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Dummy implementation of the roff(7) \V (interpolate environment variable)
escape sequence.  This is needed to get \V into the correct parsing
class, ESCAPE_EXPAND.

It is intentional that mandoc(1) output is *not* influenced by environment
variables, so interpolate the name of the variable with some decorating
punctuation rather than interpolating its value.

/* $OpenBSD$ */
/*
 * Copyright (c) 2011, 2012, 2013, 2014, 2015, 2017, 2018, 2020, 2022
 *               Ingo Schwarze <schwarze@openbsd.org>
 * Copyright (c) 2010, 2011 Kristaps Dzonsons <kristaps@bsd.lv>
 *
 * 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.
 *
 * Parser for roff(7) escape sequences.
 * To be used by all mandoc(1) parsers and formatters.
 */
#include <assert.h>
#include <ctype.h>
#include <limits.h>
#include <stdio.h>
#include <string.h>

#include "mandoc.h"
#include "roff.h"
#include "roff_int.h"

/*
 * Traditional escape sequence interpreter for general use
 * including in high-level formatters.  This function does not issue
 * diagnostics and is not usable for expansion in the roff(7) parser.
 * It is documented in the mandoc_escape(3) manual page.
 */
enum mandoc_esc
mandoc_escape(const char **rendarg, const char **rarg, int *rargl)
{
        int		 iarg, iendarg, iend;
        enum mandoc_esc  rval;

        rval = roff_escape(--*rendarg, 0, 0, NULL, &iarg, &iendarg, &iend);
        assert(rval != ESCAPE_EXPAND);
        if (rarg != NULL)
	       *rarg = *rendarg + iarg;
        if (rargl != NULL)
	       *rargl = iendarg - iarg;
        *rendarg += iend;
        return rval;
}

/*
 * Full-featured escape sequence parser.
 * If it encounters a nested escape sequence that requires expansion
 * by the parser and re-parsing, the positions of that inner escape
 * sequence are returned in *resc ... *rend.
 * Otherwise, *resc is set to aesc and the positions of the escape
 * sequence starting at aesc are returned.
 * Diagnostic messages are generated if and only if resc != NULL,
 * that is, if and only if called by roff_expand().
 */
enum mandoc_esc
roff_escape(const char *buf, const int ln, const int aesc,
    int *resc, int *rarg, int *rendarg, int *rend)
{
	int		 iesc;		/* index of leading escape char */
	int		 iarg;		/* index beginning the argument */
	int		 iendarg;	/* index right after the argument */
	int		 iend;		/* index right after the sequence */
	int		 sesc, sarg, sendarg, send; /* for sub-escape */
	int		 maxl;		/* expected length of the argument */
	int		 argl;		/* actual length of the argument */
	int		 c, i;		/* for \[char...] parsing */
	enum mandoc_esc	 rval;		/* return value */
	enum mandocerr	 err;		/* diagnostic code */
	char		 esc_name;
	char		 term;		/* byte terminating the argument */

	/*
	 * Treat "\E" just like "\";
	 * it only makes a difference in copy mode.
	 */

	iesc = iarg = aesc;
	do {
		iarg++;
	} while (buf[iarg] == 'E');

	/*
	 * Sort the following cases first by syntax category,
	 * then by escape sequence type, and finally by ASCII code.
	 */

	esc_name = buf[iarg];
	iendarg = iend = ++iarg;
	maxl = INT_MAX;
	term = '\0';
	switch (esc_name) {

	/* Escape sequences taking no arguments at all. */

	case '!':
	case '?':
	case 'r':
		rval = ESCAPE_UNSUPP;
		goto out;

	case '%':
	case '&':
	case ')':
	case ',':
	case '/':
	case '^':
	case 'a':
	case 'd':
	case 't':
	case 'u':
	case '{':
	case '|':
	case '}':
		rval = ESCAPE_IGNORE;
		goto out;

	case '\\':
	default:
		iarg--;
		rval = ESCAPE_UNDEF;
		goto out;

	case ' ':
	case '\'':
	case '-':
	case '.':
	case '0':
	case ':':
	case '_':
	case '`':
	case 'e':
	case '~':
		iarg--;
		argl = 1;
		rval = ESCAPE_SPECIAL;
		goto out;
	case 'p':
		rval = ESCAPE_BREAK;
		goto out;
	case 'c':
		rval = ESCAPE_NOSPACE;
		goto out;
	case 'z':
		rval = ESCAPE_SKIPCHAR;
		goto out;

