Fix usage of "tableoid" in GENERATED expressions.

We consider this supported (though I've got my doubts that it's a
good idea, because tableoid is not immutable).  However, several
code paths failed to fill the field in soon enough, causing such
a GENERATED expression to see zero or the wrong value.  This
occurred when ALTER TABLE adds a new GENERATED column to a table
with existing rows, and during regular INSERT or UPDATE on a
foreign table with GENERATED columns.

Noted during investigation of a report from Vitaly Ustinov.
Back-patch to v12 where GENERATED came in.

Discussion: https://postgr.es/m/CAM_DEiWR2DPT6U4xb-Ehigozzd3n3G37ZB1+867zbsEVtYoJww@mail.gmail.com

2 files changed, 26 insertions, 11 deletions

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index ebc62034d26..85dcc330638 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -5762,6 +5762,14 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap, LOCKMODE lockmode)
 					newslot->tts_isnull[lfirst_int(lc)] = true;
 
 				/*
+				 * Constraints and GENERATED expressions might reference the
+				 * tableoid column, so fill tts_tableOid with the desired
+				 * value.  (We must do this each time, because it gets
+				 * overwritten with newrel's OID during storing.)
+				 */
+				newslot->tts_tableOid = RelationGetRelid(oldrel);
+
+				/*
 				 * Process supplied expressions to replace selected columns.
 				 *
 				 * First, evaluate expressions whose inputs come from the old
@@ -5804,11 +5812,6 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap, LOCKMODE lockmode)
 									   &newslot->tts_isnull[ex->attnum - 1]);
 				}
 
-				/*
-				 * Constraints might reference the tableoid column, so
-				 * initialize t_tableOid before evaluating them.
-				 */
-				newslot->tts_tableOid = RelationGetRelid(oldrel);
 				insertslot = newslot;
 			}
 			else
diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
index 0816027f7f7..379b0563105 100644
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -659,6 +659,12 @@ ExecInsert(ModifyTableState *mtstate,
 	else if (resultRelInfo->ri_FdwRoutine)
 	{
 		/*
+		 * GENERATED expressions might reference the tableoid column, so
+		 * (re-)initialize tts_tableOid before evaluating them.
+		 */
+		slot->tts_tableOid = RelationGetRelid(resultRelInfo->ri_RelationDesc);
+
+		/*
 		 * Compute stored generated columns
 		 */
 		if (resultRelationDesc->rd_att->constr &&
@@ -729,7 +735,7 @@ ExecInsert(ModifyTableState *mtstate,
 		/*
 		 * AFTER ROW Triggers or RETURNING expressions might reference the
 		 * tableoid column, so (re-)initialize tts_tableOid before evaluating
-		 * them.
+		 * them.  (This covers the case where the FDW replaced the slot.)
 		 */
 		slot->tts_tableOid = RelationGetRelid(resultRelInfo->ri_RelationDesc);
 	}
@@ -738,8 +744,8 @@ ExecInsert(ModifyTableState *mtstate,
 		WCOKind		wco_kind;
 
 		/*
-		 * Constraints might reference the tableoid column, so (re-)initialize
-		 * tts_tableOid before evaluating them.
+		 * Constraints and GENERATED expressions might reference the tableoid
+		 * column, so (re-)initialize tts_tableOid before evaluating them.
 		 */
 		slot->tts_tableOid = RelationGetRelid(resultRelationDesc);
 
@@ -1630,6 +1636,12 @@ ExecUpdate(ModifyTableState *mtstate,
 	else if (resultRelInfo->ri_FdwRoutine)
 	{
 		/*
+		 * GENERATED expressions might reference the tableoid column, so
+		 * (re-)initialize tts_tableOid before evaluating them.
+		 */
+		slot->tts_tableOid = RelationGetRelid(resultRelInfo->ri_RelationDesc);
+
+		/*
 		 * Compute stored generated columns
 		 */
 		if (resultRelationDesc->rd_att->constr &&
@@ -1651,7 +1663,7 @@ ExecUpdate(ModifyTableState *mtstate,
 		/*
 		 * AFTER ROW Triggers or RETURNING expressions might reference the
 		 * tableoid column, so (re-)initialize tts_tableOid before evaluating
-		 * them.
+		 * them.  (This covers the case where the FDW replaced the slot.)
 		 */
 		slot->tts_tableOid = RelationGetRelid(resultRelationDesc);
 	}
@@ -1662,8 +1674,8 @@ ExecUpdate(ModifyTableState *mtstate,
 		bool		update_indexes;
 
 		/*
-		 * Constraints might reference the tableoid column, so (re-)initialize
-		 * tts_tableOid before evaluating them.
+		 * Constraints and GENERATED expressions might reference the tableoid
+		 * column, so (re-)initialize tts_tableOid before evaluating them.
 		 */
 		slot->tts_tableOid = RelationGetRelid(resultRelationDesc);