Use the correct span for displaying the line following a derive suggestion

Author: clubby789

compiler/rustc_errors/src/emitter.rs

@@ -1982,7 +1982,7 @@ impl EmitterWriter {
                 // We special case `#[derive(_)]\n` and other attribute suggestions, because those
                 // are the ones where context is most useful.
                 let file_lines = sm
-                    .span_to_lines(span.primary_span().unwrap().shrink_to_hi())
+                    .span_to_lines(parts[0].span.shrink_to_hi())
                     .expect("span_to_lines failed when emitting suggestion");
                 let line_num = sm.lookup_char_pos(parts[0].span.lo()).line;
                 if let Some(line) = file_lines.file.get_line(line_num - 1) {

tests/ui/modules/issue-107649.stderr

@@ -11,7 +11,7 @@ help: consider annotating `Dummy` with `#[derive(Debug)]`
    --> $DIR/auxiliary/dummy_lib.rs:2:1
     |
 2   + #[derive(Debug)]
-3   | #[path = "auxiliary/dummy_lib.rs"]
+3   | pub struct Dummy;
     |
 
 error: aborting due to previous error