Add 'missing_ok' argument to build_attrmap_by_name

When it's given as true, return a 0 in the position of the missing
column rather than raising an error.

This is currently unused, but it allows us to reimplement column
permission checking in a subsequent commit.  It seems worth breaking
into a separate commit because it affects unrelated code.

Author: Amit Langote <amitlangote09@gmail.com>
Discussion: https://postgr.es/m/CA+HiwqFfiai=qBxPDTjaio_ZcaqUKh+FC=prESrB8ogZgFNNNQ@mail.gmail.com

src/backend/access/common/attmap.c

@@ -169,10 +169,15 @@ build_attrmap_by_position(TupleDesc indesc,
  * and output columns by name.  (Dropped columns are ignored in both input and
  * output.)  This is normally a subroutine for convert_tuples_by_name in
  * tupconvert.c, but can be used standalone.
+ *
+ * If 'missing_ok' is true, a column from 'outdesc' not being present in
+ * 'indesc' is not flagged as an error; AttrMap.attnums[] entry for such an
+ * outdesc column will be 0 in that case.
  */
 AttrMap *
 build_attrmap_by_name(TupleDesc indesc,
-					  TupleDesc outdesc)
+					  TupleDesc outdesc,
+					  bool missing_ok)
 {
 	AttrMap    *attrMap;
 	int			outnatts;
@@ -235,7 +240,7 @@ build_attrmap_by_name(TupleDesc indesc,
 				break;
 			}
 		}
-		if (attrMap->attnums[i] == 0)
+		if (attrMap->attnums[i] == 0 && !missing_ok)
 			ereport(ERROR,
 					(errcode(ERRCODE_DATATYPE_MISMATCH),
 					 errmsg("could not convert row type"),
@@ -257,12 +262,13 @@ build_attrmap_by_name(TupleDesc indesc,
  */
 AttrMap *
 build_attrmap_by_name_if_req(TupleDesc indesc,
-							 TupleDesc outdesc)
+							 TupleDesc outdesc,
+							 bool missing_ok)
 {
 	AttrMap    *attrMap;
 
 	/* Verify compatibility and prepare attribute-number map */
-	attrMap = build_attrmap_by_name(indesc, outdesc);
+	attrMap = build_attrmap_by_name(indesc, outdesc, missing_ok);
 
 	/* Check if the map has a one-to-one match */
 	if (check_attrmap_match(indesc, outdesc, attrMap))

src/backend/access/common/tupconvert.c

@@ -107,7 +107,7 @@ convert_tuples_by_name(TupleDesc indesc,
 	int			n = outdesc->natts;
 
 	/* Verify compatibility and prepare attribute-number map */
-	attrMap = build_attrmap_by_name_if_req(indesc, outdesc);
+	attrMap = build_attrmap_by_name_if_req(indesc, outdesc, false);
 
 	if (attrMap == NULL)
 	{

src/backend/catalog/partition.c

@@ -227,7 +227,8 @@ map_partition_varattnos(List *expr, int fromrel_varno,
 		bool		found_whole_row;
 
 		part_attmap = build_attrmap_by_name(RelationGetDescr(to_rel),
-											RelationGetDescr(from_rel));
+											RelationGetDescr(from_rel),
+											false);
 		expr = (List *) map_variable_attnos((Node *) expr,
 											fromrel_varno, 0,
 											part_attmap,

src/backend/commands/indexcmds.c

@@ -1290,7 +1290,8 @@ DefineIndex(Oid relationId,
 				childidxs = RelationGetIndexList(childrel);
 				attmap =
 					build_attrmap_by_name(RelationGetDescr(childrel),
-										  parentDesc);
+										  parentDesc,
+										  false);
 
 				foreach(cell, childidxs)
 				{

src/backend/commands/tablecmds.c

@@ -1206,7 +1206,8 @@ DefineRelation(CreateStmt *stmt, char relkind, Oid ownerId,
 			}
 
 			attmap = build_attrmap_by_name(RelationGetDescr(rel),
-										   RelationGetDescr(parent));
+										   RelationGetDescr(parent),
+										   false);
 			idxstmt =
 				generateClonedIndexStmt(NULL, idxRel,
 										attmap, &constraintOid);
@@ -9647,7 +9648,8 @@ addFkRecurseReferenced(List **wqueue, Constraint *fkconstraint, Relation rel,
 			 * definition to match the partition's column layout.
 			 */
 			map = build_attrmap_by_name_if_req(RelationGetDescr(partRel),
-											   RelationGetDescr(pkrel));
+											   RelationGetDescr(pkrel),
+											   false);
 			if (map)
 			{
 				mapped_pkattnum = palloc(sizeof(AttrNumber) * numfks);
@@ -9814,7 +9816,8 @@ addFkRecurseReferencing(List **wqueue, Constraint *fkconstraint, Relation rel,
 			CheckTableNotInUse(partition, "ALTER TABLE");
 
 			attmap = build_attrmap_by_name(RelationGetDescr(partition),
-										   RelationGetDescr(rel));
+										   RelationGetDescr(rel),
+										   false);
 			for (int j = 0; j < numfks; j++)
 				mapped_fkattnum[j] = attmap->attnums[fkattnum[j] - 1];
 
