alter-type-readd-constraint.patch

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 359d478..50c93fe 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -335,13 +335,15 @@ static void ATExecAddIndex(AlteredTableInfo *tab, Relation rel,
 			   IndexStmt *stmt, bool is_rebuild, LOCKMODE lockmode);
 static void ATExecAddConstraint(List **wqueue,
 					AlteredTableInfo *tab, Relation rel,
-				 Constraint *newConstraint, bool recurse, LOCKMODE lockmode);
+				 Constraint *newConstraint, bool recurse, bool check_no_children,
+				 LOCKMODE lockmode);
 static void ATExecAddIndexConstraint(AlteredTableInfo *tab, Relation rel,
 						 IndexStmt *stmt, LOCKMODE lockmode);
 static void ATAddCheckConstraint(List **wqueue,
 					 AlteredTableInfo *tab, Relation rel,
 					 Constraint *constr,
-					 bool recurse, bool recursing, LOCKMODE lockmode);
+					 bool recurse, bool recursing, bool check_no_children,
+					 LOCKMODE lockmode);
 static void ATAddForeignKeyConstraint(AlteredTableInfo *tab, Relation rel,
 						  Constraint *fkconstraint, LOCKMODE lockmode);
 static void ATExecDropConstraint(Relation rel, const char *constrName,
@@ -3248,11 +3250,15 @@ ATExecCmd(List **wqueue, AlteredTableInfo *tab, Relation rel,
 			break;
 		case AT_AddConstraint:	/* ADD CONSTRAINT */
 			ATExecAddConstraint(wqueue, tab, rel, (Constraint *) cmd->def,
-								false, lockmode);
+								false, true, lockmode);
+			break;
+		case AT_ReAddConstraint:	/* Re-add previously dropped CONSTRAINT */
+			ATExecAddConstraint(wqueue, tab, rel, (Constraint *) cmd->def,
+								false, false, lockmode);
 			break;
 		case AT_AddConstraintRecurse:	/* ADD CONSTRAINT with recursion */
 			ATExecAddConstraint(wqueue, tab, rel, (Constraint *) cmd->def,
-								true, lockmode);
+								true, true, lockmode);
 			break;
 		case AT_AddIndexConstraint:		/* ADD CONSTRAINT USING INDEX */
 			ATExecAddIndexConstraint(tab, rel, (IndexStmt *) cmd->def, lockmode);
@@ -5499,7 +5505,8 @@ ATExecAddIndexConstraint(AlteredTableInfo *tab, Relation rel,
  */
 static void
 ATExecAddConstraint(List **wqueue, AlteredTableInfo *tab, Relation rel,
-				  Constraint *newConstraint, bool recurse, LOCKMODE lockmode)
+				  Constraint *newConstraint, bool recurse, bool check_no_children,
+				  LOCKMODE lockmode)
 {
 	Assert(IsA(newConstraint, Constraint));
 
@@ -5512,7 +5519,8 @@ ATExecAddConstraint(List **wqueue, AlteredTableInfo *tab, Relation rel,
 	{
 		case CONSTR_CHECK:
 			ATAddCheckConstraint(wqueue, tab, rel,
-								 newConstraint, recurse, false, lockmode);
+								 newConstraint, recurse, false, check_no_children,
+								 lockmode);
 			break;
 
 		case CONSTR_FOREIGN:
@@ -5568,7 +5576,7 @@ ATExecAddConstraint(List **wqueue, AlteredTableInfo *tab, Relation rel,
 static void
 ATAddCheckConstraint(List **wqueue, AlteredTableInfo *tab, Relation rel,
 					 Constraint *constr, bool recurse, bool recursing,
-					 LOCKMODE lockmode)
+					 bool check_no_children, LOCKMODE lockmode)
 {
 	List	   *newcons;
 	ListCell   *lcon;
@@ -5646,14 +5654,24 @@ ATAddCheckConstraint(List **wqueue, AlteredTableInfo *tab, Relation rel,
 	children = find_inheritance_children(RelationGetRelid(rel), lockmode);
 
 	/*
-	 * Check if ONLY was specified with ALTER TABLE.  If so, allow the
-	 * contraint creation only if there are no children currently.	Error out
-	 * otherwise.
+	 * Check if either ONLY was specified with ALTER TABLE or if we are adding
+	 * back a constraint in AT_PASS_OLD_CONSTR pass, that was previously
+	 * dropped constraint. We don't recurse in both the cases.
 	 */
-	if (!recurse && children != NIL)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-				 errmsg("constraint must be added to child tables too")));
+	if (!recurse)
+	{	
+		/*
+		 * We have been told not to recurse. Unless we have been explicitly
+		 * told not to check for exitsing children, error out if there are
+		 * existing children
+		 */
+		if (check_no_children && children != NIL)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+					 errmsg("constraint must be added to child tables too")));
+		else
+			return;
+	}
 
 	foreach(child, children)
 	{
@@ -5670,7 +5688,7 @@ ATAddCheckConstraint(List **wqueue, AlteredTableInfo *tab, Relation rel,
 
 		/* Recurse to child */
 		ATAddCheckConstraint(wqueue, childtab, childrel,
-							 constr, recurse, true, lockmode);
+							 constr, recurse, true, true, lockmode);
 
 		heap_close(childrel, NoLock);
 	}
@@ -7914,6 +7932,7 @@ ATPostAlterTypeParse(Oid oldId, char *cmd,
 							case AT_AddConstraint:
 								Assert(IsA(cmd->def, Constraint));
 								con = (Constraint *) cmd->def;
+								cmd->subtype = AT_ReAddConstraint;
 								/* rewriting neither side of a FK */
 								if (con->contype == CONSTR_FOREIGN &&
 									!rewrite && !tab->rewrite)
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index 09b15e7..b58fa82 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -1196,6 +1196,7 @@ typedef enum AlterTableType
 	AT_AddIndex,				/* add index */
 	AT_ReAddIndex,				/* internal to commands/tablecmds.c */
 	AT_AddConstraint,			/* add constraint */
+	AT_ReAddConstraint,			/* re-add previously dropped constraint */
 	AT_AddConstraintRecurse,	/* internal to commands/tablecmds.c */
 	AT_ValidateConstraint,		/* validate constraint */
 	AT_ValidateConstraintRecurse,		/* internal to commands/tablecmds.c */