Use impl's def id when calculating type to specify UFCS

compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

@@ -2290,14 +2290,15 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                         let trait_impls = self.tcx.trait_impls_of(data.trait_ref.def_id);
 
                         if trait_impls.blanket_impls().is_empty()
-                            && let Some((impl_ty, _)) = trait_impls.non_blanket_impls().iter().next()
-                            && let Some(impl_def_id) = impl_ty.def() {
-                            let message = if trait_impls.non_blanket_impls().len() == 1 {
+                            && let Some(impl_def_id) = trait_impls.non_blanket_impls().values().flatten().next()
+                        {
+                            let non_blanket_impl_count = trait_impls.non_blanket_impls().values().flatten().count();
+                            let message = if non_blanket_impl_count == 1 {
                                 "use the fully-qualified path to the only available implementation".to_string()
                             } else {
                                 format!(
                                     "use a fully-qualified path to a specific available implementation ({} found)",
-                                    trait_impls.non_blanket_impls().len()
+                                    non_blanket_impl_count
                                 )
                             };
                             let mut suggestions = vec![(

src/test/ui/associated-types/associated-types-unconstrained.stderr

@@ -6,6 +6,11 @@ LL |     fn bar() -> isize;
 ...
 LL |     let x: isize = Foo::bar();
    |                    ^^^^^^^^ cannot call associated function of trait
+   |
+help: use the fully-qualified path to the only available implementation
+   |
+LL |     let x: isize = <isize as Foo>::bar();
+   |                    +++++++++    +
 
 error: aborting due to previous error
 

src/test/ui/suggestions/issue-104327.rs

@@ -0,0 +1,12 @@
+trait Bar {}
+
+trait Foo {
+    fn f() {}
+}
+
+impl Foo for dyn Bar {}
+
+fn main() {
+    Foo::f();
+    //~^ ERROR cannot call associated function on trait without specifying the corresponding `impl` type
+}

src/test/ui/suggestions/issue-104327.stderr

@@ -0,0 +1,17 @@
+error[E0790]: cannot call associated function on trait without specifying the corresponding `impl` type
+  --> $DIR/issue-104327.rs:10:5
+   |
+LL |     fn f() {}
+   |     --------- `Foo::f` defined here
+...
+LL |     Foo::f();
+   |     ^^^^^^ cannot call associated function of trait
+   |
+help: use the fully-qualified path to the only available implementation
+   |
+LL |     <(dyn Bar + 'static) as Foo>::f();
+   |     +++++++++++++++++++++++    +
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0790`.

src/test/ui/suggestions/issue-104328.rs

@@ -0,0 +1,12 @@
+#![feature(object_safe_for_dispatch)]
+
+trait Foo {
+    fn f() {}
+}
+
+impl Foo for dyn Sized {}
+
+fn main() {
+    Foo::f();
+    //~^ ERROR cannot call associated function on trait without specifying the corresponding `impl` type
+}

src/test/ui/suggestions/issue-104328.stderr

@@ -0,0 +1,17 @@
+error[E0790]: cannot call associated function on trait without specifying the corresponding `impl` type
+  --> $DIR/issue-104328.rs:10:5
+   |
+LL |     fn f() {}
+   |     --------- `Foo::f` defined here
+...
+LL |     Foo::f();
+   |     ^^^^^^ cannot call associated function of trait
+   |
+help: use the fully-qualified path to the only available implementation
+   |
+LL |     <(dyn Sized + 'static) as Foo>::f();
+   |     +++++++++++++++++++++++++    +
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0790`.