Mention "signature" rather than "fn pointer" when impl/trait methods are incompatible

compiler/rustc_error_messages/locales/en-US/infer.ftl

@@ -253,8 +253,8 @@ infer_trait_placeholder_mismatch = implementation of `{$trait_def_id}` is not ge
 infer_trait_impl_diff = `impl` item signature doesn't match `trait` item signature
     .found = found `{$found}`
     .expected = expected `{$expected}`
-    .expected_found = expected `{$expected}`
-               {"   "}found `{$found}`
+    .expected_found = expected signature `{$expected}`
+               {"   "}found signature `{$found}`
 
 infer_tid_rel_help = verify the lifetime relationships in the `trait` and `impl` between the `self` argument, the other inputs and its output
 infer_tid_consider_borrowing = consider borrowing this type parameter in the trait

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -270,8 +270,8 @@ fn compare_method_predicate_entailment<'tcx>(
     let unnormalized_impl_fty = tcx.mk_fn_ptr(ty::Binder::dummy(unnormalized_impl_sig));
 
     let norm_cause = ObligationCause::misc(impl_m_span, impl_m_hir_id);
-    let impl_fty = ocx.normalize(&norm_cause, param_env, unnormalized_impl_fty);
-    debug!("compare_impl_method: impl_fty={:?}", impl_fty);
+    let impl_sig = ocx.normalize(&norm_cause, param_env, unnormalized_impl_sig);
+    debug!("compare_impl_method: impl_fty={:?}", impl_sig);
 
     let trait_sig = tcx.bound_fn_sig(trait_m.def_id).subst(tcx, trait_to_placeholder_substs);
     let trait_sig = tcx.liberate_late_bound_regions(impl_m.def_id, trait_sig);
@@ -294,18 +294,17 @@ fn compare_method_predicate_entailment<'tcx>(
     // type would be more appropriate. In other places we have a `Vec<Span>`
     // corresponding to their `Vec<Predicate>`, but we don't have that here.
     // Fixing this would improve the output of test `issue-83765.rs`.
-    let result = ocx.sup(&cause, param_env, trait_fty, impl_fty);
+    let result = ocx.sup(&cause, param_env, trait_sig, impl_sig);
 
     if let Err(terr) = result {
-        debug!(?terr, "sub_types failed: impl ty {:?}, trait ty {:?}", impl_fty, trait_fty);
+        debug!(?impl_sig, ?trait_sig, ?terr, "sub_types failed");
 
         let emitted = report_trait_method_mismatch(
             &infcx,
             cause,
             terr,
-            (trait_m, trait_fty),
-            (impl_m, impl_fty),
-            trait_sig,
+            (trait_m, trait_sig),
+            (impl_m, impl_sig),
             impl_trait_ref,
         );
         return Err(emitted);
@@ -484,7 +483,8 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
     let impl_trait_ref = tcx.impl_trait_ref(impl_m.impl_container(tcx).unwrap()).unwrap();
     let param_env = tcx.param_env(def_id);
 
-    // First, check a few of the same thing as `compare_impl_method`, just so we don't ICE during substitutions later.
+    // First, check a few of the same things as `compare_impl_method`,
+    // just so we don't ICE during substitution later.
     compare_number_of_generics(tcx, impl_m, trait_m, tcx.hir().span_if_local(impl_m.def_id), true)?;
     compare_generic_param_kinds(tcx, impl_m, trait_m, true)?;
     check_region_bounds_on_impl_item(tcx, impl_m, trait_m, true)?;
@@ -577,14 +577,11 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
 
     debug!(?trait_sig, ?impl_sig, "equating function signatures");
 
