Fix MutVisitor's default implementations to visit Stmt's and BinOp's spans

[dtolnay]

The Stmt case is a bug introduced almost certainly unintentionally by #126993. The code used to visit and mutate span correctly, but got changed as follows by that PR. Notice how span is copied into the output by |kind| Stmt { id, kind, span } which happens after the mutation in the correct code (red) and before the mutation in the incorrect code (green).

  pub fn noop_flat_map_stmt<T: MutVisitor>(
      Stmt { kind, mut span, mut id }: Stmt,
      vis: &mut T,
  ) -> SmallVec<[Stmt; 1]> {
      vis.visit_id(&mut id);
-     vis.visit_span(&mut span);
      let stmts: SmallVec<_> = noop_flat_map_stmt_kind(kind, vis)
          .into_iter()
          .map(|kind| Stmt { id, kind, span })
          .collect();
      if stmts.len() > 1 {
          panic!(...);
      }
+     vis.visit_span(&mut span);
      stmts
  }

[rustbot]

r? @chenyukang

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[tjallingt]

Suggested change

	ExprKind::Binary(binop, lhs, rhs) => {
	vis.visit_span(&mut binop.span);
	vis.visit_expr(lhs);
	vis.visit_expr(rhs);
	}
	ExprKind::Binary(binop, lhs, rhs) => {
	vis.visit_expr(lhs);
	vis.visit_expr(rhs);
	vis.visit_span(&mut binop.span);
	}

To match the order defined by #126993

[compiler-errors]

r? compiler-errors @bors r+

[bors]

📌 Commit a3cfe2f has been approved by compiler-errors

It is now in the queue for this repository.