Check & before suggest remove deref when trait_selection

Signed-off-by: xizheyin <xizheyin@smail.nju.edu.cn>

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

@@ -1516,6 +1516,12 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 } else {
                     expr.span.with_hi(expr.span.lo() + BytePos(1))
                 };
+
+                match self.tcx.sess.source_map().span_to_snippet(span) {
+                    Ok(snippet) if snippet.starts_with("&") => {}
+                    _ => break 'outer,
+                }
+
                 suggestions.push((span, String::new()));
 
                 let ty::Ref(_, inner_ty, _) = suggested_ty.kind() else {

tests/ui/traits/suggest-remove-deref-issue-140166.stderr

@@ -6,6 +6,7 @@ LL |     format_args!("{:?}", FlatMap(&Chars));
    |                   |
    |                   required by a bound introduced by this call
    |
+   = help: the trait `Trait` is implemented for `Chars`
 note: required for `FlatMap<&Chars>` to implement `Debug`
   --> $DIR/suggest-remove-deref-issue-140166.rs:7:16
    |
@@ -15,11 +16,6 @@ LL | impl<T: Trait> std::fmt::Debug for FlatMap<T> {
    |         unsatisfied trait bound introduced here
 note: required by a bound in `core::fmt::rt::Argument::<'_>::new_debug`
   --> $SRC_DIR/core/src/fmt/rt.rs:LL:COL
-help: consider removing the leading `&`-reference
-   |
-LL -     format_args!("{:?}", FlatMap(&Chars));
-LL +     format_args!("{:?}", latMap(&Chars));
-   |
 
 error: aborting due to 1 previous error