-    let trait_fty = tcx.mk_fn_ptr(ty::Binder::dummy(trait_sig));
-    let impl_fty = tcx.mk_fn_ptr(ty::Binder::dummy(impl_sig));
-
     // Unify the whole function signature. We need to do this to fully infer
     // the lifetimes of the return type, but do this after unifying just the
     // return types, since we want to avoid duplicating errors from
     // `compare_method_predicate_entailment`.
-    match ocx.eq(&cause, param_env, trait_fty, impl_fty) {
+    match ocx.eq(&cause, param_env, trait_sig, impl_sig) {
         Ok(()) => {}
         Err(terr) => {
             // This function gets called during `compare_method_predicate_entailment` when normalizing a
@@ -595,9 +592,8 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
                 infcx,
                 cause,
                 terr,
-                (trait_m, trait_fty),
-                (impl_m, impl_fty),
-                trait_sig,
+                (trait_m, trait_sig),
+                (impl_m, impl_sig),
                 impl_trait_ref,
             );
             return Err(emitted);
@@ -771,9 +767,8 @@ fn report_trait_method_mismatch<'tcx>(
     infcx: &InferCtxt<'tcx>,
     mut cause: ObligationCause<'tcx>,
     terr: TypeError<'tcx>,
-    (trait_m, trait_fty): (&ty::AssocItem, Ty<'tcx>),
-    (impl_m, impl_fty): (&ty::AssocItem, Ty<'tcx>),
-    trait_sig: ty::FnSig<'tcx>,
+    (trait_m, trait_sig): (&ty::AssocItem, ty::FnSig<'tcx>),
+    (impl_m, impl_sig): (&ty::AssocItem, ty::FnSig<'tcx>),
     impl_trait_ref: ty::TraitRef<'tcx>,
 ) -> ErrorGuaranteed {
     let tcx = infcx.tcx;
@@ -858,10 +853,7 @@ fn report_trait_method_mismatch<'tcx>(
         &mut diag,
         &cause,
         trait_err_span.map(|sp| (sp, "type in trait".to_owned())),
-        Some(infer::ValuePairs::Terms(ExpectedFound {
-            expected: trait_fty.into(),
-            found: impl_fty.into(),
-        })),
+        Some(infer::ValuePairs::Sigs(ExpectedFound { expected: trait_sig, found: impl_sig })),
         terr,
         false,
         false,

compiler/rustc_infer/src/infer/at.rs

@@ -427,3 +427,15 @@ impl<'tcx> ToTrace<'tcx> for ty::AliasTy<'tcx> {
         }
     }
 }
+
+impl<'tcx> ToTrace<'tcx> for ty::FnSig<'tcx> {
+    fn to_trace(
+        _: TyCtxt<'tcx>,
+        cause: &ObligationCause<'tcx>,
+        a_is_expected: bool,
+        a: Self,
+        b: Self,
+    ) -> TypeTrace<'tcx> {
+        TypeTrace { cause: cause.clone(), values: Sigs(ExpectedFound::new(a_is_expected, a, b)) }
+    }
+}

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -1429,8 +1429,8 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         impl<'tcx> OpaqueTypesVisitor<'tcx> {
             fn visit_expected_found(
                 tcx: TyCtxt<'tcx>,
-                expected: Ty<'tcx>,
-                found: Ty<'tcx>,
+                expected: impl TypeVisitable<'tcx>,
+                found: impl TypeVisitable<'tcx>,
                 ignore_span: Span,
             ) -> Self {
                 let mut types_visitor = OpaqueTypesVisitor {
@@ -1570,6 +1570,11 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                             _ => (false, Mismatch::Fixed("type")),
                         }
                     }
+                    ValuePairs::Sigs(infer::ExpectedFound { expected, found }) => {
+                        OpaqueTypesVisitor::visit_expected_found(self.tcx, expected, found, span)
+                            .report(diag);
+                        (false, Mismatch::Fixed("signature"))
+                    }
                     ValuePairs::TraitRefs(_) | ValuePairs::PolyTraitRefs(_) => {
                         (false, Mismatch::Fixed("trait"))
                     }
@@ -2041,6 +2046,17 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     ret => ret,
                 }
             }
+            infer::Sigs(exp_found) => {
+                let exp_found = self.resolve_vars_if_possible(exp_found);
+                if exp_found.references_error() {
+                    return None;
+                }
+                let (exp, fnd) = self.cmp_fn_sig(
+                    &ty::Binder::dummy(exp_found.expected),
+                    &ty::Binder::dummy(exp_found.found),
+                );
+                Some((exp, fnd, None, None))
+            }
         }
     }
 

