fix: misleading add dyn to derive macro suggestion

Author: eopb

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -3116,7 +3116,13 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 let label = "add `dyn` keyword before this trait";
                 let mut diag =
                     rustc_errors::struct_span_err!(tcx.sess, self_ty.span, E0782, "{}", msg);
-                diag.multipart_suggestion_verbose(label, sugg, Applicability::MachineApplicable);
+                if self_ty.span.can_be_used_for_suggestions() {
+                    diag.multipart_suggestion_verbose(
+                        label,
+                        sugg,
+                        Applicability::MachineApplicable,
+                    );
+                }
                 // check if the impl trait that we are considering is a impl of a local trait
                 self.maybe_lint_blanket_trait_impl(&self_ty, &mut diag);
                 diag.emit();

src/test/ui/traits/issue-106072.rs

@@ -0,0 +1,5 @@
+#[derive(Clone)] //~  trait objects must include the `dyn` keyword
+                 //~| trait objects must include the `dyn` keyword
+struct Foo;
+trait Foo {} //~ the name `Foo` is defined multiple times
+fn main() {}

src/test/ui/traits/issue-106072.stderr

@@ -0,0 +1,30 @@
+error[E0428]: the name `Foo` is defined multiple times
+  --> $DIR/issue-106072.rs:4:1
+   |
+LL | struct Foo;
+   | ----------- previous definition of the type `Foo` here
+LL | trait Foo {}
+   | ^^^^^^^^^ `Foo` redefined here
+   |
+   = note: `Foo` must be defined only once in the type namespace of this module
+
+error[E0782]: trait objects must include the `dyn` keyword
+  --> $DIR/issue-106072.rs:1:10
+   |
+LL | #[derive(Clone)]
+   |          ^^^^^
+   |
+   = note: this error originates in the derive macro `Clone` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0782]: trait objects must include the `dyn` keyword
+  --> $DIR/issue-106072.rs:1:10
+   |
+LL | #[derive(Clone)]
+   |          ^^^^^
+   |
+   = note: this error originates in the derive macro `Clone` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0428, E0782.
+For more information about an error, try `rustc --explain E0428`.