Add support for custom_query_jumble as a node field attribute

This option gives the possibility for query jumble to define a custom
routine for the field of a Node, extending support for
custom_query_jumble as a node field attribute.  When dealing with
complex node structures, this can be simpler than having to enforce a
custom function across a full node.

Custom functions need to be defined in queryjumblefuncs.c, named as
_jumble${node}_${field}(), and use in input the JumbleState, the node
and its field.  The field is not really required if we have the Node,
but it makes custom implementations somewhat easier to think about.  The
code generated by gen_node_support.pl uses a macro called
JUMBLE_CUSTOM(), hiding the internals of the logic inside
queryjumblefuncs.c.

This will be used by an upcoming patch manipulating adding a custom
routine into a field of RangeTblEntry, but this facility can become
useful in more cases.

Reviewed-by: Christoph Berg <myon@debian.org>
Discussion: https://postgr.es/m/Z9y43-dRvb4EtxQ0@paquier.xyz

src/backend/nodes/gen_node_support.pl

@@ -471,6 +471,7 @@ foreach my $infile (@ARGV)
 								&& $attr !~ /^read_as\(\w+\)$/
 								&& !elem $attr,
 								qw(copy_as_scalar
+								custom_query_jumble
 								equal_as_scalar
 								equal_ignore
 								equal_ignore_if_zero
@@ -1283,12 +1284,17 @@ _jumble${n}(JumbleState *jstate, Node *node)
 		my $t = $node_type_info{$n}->{field_types}{$f};
 		my @a = @{ $node_type_info{$n}->{field_attrs}{$f} };
 		my $query_jumble_ignore = $struct_no_query_jumble;
+		my $query_jumble_custom = 0;
 		my $query_jumble_location = 0;
 		my $query_jumble_squash = 0;
 
 		# extract per-field attributes
 		foreach my $a (@a)
 		{
+			if ($a eq 'custom_query_jumble')
+			{
+				$query_jumble_custom = 1;
+			}
 			if ($a eq 'query_jumble_ignore')
 			{
 				$query_jumble_ignore = 1;
@@ -1304,7 +1310,12 @@ _jumble${n}(JumbleState *jstate, Node *node)
 		}
 
 		# node type
-		if (($t =~ /^(\w+)\*$/ or $t =~ /^struct\s+(\w+)\*$/)
+		if ($query_jumble_custom)
+		{
+			# Custom function that applies to one field of a node.
+			print $jff "\tJUMBLE_CUSTOM($n, $f);\n";
+		}
+		elsif (($t =~ /^(\w+)\*$/ or $t =~ /^struct\s+(\w+)\*$/)
 			and elem $1, @node_types)
 		{
 			# Squash constants if requested.

src/backend/nodes/queryjumblefuncs.c

@@ -333,6 +333,9 @@ do { \
 	if (expr->str) \
 		AppendJumble(jstate, (const unsigned char *) (expr->str), strlen(expr->str) + 1); \
 } while(0)
+/* Function name used for the node field attribute custom_query_jumble. */
+#define JUMBLE_CUSTOM(nodetype, item) \
+	_jumble##nodetype##_##item(jstate, expr, expr->item)
 
 #include "queryjumblefuncs.funcs.c"
 

src/include/nodes/nodes.h

@@ -54,6 +54,7 @@ typedef enum NodeTag
  *   readfuncs.c.
  *
  * - custom_query_jumble: Has custom implementation in queryjumblefuncs.c.
+ *   Also available as a node field attribute.
  *
  * - no_copy: Does not support copyObject() at all.
  *
@@ -101,6 +102,9 @@ typedef enum NodeTag
  * - equal_ignore_if_zero: Ignore the field for equality if it is zero.
  *   (Otherwise, compare normally.)
  *
+ * - custom_query_jumble: Has custom implementation in queryjumblefuncs.c
+ *   for the field of a node.  Also available as a node attribute.
+ *
  * - query_jumble_ignore: Ignore the field for the query jumbling.  Note
  *   that typmod and collation information are usually irrelevant for the
  *   query jumbling.