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

@@ -3,14 +3,15 @@
 use crate::errors::{ConsiderBorrowingParamHelp, RelationshipHelp, TraitImplDiff};
 use crate::infer::error_reporting::nice_region_error::NiceRegionError;
 use crate::infer::lexical_region_resolve::RegionResolutionError;
-use crate::infer::Subtype;
+use crate::infer::{Subtype, ValuePairs};
 use crate::traits::ObligationCauseCode::CompareImplItemObligation;
 use rustc_errors::ErrorGuaranteed;
 use rustc_hir as hir;
 use rustc_hir::def::Res;
 use rustc_hir::def_id::DefId;
 use rustc_hir::intravisit::Visitor;
 use rustc_middle::hir::nested_filter;
+use rustc_middle::ty::error::ExpectedFound;
 use rustc_middle::ty::print::RegionHighlightMode;
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeSuperVisitable, TypeVisitor};
 use rustc_span::Span;
@@ -23,22 +24,27 @@ 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,
-                _,
-            ) = error.clone()
+            _,
+            var_origin,
+            sub_origin,
+            _sub,
+            sup_origin,
+            _sup,
+            _,
+        ) = error.clone()
             && 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 CompareImplItemObligation { trait_item_def_id, .. } = sub_trace.cause.code()
-            && sup_expected_found == sub_expected_found
+            && sub_trace.values == sup_trace.values
+            && let ValuePairs::Sigs(ExpectedFound { expected, found }) = sub_trace.values
         {
-            let guar =
-                self.emit_err(var_origin.span(), sub_expected, sub_found, *trait_item_def_id);
+            // FIXME(compiler-errors): Don't like that this needs `Ty`s, but
+            // all of the region highlighting machinery only deals with those.
+            let guar = self.emit_err(
+                var_origin.span(),
+                self.cx.tcx.mk_fn_ptr(ty::Binder::dummy(expected)),
+                self.cx.tcx.mk_fn_ptr(ty::Binder::dummy(found)),
+                *trait_item_def_id,
+            );
             return Some(guar);
         }
         None

compiler/rustc_infer/src/infer/mod.rs

@@ -361,6 +361,7 @@ pub enum ValuePairs<'tcx> {
     Terms(ExpectedFound<ty::Term<'tcx>>),
     TraitRefs(ExpectedFound<ty::TraitRef<'tcx>>),
     PolyTraitRefs(ExpectedFound<ty::PolyTraitRef<'tcx>>),
+    Sigs(ExpectedFound<ty::FnSig<'tcx>>),
 }
 
 impl<'tcx> ValuePairs<'tcx> {

src/test/ui/associated-types/defaults-specialization.stderr

@@ -22,8 +22,8 @@ note: type in trait
    |
 LL |     fn make() -> Self::Ty {
    |                  ^^^^^^^^
-   = note: expected fn pointer `fn() -> <A<T> as Tr>::Ty`
-              found fn pointer `fn() -> u8`
+   = note: expected signature `fn() -> <A<T> as Tr>::Ty`
+              found signature `fn() -> u8`
 
 error[E0053]: method `make` has an incompatible type for trait
   --> $DIR/defaults-specialization.rs:35:18
@@ -42,8 +42,8 @@ note: type in trait
    |
 LL |     fn make() -> Self::Ty {
    |                  ^^^^^^^^
-   = note: expected fn pointer `fn() -> <B<T> as Tr>::Ty`
-              found fn pointer `fn() -> bool`
+   = note: expected signature `fn() -> <B<T> as Tr>::Ty`
+              found signature `fn() -> bool`
 
 error[E0308]: mismatched types
   --> $DIR/defaults-specialization.rs:10:9

src/test/ui/async-await/in-trait/async-example-desugared-boxed-in-trait.stderr

@@ -9,8 +9,8 @@ note: type in trait
    |
 LL |     fn foo(&self) -> Pin<Box<dyn Future<Output = i32> + '_>>;
    |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   = note: expected fn pointer `fn(&i32) -> Pin<Box<dyn Future<Output = i32>>>`
-              found fn pointer `fn(&i32) -> impl Future<Output = i32>`
+   = note: expected signature `fn(&i32) -> Pin<Box<dyn Future<Output = i32>>>`
+              found signature `fn(&i32) -> impl Future<Output = i32>`
 
