Represent command completion tags as structs

The backend was using strings to represent command tags and doing string
comparisons in multiple places, but that's slow and unhelpful.  Create a
new command list with a supporting structure to use instead; this is
stored in a tag-list-file that can be tailored to specific purposes with
a caller-definable C macro, similar to what we do for WAL resource
managers.  The first first such uses are a new CommandTag enum and a
CommandTagBehavior struct.

Replace numerous occurrences of char *completionTag with a
QueryCompletion struct so that the code no longer stores information
about completed queries in a cstring.  Only at the last moment, in
EndCommand(), does this get converted to a string.

EventTriggerCacheItem no longer holds an array of palloc’d tag strings
in sorted order, but rather just a Bitmapset over the CommandTags.

Author: Mark Dilger, with unsolicited help from Álvaro Herrera
Reviewed-by: John Naylor, Tom Lane
Discussion: https://postgr.es/m/981A9DB4-3F0C-4DA5-88AD-CB9CFF4D6CAD@enterprisedb.com

src/include/commands/createas.h

@@ -22,7 +22,8 @@
 
 
 extern ObjectAddress ExecCreateTableAs(ParseState *pstate, CreateTableAsStmt *stmt,
-									   ParamListInfo params, QueryEnvironment *queryEnv, char *completionTag);
+									   ParamListInfo params, QueryEnvironment *queryEnv,
+									   QueryCompletion *qc);
 
 extern int	GetIntoRelEFlags(IntoClause *intoClause);
 

src/include/commands/event_trigger.h

@@ -17,6 +17,7 @@
 #include "catalog/objectaddress.h"
 #include "catalog/pg_event_trigger.h"
 #include "nodes/parsenodes.h"
+#include "tcop/cmdtag.h"
 #include "tcop/deparse_utility.h"
 #include "utils/aclchk_internal.h"
 
@@ -25,7 +26,7 @@ typedef struct EventTriggerData
 	NodeTag		type;
 	const char *event;			/* event name */
 	Node	   *parsetree;		/* parse tree */
-	const char *tag;			/* command tag */
+	CommandTag	tag;
 } EventTriggerData;
 
 #define AT_REWRITE_ALTER_PERSISTENCE	0x01

src/include/commands/matview.h

@@ -24,7 +24,7 @@
 extern void SetMatViewPopulatedState(Relation relation, bool newstate);
 
 extern ObjectAddress ExecRefreshMatView(RefreshMatViewStmt *stmt, const char *queryString,
-										ParamListInfo params, char *completionTag);
+										ParamListInfo params, QueryCompletion *qc);
 
 extern DestReceiver *CreateTransientRelDestReceiver(Oid oid);
 

src/include/commands/portalcmds.h

@@ -23,7 +23,7 @@ extern void PerformCursorOpen(ParseState *pstate, DeclareCursorStmt *cstmt, Para
 							  bool isTopLevel);
 
 extern void PerformPortalFetch(FetchStmt *stmt, DestReceiver *dest,
-							   char *completionTag);
+							   QueryCompletion *qc);
 
 extern void PerformPortalClose(const char *name);
 

src/include/commands/prepare.h

@@ -40,7 +40,7 @@ extern void PrepareQuery(ParseState *pstate, PrepareStmt *stmt,
 extern void ExecuteQuery(ParseState *pstate,
 						 ExecuteStmt *stmt, IntoClause *intoClause,
 						 ParamListInfo params,
-						 DestReceiver *dest, char *completionTag);
+						 DestReceiver *dest, QueryCompletion *qc);
 extern void DeallocateQuery(DeallocateStmt *stmt);
 extern void ExplainExecuteQuery(ExecuteStmt *execstmt, IntoClause *into,
 								ExplainState *es, const char *queryString,