WIP for varnullingrels issue (#47)

This is a work in progress for the new field that was
added to the struct Var called "varnullingrels".
According to the documentation, this field is responsible
for marking the Vars as nullable, if they are coming from
a JOIN, either LEFT JOIN, RIGHT JOIN, or FULL OUTER JOIN.
The changes were made following an "optional match" clause
which is being treated as a LEFT JOIN from our extension.

A function markRelsAsNulledBy is added because its internal
in Postgres and doesn't belong in a header file, therefore
it can't be exported. This function is added before the creation
of the Vars from the "make_vertex_expr" and "make_edge_expr",
to correctly mark the specific PNSI as nullable, so later in
the planner stage, the Vars will be correctly nulled.

Signed-off-by: Panagiotis Foliadis <[email protected]>

src/backend/parser/cypher_clause.c

@@ -337,6 +337,7 @@ static bool isa_special_VLE_case(cypher_path *path);
 
 static ParseNamespaceItem *find_pnsi(cypher_parsestate *cpstate, char *varname);
 
+static void  markRelsAsNulledBy(ParseState *pstate, int n, int jindex);
 /*
  * transform a cypher_clause
  */
@@ -4462,6 +4463,8 @@ static Expr *transform_cypher_edge(cypher_parsestate *cpstate,
     Node *expr = NULL;
     bool refs_var = false;
     ParseNamespaceItem *pnsi = NULL;
+    int jindex;
+
 
     /*
      * If we have an edge name, get any potential variable or column
@@ -4662,6 +4665,10 @@ static Expr *transform_cypher_edge(cypher_parsestate *cpstate,
     pnsi = addRangeTableEntry(pstate, label_range_var, alias,
                              label_range_var->inh, true);
     Assert(pnsi != NULL);
+    if (pstate->parentParseState->p_lateral_active) {
+      jindex = list_length(pstate->p_rtable + 1);
+      markRelsAsNulledBy(pstate, pnsi->p_rtindex, jindex);
+    }
 
     /*
      * relation is visible (r.a in expression works) but attributes in the
@@ -4705,6 +4712,7 @@ static Expr *transform_cypher_node(cypher_parsestate *cpstate,
     cypher_node *cn = NULL;
     bool refs_var = false;
     ParseNamespaceItem *pnsi;
+    int jindex;
 
     /* if we have a node name, get any potential variable references */
     if (node->name != NULL)
@@ -4898,8 +4906,13 @@ static Expr *transform_cypher_node(cypher_parsestate *cpstate,
     pnsi = addRangeTableEntry(pstate, label_range_var, alias,
                              label_range_var->inh, true);
 
-    Assert(pnsi != NULL);
 
+
+    Assert(pnsi != NULL);
+    if (pstate->parentParseState->p_lateral_active) {
+      jindex = list_length(pstate->p_rtable + 1);
+      markRelsAsNulledBy(pstate, pnsi->p_rtindex, jindex);
+    }
     /*
      * relation is visible (r.a in expression works) but attributes in the
      * relation are not visible (a in expression doesn't work)
@@ -6860,3 +6873,42 @@ ParseNamespaceItem *find_pnsi(cypher_parsestate *cpstate, char *varname)
 
     return NULL;
 }
+
+ static void
+ markRelsAsNulledBy(ParseState *pstate, int n, int jindex)
+ {
+     int         varno;
+     ListCell   *lc;
+     varno = n;
+
+     /* Note: we can't see FromExpr here */
+     /* if (IsA(n, RangeTblRef)) */
+     /* { */
+     /*     varno = ((RangeTblRef *) n)->rtindex; */
+     /* } */
+     /* else if (IsA(n, JoinExpr)) */
+     /* { */
+     /*     JoinExpr   *j = (JoinExpr *) n; */
+
+     /*     /\* recurse to children *\/ */
+     /*     markRelsAsNulledBy(pstate, j->larg, jindex); */
+     /*     markRelsAsNulledBy(pstate, j->rarg, jindex); */
+     /*     varno = j->rtindex; */
+     /* } */
+     /* else */
+     /* { */
+     /*     elog(ERROR, "unrecognized node type: %d", (int) nodeTag(n)); */
+     /*     varno = 0;              /\* keep compiler quiet *\/ */
+     /* } */
+
+     /*
+      * Now add jindex to the p_nullingrels set for relation varno.  Since we
+      * maintain the p_nullingrels list lazily, we might need to extend it to
+      * make the varno'th entry exist.
+      */
+     while (list_length(pstate->p_nullingrels) < varno)
+         pstate->p_nullingrels = lappend(pstate->p_nullingrels, NULL);
+     lc = list_nth_cell(pstate->p_nullingrels, varno - 1);
+     lfirst(lc) = bms_add_member((Bitmapset *) lfirst(lc), jindex);
+ }
+