 error: aborting due to previous error
 

src/test/ui/borrowck/regions-bound-missing-bound-in-impl.stderr

@@ -22,8 +22,8 @@ error[E0308]: method not compatible with trait
 LL |     fn wrong_bound1<'b,'c,'d:'a+'c>(self, b: Inv<'b>, c: Inv<'c>, d: Inv<'d>) {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
    |
-   = note: expected fn pointer `fn(&'a isize, Inv<'c>, Inv<'c>, Inv<'_>)`
-              found fn pointer `fn(&'a isize, Inv<'_>, Inv<'c>, Inv<'_>)`
+   = note: expected signature `fn(&'a isize, Inv<'c>, Inv<'c>, Inv<'_>)`
+              found signature `fn(&'a isize, Inv<'_>, Inv<'c>, Inv<'_>)`
 note: the lifetime `'c` as defined here...
   --> $DIR/regions-bound-missing-bound-in-impl.rs:27:24
    |
@@ -41,8 +41,8 @@ error[E0308]: method not compatible with trait
 LL |     fn wrong_bound1<'b,'c,'d:'a+'c>(self, b: Inv<'b>, c: Inv<'c>, d: Inv<'d>) {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
    |
-   = note: expected fn pointer `fn(&'a isize, Inv<'c>, Inv<'c>, Inv<'_>)`
-              found fn pointer `fn(&'a isize, Inv<'_>, Inv<'c>, Inv<'_>)`
+   = note: expected signature `fn(&'a isize, Inv<'c>, Inv<'c>, Inv<'_>)`
+              found signature `fn(&'a isize, Inv<'_>, Inv<'c>, Inv<'_>)`
 note: the lifetime `'c` as defined here...
   --> $DIR/regions-bound-missing-bound-in-impl.rs:27:24
    |

src/test/ui/compare-method/bad-self-type.stderr

@@ -7,8 +7,8 @@ LL |     fn poll(self, _: &mut Context<'_>) -> Poll<()> {
    |             expected struct `Pin`, found struct `MyFuture`
    |             help: change the self-receiver type to match the trait: `self: Pin<&mut MyFuture>`
    |
-   = note: expected fn pointer `fn(Pin<&mut MyFuture>, &mut Context<'_>) -> Poll<_>`
-              found fn pointer `fn(MyFuture, &mut Context<'_>) -> Poll<_>`
+   = note: expected signature `fn(Pin<&mut MyFuture>, &mut Context<'_>) -> Poll<_>`
+              found signature `fn(MyFuture, &mut Context<'_>) -> Poll<_>`
 
 error[E0053]: method `foo` has an incompatible type for trait
   --> $DIR/bad-self-type.rs:22:18
@@ -24,8 +24,8 @@ note: type in trait
    |
 LL |     fn foo(self);
    |            ^^^^
-   = note: expected fn pointer `fn(MyFuture)`
-              found fn pointer `fn(Box<MyFuture>)`
+   = note: expected signature `fn(MyFuture)`
+              found signature `fn(Box<MyFuture>)`
 
 error[E0053]: method `bar` has an incompatible type for trait
   --> $DIR/bad-self-type.rs:24:18
@@ -38,8 +38,8 @@ note: type in trait
    |
 LL |     fn bar(self) -> Option<()>;
    |                     ^^^^^^^^^^
-   = note: expected fn pointer `fn(MyFuture) -> Option<()>`
-              found fn pointer `fn(MyFuture)`
+   = note: expected signature `fn(MyFuture) -> Option<()>`
+              found signature `fn(MyFuture)`
 help: change the output type to match the trait
    |
 LL |     fn bar(self) -> Option<()> {}

