Rearrange "add column" logic to merge columns at exec time.

The previous coding set attinhcount too high in some cases, resulting in
an undumpable, undroppable column.  Per bug #5856, reported by Naoya
Anzai.  See also commit 31b6fc06, which
fixes a similar bug in ALTER TABLE .. ADD CONSTRAINT.

Patch by Noah Misch.

src/backend/commands/tablecmds.c

@@ -285,16 +285,15 @@ static void ATSimplePermissions(Relation rel, int allowed_targets);
 static void ATWrongRelkindError(Relation rel, int allowed_targets);
 static void ATSimpleRecursion(List **wqueue, Relation rel,
 				  AlterTableCmd *cmd, bool recurse, LOCKMODE lockmode);
-static void ATOneLevelRecursion(List **wqueue, Relation rel,
-					AlterTableCmd *cmd, LOCKMODE lockmode);
 static void ATTypedTableRecursion(List **wqueue, Relation rel, AlterTableCmd *cmd,
 								  LOCKMODE lockmode);
 static List *find_typed_table_dependencies(Oid typeOid, const char *typeName,
 										   DropBehavior behavior);
 static void ATPrepAddColumn(List **wqueue, Relation rel, bool recurse, bool recursing,
 				AlterTableCmd *cmd, LOCKMODE lockmode);
-static void ATExecAddColumn(AlteredTableInfo *tab, Relation rel,
-				ColumnDef *colDef, bool isOid, LOCKMODE lockmode);
+static void ATExecAddColumn(List **wqueue, AlteredTableInfo *tab, Relation rel,
+				ColumnDef *colDef, bool isOid,
+				bool recurse, bool recursing, LOCKMODE lockmode);
 static void add_column_datatype_dependency(Oid relid, int32 attnum, Oid typid, Oid collid);
 static void ATPrepAddOids(List **wqueue, Relation rel, bool recurse,
 			  AlterTableCmd *cmd, LOCKMODE lockmode);
@@ -2775,15 +2774,15 @@ ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
 		case AT_AddColumn:		/* ADD COLUMN */
 			ATSimplePermissions(rel,
 				ATT_TABLE|ATT_COMPOSITE_TYPE|ATT_FOREIGN_TABLE);
-			/* Performs own recursion */
 			ATPrepAddColumn(wqueue, rel, recurse, recursing, cmd, lockmode);
+			/* Recursion occurs during execution phase */
 			pass = AT_PASS_ADD_COL;
 			break;
 		case AT_AddColumnToView:		/* add column via CREATE OR REPLACE
 										 * VIEW */
 			ATSimplePermissions(rel, ATT_VIEW);
-			/* Performs own recursion */
 			ATPrepAddColumn(wqueue, rel, recurse, recursing, cmd, lockmode);
+			/* Recursion occurs during execution phase */
 			pass = AT_PASS_ADD_COL;
 			break;
 		case AT_ColumnDefault:	/* ALTER COLUMN DEFAULT */
@@ -2885,9 +2884,9 @@ ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
 			break;
 		case AT_AddOids:		/* SET WITH OIDS */
 			ATSimplePermissions(rel, ATT_TABLE);
-			/* Performs own recursion */
 			if (!rel->rd_rel->relhasoids || recursing)
 				ATPrepAddOids(wqueue, rel, recurse, cmd, lockmode);
+			/* Recursion occurs during execution phase */
 			pass = AT_PASS_ADD_COL;
 			break;
 		case AT_DropOids:		/* SET WITHOUT OIDS */
@@ -3043,7 +3042,12 @@ ATExecCmd(List **wqueue, AlteredTableInfo *tab, Relation rel,
 		case AT_AddColumn:		/* ADD COLUMN */
 		case AT_AddColumnToView:		/* add column via CREATE OR REPLACE
 										 * VIEW */
-			ATExecAddColumn(tab, rel, (ColumnDef *) cmd->def, false, lockmode);
+			ATExecAddColumn(wqueue, tab, rel, (ColumnDef *) cmd->def,
+							false, false, false, lockmode);
+			break;
+		case AT_AddColumnRecurse:
+			ATExecAddColumn(wqueue, tab, rel, (ColumnDef *) cmd->def,
+							false, true, false, lockmode);
 			break;
 		case AT_ColumnDefault:	/* ALTER COLUMN DEFAULT */
 			ATExecColumnDefault(rel, cmd->name, cmd->def, lockmode);
@@ -3121,7 +3125,14 @@ ATExecCmd(List **wqueue, AlteredTableInfo *tab, Relation rel,
 		case AT_AddOids:		/* SET WITH OIDS */
 			/* Use the ADD COLUMN code, unless prep decided to do nothing */
 			if (cmd->def != NULL)
-				ATExecAddColumn(tab, rel, (ColumnDef *) cmd->def, true, lockmode);
+				ATExecAddColumn(wqueue, tab, rel, (ColumnDef *) cmd->def,
+								true, false, false, lockmode);
+			break;
+		case AT_AddOidsRecurse:	/* SET WITH OIDS */
+			/* Use the ADD COLUMN code, unless prep decided to do nothing */
+			if (cmd->def != NULL)
+				ATExecAddColumn(wqueue, tab, rel, (ColumnDef *) cmd->def,
+								true, true, false, lockmode);
 			break;
 		case AT_DropOids:		/* SET WITHOUT OIDS */
 