@@ -10022,7 +10025,8 @@ CloneFkReferenced(Relation parentRel, Relation partitionRel)
 	trigrel = table_open(TriggerRelationId, RowExclusiveLock);
 
 	attmap = build_attrmap_by_name(RelationGetDescr(partitionRel),
-								   RelationGetDescr(parentRel));
+								   RelationGetDescr(parentRel),
+								   false);
 	foreach(cell, clone)
 	{
 		Oid			constrOid = lfirst_oid(cell);
@@ -10219,7 +10223,8 @@ CloneFkReferencing(List **wqueue, Relation parentRel, Relation partRel)
 	 * different.  This map is used to convert them.
 	 */
 	attmap = build_attrmap_by_name(RelationGetDescr(partRel),
-								   RelationGetDescr(parentRel));
+								   RelationGetDescr(parentRel),
+								   false);
 
 	partFKs = copyObject(RelationGetFKeyList(partRel));
 
@@ -12335,7 +12340,8 @@ ATPrepAlterColumnType(List **wqueue,
 				cmd = copyObject(cmd);
 
 				attmap = build_attrmap_by_name(RelationGetDescr(childrel),
-											   RelationGetDescr(rel));
+											   RelationGetDescr(rel),
+											   false);
 				((ColumnDef *) cmd->def)->cooked_default =
 					map_variable_attnos(def->cooked_default,
 										1, 0,
@@ -18043,7 +18049,8 @@ AttachPartitionEnsureIndexes(Relation rel, Relation attachrel)
 		/* construct an indexinfo to compare existing indexes against */
 		info = BuildIndexInfo(idxRel);
 		attmap = build_attrmap_by_name(RelationGetDescr(attachrel),
-									   RelationGetDescr(rel));
+									   RelationGetDescr(rel),
+									   false);
 		constraintOid = get_relation_idx_constraint_oid(RelationGetRelid(rel), idx);
 
 		/*
@@ -18981,7 +18988,8 @@ ATExecAttachPartitionIdx(List **wqueue, Relation parentIdx, RangeVar *name)
 		childInfo = BuildIndexInfo(partIdx);
 		parentInfo = BuildIndexInfo(parentIdx);
 		attmap = build_attrmap_by_name(RelationGetDescr(partTbl),
-									   RelationGetDescr(parentTbl));
+									   RelationGetDescr(parentTbl),
+									   false);
 		if (!CompareIndexInfo(childInfo, parentInfo,
 							  partIdx->rd_indcollation,
 							  parentIdx->rd_indcollation,

src/backend/executor/execMain.c

@@ -1859,7 +1859,7 @@ ExecPartitionCheckEmitError(ResultRelInfo *resultRelInfo,
 
 		old_tupdesc = RelationGetDescr(resultRelInfo->ri_RelationDesc);
 		/* a reverse map */
-		map = build_attrmap_by_name_if_req(old_tupdesc, tupdesc);
+		map = build_attrmap_by_name_if_req(old_tupdesc, tupdesc, false);
 
 		/*
 		 * Partition-specific slot's tupdesc can't be changed, so allocate a
@@ -1944,7 +1944,8 @@ ExecConstraints(ResultRelInfo *resultRelInfo,
 					tupdesc = RelationGetDescr(rootrel->ri_RelationDesc);
 					/* a reverse map */
 					map = build_attrmap_by_name_if_req(orig_tupdesc,
-													   tupdesc);
+													   tupdesc,
+													   false);
 
 					/*
 					 * Partition-specific slot's tupdesc can't be changed, so
@@ -1996,7 +1997,8 @@ ExecConstraints(ResultRelInfo *resultRelInfo,
 				tupdesc = RelationGetDescr(rootrel->ri_RelationDesc);
 				/* a reverse map */
 				map = build_attrmap_by_name_if_req(old_tupdesc,
-												   tupdesc);
+												   tupdesc,
+												   false);
 
