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The expat library aborts parsing as soon as it encounters invalid
input, and the basic design of the library practically precludes
fixing it.  However, whether the input is well-formed XML or not
is totally irrelevant, and in fact, i have seen real-world documents
from X.org that expat rejects as not well-formed.  Kristaps reports
the same from OpenGL.

We really want to parse *ANYTHING* whatsoever without ever throwing
a fatal error - after all, the point is to convert legacy documents
to a better format, and nitpicking about the syntax merely alienates
users (including myself).

Consequently, ditch expat and write a parser from scratch, optimized
for robustness on invalid input.

Oh, and by the way, it only requires 200 lines of code,
compared to 15,000 lines in expat - an economy of 98.5%
at the sime time as being much more useful in practice.

/* $Id: main.c,v 1.3 2019/03/28 12:21:10 schwarze Exp $ */
/*
 * Copyright (c) 2014 Kristaps Dzonsons <kristaps@bsd.lv>
 * Copyright (c) 2019 Ingo Schwarze <schwarze@openbsd.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHORS DISCLAIM ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */
#include <fcntl.h>
#include <getopt.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

#include "node.h"
#include "parse.h"
#include "format.h"

/*
 * The steering function of the docbook2mdoc(1) program.
 */

int
main(int argc, char *argv[])
{
	struct parse	*parser;
	struct ptree	*tree;
	const char	*progname;
	const char	*fname;
	int		 ch, fd, rc, warn;

	if ((progname = strrchr(argv[0], '/')) == NULL)
		progname = argv[0];
	else
		progname++;

	warn = 0;
	while ((ch = getopt(argc, argv, "W")) != -1) {
		switch (ch) {
		case 'W':
			warn = 1;
			break;
		default:
			goto usage;
		}
	}
	argc -= optind;
	argv += optind;

	/*
	 * Argument processing:
	 * Open file or use standard input.
	 */

	if (argc > 1) {
		fprintf(stderr, "%s: Too many arguments\n", argv[1]);
		goto usage;
	} else
		fname = argc > 0 ? argv[0] : "-";

	fd = strcmp(fname, "-") == 0 ?
		STDIN_FILENO : open(fname, O_RDONLY, 0);

	if (fd == -1) {
		perror(fname);
		return 1;
	}

	/* Parse and format. */

	rc = 1;
	if ((parser = parse_alloc(warn)) != NULL) {
		if ((tree = parse_file(parser, fd, fname)) != NULL) {
			if (tree->flags & TREE_FAIL)
				fputc('\n', stderr);
			else
				rc = 0;
			ptree_print(tree);
			if (tree->flags & TREE_FAIL)
				fputs("\nThe output may be incomplete, see"
				    " the parse error reported above.\n\n",
				    stderr);
			pnode_unlink(tree->root);
			tree->root = NULL;
		}
		parse_free(parser);
	} else
		perror(NULL);

	if (fd != STDIN_FILENO)
		close(fd);
	return rc;

usage:
	fprintf(stderr, "usage: %s [-W] [input_filename]\n", progname);
	return 1;
}