Add stack depth checks to key recursive functions in backend/nodes/*.c.

Although copyfuncs.c has a check_stack_depth call in its recursion,
equalfuncs.c, outfuncs.c, and readfuncs.c lacked one.  This seems
unwise.

Likewise fix planstate_tree_walker(), in branches where that exists.

Discussion: https://postgr.es/m/30253.1544286631@sss.pgh.pa.us

src/backend/nodes/equalfuncs.c

@@ -29,6 +29,7 @@
 
 #include "postgres.h"
 
+#include "miscadmin.h"
 #include "nodes/extensible.h"
 #include "nodes/relation.h"
 #include "utils/datum.h"
@@ -3002,6 +3003,9 @@ equal(const void *a, const void *b)
 	if (nodeTag(a) != nodeTag(b))
 		return false;
 
+	/* Guard against stack overflow due to overly complex expressions */
+	check_stack_depth();
+
 	switch (nodeTag(a))
 	{
 			/*

src/backend/nodes/nodeFuncs.c

@@ -3726,6 +3726,9 @@ planstate_tree_walker(PlanState *planstate,
 	Plan	   *plan = planstate->plan;
 	ListCell   *lc;
 
+	/* Guard against stack overflow due to overly complex plan trees */
+	check_stack_depth();
+
 	/* initPlan-s */
 	if (planstate_walk_subplans(planstate->initPlan, walker, context))
 		return true;

src/backend/nodes/outfuncs.c

@@ -30,6 +30,7 @@
 #include <ctype.h>
 
 #include "lib/stringinfo.h"
+#include "miscadmin.h"
 #include "nodes/extensible.h"
 #include "nodes/plannodes.h"
 #include "nodes/relation.h"
@@ -3701,6 +3702,9 @@ _outPartitionRangeDatum(StringInfo str, const PartitionRangeDatum *node)
 void
 outNode(StringInfo str, const void *obj)
 {
+	/* Guard against stack overflow due to overly complex expressions */
+	check_stack_depth();
+
 	if (obj == NULL)
 		appendStringInfoString(str, "<>");
 	else if (IsA(obj, List) ||IsA(obj, IntList) || IsA(obj, OidList))

src/backend/nodes/readfuncs.c

@@ -33,6 +33,7 @@
 #include <math.h>
 
 #include "fmgr.h"
+#include "miscadmin.h"
 #include "nodes/extensible.h"
 #include "nodes/parsenodes.h"
 #include "nodes/plannodes.h"
@@ -2549,6 +2550,9 @@ parseNodeString(void)
 
 	READ_TEMP_LOCALS();
 
+	/* Guard against stack overflow due to overly complex expressions */
+	check_stack_depth();
+
 	token = pg_strtok(&length);
 
 #define MATCH(tokname, namelen) \