Don't allow system columns in CHECK constraints, except tableoid.

Previously, arbitray system columns could be mentioned in table
constraints, but they were not correctly checked at runtime, because
the values weren't actually set correctly in the tuple.  Since it
seems easy enough to initialize the table OID properly, do that,
and continue allowing that column, but disallow the rest unless and
until someone figures out a way to make them work properly.

No back-patch, because this doesn't seem important enough to take the
risk of destabilizing the back branches.  In fact, this will pose a
dump-and-reload hazard for those upgrading from previous versions:
constraints that were accepted before but were not correctly enforced
will now either be enforced correctly or not accepted at all.  Either
could result in restore failures, but in practice I think very few
users will notice the difference, since the use case is pretty
marginal anyway and few users will be relying on features that have
not historically worked.

Amit Kapila, reviewed by Rushabh Lathia, with doc changes by me.

doc/src/sgml/ref/create_table.sgml

@@ -430,7 +430,8 @@ CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXI
      <para>
       Currently, <literal>CHECK</literal> expressions cannot contain
       subqueries nor refer to variables other than columns of the
-      current row.
+      current row.  The system column <literal>tableoid</literal>
+      may be referenced, but not any other system column.
      </para>
 
      <para>

src/backend/commands/copy.c

@@ -2217,6 +2217,12 @@ CopyFrom(CopyState cstate)
 		if (loaded_oid != InvalidOid)
 			HeapTupleSetOid(tuple, loaded_oid);
 
+		/*
+		 * Constraints might reference the tableoid column, so initialize
+		 * t_tableOid before evaluating them.
+		 */
+		tuple->t_tableOid = RelationGetRelid(resultRelInfo->ri_RelationDesc);
+
 		/* Triggers and stuff need to be invoked in query context. */
 		MemoryContextSwitchTo(oldcontext);
 

src/backend/commands/tablecmds.c

@@ -3857,6 +3857,12 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap, LOCKMODE lockmode)
 				/* Preserve OID, if any */
 				if (newTupDesc->tdhasoid)
 					HeapTupleSetOid(tuple, tupOid);
+
+				/*
+				 * Constraints might reference the tableoid column, so initialize
+				 * t_tableOid before evaluating them.
+				 */
+				tuple->t_tableOid = RelationGetRelid(oldrel);
 			}
 
 			/* Now check any constraints on the possibly-changed tuple */

src/backend/executor/nodeModifyTable.c

@@ -246,6 +246,12 @@ ExecInsert(TupleTableSlot *slot,
 	}
 	else
 	{
+		/*
+		 * Constraints might reference the tableoid column, so initialize
+		 * t_tableOid before evaluating them.
+		 */
+		tuple->t_tableOid = RelationGetRelid(resultRelationDesc);
+
 		/*
 		 * Check the constraints of the tuple
 		 */
@@ -653,6 +659,12 @@ ExecUpdate(ItemPointer tupleid,
 	{
 		LockTupleMode lockmode;
 
+		/*
+		 * Constraints might reference the tableoid column, so initialize
+		 * t_tableOid before evaluating them.
+		 */
+		tuple->t_tableOid = RelationGetRelid(resultRelationDesc);
+
 		/*
 		 * Check the constraints of the tuple
 		 *

src/backend/parser/parse_relation.c

@@ -551,6 +551,16 @@ scanRTEForColumn(ParseState *pstate, RangeTblEntry *rte, char *colname,
 	{
 		/* quick check to see if name could be a system column */
 		attnum = specialAttNum(colname);
+
+		/* In constraint check, no system column is allowed except tableOid */
+		if (pstate->p_expr_kind == EXPR_KIND_CHECK_CONSTRAINT &&
+			attnum < InvalidAttrNumber && attnum !=  TableOidAttributeNumber)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
+					 errmsg("system column \"%s\" reference in check constraint is invalid",
+						colname),
+					 parser_errposition(pstate, location)));
+
 		if (attnum != InvalidAttrNumber)
 		{
 			/* now check to see if column actually is defined */

src/test/regress/input/constraints.source

@@ -126,6 +126,28 @@ INSERT INTO INSERT_TBL VALUES (null, null, null);
 
 SELECT '' AS nine, * FROM INSERT_TBL;
 
+--
+-- Check constraints on system columns
+--
+
+CREATE TABLE SYS_COL_CHECK_TBL (city text, state text, is_capital bool,
+                  altitude int,
+                  CHECK (NOT (is_capital AND tableoid::regclass::text = 'sys_col_check_tbl')));
+
+INSERT INTO SYS_COL_CHECK_TBL VALUES ('Seattle', 'Washington', false, 100);
+INSERT INTO SYS_COL_CHECK_TBL VALUES ('Olympia', 'Washington', true, 100);
+
+SELECT *, tableoid::regclass::text FROM SYS_COL_CHECK_TBL;
+
+DROP TABLE SYS_COL_CHECK_TBL;
+
+--
+-- Check constraints on system columns other then TableOid should return error
+--
+CREATE TABLE SYS_COL_CHECK_TBL (city text, state text, is_capital bool,
+                  altitude int,
+				  CHECK (NOT (is_capital AND ctid::text = 'sys_col_check_tbl')));
+
 --
 -- Check inheritance of defaults and constraints
 --

src/test/regress/output/constraints.source

@@ -204,6 +204,30 @@ SELECT '' AS nine, * FROM INSERT_TBL;
       |   |               |   
 (7 rows)
 
+--
+-- Check constraints on system columns
+--
+CREATE TABLE SYS_COL_CHECK_TBL (city text, state text, is_capital bool,
+                  altitude int,
+                  CHECK (NOT (is_capital AND tableoid::regclass::text = 'sys_col_check_tbl')));
+INSERT INTO SYS_COL_CHECK_TBL VALUES ('Seattle', 'Washington', false, 100);
+INSERT INTO SYS_COL_CHECK_TBL VALUES ('Olympia', 'Washington', true, 100);
+ERROR:  new row for relation "sys_col_check_tbl" violates check constraint "sys_col_check_tbl_check"
+DETAIL:  Failing row contains (Olympia, Washington, t, 100).
+SELECT *, tableoid::regclass::text FROM SYS_COL_CHECK_TBL;
+  city   |   state    | is_capital | altitude |     tableoid      
+---------+------------+------------+----------+-------------------
+ Seattle | Washington | f          |      100 | sys_col_check_tbl
+(1 row)
+
+DROP TABLE SYS_COL_CHECK_TBL;
+--
+-- Check constraints on system columns other then TableOid should return error
+--
+CREATE TABLE SYS_COL_CHECK_TBL (city text, state text, is_capital bool,
+                  altitude int,
+				  CHECK (NOT (is_capital AND ctid::text = 'sys_col_check_tbl')));
+ERROR:  system column "ctid" reference in check constraint is invalid
 --
 -- Check inheritance of defaults and constraints
 --