Automatically generate node support functions

Add a script to automatically generate the node support functions
(copy, equal, out, and read, as well as the node tags enum) from the
struct definitions.

For each of the four node support files, it creates two include files,
e.g., copyfuncs.funcs.c and copyfuncs.switch.c, to include in the main
file.  All the scaffolding of the main file stays in place.

I have tried to mostly make the coverage of the output match what is
currently there.  For example, one could now do out/read coverage of
utility statement nodes, but I have manually excluded those for now.
The reason is mainly that it's easier to diff the before and after,
and adding a bunch of stuff like this might require a separate
analysis and review.

Subtyping (TidScan -> Scan) is supported.

For the hard cases, you can just write a manual function and exclude
generating one.  For the not so hard cases, there is a way of
annotating struct fields to get special behaviors.  For example,
pg_node_attr(equal_ignore) has the field ignored in equal functions.

(In this patch, I have only ifdef'ed out the code to could be removed,
mainly so that it won't constantly have merge conflicts.  It will be
deleted in a separate patch.  All the code comments that are worth
keeping from those sections have already been moved to the header
files where the structs are defined.)

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://www.postgresql.org/message-id/flat/c1097590-a6a4-486a-64b1-e1f9cc0533ce%40enterprisedb.com

src/backend/nodes/equalfuncs.c

@@ -10,9 +10,6 @@
  * because the circular linkages between RelOptInfo and Path nodes can't
  * be handled easily in a simple depth-first traversal.
  *
- * Currently, in fact, equal() doesn't know how to compare Plan trees
- * either.  This might need to be fixed someday.
- *
  * NOTE: it is intentional that parse location fields (in nodes that have
  * one) are not compared.  This is because we want, for example, a variable
  * "x" to be considered equal() to another reference to "x" in the query.
@@ -30,8 +27,6 @@
 #include "postgres.h"
 
 #include "miscadmin.h"
-#include "nodes/extensible.h"
-#include "nodes/pathnodes.h"
 #include "utils/datum.h"
 
 
@@ -97,6 +92,9 @@
 	((void) 0)
 
 
+#include "equalfuncs.funcs.c"
+
+#ifdef OBSOLETE
 /*
  *	Stuff from primnodes.h
  */
@@ -258,6 +256,7 @@ _equalVar(const Var *a, const Var *b)
 
 	return true;
 }
+#endif							/* OBSOLETE */
 
 static bool
 _equalConst(const Const *a, const Const *b)
@@ -280,6 +279,7 @@ _equalConst(const Const *a, const Const *b)
 						a->constbyval, a->constlen);
 }
 
+#ifdef OBSOLETE
 static bool
 _equalParam(const Param *a, const Param *b)
 {
@@ -1304,6 +1304,7 @@ _equalPlaceHolderInfo(const PlaceHolderInfo *a, const PlaceHolderInfo *b)
 
 	return true;
 }
+#endif							/* OBSOLETE */
 
 /*
  * Stuff from extensible.h
@@ -1325,6 +1326,7 @@ _equalExtensibleNode(const ExtensibleNode *a, const ExtensibleNode *b)
 	return true;
 }
 
+#ifdef OBSOLETE
 /*
  * Stuff from parsenodes.h
  */
@@ -2815,6 +2817,7 @@ _equalParamRef(const ParamRef *a, const ParamRef *b)
 
 	return true;
 }
+#endif							/* OBSOLETE */
 
 static bool
 _equalA_Const(const A_Const *a, const A_Const *b)
@@ -2831,6 +2834,7 @@ _equalA_Const(const A_Const *a, const A_Const *b)
 	return true;
 }
 
+#ifdef OBSOLETE
 static bool
 _equalFuncCall(const FuncCall *a, const FuncCall *b)
 {
@@ -3468,6 +3472,7 @@ _equalPartitionCmd(const PartitionCmd *a, const PartitionCmd *b)
 
 	return true;
 }
+#endif							/* OBSOLETE */
 
 /*
  * Stuff from pg_list.h
@@ -3528,6 +3533,7 @@ _equalList(const List *a, const List *b)
 	return true;
 }
 
+#ifdef OBSOLETE
 /*
  * Stuff from value.h
  */
@@ -3571,6 +3577,7 @@ _equalBitString(const BitString *a, const BitString *b)
 
 	return true;
 }
+#endif							/* OBSOLETE */
 
 /*
  * equal
@@ -3601,6 +3608,8 @@ equal(const void *a, const void *b)
 
 	switch (nodeTag(a))
 	{
+#include "equalfuncs.switch.c"
+#ifdef OBSOLETE
 			/*
 			 * PRIMITIVE NODES
 			 */
@@ -3821,6 +3830,7 @@ equal(const void *a, const void *b)
 		case T_PlaceHolderInfo:
 			retval = _equalPlaceHolderInfo(a, b);
 			break;
+#endif							/* OBSOLETE */
 
 		case T_List:
 		case T_IntList:
@@ -3828,6 +3838,7 @@ equal(const void *a, const void *b)
 			retval = _equalList(a, b);
 			break;
 
+#ifdef OBSOLETE
 		case T_Integer:
 			retval = _equalInteger(a, b);
 			break;
@@ -4430,6 +4441,7 @@ equal(const void *a, const void *b)
 		case T_JsonTableColumn:
 			retval = _equalJsonTableColumn(a, b);
 			break;
+#endif							/* OBSOLETE */
 
 		default:
 			elog(ERROR, "unrecognized node type: %d",