@@ -3842,37 +3853,6 @@ ATSimpleRecursion(List **wqueue, Relation rel,
 	}
 }
 
-/*
- * ATOneLevelRecursion
- *
- * Here, we visit only direct inheritance children.  It is expected that
- * the command's prep routine will recurse again to find indirect children.
- * When using this technique, a multiply-inheriting child will be visited
- * multiple times.
- */
-static void
-ATOneLevelRecursion(List **wqueue, Relation rel,
-					AlterTableCmd *cmd, LOCKMODE lockmode)
-{
-	Oid			relid = RelationGetRelid(rel);
-	ListCell   *child;
-	List	   *children;
-
-	children = find_inheritance_children(relid, lockmode);
-
-	foreach(child, children)
-	{
-		Oid			childrelid = lfirst_oid(child);
-		Relation	childrel;
-
-		/* find_inheritance_children already got lock */
-		childrel = relation_open(childrelid, NoLock);
-		CheckTableNotInUse(childrel, "ALTER TABLE");
-		ATPrepCmd(wqueue, childrel, cmd, true, true, lockmode);
-		relation_close(childrel, NoLock);
-	}
-}
-
 /*
  * ATTypedTableRecursion
  *
@@ -4060,6 +4040,12 @@ find_typed_table_dependencies(Oid typeOid, const char *typeName, DropBehavior be
  * CHECK, NOT NULL, and FOREIGN KEY constraints will be removed from the
  * AT_AddColumn AlterTableCmd by parse_utilcmd.c and added as independent
  * AlterTableCmd's.
+ *
+ * ADD COLUMN cannot use the normal ALTER TABLE recursion mechanism, because we
+ * have to decide at runtime whether to recurse or not depending on whether we
+ * actually add a column or merely merge with an existing column.  (We can't
+ * check this in a static pre-pass because it won't handle multiple inheritance
+ * situations correctly.)
  */
 static void
 ATPrepAddColumn(List **wqueue, Relation rel, bool recurse, bool recursing,
@@ -4070,43 +4056,17 @@ ATPrepAddColumn(List **wqueue, Relation rel, bool recurse, bool recursing,
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 				 errmsg("cannot add column to typed table")));
 
-	/*
-	 * Recurse to add the column to child classes, if requested.
-	 *
-	 * We must recurse one level at a time, so that multiply-inheriting
-	 * children are visited the right number of times and end up with the
-	 * right attinhcount.
-	 */
-	if (recurse)
-	{
-		AlterTableCmd *childCmd = copyObject(cmd);
-		ColumnDef  *colDefChild = (ColumnDef *) childCmd->def;
-
-		/* Child should see column as singly inherited */
-		colDefChild->inhcount = 1;
-		colDefChild->is_local = false;
-
-		ATOneLevelRecursion(wqueue, rel, childCmd, lockmode);
-	}
-	else
-	{
-		/*
-		 * If we are told not to recurse, there had better not be any child
-		 * tables; else the addition would put them out of step.
-		 */
-		if (find_inheritance_children(RelationGetRelid(rel), NoLock) != NIL)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-					 errmsg("column must be added to child tables too")));
-	}
-
 	if (rel->rd_rel->relkind == RELKIND_COMPOSITE_TYPE)
 		ATTypedTableRecursion(wqueue, rel, cmd, lockmode);
+
+	if (recurse)
+		cmd->subtype = AT_AddColumnRecurse;
 }
 
 static void
-ATExecAddColumn(AlteredTableInfo *tab, Relation rel,
-				ColumnDef *colDef, bool isOid, LOCKMODE lockmode)
+ATExecAddColumn(List **wqueue, AlteredTableInfo *tab, Relation rel,
+				ColumnDef *colDef, bool isOid,
+				bool recurse, bool recursing, LOCKMODE lockmode)
 {
 	Oid			myrelid = RelationGetRelid(rel);
 	Relation	pgclass,
@@ -4121,12 +4081,20 @@ ATExecAddColumn(AlteredTableInfo *tab, Relation rel,
 	Oid			collOid;
 	Form_pg_type tform;
 	Expr	   *defval;
+	List	   *children;
+	ListCell   *child;
+
+	/* At top level, permission check was done in ATPrepCmd, else do it */
+	if (recursing)
+		ATSimplePermissions(rel, ATT_TABLE);
 
 	attrdesc = heap_open(AttributeRelationId, RowExclusiveLock);
 
