Re-introduce pgstat_drop_entry(), keeping ABI compatibility

This routine acts as a wrapper of a new pgstat_drop_entry_ext(), used in
the core code with a missing_ok argument.

This includes an update of .abi-compliance-history, removing the latest
entry that has documented the change of pgstat_drop_entry().  This
change is applied across v15~v18.  HEAD keeps pgstat_drop_entry() as
single entry point, with the new missing_ok.

Per discussion with Álvaro Herrera and Lukas Fittl.  This is a follow-up
of 850b9218c8.

Discussion: https://postgr.es/m/ajZz_sVJVX7pmPHo@alvherre.pgsql
Backpatch-through: 15-18

.abi-compliance-history

@@ -18,15 +18,6 @@
 # Be sure to replace "<ADD JUSTIFICATION HERE>" with details of your change and
 # why it is deemed acceptable.
 
-2e0c61aed6241bb66547bfab7467d43f889f78ba
-#
-# Fix PANIC with track_functions due to concurrent drop of pgstats entries
-# 2026-06-18 11:49:36 +0900
-#
-# This commit has added a "missing_ok" argument to pgstat_drop_entry().  All
-# the callers of this routine are in core for v15-v17.  One custom stats kinds
-# available in the public since v18 is impacted (maintainer informed).
-
 586f4266fb4945f6ea3564b9c1bab093eb74bee4
 #
 # Fix ABI break by moving PROCSIG_SLOTSYNC_MESSAGE in ProcSignalReason

src/backend/utils/activity/pgstat_function.c

@@ -112,8 +112,8 @@ pgstat_init_function_usage(FunctionCallInfo fcinfo,
 		AcceptInvalidationMessages();
 		if (!SearchSysCacheExists1(PROCOID, ObjectIdGetDatum(fcinfo->flinfo->fn_oid)))
 		{
-			pgstat_drop_entry(PGSTAT_KIND_FUNCTION, MyDatabaseId,
-							  fcinfo->flinfo->fn_oid, true);
+			pgstat_drop_entry_ext(PGSTAT_KIND_FUNCTION, MyDatabaseId,
+								  fcinfo->flinfo->fn_oid, true);
 			ereport(ERROR, errcode(ERRCODE_UNDEFINED_FUNCTION),
 					errmsg("function call to dropped function"));
 		}

src/backend/utils/activity/pgstat_replslot.c

@@ -157,8 +157,8 @@ pgstat_drop_replslot(ReplicationSlot *slot)
 {
 	Assert(LWLockHeldByMeInMode(ReplicationSlotAllocationLock, LW_EXCLUSIVE));
 
-	if (!pgstat_drop_entry(PGSTAT_KIND_REPLSLOT, InvalidOid,
-						   ReplicationSlotIndex(slot), false))
+	if (!pgstat_drop_entry_ext(PGSTAT_KIND_REPLSLOT, InvalidOid,
+							   ReplicationSlotIndex(slot), false))
 		pgstat_request_entry_refs_gc();
 }
 

src/backend/utils/activity/pgstat_shmem.c

@@ -844,7 +844,7 @@ pgstat_free_entry(PgStatShared_HashEntry *shent, dshash_seq_status *hstat)
 
 /*
  * Helper for both pgstat_drop_database_and_contents() and
- * pgstat_drop_entry(). If hstat is non-null delete the shared entry using
+ * pgstat_drop_entry_ext(). If hstat is non-null delete the shared entry using
  * dshash_delete_current(), otherwise use dshash_delete_entry(). In either
  * case the entry needs to be already locked.
  */
@@ -932,6 +932,17 @@ pgstat_drop_database_and_contents(Oid dboid)
 		pgstat_request_entry_refs_gc();
 }
 
+/*
+ * ABI-preserving wrapper around pgstat_drop_entry_ext().
+ *
+ * The original routine introduced in v15 did not include "missing_ok".
+ */
+bool
+pgstat_drop_entry(PgStat_Kind kind, Oid dboid, Oid objoid)
+{
+	return pgstat_drop_entry_ext(kind, dboid, objoid, false);
+}
+
 /*
  * Drop a single stats entry.
  *
@@ -946,8 +957,8 @@ pgstat_drop_database_and_contents(Oid dboid)
  * pgstat_gc_entry_refs().
  */
 bool
-pgstat_drop_entry(PgStat_Kind kind, Oid dboid, Oid objoid,
-				  bool missing_ok)
+pgstat_drop_entry_ext(PgStat_Kind kind, Oid dboid, Oid objoid,
+					  bool missing_ok)
 {
 	PgStat_HashKey key;
 	PgStatShared_HashEntry *shent;

src/backend/utils/activity/pgstat_xact.c

@@ -84,7 +84,7 @@ AtEOXact_PgStat_DroppedStats(PgStat_SubXactStatus *xact_state, bool isCommit)
 			 * Transaction that dropped an object committed. Drop the stats
 			 * too.
 			 */
-			if (!pgstat_drop_entry(it->kind, it->dboid, it->objoid, true))
+			if (!pgstat_drop_entry_ext(it->kind, it->dboid, it->objoid, true))
 				not_freed_count++;
 		}
 		else if (!isCommit && pending->is_create)
@@ -93,7 +93,7 @@ AtEOXact_PgStat_DroppedStats(PgStat_SubXactStatus *xact_state, bool isCommit)
 			 * Transaction that created an object aborted. Drop the stats
 			 * associated with the object.
 			 */
-			if (!pgstat_drop_entry(it->kind, it->dboid, it->objoid, true))
+			if (!pgstat_drop_entry_ext(it->kind, it->dboid, it->objoid, true))
 				not_freed_count++;
 		}
 
@@ -158,7 +158,7 @@ AtEOSubXact_PgStat_DroppedStats(PgStat_SubXactStatus *xact_state,
 			 * Subtransaction creating a new stats object aborted. Drop the
 			 * stats object.
 			 */
-			if (!pgstat_drop_entry(it->kind, it->dboid, it->objoid, true))
+			if (!pgstat_drop_entry_ext(it->kind, it->dboid, it->objoid, true))
 				not_freed_count++;
 			pfree(pending);
 		}
@@ -320,7 +320,7 @@ pgstat_execute_transactional_drops(int ndrops, struct xl_xact_stats_item *items,
 	{
 		xl_xact_stats_item *it = &items[i];
 
-		if (!pgstat_drop_entry(it->kind, it->dboid, it->objoid, true))
+		if (!pgstat_drop_entry_ext(it->kind, it->dboid, it->objoid, true))
 			not_freed_count++;
 	}
 

src/include/utils/pgstat_internal.h

@@ -625,8 +625,9 @@ extern PgStat_EntryRef *pgstat_get_entry_ref(PgStat_Kind kind, Oid dboid, Oid ob
 extern bool pgstat_lock_entry(PgStat_EntryRef *entry_ref, bool nowait);
 extern bool pgstat_lock_entry_shared(PgStat_EntryRef *entry_ref, bool nowait);
 extern void pgstat_unlock_entry(PgStat_EntryRef *entry_ref);
-extern bool pgstat_drop_entry(PgStat_Kind kind, Oid dboid, Oid objoid,
-							  bool missing_ok);
+extern bool pgstat_drop_entry(PgStat_Kind kind, Oid dboid, Oid objoid);
+extern bool pgstat_drop_entry_ext(PgStat_Kind kind, Oid dboid, Oid objoid,
+								  bool missing_ok);
 extern void pgstat_drop_all_entries(void);
 extern PgStat_EntryRef *pgstat_get_entry_ref_locked(PgStat_Kind kind, Oid dboid, Oid objoid,
 													bool nowait);