Make ExecGetInsertedCols() and friends more robust and improve comments.

If ExecGetInsertedCols(), ExecGetUpdatedCols() or ExecGetExtraUpdatedCols()
were called with a ResultRelInfo that's not in the range table and isn't a
partition routing target, the functions would dereference a NULL pointer,
relinfo->ri_RootResultRelInfo. Such ResultRelInfos are created when firing
RI triggers in tables that are not modified directly. None of the current
callers of these functions pass such relations, so this isn't a live bug,
but let's make them more robust.

Also update comment in ResultRelInfo; after commit 6214e2b228,
ri_RangeTableIndex is zero for ResultRelInfos created for partition tuple
routing.

Noted by Coverity. Backpatch down to v11, like commit 6214e2b228.

Reviewed-by: Tom Lane, Amit Langote

src/backend/executor/execUtils.c

@@ -1231,9 +1231,9 @@ ExecGetInsertedCols(ResultRelInfo *relinfo, EState *estate)
 {
 	/*
 	 * The columns are stored in the range table entry.  If this ResultRelInfo
-	 * doesn't have an entry in the range table (i.e. if it represents a
+	 * represents a partition routing target, and doesn't have an entry of its
-	 * partition routing target), fetch the parent's RTE and map the columns
+	 * own in the range table, fetch the parent's RTE and map the columns to
-	 * to the order they are in the partition.
+	 * the order they are in the partition.
 	 */
 	if (relinfo->ri_RangeTableIndex != 0)
 	{
@@ -1241,7 +1241,7 @@ ExecGetInsertedCols(ResultRelInfo *relinfo, EState *estate)
 
 		return rte->insertedCols;
 	}
-	else
+	else if (relinfo->ri_RootResultRelInfo)
 	{
 		ResultRelInfo *rootRelInfo = relinfo->ri_RootResultRelInfo;
 		RangeTblEntry *rte = exec_rt_fetch(rootRelInfo->ri_RangeTableIndex, estate);
@@ -1252,6 +1252,16 @@ ExecGetInsertedCols(ResultRelInfo *relinfo, EState *estate)
 		else
 			return rte->insertedCols;
 	}
+	else
+	{
+		/*
+		 * The relation isn't in the range table and it isn't a partition
+		 * routing target.  This ResultRelInfo must've been created only for
+		 * firing triggers and the relation is not being inserted into.  (See
+		 * ExecGetTriggerResultRel.)
+		 */
+		return NULL;
+	}
 }
 
 /* Return a bitmap representing columns being updated */
@@ -1265,7 +1275,7 @@ ExecGetUpdatedCols(ResultRelInfo *relinfo, EState *estate)
 
 		return rte->updatedCols;
 	}
-	else
+	else if (relinfo->ri_RootResultRelInfo)
 	{
 		ResultRelInfo *rootRelInfo = relinfo->ri_RootResultRelInfo;
 		RangeTblEntry *rte = exec_rt_fetch(rootRelInfo->ri_RangeTableIndex, estate);
@@ -1276,6 +1286,8 @@ ExecGetUpdatedCols(ResultRelInfo *relinfo, EState *estate)
 		else
 			return rte->updatedCols;
 	}
+	else
+		return NULL;
 }
 
 /* Return a bitmap representing generated columns being updated */
@@ -1289,7 +1301,7 @@ ExecGetExtraUpdatedCols(ResultRelInfo *relinfo, EState *estate)
 
 		return rte->extraUpdatedCols;
 	}
-	else
+	else if (relinfo->ri_RootResultRelInfo)
 	{
 		ResultRelInfo *rootRelInfo = relinfo->ri_RootResultRelInfo;
 		RangeTblEntry *rte = exec_rt_fetch(rootRelInfo->ri_RangeTableIndex, estate);
@@ -1300,6 +1312,8 @@ ExecGetExtraUpdatedCols(ResultRelInfo *relinfo, EState *estate)
 		else
 			return rte->extraUpdatedCols;
 	}
+	else
+		return NULL;
 }
 
 /* Return columns being updated, including generated columns */

src/include/nodes/execnodes.h

@@ -394,12 +394,15 @@ typedef struct OnConflictSetState
  * relation, and perhaps also fire triggers.  ResultRelInfo holds all the
  * information needed about a result relation, including indexes.
  *
- * Normally, a ResultRelInfo refers to a table that is in the query's
+ * Normally, a ResultRelInfo refers to a table that is in the query's range
- * range table; then ri_RangeTableIndex is the RT index and ri_RelationDesc
+ * table; then ri_RangeTableIndex is the RT index and ri_RelationDesc is
- * is just a copy of the relevant es_relations[] entry.  But sometimes,
+ * just a copy of the relevant es_relations[] entry.  However, in some
- * in ResultRelInfos used only for triggers, ri_RangeTableIndex is zero
+ * situations we create ResultRelInfos for relations that are not in the
- * and ri_RelationDesc is a separately-opened relcache pointer that needs
+ * range table, namely for targets of tuple routing in a partitioned table,
- * to be separately closed.  See ExecGetTriggerResultRel.
+ * and when firing triggers in tables other than the target tables (See
+ * ExecGetTriggerResultRel).  In these situations, ri_RangeTableIndex is 0
+ * and ri_RelationDesc is a separately-opened relcache pointer that needs to
+ * be separately closed.
  */
 typedef struct ResultRelInfo
 {