Add some const decorations

Discussion: https://www.postgresql.org/message-id/flat/5ac50071-f2ed-4ace-a8fd-b892cffd33eb@www.fastmail.com

src/fe_utils/recovery_gen.c

@@ -20,7 +20,7 @@ static char *escape_quotes(const char *src);
  * return it.
  */
 PQExpBuffer
-GenerateRecoveryConfig(PGconn *pgconn, char *replication_slot)
+GenerateRecoveryConfig(PGconn *pgconn, const char *replication_slot)
 {
 	PQconninfoOption *connOptions;
 	PQExpBufferData conninfo_buf;
@@ -102,7 +102,7 @@ GenerateRecoveryConfig(PGconn *pgconn, char *replication_slot)
  * configuration is written to recovery.conf.
  */
 void
-WriteRecoveryConfig(PGconn *pgconn, char *target_dir, PQExpBuffer contents)
+WriteRecoveryConfig(PGconn *pgconn, const char *target_dir, PQExpBuffer contents)
 {
 	char		filename[MAXPGPATH];
 	FILE	   *cf;

src/include/fe_utils/recovery_gen.h

@@ -21,8 +21,8 @@
 #define MINIMUM_VERSION_FOR_RECOVERY_GUC 120000
 
 extern PQExpBuffer GenerateRecoveryConfig(PGconn *pgconn,
-										  char *replication_slot);
-extern void WriteRecoveryConfig(PGconn *pgconn, char *target_dir,
+										  const char *replication_slot);
+extern void WriteRecoveryConfig(PGconn *pgconn, const char *target_dir,
 								PQExpBuffer contents);
 
 #endif							/* RECOVERY_GEN_H */