Remove ATPrepSetStatistics

It was once possible to do ALTER TABLE ... SET STATISTICS on system
tables without allow_sytem_table_mods.  This was changed apparently by
accident between PostgreSQL 9.1 and 9.2, but a code comment still
claimed this was possible.  Without that functionality, having a
separate ATPrepSetStatistics() is useless, so use the generic
ATSimplePermissions() instead and move the remaining custom code into
ATExecSetStatistics().
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://www.postgresql.org/message-id/flat/cc8d2648-a0ec-7a86-13e5-db473484e19e%402ndquadrant.com

src/backend/commands/tablecmds.c

@@ -386,8 +386,6 @@ static ObjectAddress ATExecAddIdentity(Relation rel, const char *colName,
 static ObjectAddress ATExecSetIdentity(Relation rel, const char *colName,
 									   Node *def, LOCKMODE lockmode);
 static ObjectAddress ATExecDropIdentity(Relation rel, const char *colName, bool missing_ok, LOCKMODE lockmode);
-static void ATPrepSetStatistics(Relation rel, const char *colName, int16 colNum,
-								Node *newValue, LOCKMODE lockmode);
 static ObjectAddress ATExecSetStatistics(Relation rel, const char *colName, int16 colNum,
 										 Node *newValue, LOCKMODE lockmode);
 static ObjectAddress ATExecSetOptions(Relation rel, const char *colName,
@@ -3948,9 +3946,9 @@ ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
 			pass = AT_PASS_COL_ATTRS;
 			break;
 		case AT_SetStatistics:	/* ALTER COLUMN SET STATISTICS */
+			ATSimplePermissions(rel, ATT_TABLE | ATT_MATVIEW | ATT_INDEX | ATT_PARTITIONED_INDEX | ATT_FOREIGN_TABLE);
 			ATSimpleRecursion(wqueue, rel, cmd, recurse, lockmode);
-			/* Performs own permission checks */
-			ATPrepSetStatistics(rel, cmd->name, cmd->num, cmd->def, lockmode);
+			/* No command-specific prep needed */
 			pass = AT_PASS_MISC;
 			break;
 		case AT_SetOptions:		/* ALTER COLUMN SET ( options ) */
@@ -6702,26 +6700,18 @@ ATExecDropIdentity(Relation rel, const char *colName, bool missing_ok, LOCKMODE
 
 /*
  * ALTER TABLE ALTER COLUMN SET STATISTICS
+ *
+ * Return value is the address of the modified column
  */
-static void
-ATPrepSetStatistics(Relation rel, const char *colName, int16 colNum, Node *newValue, LOCKMODE lockmode)
+static ObjectAddress
+ATExecSetStatistics(Relation rel, const char *colName, int16 colNum, Node *newValue, LOCKMODE lockmode)
 {
-	/*
-	 * We do our own permission checking because (a) we want to allow SET
-	 * STATISTICS on indexes (for expressional index columns), and (b) we want
-	 * to allow SET STATISTICS on system catalogs without requiring
-	 * allowSystemTableMods to be turned on.
-	 */
-	if (rel->rd_rel->relkind != RELKIND_RELATION &&
-		rel->rd_rel->relkind != RELKIND_MATVIEW &&
-		rel->rd_rel->relkind != RELKIND_INDEX &&
-		rel->rd_rel->relkind != RELKIND_PARTITIONED_INDEX &&
-		rel->rd_rel->relkind != RELKIND_FOREIGN_TABLE &&
-		rel->rd_rel->relkind != RELKIND_PARTITIONED_TABLE)
-		ereport(ERROR,
-				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-				 errmsg("\"%s\" is not a table, materialized view, index, or foreign table",
-						RelationGetRelationName(rel))));
+	int			newtarget;
+	Relation	attrelation;
+	HeapTuple	tuple;
+	Form_pg_attribute attrtuple;
+	AttrNumber	attnum;
+	ObjectAddress address;
 
 	/*
 	 * We allow referencing columns by numbers only for indexes, since table
@@ -6734,25 +6724,6 @@ ATPrepSetStatistics(Relation rel, const char *colName, int16 colNum, Node *newVa
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 				 errmsg("cannot refer to non-index column by number")));
 
-	/* Permissions checks */
-	if (!pg_class_ownercheck(RelationGetRelid(rel), GetUserId()))
-		aclcheck_error(ACLCHECK_NOT_OWNER, get_relkind_objtype(rel->rd_rel->relkind),
-					   RelationGetRelationName(rel));
-}
-
-/*
- * Return value is the address of the modified column
- */
-static ObjectAddress
-ATExecSetStatistics(Relation rel, const char *colName, int16 colNum, Node *newValue, LOCKMODE lockmode)
-{
-	int			newtarget;
-	Relation	attrelation;
-	HeapTuple	tuple;
-	Form_pg_attribute attrtuple;
-	AttrNumber	attnum;
-	ObjectAddress address;
-
 	Assert(IsA(newValue, Integer));
 	newtarget = intVal(newValue);