 				/*
 				 * Partition-specific slot's tupdesc can't be changed, so
@@ -2103,7 +2105,8 @@ ExecWithCheckOptions(WCOKind kind, ResultRelInfo *resultRelInfo,
 						tupdesc = RelationGetDescr(rootrel->ri_RelationDesc);
 						/* a reverse map */
 						map = build_attrmap_by_name_if_req(old_tupdesc,
-														   tupdesc);
+														   tupdesc,
+														   false);
 
 						/*
 						 * Partition-specific slot's tupdesc can't be changed,

src/backend/executor/execPartition.c

@@ -582,7 +582,8 @@ ExecInitPartitionInfo(ModifyTableState *mtstate, EState *estate,
 		 */
 		part_attmap =
 			build_attrmap_by_name(RelationGetDescr(partrel),
-								  RelationGetDescr(firstResultRel));
+								  RelationGetDescr(firstResultRel),
+								  false);
 		wcoList = (List *)
 			map_variable_attnos((Node *) wcoList,
 								firstVarno, 0,
@@ -639,7 +640,8 @@ ExecInitPartitionInfo(ModifyTableState *mtstate, EState *estate,
 		if (part_attmap == NULL)
 			part_attmap =
 				build_attrmap_by_name(RelationGetDescr(partrel),
-									  RelationGetDescr(firstResultRel));
+									  RelationGetDescr(firstResultRel),
+									  false);
 		returningList = (List *)
 			map_variable_attnos((Node *) returningList,
 								firstVarno, 0,
@@ -780,7 +782,8 @@ ExecInitPartitionInfo(ModifyTableState *mtstate, EState *estate,
 				if (part_attmap == NULL)
 					part_attmap =
 						build_attrmap_by_name(RelationGetDescr(partrel),
-											  RelationGetDescr(firstResultRel));
+											  RelationGetDescr(firstResultRel),
+											  false);
 				onconflset = (List *)
 					map_variable_attnos((Node *) onconflset,
 										INNER_VAR, 0,
@@ -878,7 +881,8 @@ ExecInitPartitionInfo(ModifyTableState *mtstate, EState *estate,
 		if (part_attmap == NULL)
 			part_attmap =
 				build_attrmap_by_name(RelationGetDescr(partrel),
-									  RelationGetDescr(firstResultRel));
+									  RelationGetDescr(firstResultRel),
+									  false);
 
 		if (unlikely(!leaf_part_rri->ri_projectNewInfoValid))
 			ExecInitMergeTupleSlots(mtstate, leaf_part_rri);
@@ -1147,7 +1151,8 @@ ExecInitPartitionDispatchInfo(EState *estate,
 		 * routing.
 		 */
 		pd->tupmap = build_attrmap_by_name_if_req(RelationGetDescr(parent_pd->reldesc),
-												  tupdesc);
+												  tupdesc,
+												  false);
 		pd->tupslot = pd->tupmap ?
 			MakeSingleTupleTableSlot(tupdesc, &TTSOpsVirtual) : NULL;
 	}

src/backend/parser/parse_utilcmd.c

@@ -1232,7 +1232,8 @@ expandTableLikeClause(RangeVar *heapRel, TableLikeClause *table_like_clause)
 	 * have a failure since both tables are locked.
 	 */
 	attmap = build_attrmap_by_name(RelationGetDescr(childrel),
-								   tupleDesc);
+								   tupleDesc,
+								   false);
 
 	/*
 	 * Process defaults, if required.

src/backend/replication/pgoutput/pgoutput.c

@@ -1125,7 +1125,7 @@ init_tuple_slot(PGOutputData *data, Relation relation,
 		/* Map must live as long as the session does. */
 		oldctx = MemoryContextSwitchTo(CacheMemoryContext);
 
-		entry->attrmap = build_attrmap_by_name_if_req(indesc, outdesc);
+		entry->attrmap = build_attrmap_by_name_if_req(indesc, outdesc, false);
 
 		MemoryContextSwitchTo(oldctx);
 		RelationClose(ancestor);

src/include/access/attmap.h

@@ -42,9 +42,11 @@ extern void free_attrmap(AttrMap *map);
 
 /* Conversion routines to build mappings */
 extern AttrMap *build_attrmap_by_name(TupleDesc indesc,
-									  TupleDesc outdesc);
+									  TupleDesc outdesc,
+									  bool missing_ok);
 extern AttrMap *build_attrmap_by_name_if_req(TupleDesc indesc,
-											 TupleDesc outdesc);
+											 TupleDesc outdesc,
+											 bool missing_ok);
 extern AttrMap *build_attrmap_by_position(TupleDesc indesc,
 										  TupleDesc outdesc,
 										  const char *msg);