Don't ICE while suggesting updating item path.

When an item isn't found, we may suggest an appropriate import to
`use`. Along with that, we also suggest updating the path to work
with the `use`. Unfortunately, if the code in question originates
from a macro, the span used to indicate which part of the path
needs updating may not be suitable and cause an ICE. Since, such
code is not adjustable directly by the user without modifying the
macro, just skip the suggestion in such cases.

compiler/rustc_resolve/src/diagnostics.rs

@@ -2544,12 +2544,15 @@ fn show_candidates(
                 Applicability::MaybeIncorrect,
             );
             if let [first, .., last] = &path[..] {
-                err.span_suggestion_verbose(
-                    first.ident.span.until(last.ident.span),
-                    &format!("if you import `{}`, refer to it directly", last.ident),
-                    "",
-                    Applicability::Unspecified,
-                );
+                let sp = first.ident.span.until(last.ident.span);
+                if sp.can_be_used_for_suggestions() {
+                    err.span_suggestion_verbose(
+                        sp,
+                        &format!("if you import `{}`, refer to it directly", last.ident),
+                        "",
+                        Applicability::Unspecified,
+                    );
+                }
             }
         } else {
             msg.push(':');