Clean up handling of dropped columns in NAMEDTUPLESTORE RTEs.

The NAMEDTUPLESTORE patch piggybacked on the infrastructure for
TABLEFUNC/VALUES/CTE RTEs, none of which can ever have dropped columns,
so the possibility was ignored most places.  Fix that, including adding a
specification to parsenodes.h about what it's supposed to look like.

In passing, clean up assorted comments that hadn't been maintained
properly by said patch.

Per bug #14799 from Philippe Beaudoin.  Back-patch to v10.

Discussion: https://postgr.es/m/20170906120005.25630.84360@wrigleys.postgresql.org

src/backend/optimizer/util/relnode.c

@@ -178,8 +178,8 @@ build_simple_rel(PlannerInfo *root, int relid, RelOptInfo *parent)
 		case RTE_NAMEDTUPLESTORE:
 
 			/*
-			 * Subquery, function, tablefunc, or values list --- set up attr
-			 * range and arrays
+			 * Subquery, function, tablefunc, values list, CTE, or ENR --- set
+			 * up attr range and arrays
 			 *
 			 * Note: 0 is included in range to support whole-row Vars
 			 */

src/backend/parser/parse_relation.c

@@ -2014,11 +2014,13 @@ addRangeTableEntryForENR(ParseState *pstate,
 
 	/*
 	 * Build the list of effective column names using user-supplied aliases
-	 * and/or actual column names.  Also build the cannibalized fields.
+	 * and/or actual column names.
 	 */
 	tupdesc = ENRMetadataGetTupDesc(enrmd);
 	rte->eref = makeAlias(refname, NIL);
 	buildRelationAliases(tupdesc, alias, rte->eref);
+
+	/* Record additional data for ENR, including column type info */
 	rte->enrname = enrmd->name;
 	rte->enrtuples = enrmd->enrtuples;
 	rte->coltypes = NIL;
@@ -2028,16 +2030,24 @@ addRangeTableEntryForENR(ParseState *pstate,
 	{
 		Form_pg_attribute att = TupleDescAttr(tupdesc, attno - 1);
 
-		if (att->atttypid == InvalidOid &&
-			!(att->attisdropped))
-			elog(ERROR, "atttypid was invalid for column which has not been dropped from \"%s\"",
+		if (att->attisdropped)
+		{
+			/* Record zeroes for a dropped column */
+			rte->coltypes = lappend_oid(rte->coltypes, InvalidOid);
+			rte->coltypmods = lappend_int(rte->coltypmods, 0);
+			rte->colcollations = lappend_oid(rte->colcollations, InvalidOid);
+		}
+		else
+		{
+			/* Let's just make sure we can tell this isn't dropped */
+			if (att->atttypid == InvalidOid)
+				elog(ERROR, "atttypid is invalid for non-dropped column in \"%s\"",
 					 rv->relname);
-		rte->coltypes =
-			lappend_oid(rte->coltypes, att->atttypid);
-		rte->coltypmods =
-			lappend_int(rte->coltypmods, att->atttypmod);
-		rte->colcollations =
-			lappend_oid(rte->colcollations, att->attcollation);
+			rte->coltypes = lappend_oid(rte->coltypes, att->atttypid);
+			rte->coltypmods = lappend_int(rte->coltypmods, att->atttypmod);
+			rte->colcollations = lappend_oid(rte->colcollations,
+											 att->attcollation);
+		}
 	}
 
 	/*
@@ -2416,7 +2426,7 @@ expandRTE(RangeTblEntry *rte, int rtindex, int sublevels_up,
 		case RTE_CTE:
 		case RTE_NAMEDTUPLESTORE:
 			{
-				/* Tablefunc, Values or CTE RTE */
+				/* Tablefunc, Values, CTE, or ENR RTE */
 				ListCell   *aliasp_item = list_head(rte->eref->colnames);
 				ListCell   *lct;
 				ListCell   *lcm;
@@ -2436,14 +2446,23 @@ expandRTE(RangeTblEntry *rte, int rtindex, int sublevels_up,
 					if (colnames)
 					{
 						/* Assume there is one alias per output column */
+						if (OidIsValid(coltype))
+						{
 							char	   *label = strVal(lfirst(aliasp_item));
 
 							*colnames = lappend(*colnames,
 												makeString(pstrdup(label)));
+						}
+						else if (include_dropped)
+							*colnames = lappend(*colnames,
+												makeString(pstrdup("")));
+
 						aliasp_item = lnext(aliasp_item);
 					}
 
 					if (colvars)
+					{
+						if (OidIsValid(coltype))
 						{
 							Var		   *varnode;
 
