Harden range_table_mutator() against null RangeTblEntry.subquery.

Commit 64919aaab made pull_up_simple_subquery set rte->subquery = NULL
after doing the deed, so that we don't waste cycles copying a
now-useless subquery tree around.  This turns out to create a core dump
hazard in range_table_mutator, which supposes that that field is never
NULL.  Apparently none of our own code invokes query_tree_mutator or
range_table_mutator on the top Query after subquery pullup; but it
wouldn't be surprising if outside code does, and anyway I'm working
on a v16 patch that will need it.

We can fix this cleanly by just getting rid of the special-case
handling of this field and treating it more like all the rest.
I think the special case might be left over from a time when
QTW_DONT_COPY_QUERY was the default behavior, but that was eons ago.

Thanks to Dean Rasheed for review.

Discussion: https://postgr.es/m/545569.1656107045@sss.pgh.pa.us

diff --git a/src/backend/nodes/nodeFuncs.c b/src/backend/nodes/nodeFuncs.c
index 3b3ef3a4cdda48d0afea6cc6fef59b7e44b13fa8..4cb1744da6ccb67e23353e101ff8d5896c0ce60c 100644 (file)
--- a/src/backend/nodes/nodeFuncs.c
+++ b/src/backend/nodes/nodeFuncs.c
@@ -2825,11 +2825,6 @@ expression_tree_mutator(Node *node,
    ( (newnode) = (nodetype *) palloc(sizeof(nodetype)), \
      memcpy((newnode), (node), sizeof(nodetype)) )
 
-#define CHECKFLATCOPY(newnode, node, nodetype) \
-   ( AssertMacro(IsA((node), nodetype)), \
-     (newnode) = (nodetype *) palloc(sizeof(nodetype)), \
-     memcpy((newnode), (node), sizeof(nodetype)) )
-
 #define MUTATE(newfield, oldfield, fieldtype)  \
        ( (newfield) = (fieldtype) mutator((Node *) (oldfield), context) )
 
@@ -3640,9 +3635,9 @@ expression_tree_mutator(Node *node,
  * which is the bitwise OR of flag values to suppress mutating of
  * indicated items.  (More flag bits may be added as needed.)
  *
- * Normally the Query node itself is copied, but some callers want it to be
- * modified in-place; they must pass QTW_DONT_COPY_QUERY in flags.  All
- * modified substructure is safely copied in any case.
+ * Normally the top-level Query node itself is copied, but some callers want
+ * it to be modified in-place; they must pass QTW_DONT_COPY_QUERY in flags.
+ * All modified substructure is safely copied in any case.
  */
 Query *
 query_tree_mutator(Query *query,
@@ -3758,10 +3753,7 @@ range_table_mutator(List *rtable,
                break;
            case RTE_SUBQUERY:
                if (!(flags & QTW_IGNORE_RT_SUBQUERIES))
-               {
-                   CHECKFLATCOPY(newrte->subquery, rte->subquery, Query);
-                   MUTATE(newrte->subquery, newrte->subquery, Query *);
-               }
+                   MUTATE(newrte->subquery, rte->subquery, Query *);
                else
                {
                    /* else, copy RT subqueries as-is */