	/* Standard argument format. */

	case '$':
	case '*':
	case 'V':
	case 'n':
		rval = ESCAPE_EXPAND;
		break;
	case 'F':
	case 'M':
	case 'O':
	case 'Y':
	case 'g':
	case 'k':
	case 'm':
		rval = ESCAPE_IGNORE;
		break;
	case '(':
	case '[':
		rval = ESCAPE_SPECIAL;
		iendarg = iend = --iarg;
		break;
	case 'f':
		rval = ESCAPE_FONT;
		break;

	/* Quoted arguments */

	case 'B':
	case 'w':
		rval = ESCAPE_EXPAND;
		term = '\b';
		break;
	case 'A':
	case 'D':
	case 'H':
	case 'L':
	case 'R':
	case 'S':
	case 'X':
	case 'Z':
	case 'b':
	case 'v':
	case 'x':
		rval = ESCAPE_IGNORE;
		term = '\b';
		break;
	case 'C':
		if (buf[iarg] != '\'') {
			rval = ESCAPE_ERROR;
			goto out;
		}
		rval = ESCAPE_SPECIAL;
		term = '\b';
		break;
	case 'N':
		rval = ESCAPE_NUMBERED;
		term = '\b';
		break;
	case 'h':
		rval = ESCAPE_HORIZ;
		term = '\b';
		break;
	case 'l':
		rval = ESCAPE_HLINE;
		term = '\b';
		break;
	case 'o':
		rval = ESCAPE_OVERSTRIKE;
		term = '\b';
		break;

	/* Sizes support both forms, with additional peculiarities. */

	case 's':
		rval = ESCAPE_IGNORE;
		if (buf[iarg] == '+' || buf[iarg] == '-'||
		    buf[iarg] == ASCII_HYPH)
			iarg++;
		switch (buf[iarg]) {
		case '(':
			maxl = 2;
			iarg++;
			break;
		case '[':
			term = ']';
			iarg++;
			break;
		case '\'':
			term = '\'';
			iarg++;
			break;
		case '1':
		case '2':
		case '3':
			if (buf[iarg - 1] == 's' &&
			    isdigit((unsigned char)buf[iarg + 1])) {
				maxl = 2;
				break;
			}
			/* FALLTHROUGH */
		default:
			maxl = 1;
			break;
		}
		iendarg = iend = iarg;
	}

	/* Decide how to end the argument. */

	if ((term == '\b' || (term == '\0' && maxl == INT_MAX)) &&
	    buf[iarg] == buf[iesc] && roff_escape(buf, ln, iendarg,
	    &sesc, &sarg, &sendarg, &send) == ESCAPE_EXPAND)
		goto out_sub;

	if (term == '\b') {
		if ((esc_name == 'N' && isdigit((unsigned char)buf[iarg])) ||
		    (esc_name == 'h' && strchr(" %&()*+-./0123456789:<=>",
		     buf[iarg]) != NULL)) {
			iendarg = iend = iarg + 1;
			rval = ESCAPE_ERROR;
			goto out;
		}
		term = buf[iarg++];
	} else if (term == '\0' && maxl == INT_MAX) {
		if (esc_name == 'n' && (buf[iarg] == '+' || buf[iarg] == '-'))
			iarg++;
		switch (buf[iarg]) {
		case '(':
			maxl = 2;
			iarg++;
			break;
		case '[':
			if (buf[++iarg] == ' ') {
				iendarg = iend = iarg + 1;
				rval = ESCAPE_ERROR;
				goto out;
			}
			term = ']';
			break;
		default:
			maxl = 1;
			break;
		}
	}

	/* Advance to the end of the argument. */

	iendarg = iarg;
	while (maxl > 0) {
		if (buf[iendarg] == '\0') {
			/* Ignore an incomplete argument except for \w. */
			if (esc_name != 'w')
				iendarg = iarg;
			break;
		}
		if (buf[iendarg] == term) {
			iend = iendarg + 1;
			break;
		}
		if (esc_name == 'N' &&
		    isdigit((unsigned char)buf[iendarg]) == 0) {
			iend = iendarg + 1;
			break;
		}
		if (buf[iendarg] == buf[iesc]) {
			if (roff_escape(buf, ln, iendarg,
			    &sesc, &sarg, &sendarg, &send) == ESCAPE_EXPAND)
				goto out_sub;
			iendarg = iend = send;
		} else {
			if (maxl != INT_MAX)
				maxl--;
			iend = ++iendarg;
		}
	}
	if (resc != NULL && ((maxl != INT_MAX && maxl != 0) ||
	    (term != '\0' && buf[iendarg] != term)))
		mandoc_msg(MANDOCERR_ESC_BAD, ln, iesc, "%s", buf + iesc);

