Use an enum instead of two bools to indicate wal inclusion in base backups

This makes the code easier to read as it becomes more explicit what the
different allowed combinations really are.

Suggested by Michael Paquier

src/bin/pg_basebackup/pg_basebackup.c

@@ -61,6 +61,16 @@ typedef struct TablespaceList
  */
 #define MINIMUM_VERSION_FOR_PG_WAL	100000
 
+/*
+ * Different ways to include WAL
+ */
+typedef enum
+{
+	NO_WAL,
+	FETCH_WAL,
+	STREAM_WAL
+} IncludeWal;
+
 /* Global options */
 static char *basedir = NULL;
 static TablespaceList tablespace_dirs = {NULL, NULL};
@@ -71,8 +81,7 @@ static bool noclean = false;
 static bool showprogress = false;
 static int	verbose = 0;
 static int	compresslevel = 0;
-static bool includewal = true;
-static bool streamwal = true;
+static IncludeWal includewal = STREAM_WAL;
 static bool fastcheckpoint = false;
 static bool writerecoveryconf = false;
 static bool do_sync = true;
@@ -1697,7 +1706,7 @@ BaseBackup(void)
 	 * If WAL streaming was requested, also check that the server is new
 	 * enough for that.
 	 */
-	if (streamwal && !CheckServerVersionForStreaming(conn))
+	if (includewal == STREAM_WAL && !CheckServerVersionForStreaming(conn))
 	{
 		/*
 		 * Error message already written in CheckServerVersionForStreaming(),
@@ -1731,9 +1740,9 @@ BaseBackup(void)
 		psprintf("BASE_BACKUP LABEL '%s' %s %s %s %s %s %s",
 				 escaped_label,
 				 showprogress ? "PROGRESS" : "",
-				 includewal && !streamwal ? "WAL" : "",
+				 includewal == FETCH_WAL ? "WAL" : "",
 				 fastcheckpoint ? "FAST" : "",
-				 includewal ? "NOWAIT" : "",
+				 includewal == NO_WAL ? "" : "NOWAIT",
 				 maxrate_clause ? maxrate_clause : "",
 				 format == 't' ? "TABLESPACE_MAP" : "");
 
@@ -1776,7 +1785,7 @@ BaseBackup(void)
 	PQclear(res);
 	MemSet(xlogend, 0, sizeof(xlogend));
 
-	if (verbose && includewal)
+	if (verbose && includewal != NO_WAL)
 		fprintf(stderr, _("transaction log start point: %s on timeline %u\n"),
 				xlogstart, starttli);
 
@@ -1833,7 +1842,7 @@ BaseBackup(void)
 	 * If we're streaming WAL, start the streaming session before we start
 	 * receiving the actual data chunks.
 	 */
-	if (streamwal)
+	if (includewal == STREAM_WAL)
 	{
 		if (verbose)
 			fprintf(stderr, _("%s: starting background WAL receiver\n"),
@@ -1879,7 +1888,7 @@ BaseBackup(void)
 		disconnect_and_exit(1);
 	}
 	strlcpy(xlogend, PQgetvalue(res, 0, 0), sizeof(xlogend));
-	if (verbose && includewal)
+	if (verbose && includewal != NO_WAL)
 		fprintf(stderr, "transaction log end point: %s\n", xlogend);
 	PQclear(res);
 
@@ -2117,20 +2126,17 @@ main(int argc, char **argv)
 				if (strcmp(optarg, "n") == 0 ||
 					strcmp(optarg, "none") == 0)
 				{
-					includewal = false;
-					streamwal = false;
+					includewal = NO_WAL;
 				}
 				else if (strcmp(optarg, "f") == 0 ||
 					strcmp(optarg, "fetch") == 0)
 				{
-					includewal = true;
-					streamwal = false;
+					includewal = FETCH_WAL;
 				}
 				else if (strcmp(optarg, "s") == 0 ||
 						 strcmp(optarg, "stream") == 0)
 				{
-					includewal = true;
-					streamwal = true;
+					includewal = STREAM_WAL;
 				}
 				else
 				{
@@ -2261,7 +2267,7 @@ main(int argc, char **argv)
 		exit(1);
 	}
 
-	if (format == 't' && streamwal && strcmp(basedir, "-") == 0)
+	if (format == 't' && includewal == STREAM_WAL && strcmp(basedir, "-") == 0)
 	{
 		fprintf(stderr,
 			_("%s: cannot stream transaction logs in tar mode to stdout\n"),
@@ -2271,7 +2277,7 @@ main(int argc, char **argv)
 		exit(1);
 	}
 
-	if (replication_slot && !streamwal)
+	if (replication_slot && includewal != STREAM_WAL)
 	{
 		fprintf(stderr,
 			_("%s: replication slots can only be used with WAL streaming\n"),