Syntax support and documentation for event triggers.

They don't actually do anything yet; that will get fixed in a
follow-on commit.  But this gets the basic infrastructure in place,
including CREATE/ALTER/DROP EVENT TRIGGER; support for COMMENT,
SECURITY LABEL, and ALTER EXTENSION .. ADD/DROP EVENT TRIGGER;
pg_dump and psql support; and documentation for the anticipated
initial feature set.

Dimitri Fontaine, with review and a bunch of additional hacking by me.
Thom Brown extensively reviewed earlier versions of this patch set,
but there's not a whole lot of that code left in this commit, as it
turns out.

src/backend/tcop/utility.c

@@ -33,6 +33,7 @@
 #include "commands/dbcommands.h"
 #include "commands/defrem.h"
 #include "commands/discard.h"
+#include "commands/event_trigger.h"
 #include "commands/explain.h"
 #include "commands/extension.h"
 #include "commands/lockcmds.h"
@@ -183,6 +184,8 @@ check_xact_readonly(Node *parsetree)
 		case T_CommentStmt:
 		case T_DefineStmt:
 		case T_CreateCastStmt:
+		case T_CreateEventTrigStmt:
+		case T_AlterEventTrigStmt:
 		case T_CreateConversionStmt:
 		case T_CreatedbStmt:
 		case T_CreateDomainStmt:
@@ -1056,6 +1059,14 @@ standard_ProcessUtility(Node *parsetree,
 								 InvalidOid, InvalidOid, false);
 			break;
 
+		case T_CreateEventTrigStmt:
+			CreateEventTrigger((CreateEventTrigStmt *) parsetree);
+			break;
+
+		case T_AlterEventTrigStmt:
+			AlterEventTrigger((AlterEventTrigStmt *) parsetree);
+			break;
+
 		case T_CreatePLangStmt:
 			CreateProceduralLanguage((CreatePLangStmt *) parsetree);
 			break;
@@ -1472,6 +1483,9 @@ AlterObjectTypeCommandTag(ObjectType objtype)
 		case OBJECT_TRIGGER:
 			tag = "ALTER TRIGGER";
 			break;
+		case OBJECT_EVENT_TRIGGER:
+			tag = "ALTER EVENT TRIGGER";
+			break;
 		case OBJECT_TSCONFIGURATION:
 			tag = "ALTER TEXT SEARCH CONFIGURATION";
 			break;
@@ -1741,6 +1755,9 @@ CreateCommandTag(Node *parsetree)
 				case OBJECT_TRIGGER:
 					tag = "DROP TRIGGER";
 					break;
+				case OBJECT_EVENT_TRIGGER:
+					tag = "DROP EVENT TRIGGER";
+					break;
 				case OBJECT_RULE:
 					tag = "DROP RULE";
 					break;
@@ -1994,6 +2011,14 @@ CreateCommandTag(Node *parsetree)
 			tag = "CREATE TRIGGER";
 			break;
 
+		case T_CreateEventTrigStmt:
+			tag = "CREATE EVENT TRIGGER";
+			break;
+
+		case T_AlterEventTrigStmt:
+			tag = "ALTER EVENT TRIGGER";
+			break;
+
 		case T_CreatePLangStmt:
 			tag = "CREATE LANGUAGE";
 			break;
@@ -2489,6 +2514,14 @@ GetCommandLogLevel(Node *parsetree)
 			lev = LOGSTMT_DDL;
 			break;
 
+		case T_CreateEventTrigStmt:
+			lev = LOGSTMT_DDL;
+			break;
+
+		case T_AlterEventTrigStmt:
+			lev = LOGSTMT_DDL;
+			break;
+
 		case T_CreatePLangStmt:
 			lev = LOGSTMT_DDL;
 			break;