@@ -2454,6 +2473,17 @@ expandRTE(RangeTblEntry *rte, int rtindex, int sublevels_up,
 
 							*colvars = lappend(*colvars, varnode);
 						}
+						else if (include_dropped)
+						{
+							/*
+							 * It doesn't really matter what type the Const
+							 * claims to be.
+							 */
+							*colvars = lappend(*colvars,
+											   makeNullConst(INT4OID, -1,
+															 InvalidOid));
+						}
+					}
 				}
 			}
 			break;
@@ -2831,13 +2861,21 @@ get_rte_attribute_type(RangeTblEntry *rte, AttrNumber attnum,
 		case RTE_NAMEDTUPLESTORE:
 			{
 				/*
-				 * tablefunc, VALUES or CTE RTE --- get type info from lists
-				 * in the RTE
+				 * tablefunc, VALUES, CTE, or ENR RTE --- get type info from
+				 * lists in the RTE
 				 */
 				Assert(attnum > 0 && attnum <= list_length(rte->coltypes));
 				*vartype = list_nth_oid(rte->coltypes, attnum - 1);
 				*vartypmod = list_nth_int(rte->coltypmods, attnum - 1);
 				*varcollid = list_nth_oid(rte->colcollations, attnum - 1);
+
+				/* For ENR, better check for dropped column */
+				if (!OidIsValid(*vartype))
+					ereport(ERROR,
+							(errcode(ERRCODE_UNDEFINED_COLUMN),
+							 errmsg("column %d of relation \"%s\" does not exist",
+									attnum,
+									rte->eref->aliasname)));
 			}
 			break;
 		default:
@@ -2888,15 +2926,11 @@ get_rte_attribute_is_dropped(RangeTblEntry *rte, AttrNumber attnum)
 			break;
 		case RTE_NAMEDTUPLESTORE:
 			{
-				Assert(rte->enrname);
-
-				/*
-				 * We checked when we loaded coltypes for the tuplestore that
-				 * InvalidOid was only used for dropped columns, so it is safe
-				 * to count on that here.
-				 */
-				result =
-					((list_nth_oid(rte->coltypes, attnum - 1) == InvalidOid));
+				/* Check dropped-ness by testing for valid coltype */
+				if (attnum <= 0 ||
+					attnum > list_length(rte->coltypes))
+					elog(ERROR, "invalid varattno %d", attnum);
+				result = !OidIsValid((list_nth_oid(rte->coltypes, attnum - 1)));
 			}
 			break;
 		case RTE_JOIN:

src/backend/parser/parse_target.c

@@ -1511,8 +1511,8 @@ expandRecordVariable(ParseState *pstate, Var *var, int levelsup)
 		case RTE_NAMEDTUPLESTORE:
 
 			/*
-			 * This case should not occur: a column of a table or values list
-			 * shouldn't have type RECORD.  Fall through and fail (most
+			 * This case should not occur: a column of a table, values list,
+			 * or ENR shouldn't have type RECORD.  Fall through and fail (most
 			 * likely) at the bottom.
 			 */
 			break;

src/backend/utils/adt/ruleutils.c

@@ -6846,8 +6846,8 @@ get_name_for_var_field(Var *var, int fieldno,
 		case RTE_NAMEDTUPLESTORE:
 
 			/*
-			 * This case should not occur: a column of a table or values list
-			 * shouldn't have type RECORD.  Fall through and fail (most
+			 * This case should not occur: a column of a table, values list,
+			 * or ENR shouldn't have type RECORD.  Fall through and fail (most
 			 * likely) at the bottom.
 			 */
 			break;

src/include/nodes/parsenodes.h

@@ -1025,6 +1025,11 @@ typedef struct RangeTblEntry
 	 * from the catalogs if 'relid' was supplied, but we'd still need these
 	 * for TupleDesc-based ENRs, so we might as well always store the type
 	 * info here).
+	 *
+	 * For ENRs only, we have to consider the possibility of dropped columns.
+	 * A dropped column is included in these lists, but it will have zeroes in
+	 * all three lists (as well as an empty-string entry in eref).  Testing
+	 * for zero coltype is the standard way to detect a dropped column.
 	 */
 	List	   *coltypes;		/* OID list of column type OIDs */
 	List	   *coltypmods;		/* integer list of column typmods */