^^^^^^^^^^^^^ impl has extra requirement `T: Iterator`
+   |                                      ^^^^^^^^ impl has extra requirement `T: Iterator`
 
 error: aborting due to previous error
 

src/test/ui/generic-associated-types/missing-where-clause-on-trait.rs

@@ -7,7 +7,7 @@ trait Foo {
 }
 impl Foo for () {
     type Assoc<'a, 'b> = () where 'a: 'b;
-    //~^ `impl` associated type
+    //~^ impl has stricter requirements than trait
 }
 
 fn main() {}

src/test/ui/generic-associated-types/missing-where-clause-on-trait.stderr

@@ -1,11 +1,12 @@
-error: `impl` associated type signature for `Assoc` doesn't match `trait` associated type signature
-  --> $DIR/missing-where-clause-on-trait.rs:9:5
+error[E0276]: impl has stricter requirements than trait
+  --> $DIR/missing-where-clause-on-trait.rs:9:39
    |
 LL |     type Assoc<'a, 'b>;
-   |     ------------------ expected
+   |     ------------------ definition of `Assoc` from trait
 ...
 LL |     type Assoc<'a, 'b> = () where 'a: 'b;
-   |     ^^^^^^^^^^^^^^^^^^ found
+   |                                       ^^ impl has extra requirement `'a: 'b`
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0276`.