Tighten up parsing logic in gen_node_support.pl.

Teach this script to handle function pointer fields honestly.
Previously they were just silently ignored, but that's not likely to
be a behavior we can accept indefinitely.  This mostly entails fixing
it so that a field declaration spanning multiple lines can be parsed,
because we have a bunch of such fields that're laid out that way.
But that's a good improvement in its own right.

With that change and a minor regex adjustment, the only struct it
fails to parse in the node-defining headers is A_Const, because
of the embedded union.  The path of least resistance is to move
that union declaration outside the struct.

Having done those things, we can make it error out if it finds
any within-struct syntax it doesn't understand, which seems like
a pretty important property for robustness.

This commit doesn't change the output files at all; it's just in
the way of future-proofing.

Discussion: https://postgr.es/m/2593369.1657759779@sss.pgh.pa.us

src/backend/nodes/gen_node_support.pl

@@ -213,15 +213,39 @@ foreach my $infile (@ARGV)
 	}
 	$file_content .= $raw_file_content;
 
-	my $lineno = 0;
+	my $lineno   = 0;
+	my $prevline = '';
 	foreach my $line (split /\n/, $file_content)
 	{
+		# per-physical-line processing
 		$lineno++;
 		chomp $line;
 		$line =~ s/\s*$//;
 		next if $line eq '';
 		next if $line =~ /^#(define|ifdef|endif)/;
 
+		# within a struct, don't process until we have whole logical line
+		if ($in_struct && $subline > 0)
+		{
+			if ($line =~ /;$/)
+			{
+				# found the end, re-attach any previous line(s)
+				$line     = $prevline . $line;
+				$prevline = '';
+			}
+			elsif ($prevline eq ''
+				&& $line =~ /^\s*pg_node_attr\(([\w(), ]*)\)$/)
+			{
+				# special case: node-attributes line doesn't end with semi
+			}
+			else
+			{
+				# set it aside for a moment
+				$prevline .= $line . ' ';
+				next;
+			}
+		}
+
 		# we are analyzing a struct definition
 		if ($in_struct)
 		{
@@ -394,7 +418,7 @@ foreach my $infile (@ARGV)
 			}
 			# normal struct field
 			elsif ($line =~
-				/^\s*(.+)\s*\b(\w+)(\[\w+\])?\s*(?:pg_node_attr\(([\w(), ]*)\))?;/
+				/^\s*(.+)\s*\b(\w+)(\[[\w\s+]+\])?\s*(?:pg_node_attr\(([\w(), ]*)\))?;/
 			  )
 			{
 				if ($is_node_struct)
@@ -441,13 +465,46 @@ foreach my $infile (@ARGV)
 					$my_field_attrs{$name} = \@attrs;
 				}
 			}
-			else
+			# function pointer field
+			elsif ($line =~
+				/^\s*([\w\s*]+)\s*\(\*(\w+)\)\s*\((.*)\)\s*(?:pg_node_attr\(([\w(), ]*)\))?;/
+			  )
 			{
 				if ($is_node_struct)
 				{
-					#warn "$infile:$lineno: could not parse \"$line\"\n";
+					my $type  = $1;
+					my $name  = $2;
+					my $args  = $3;
+					my $attrs = $4;
+
+					my @attrs;
+					if ($attrs)
+					{
+						@attrs = split /,\s*/, $attrs;
+						foreach my $attr (@attrs)
+						{
+							if (   $attr !~ /^copy_as\(\w+\)$/
+								&& $attr !~ /^read_as\(\w+\)$/
+								&& !elem $attr,
+								qw(equal_ignore read_write_ignore))
+							{
+								die
+								  "$infile:$lineno: unrecognized attribute \"$attr\"\n";
+							}
+						}
+					}
+
+					push @my_fields, $name;
+					$my_field_types{$name} = 'function pointer';
+					$my_field_attrs{$name} = \@attrs;
 				}
 			}
+			else
+			{
+				# We're not too picky about what's outside structs,
+				# but we'd better understand everything inside.
+				die "$infile:$lineno: could not parse \"$line\"\n";
+			}
 		}
 		# not in a struct
 		else
@@ -709,6 +766,12 @@ _equal${n}(const $n *a, const $n *b)
 				  unless $equal_ignore;
 			}
 		}
+		elsif ($t eq 'function pointer')
+		{
+			# we can copy and compare as a scalar
+			print $cff "\tCOPY_SCALAR_FIELD($f);\n"    unless $copy_ignore;
+			print $eff "\tCOMPARE_SCALAR_FIELD($f);\n" unless $equal_ignore;
+		}
 		# node type
 		elsif ($t =~ /(\w+)\*/ and elem $1, @node_types)
 		{
@@ -980,6 +1043,12 @@ _read${n}(void)
 				  unless $no_read;
 			}
 		}
+		elsif ($t eq 'function pointer')
+		{
+			# We don't print these, and we can't read them either
+			die "cannot read function pointer in struct \"$n\" field \"$f\"\n"
+			  unless $no_read;
+		}
 		# Special treatments of several Path node fields
 		elsif ($t eq 'RelOptInfo*' && elem 'write_only_relids', @a)
 		{

src/include/nodes/parsenodes.h

@@ -303,26 +303,26 @@ typedef struct A_Expr
 
 /*
  * A_Const - a literal constant
+ *
+ * Value nodes are inline for performance.  You can treat 'val' as a node,
+ * as in IsA(&val, Integer).  'val' is not valid if isnull is true.
  */
+union ValUnion
+{
+	Node		node;
+	Integer		ival;
+	Float		fval;
+	Boolean		boolval;
+	String		sval;
+	BitString	bsval;
+};
+
 typedef struct A_Const
 {
 	pg_node_attr(custom_copy_equal, custom_read_write, no_read)
 
 	NodeTag		type;
-
+	union ValUnion val;
-	/*
-	 * Value nodes are inline for performance.  You can treat 'val' as a node,
-	 * as in IsA(&val, Integer).  'val' is not valid if isnull is true.
-	 */
-	union ValUnion
-	{
-		Node		node;
-		Integer		ival;
-		Float		fval;
-		Boolean		boolval;
-		String		sval;
-		BitString	bsval;
-	}			val;
 	bool		isnull;			/* SQL NULL constant */
 	int			location;		/* token location, or -1 if unknown */
 } A_Const;

src/include/nodes/pathnodes.h

@@ -1098,7 +1098,7 @@ struct IndexOptInfo
 
 	/*
 	 * Remaining fields are copied from the index AM's API struct
-	 * (IndexAmRoutine)
+	 * (IndexAmRoutine).  We don't bother to dump them.
 	 */
 	bool		amcanorderbyop pg_node_attr(read_write_ignore);
 	bool		amoptionalkey pg_node_attr(read_write_ignore);
@@ -1111,8 +1111,9 @@ struct IndexOptInfo
 	bool		amcanparallel pg_node_attr(read_write_ignore);
 	/* does AM have ammarkpos interface? */
 	bool		amcanmarkpos pg_node_attr(read_write_ignore);
+	/* AM's cost estimator */
 	/* Rather than include amapi.h here, we declare amcostestimate like this */
-	void		(*amcostestimate) ();	/* AM's cost estimator */
+	void		(*amcostestimate) () pg_node_attr(read_write_ignore);
 };
 
 /*