During identifier parsing, handle undefined escape sequences

in the same way as groff:
* \\ is always reduced to \
* \. is always reduced to .
* other undefined escape sequences are usually reduced to the escape name,
for example \G to G, except during the expansion of expanding escape
sequences having the standard argument form (in particular \* and \n),
in which case the backslash is preserved literally.

Yes, this is confusing indeed.
For example, the following have the same meaning:
* .ds \.   and   .ds .     which is not the same as   .ds \\.
* \*[\.]   and   \*[.]     which is not the same as   \*[\\.]
* .ds \G   and   .ds G     which is not the same as   .ds \\G
* \*[\G]   and   \*[\\G]   which is not the same as   \*[G]   <- sic!

To feel less dirty, have a leaning toothpick, if you are so inclined.

This patch also slightly improves the string shown by the "escaped
character not allowed in a name" error message.

1 files changed, 48 insertions, 10 deletions

diff --git a/roff.c b/roff.c
index dbe47b43..785097b6 100644
--- a/roff.c
+++ b/roff.c
@@ -1375,6 +1375,7 @@ roff_expand(struct roff *r, struct buf *buf, int ln, int pos, char ec)
 	int		 iarg;		/* index beginning the argument */
 	int		 iendarg;	/* index right after the argument */
 	int		 iend;		/* index right after the sequence */
+	int		 isrc, idst;	/* to reduce \\ and \. in names */
 	int		 deftype;	/* type of definition to paste */
 	int		 argi;		/* macro argument index */
 	int		 quote_args;	/* true for \\$@, false for \\$* */
@@ -1428,6 +1429,21 @@ roff_expand(struct roff *r, struct buf *buf, int ln, int pos, char ec)
 			continue;
 		}
 
+		/* Reduce \\ and \. in names. */
+
+		if (buf->buf[inam] == '*' || buf->buf[inam] == 'n') {
+			isrc = idst = iarg;
+			while (isrc < iendarg) {
+				if (isrc + 1 < iendarg &&
+				    buf->buf[isrc] == '\\' &&
+				    (buf->buf[isrc + 1] == '\\' ||
+				     buf->buf[isrc + 1] == '.'))
+					isrc++;
+				buf->buf[idst++] = buf->buf[isrc++];
+			}
+			iendarg -= isrc - idst;
+		}
+
 		/* Handle expansion. */
 
 		res = NULL;
@@ -4002,7 +4018,7 @@ static size_t
 roff_getname(struct roff *r, char **cpp, int ln, int pos)
 {
 	char	 *name, *cp;
-	size_t	  namesz;
+	int	  namesz, inam, iend;
 
 	name = *cpp;
 	if (*name == '\0')
@@ -4010,24 +4026,46 @@ roff_getname(struct roff *r, char **cpp, int ln, int pos)
 
 	/* Advance cp to the byte after the end of the name. */
 
-	for (cp = name; 1; cp++) {
-		namesz = cp - name;
+	cp = name;
+	namesz = 0;
+	for (;;) {
 		if (*cp == '\0')
 			break;
 		if (*cp == ' ' || *cp == '\t') {
 			cp++;
 			break;
 		}
-		if (*cp != '\\')
+		if (*cp != '\\') {
+			if (name + namesz < cp) {
+				name[namesz] = *cp;
+				*cp = ' ';
+			}
+			namesz++;
+			cp++;
 			continue;
+		}
 		if (cp[1] == '{' || cp[1] == '}')
 			break;
-		if (*++cp == '\\')
-			continue;
-		mandoc_msg(MANDOCERR_NAMESC, ln, pos,
-		    "%.*s", (int)(cp - name + 1), name);
-		mandoc_escape((const char **)&cp, NULL, NULL);
-		break;
+		if (roff_escape(cp, 0, 0, NULL, &inam,
+		    NULL, NULL, &iend) != ESCAPE_UNDEF) {
+			mandoc_msg(MANDOCERR_NAMESC, ln, pos,
+			    "%.*s%.*s", namesz, name, iend, cp);
+			cp += iend;
+			break;
+		}
+
+		/*
+		 * In an identifier, \\, \., \G and so on
+		 * are reduced to \, ., G and so on,
+		 * vaguely similar to copy mode.
+		 */
+
+		name[namesz++] = cp[inam];
+		while (iend--) {
+			if (cp >= name + namesz)
+				*cp = ' ';
+			cp++;
+		}
 	}
 
 	/* Read past spaces. */