Clean up MergeCheckConstraint()

If the constraint is not already in the list, add it ourselves,
instead of making the caller do it.  This makes the interface more
consistent with other "merge" functions in this file.

Discussion: https://www.postgresql.org/message-id/flat/52a125e4-ff9a-95f5-9f61-b87cf447e4da%40eisentraut.org

src/backend/commands/tablecmds.c

@@ -353,7 +353,7 @@ static void RangeVarCallbackForTruncate(const RangeVar *relation,
 static List *MergeAttributes(List *schema, List *supers, char relpersistence,
 							 bool is_partition, List **supconstr,
 							 List **supnotnulls);
-static bool MergeCheckConstraint(List *constraints, char *name, Node *expr);
+static List *MergeCheckConstraint(List *constraints, const char *name, Node *expr);
 static void MergeAttributesIntoExisting(Relation child_rel, Relation parent_rel);
 static void MergeConstraintsIntoExisting(Relation child_rel, Relation parent_rel);
 static void StoreCatalogInheritance(Oid relationId, List *supers,
@@ -2913,24 +2913,7 @@ MergeAttributes(List *schema, List *supers, char relpersistence,
 									   name,
 									   RelationGetRelationName(relation))));
 
-				/* check for duplicate */
-				if (!MergeCheckConstraint(constraints, name, expr))
-				{
-					/* nope, this is a new one */
-					CookedConstraint *cooked;
-
-					cooked = (CookedConstraint *) palloc(sizeof(CookedConstraint));
-					cooked->contype = CONSTR_CHECK;
-					cooked->conoid = InvalidOid;	/* until created */
-					cooked->name = pstrdup(name);
-					cooked->attnum = 0; /* not used for constraints */
-					cooked->expr = expr;
-					cooked->skip_validation = false;
-					cooked->is_local = false;
-					cooked->inhcount = 1;
-					cooked->is_no_inherit = false;
-					constraints = lappend(constraints, cooked);
-				}
+				constraints = MergeCheckConstraint(constraints, name, expr);
 			}
 		}
 
@@ -3277,13 +3260,17 @@ MergeAttributes(List *schema, List *supers, char relpersistence,
  *
  * constraints is a list of CookedConstraint structs for previous constraints.
  *
- * Returns true if merged (constraint is a duplicate), or false if it's
- * got a so-far-unique name, or throws error if conflict.
+ * If the new constraint matches an existing one, then the existing
+ * constraint's inheritance count is updated.  If there is a conflict (same
+ * name but different expression), throw an error.  If the constraint neither
+ * matches nor conflicts with an existing one, a new constraint is appended to
+ * the list.
  */
-static bool
-MergeCheckConstraint(List *constraints, char *name, Node *expr)
+static List *
+MergeCheckConstraint(List *constraints, const char *name, Node *expr)
 {
 	ListCell   *lc;
+	CookedConstraint *newcon;
 
 	foreach(lc, constraints)
 	{
@@ -3297,13 +3284,13 @@ MergeCheckConstraint(List *constraints, char *name, Node *expr)
 
 		if (equal(expr, ccon->expr))
 		{
-			/* OK to merge */
+			/* OK to merge constraint with existing */
 			ccon->inhcount++;
 			if (ccon->inhcount < 0)
 				ereport(ERROR,
 						errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
 						errmsg("too many inheritance parents"));
-			return true;
+			return constraints;
 		}
 
 		ereport(ERROR,
@@ -3312,7 +3299,16 @@ MergeCheckConstraint(List *constraints, char *name, Node *expr)
 						name)));
 	}
 
-	return false;
+	/*
+	 * Constraint couldn't be merged with an existing one and also didn't
+	 * conflict with an existing one, so add it as a new one to the list.
+	 */
+	newcon = palloc0_object(CookedConstraint);
+	newcon->contype = CONSTR_CHECK;
+	newcon->name = pstrdup(name);
+	newcon->expr = expr;
+	newcon->inhcount = 1;
+	return lappend(constraints, newcon);
 }