Surprisingly, every escape sequence can also be used as an argument

delimiter for an outer escape sequence, in which case the delimiting
escape sequence retains its syntax but usually ignores its argument
and loses its inherent effect.  Add rudimentary support for this
syntax quirk in order to improve parsing compatibility with groff.

1 files changed, 49 insertions, 26 deletions

diff --git a/usr.bin/mandoc/roff_escape.c b/usr.bin/mandoc/roff_escape.c
index eeec825043c..ab4ea7343d0 100644
--- a/usr.bin/mandoc/roff_escape.c
+++ b/usr.bin/mandoc/roff_escape.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: roff_escape.c,v 1.13 2022/06/07 09:51:03 schwarze Exp $ */
+/* $OpenBSD: roff_escape.c,v 1.14 2022/06/08 13:08:00 schwarze Exp $ */
 /*
  * Copyright (c) 2011, 2012, 2013, 2014, 2015, 2017, 2018, 2020, 2022
  *               Ingo Schwarze <schwarze@openbsd.org>
@@ -59,7 +59,7 @@ mandoc_escape(const char **rendarg, const char **rarg, int *rargl)
  * 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,
+ * Diagnostic messages are generated if and only if ln != 0,
  * that is, if and only if called by roff_expand().
  */
 enum mandoc_esc
@@ -72,11 +72,13 @@ roff_escape(const char *buf, const int ln, const int aesc,
 	int		 iendarg;	/* index right after the argument */
 	int		 iend;		/* index right after the sequence */
 	int		 sesc, snam, sarg, sendarg, send; /* for sub-escape */
+	int		 escterm;	/* whether term is escaped */
 	int		 maxl;		/* expected length of the argument */
 	int		 argl;		/* actual length of the argument */
 	int		 c, i;		/* for \[char...] parsing */
 	int 		 valid_A;	/* for \A parsing */
 	enum mandoc_esc	 rval;		/* return value */
+	enum mandoc_esc	 stype;		/* for sub-escape */
 	enum mandocerr	 err;		/* diagnostic code */
 	char		 term;		/* byte terminating the argument */
 
@@ -264,13 +266,32 @@ roff_escape(const char *buf, const int ln, const int aesc,
 
 	/* Decide how to end the argument. */
 
+	escterm = 0;
+	stype = ESCAPE_EXPAND;
 	if ((term == '\b' || (term == '\0' && maxl == INT_MAX)) &&
-	    buf[iarg] == buf[iesc] && roff_escape(buf, ln, iendarg,
-	    &sesc, &snam, &sarg, &sendarg, &send) == ESCAPE_EXPAND)
-		goto out_sub;
+	    buf[iarg] == buf[iesc]) {
+		stype = roff_escape(buf, ln, iendarg,
+		    &sesc, &snam, &sarg, &sendarg, &send);
+		if (stype == ESCAPE_EXPAND)
+			goto out_sub;
+	}
 
 	if (term == '\b') {
-		if (strchr("BDHLRSvxNhl", buf[inam]) != NULL &&
+		if (stype == ESCAPE_UNDEF)
+			iarg++;
+		if (stype != ESCAPE_EXPAND && stype != ESCAPE_UNDEF) {
+			if (strchr("BHLRSNhlvx", buf[inam]) != NULL &&
+			    strchr(" ,.0DLOXYZ^abdhlortuvx|~",
+			    buf[snam]) != NULL) {
+				err = MANDOCERR_ESC_DELIM;
+				iend = send;
+				iarg = iendarg = sesc;
+				goto out;
+			}
+			escterm = 1;
+			iarg = send;
+			term = buf[snam];
+		} else if (strchr("BDHLRSvxNhl", buf[inam]) != NULL &&
 		    strchr(" %&()*+-./0123456789:<=>", buf[iarg]) != NULL) {
 			err = MANDOCERR_ESC_DELIM;
 			if (rval != ESCAPE_EXPAND)
@@ -280,7 +301,8 @@ roff_escape(const char *buf, const int ln, const int aesc,
 				goto out;
 			}
 		}
-		term = buf[iarg++];
+		if (term == '\b')
+			term = buf[iarg++];
 	} else if (term == '\0' && maxl == INT_MAX) {
 		if (buf[inam] == 'n' && (buf[iarg] == '+' || buf[iarg] == '-'))
 			iarg++;
@@ -311,34 +333,34 @@ roff_escape(const char *buf, const int ln, const int aesc,
 	while (maxl > 0) {
 		if (buf[iendarg] == '\0') {
 			err = MANDOCERR_ESC_INCOMPLETE;
-			if (rval != ESCAPE_EXPAND)
+			if (rval != ESCAPE_EXPAND &&
+			    rval != ESCAPE_OVERSTRIKE)
 				rval = ESCAPE_ERROR;
-			/* Ignore an incomplete argument except for \w. */
-			if (buf[inam] != 'w')
+			/* Usually, ignore an incomplete argument. */
+			if (strchr("Aow", buf[inam]) == NULL)
 				iendarg = iarg;
 			break;
 		}
-		if (buf[iendarg] == term) {
-			iend = iendarg + 1;
-			break;
-		}
-		if (buf[inam] == 'N' &&
-		    isdigit((unsigned char)buf[iendarg]) == 0) {
+		if (escterm == 0 && buf[iendarg] == term) {
 			iend = iendarg + 1;
 			break;
 		}
 		if (buf[iendarg] == buf[iesc]) {
-			switch (roff_escape(buf, ln, iendarg,
-			    &sesc, &snam, &sarg, &sendarg, &send)) {
-			case ESCAPE_EXPAND:
+			stype = roff_escape(buf, ln, iendarg,
+			    &sesc, &snam, &sarg, &sendarg, &send);
+			if (stype == ESCAPE_EXPAND)
 				goto out_sub;
-			case ESCAPE_UNDEF:
+			iend = send;
+			if (escterm == 1 &&
+			    (buf[snam] == term || buf[inam] == 'N'))
 				break;
-			default:
+			if (stype != ESCAPE_UNDEF)
 				valid_A = 0;
-				break;
-			}
-			iendarg = iend = send;
+			iendarg = send;
+		} else if (buf[inam] == 'N' &&
+		    isdigit((unsigned char)buf[iendarg]) == 0) {
+			iend = iendarg + 1;
+			break;
 		} else {
 			if (buf[iendarg] == ' ' || buf[iendarg] == '\t')
 				valid_A = 0;
@@ -483,6 +505,8 @@ out_sub:
 	rval = ESCAPE_EXPAND;
 
 out:
+	if (resc != NULL)
+		*resc = iesc;
 	if (rnam != NULL)
 		*rnam = inam;
 	if (rarg != NULL)
@@ -491,7 +515,7 @@ out:
 		*rendarg = iendarg;
 	if (rend != NULL)
 		*rend = iend;
-	if (resc == NULL)
+	if (ln == 0)
 		return rval;
 
 	/*
@@ -499,7 +523,6 @@ out:
 	 * from the parser, not when called from the formatters.
 	 */
 
-	*resc = iesc;
 	switch (rval) {
 	case ESCAPE_UNSUPP:
 		err = MANDOCERR_ESC_UNSUPP;