src/test/ui/compare-method/issue-90444.stderr

@@ -7,8 +7,8 @@ LL |     fn from(_: fn((), (), &mut ())) -> Self {
    |                types differ in mutability
    |                help: change the parameter type to match the trait: `for<'a> fn((), (), &'a ())`
    |
-   = note: expected fn pointer `fn(for<'a> fn((), (), &'a ())) -> A`
-              found fn pointer `fn(for<'a> fn((), (), &'a mut ())) -> A`
+   = note: expected signature `fn(for<'a> fn((), (), &'a ())) -> A`
+              found signature `fn(for<'a> fn((), (), &'a mut ())) -> A`
 
 error[E0053]: method `from` has an incompatible type for trait
   --> $DIR/issue-90444.rs:11:16
@@ -19,8 +19,8 @@ LL |     fn from(_: fn((), (), u64)) -> Self {
    |                expected `u32`, found `u64`
    |                help: change the parameter type to match the trait: `fn((), (), u32)`
    |
-   = note: expected fn pointer `fn(fn((), (), u32)) -> B`
-              found fn pointer `fn(fn((), (), u64)) -> B`
+   = note: expected signature `fn(fn((), (), u32)) -> B`
+              found signature `fn(fn((), (), u64)) -> B`
 
 error: aborting due to 2 previous errors
 

src/test/ui/compare-method/reordered-type-param.stderr

@@ -14,8 +14,8 @@ note: type in trait
    |
 LL |   fn b<C:Clone,D>(&self, x: C) -> C;
    |                             ^
-   = note: expected fn pointer `fn(&E, F) -> F`
-              found fn pointer `fn(&E, G) -> G`
+   = note: expected signature `fn(&E, F) -> F`
+              found signature `fn(&E, G) -> G`
    = note: a type parameter was expected, but a different one was found; you might be missing a type parameter or trait bound
    = note: for more information, visit https://doc.rust-lang.org/book/ch10-02-traits.html#traits-as-parameters
 

src/test/ui/impl-trait/impl-generic-mismatch-ab.stderr

@@ -13,8 +13,8 @@ note: type in trait
    |
 LL |     fn foo<A: Debug>(&self, a: &A, b: &impl Debug);
    |                                ^^
-   = note: expected fn pointer `fn(&(), &B, &impl Debug)`
-              found fn pointer `fn(&(), &impl Debug, &B)`
+   = note: expected signature `fn(&(), &B, &impl Debug)`
+              found signature `fn(&(), &impl Debug, &B)`
    = note: a type parameter was expected, but a different one was found; you might be missing a type parameter or trait bound
    = note: for more information, visit https://doc.rust-lang.org/book/ch10-02-traits.html#traits-as-parameters
 

src/test/ui/impl-trait/in-trait/method-signature-matches.stderr

@@ -12,8 +12,8 @@ note: type in trait
    |
 LL |     fn owo(x: ()) -> impl Sized;
    |               ^^
-   = note: expected fn pointer `fn(())`
-              found fn pointer `fn(u8)`
+   = note: expected signature `fn(())`
+              found signature `fn(u8)`
 
 error[E0053]: method `owo` has an incompatible type for trait
   --> $DIR/method-signature-matches.rs:20:21
@@ -39,8 +39,8 @@ note: type in trait
    |
 LL |     async fn owo(x: ()) {}
    |                     ^^
-   = note: expected fn pointer `fn(()) -> _`
-              found fn pointer `fn(u8) -> _`
+   = note: expected signature `fn(()) -> _`
+              found signature `fn(u8) -> _`
 
 error[E0050]: method `calm_down_please` has 3 parameters but the declaration in trait `TooMuch::calm_down_please` has 0
   --> $DIR/method-signature-matches.rs:29:28
@@ -75,8 +75,8 @@ note: type in trait
    |
 LL |     fn early<'early, T>(x: &'early T) -> impl Sized;
    |                            ^^^^^^^^^
-   = note: expected fn pointer `fn(&'early T)`
-              found fn pointer `fn(&())`
+   = note: expected signature `fn(&'early T)`
+              found signature `fn(&())`
 
 error: aborting due to 5 previous errors