Refactor WaitLSNType enum to use a macro for type count

Change WAIT_LSN_TYPE_COUNT from an enum sentinel to a macro definition,
in a similar way to IOObject, IOContext, and BackendType enums.  Remove
explicit enum value assignments well.

Author: Xuneng Zhou <xunengzhou@gmail.com>

src/backend/access/transam/xlogwait.c

@@ -126,7 +126,7 @@ updateMinWaitedLSN(WaitLSNType lsnType)
 	XLogRecPtr	minWaitedLSN = PG_UINT64_MAX;
 	int			i = (int) lsnType;
 
-	Assert(i >= 0 && i < (int) WAIT_LSN_TYPE_COUNT);
+	Assert(i >= 0 && i < WAIT_LSN_TYPE_COUNT);
 
 	if (!pairingheap_is_empty(&waitLSNState->waitersHeap[i]))
 	{
@@ -147,7 +147,7 @@ addLSNWaiter(XLogRecPtr lsn, WaitLSNType lsnType)
 	WaitLSNProcInfo *procInfo = &waitLSNState->procInfos[MyProcNumber];
 	int			i = (int) lsnType;
 
-	Assert(i >= 0 && i < (int) WAIT_LSN_TYPE_COUNT);
+	Assert(i >= 0 && i < WAIT_LSN_TYPE_COUNT);
 
 	LWLockAcquire(WaitLSNLock, LW_EXCLUSIVE);
 
@@ -172,7 +172,7 @@ deleteLSNWaiter(WaitLSNType lsnType)
 	WaitLSNProcInfo *procInfo = &waitLSNState->procInfos[MyProcNumber];
 	int			i = (int) lsnType;
 
-	Assert(i >= 0 && i < (int) WAIT_LSN_TYPE_COUNT);
+	Assert(i >= 0 && i < WAIT_LSN_TYPE_COUNT);
 
 	LWLockAcquire(WaitLSNLock, LW_EXCLUSIVE);
 
@@ -213,7 +213,7 @@ wakeupWaiters(WaitLSNType lsnType, XLogRecPtr currentLSN)
 	int			numWakeUpProcs;
 	int			i = (int) lsnType;
 
-	Assert(i >= 0 && i < (int) WAIT_LSN_TYPE_COUNT);
+	Assert(i >= 0 && i < WAIT_LSN_TYPE_COUNT);
 
 	do
 	{
@@ -270,7 +270,7 @@ WaitLSNWakeup(WaitLSNType lsnType, XLogRecPtr currentLSN)
 {
 	int			i = (int) lsnType;
 
-	Assert(i >= 0 && i < (int) WAIT_LSN_TYPE_COUNT);
+	Assert(i >= 0 && i < WAIT_LSN_TYPE_COUNT);
 
 	/*
 	 * Fast path check.  Skip if currentLSN is InvalidXLogRecPtr, which means

src/include/access/xlogwait.h

@@ -35,11 +35,12 @@ typedef enum
  */
 typedef enum WaitLSNType
 {
-	WAIT_LSN_TYPE_REPLAY = 0,	/* Waiting for replay on standby */
-	WAIT_LSN_TYPE_FLUSH = 1,	/* Waiting for flush on primary */
-	WAIT_LSN_TYPE_COUNT = 2
+	WAIT_LSN_TYPE_REPLAY,		/* Waiting for replay on standby */
+	WAIT_LSN_TYPE_FLUSH,		/* Waiting for flush on primary */
 } WaitLSNType;
 
+#define WAIT_LSN_TYPE_COUNT (WAIT_LSN_TYPE_FLUSH + 1)
+
 /*
  * WaitLSNProcInfo - the shared memory structure representing information
  * about the single process, which may wait for LSN operations.  An item of