	/* Post-process depending on the content of the argument. */

	argl = iendarg - iarg;
	switch (esc_name) {
	case '*':
		if (resc == NULL && argl == 2 &&
		    buf[iarg] == '.' && buf[iarg + 1] == 'T')
			rval = ESCAPE_DEVICE;
		break;
	case 'O':
		switch (buf[iarg]) {
		case '0':
			rval = ESCAPE_UNSUPP;
			break;
		case '1':
		case '2':
		case '3':
		case '4':
			rval = argl == 1 ? ESCAPE_IGNORE : ESCAPE_ERROR;
			break;
		case '5':
			rval = buf[iarg - 1] == '[' ? ESCAPE_UNSUPP :
			    ESCAPE_ERROR;
			break;
		default:
			rval = ESCAPE_ERROR;
			break;
		}
		break;
	default:
		break;
	}

	switch (rval) {
	case ESCAPE_FONT:
		rval = mandoc_font(buf + iarg, argl);
		break;

	case ESCAPE_SPECIAL:

		/*
		 * The file chars.c only provides one common list of
		 * character names, but \[-] == \- is the only one of
		 * the characters with one-byte names that allows
		 * enclosing the name in brackets.
		 */

		if (term != '\0' && argl == 1 && buf[iarg] != '-') {
			rval = ESCAPE_ERROR;
			break;
		}

		/* Treat \[char...] as an alias for \N'...'. */

		if (buf[iarg] == 'c') {
			if (argl < 6 || argl > 7 ||
			    strncmp(buf + iarg, "char", 4) != 0 ||
			    (int)strspn(buf + iarg + 4, "0123456789")
			     + 4 < argl)
				break;
			c = 0;
			for (i = iarg; i < iendarg; i++)
				c = 10 * c + (buf[i] - '0');
			if (c < 0x21 || (c > 0x7e && c < 0xa0) || c > 0xff)
				break;
			iarg += 4;
			rval = ESCAPE_NUMBERED;
			break;
		}

		/*
		 * Unicode escapes are defined in groff as \[u0000]
		 * to \[u10FFFF], where the contained value must be
		 * a valid Unicode codepoint.  Here, however, only
		 * check the length and range.
		 */

		if (buf[iarg] != 'u' || argl < 5 || argl > 7)
			break;
		if (argl == 7 &&
		    (buf[iarg + 1] != '1' || buf[iarg + 2] != '0'))
			break;
		if (argl == 6 && buf[iarg + 1] == '0')
			break;
		if (argl == 5 && buf[iarg + 1] == 'D' &&
		    strchr("89ABCDEF", buf[iarg + 2]) != NULL)
			break;
		if ((int)strspn(buf + iarg + 1, "0123456789ABCDEFabcdef")
		    + 1 == argl)
			rval = ESCAPE_UNICODE;
		break;
	default:
		break;
	}
	goto out;

out_sub:
	iesc = sesc;
	iarg = sarg;
	iendarg = sendarg;
	iend = send;
	rval = ESCAPE_EXPAND;

out:
	if (rarg != NULL)
		*rarg = iarg;
	if (rendarg != NULL)
		*rendarg = iendarg;
	if (rend != NULL)
		*rend = iend;
	if (resc == NULL)
		return rval;

	/*
	 * Diagnostic messages are only issued when called
	 * from the parser, not when called from the formatters.
	 */

	*resc = iesc;
	switch (rval) {
	case ESCAPE_ERROR:
		err = MANDOCERR_ESC_BAD;
		break;
	case ESCAPE_UNSUPP:
		err = MANDOCERR_ESC_UNSUPP;
		break;
	case ESCAPE_UNDEF:
		if (esc_name == '\\')
			return rval;
		err = MANDOCERR_ESC_UNDEF;
		break;
	case ESCAPE_SPECIAL:
		if (mchars_spec2cp(buf + iarg, argl) >= 0)
			return rval;
		err = MANDOCERR_ESC_BAD;
		break;
	default:
		return rval;
	}
	mandoc_msg(err, ln, iesc, "%.*s", iend - iesc, buf + iesc);
	return rval;
}