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Implement -I option and M4PATH environment variable

/* $OpenBSD: gnum4.c,v 1.1 1999/09/14 08:21:36 espie Exp $ */

/*
 * Copyright (c) 1999 Marc Espie
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/* 
 * functions needed to support gnu-m4 extensions, including a fake freezing
 */

#include <sys/param.h>
#include <stddef.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <err.h>
#include "mdef.h"
#include "stdd.h"
#include "extern.h"

/*
 * Support for include path search
 * First search in the the current directory.
 * If not found, and the path is not absolute, include path kicks in.
 * First, -I options, in the order found on the command line.
 * Then M4PATH env variable
 */

struct path_entry {
	char *name;
	struct path_entry *next;
} *first, *last;

static struct path_entry *
new_path_entry(dirname)
	char *dirname;
{
	struct path_entry *n;

	n = malloc(sizeof(struct path_entry));
	if (!n)
		errx(1, "out of memory");
	n->name = strdup(dirname);
	if (!n->name)
		errx(1, "out of memory");
	n->next = 0;
	return n;
}
	
void 
addtoincludepath(dirname)
	const char *dirname;
{
	struct path_entry *n;

	n = new_path_entry(dirname);

	if (last) {
		last->next = n;
		last = n;
	}
	else
		last = first = n;
}

static void
ensure_m4path()
{
	static int envpathdone = 0;
	char *envpath;
	char *sweep;
	char *path;

	if (envpathdone)
		return;
	envpathdone = TRUE;
	envpath = getenv("M4PATH");
	if (!envpath) 
		return;
	/* for portability: getenv result is read-only */
	envpath = strdup(envpath);
	if (!envpath)
		errx(1, "out of memory");
	for (sweep = envpath; 
	    (path = strsep(&sweep, ":")) != NULL;)
	    addtoincludepath(path);
	free(envpath);
}

static
FILE *
dopath(const char *filename)
{
	char path[MAXPATHLEN];
	struct path_entry *pe;
	FILE *file;

	for (pe = first; pe; pe = pe->next) {
		snprintf(path, sizeof(path), "%s/%s", pe->name, filename);
		if ((file = fopen(path, "r")) != 0)
			return file;
	}
	return NULL;
}

FILE *
fopen_trypath(filename)
	const char *filename;
{
	FILE *f;

	f = fopen(filename, "r");
	if (f)
		return f;
	if (filename[0] == '/')
		return NULL;

	ensure_m4path();

	return dopath(filename);
}