If user re-DECLAREs an existing cursor name, close the old cursor of

that name and issue a NOTICE to the effect that we did.  Previously,
code would try to assign the new cursor declaration to the old portal,
but this didn't work reliably since new parsetree is still sitting in
blank portal and is likely to get clobbered.

src/backend/tcop/pquery.c

@@ -8,20 +8,19 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/tcop/pquery.c,v 1.31 2000/06/04 01:44:33 petere Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/tcop/pquery.c,v 1.32 2000/06/04 22:08:53 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
 
 #include "postgres.h"
 
+#include "commands/command.h"
 #include "executor/execdefs.h"
 #include "executor/executor.h"
 #include "tcop/pquery.h"
 #include "utils/ps_status.h"
 
-#include "commands/command.h"
-
 static char *CreateOperationTag(int operationType);
 static void ProcessQueryDesc(QueryDesc *queryDesc, Node *limoffset,
 				 Node *limcount);
@@ -140,15 +139,32 @@ ProcessPortal(char *portalName,
 	MemoryContext portalContext;
 
 	/* ----------------
-	 *	 convert the current blank portal into the user-specified
-	 *	 portal and initialize the state and query descriptor.
+	 *	 Check for reserved or already-in-use portal name.
 	 * ----------------
 	 */
 
 	if (PortalNameIsSpecial(portalName))
 		elog(ERROR,
-			 "The portal name %s is reserved for internal use",
+			 "The portal name \"%s\" is reserved for internal use",
+			 portalName);
+
+	portal = GetPortalByName(portalName);
+	if (PortalIsValid(portal))
+	{
+		/* XXX Should we raise an error rather than closing the old portal? */
+		elog(NOTICE, "Closing pre-existing portal \"%s\"",
 			 portalName);
+		PortalDrop(&portal);
+	}
+
+	/* ----------------
+	 *	 Convert the current blank portal into the user-specified
+	 *	 portal and initialize the state and query descriptor.
+	 *
+	 *	 Since the parsetree has been created in the current blank portal,
+	 *	 we don't have to do any work to copy it into the user-named portal.
+	 * ----------------
+	 */
 
 	portal = BlankPortalAssignName(portalName);
 
@@ -159,8 +175,8 @@ ProcessPortal(char *portalName,
 				   PortalCleanup);
 
 	/* ----------------
-	 *	now create a new blank portal and switch to it.
-	 *	Otherwise, the new named portal will be cleaned.
+	 *	Now create a new blank portal and switch to it.
+	 *	Otherwise, the new named portal will be cleaned at statement end.
 	 *
 	 *	Note: portals will only be supported within a BEGIN...END
 	 *	block in the near future.  Later, someone will fix it to