 	/*
 	 * Are we adding the column to a recursion child?  If so, check whether to
-	 * merge with an existing definition for the column.
+	 * merge with an existing definition for the column.  If we do merge,
+	 * we must not recurse.  Children will already have the column, and
+     * recursing into them would mess up attinhcount.
 	 */
 	if (colDef->inhcount > 0)
 	{
@@ -4389,6 +4357,50 @@ ATExecAddColumn(AlteredTableInfo *tab, Relation rel,
 	 * Add needed dependency entries for the new column.
 	 */
 	add_column_datatype_dependency(myrelid, newattnum, attribute.atttypid, attribute.attcollation);
+
+	/*
+	 * Propagate to children as appropriate.  Unlike most other ALTER
+	 * routines, we have to do this one level of recursion at a time; we can't
+	 * use find_all_inheritors to do it in one pass.
+	 */
+	children = find_inheritance_children(RelationGetRelid(rel), lockmode);
+
+	/*
+	 * If we are told not to recurse, there had better not be any child
+	 * tables; else the addition would put them out of step.
+	 */
+	if (children && !recurse)
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+				 errmsg("column must be added to child tables too")));
+
+	/* Children should see column as singly inherited */
+	if (!recursing)
+	{
+		colDef = copyObject(colDef);
+		colDef->inhcount = 1;
+		colDef->is_local = false;
+	}
+
+	foreach(child, children)
+	{
+		Oid			childrelid = lfirst_oid(child);
+		Relation	childrel;
+		AlteredTableInfo *childtab;
+
+		/* find_inheritance_children already got lock */
+		childrel = heap_open(childrelid, NoLock);
+		CheckTableNotInUse(childrel, "ALTER TABLE");
+
+		/* Find or create work queue entry for this table */
+		childtab = ATGetQueueEntry(wqueue, childrel);
+
+		/* Recurse to child */
+		ATExecAddColumn(wqueue, childtab, childrel,
+						colDef, isOid, recurse, true, lockmode);
+
+		heap_close(childrel, NoLock);
+	}
 }
 
 /*
@@ -4440,6 +4452,9 @@ ATPrepAddOids(List **wqueue, Relation rel, bool recurse, AlterTableCmd *cmd, LOC
 		cmd->def = (Node *) cdef;
 	}
 	ATPrepAddColumn(wqueue, rel, recurse, false, cmd, lockmode);
+
+	if (recurse)
+		cmd->subtype = AT_AddOidsRecurse;
 }
 
 /*

src/include/nodes/parsenodes.h

@@ -1173,6 +1173,7 @@ typedef struct AlterTableStmt
 typedef enum AlterTableType
 {
 	AT_AddColumn,				/* add column */
+	AT_AddColumnRecurse,		/* internal to commands/tablecmds.c */
 	AT_AddColumnToView,			/* implicitly via CREATE OR REPLACE VIEW */
 	AT_ColumnDefault,			/* alter column default */
 	AT_DropNotNull,				/* alter column drop not null */
@@ -1198,6 +1199,7 @@ typedef enum AlterTableType
 	AT_ClusterOn,				/* CLUSTER ON */
 	AT_DropCluster,				/* SET WITHOUT CLUSTER */
 	AT_AddOids,					/* SET WITH OIDS */
+	AT_AddOidsRecurse,			/* internal to commands/tablecmds.c */
 	AT_DropOids,				/* SET WITHOUT OIDS */
 	AT_SetTableSpace,			/* SET TABLESPACE */
 	AT_SetRelOptions,			/* SET (...) -- AM specific parameters */

src/test/regress/expected/alter_table.out

@@ -1198,6 +1198,23 @@ drop table p1, p2 cascade;
 NOTICE:  drop cascades to 2 other objects
 DETAIL:  drop cascades to table c1
 drop cascades to table gc1
+-- test attinhcount tracking with merged columns
+create table depth0();
+create table depth1(c text) inherits (depth0);
+create table depth2() inherits (depth1);
+alter table depth0 add c text;
+NOTICE:  merging definition of column "c" for child "depth1"
+select attrelid::regclass, attname, attinhcount, attislocal
+from pg_attribute
+where attnum > 0 and attrelid::regclass in ('depth0', 'depth1', 'depth2')
+order by attrelid::regclass::text, attnum;
+ attrelid | attname | attinhcount | attislocal 
+----------+---------+-------------+------------
+ depth0   | c       |           0 | t
+ depth1   | c       |           1 | t
+ depth2   | c       |           1 | f
+(3 rows)
+
 --
 -- Test the ALTER TABLE SET WITH/WITHOUT OIDS command
 --

src/test/regress/sql/alter_table.sql

@@ -944,6 +944,18 @@ order by relname, attnum;
 
 drop table p1, p2 cascade;
 
+-- test attinhcount tracking with merged columns
+
+create table depth0();
+create table depth1(c text) inherits (depth0);
+create table depth2() inherits (depth1);
+alter table depth0 add c text;
+
+select attrelid::regclass, attname, attinhcount, attislocal
+from pg_attribute
+where attnum > 0 and attrelid::regclass in ('depth0', 'depth1', 'depth2')
+order by attrelid::regclass::text, attnum;
+
 --
 -- Test the ALTER TABLE SET WITH/WITHOUT OIDS command
 --