Add CLOSE_AND_REPLACE helper

Similar to free_and_replace. I think this should be uppercase to make it
clear that this is a macro. free_and_replace should probably be uppercased
too.

src/basic/fd-util.c

@@ -731,8 +731,7 @@ int fd_duplicate_data_fd(int fd) {
                 if (f != 0)
                         return -errno;
 
-                safe_close(copy_fd);
-                copy_fd = TAKE_FD(tmp_fd);
+                CLOSE_AND_REPLACE(copy_fd, tmp_fd);
 
                 remains = mfree(remains);
                 remains_size = 0;
@@ -865,8 +864,7 @@ int rearrange_stdio(int original_input_fd, int original_output_fd, int original_
                                 goto finish;
                         }
 
-                        safe_close(null_fd);
-                        null_fd = copy;
+                        CLOSE_AND_REPLACE(null_fd, copy);
                 }
         }
 

src/basic/fd-util.h

@@ -93,6 +93,16 @@ static inline int make_null_stdio(void) {
                 _fd_;                           \
         })
 
+/* Like free_and_replace(), but for file descriptors */
+#define CLOSE_AND_REPLACE(a, b)                 \
+        ({                                      \
+                int *_fdp_ = &(a);              \
+                safe_close(*_fdp_);             \
+                *_fdp_ = TAKE_FD(b);            \
+                0;                              \
+        })
+
+
 int fd_reopen(int fd, int flags);
 
 int read_nr_open(void);