Don't format lines that look like troff requests, for

compatibility with old fmt(1).  New option -n permits
formatting of lines beginning with a dot character.

PR:		bin/31392
MFC after:	3 days

usr.bin/fmt/fmt.1

@@ -42,7 +42,7 @@
 .Nd simple text formatter
 .Sh SYNOPSIS
 .Nm fmt
-.Op Fl cmps
+.Op Fl cmnps
 .Op Fl d Ar chars
 .Op Fl l Ar num
 .Op Fl t Ar num
@@ -88,6 +88,14 @@ In this case, most of the other
 options are ignored; no splitting or joining of lines is done.
 .It Fl m
 Try to format mail header lines contained in the input sensibly.
+.It Fl n
+Format lines beginning with a
+.Ql \&.
+(dot) character.
+Normally,
+.Nm
+does not fill these lines, for compatibility with
+.Xr nroff 1 .
 .It Fl p
 Allow indented paragraphs.
 Without the

usr.bin/fmt/fmt.c

@@ -30,6 +30,8 @@
  *    preceded by a non-blank non-message-header line, is
  *    taken to start a new paragraph, which also contains
  *    any subsequent lines with non-empty leading whitespace.
+ *    Unless the `-n' option is given, lines beginning with
+ *    a . (dot) are not formatted.
  * 3. The "everything else" is split into words; a word
  *    includes its trailing whitespace, and a word at the
  *    end of a line is deemed to be followed by a single
@@ -222,6 +224,7 @@ static int tab_width=8;		/* Number of spaces per tab stop */
 static size_t output_tab_width=8;	/* Ditto, when squashing leading spaces */
 static const char *sentence_enders=".?!";	/* Double-space after these */
 static int grok_mail_headers=0;	/* treat embedded mail headers magically? */
+static int format_troff=0;	/* Format troff? */
 
 static int n_errors=0;		/* Number of failed files. Return on exit. */
 static char *output_buffer=0;	/* Output line will be built here */
@@ -257,10 +260,11 @@ main(int argc, char *argv[]) {
 
   /* 1. Grok parameters. */
 
-  while ((ch = getopt(argc, argv, "0123456789cd:hl:mpst:w:")) != -1)
+  while ((ch = getopt(argc, argv, "0123456789cd:hl:mnpst:w:")) != -1)
   switch(ch) {
     case 'c':
       centerP = 1;
+      format_troff = 1;
       continue;
     case 'd':
       sentence_enders = optarg;
@@ -272,6 +276,9 @@ main(int argc, char *argv[]) {
     case 'm':
       grok_mail_headers = 1;
       continue;
+    case 'n':
+      format_troff = 1;
+      continue;
     case 'p':
       allow_indented_paragraphs = 1;
       continue;
@@ -307,6 +314,7 @@ main(int argc, char *argv[]) {
 "         -d <chars> double-space after <chars> at line end\n"
 "         -l <n> turn each <n> spaces at start of line into a tab\n"
 "         -m     try to make sure mail header lines stay separate\n"
+"         -n     format lines beginning with a dot\n"
 "         -p     allow indented paragraphs\n"
 "         -s     coalesce whitespace inside lines\n"
 "         -t <n> have tabs every <n> columns\n"
@@ -395,6 +403,7 @@ process_stream(FILE *stream, const char *name) {
       }
       /* We need a new paragraph if and only if:
        *   this line is blank,
+       *   OR it's a troff request (and we don't format troff),
        *   OR it's a mail header,
        *   OR it's not a mail header AND the last line was one,
        *   OR the indentation has changed
@@ -402,6 +411,7 @@ process_stream(FILE *stream, const char *name) {
        *      AND this isn't the second line of an indented paragraph.
        */
       if ( length==0
+           || (line[0]=='.' && !format_troff)
            || header_type==hdr_Header
            || (header_type==hdr_NonHeader && prev_header_type>hdr_NonHeader)
            || (np!=last_indent
@@ -412,8 +422,11 @@ process_stream(FILE *stream, const char *name) {
         first_indent = np;
         last_indent = np;
         if (header_type==hdr_Header) last_indent=2;	/* for cont. lines */
-        if (length==0) {
-          putchar('\n');
+        if (length==0 || (line[0]=='.' && !format_troff)) {
+          if (length==0)
+            putchar('\n');
+          else
+            printf("%.*s\n", (int)length, line);
           prev_header_type=hdr_ParagraphStart;
           continue;
         }
@@ -594,11 +607,13 @@ get_line(FILE *stream, size_t *lengthp) {
   size_t len=0;
   int ch;
   size_t spaces_pending=0;
+  int troff=0;
 
   if (buf==NULL) { length=100; buf=XMALLOC(length); }
   while ((ch=getc(stream)) != '\n' && ch != EOF) {
+    if (len+spaces_pending==0 && ch=='.' && !format_troff) troff=1;
     if (ch==' ') ++spaces_pending;
-    else if (isprint(ch)) {
+    else if (troff || isprint(ch)) {
       while (len+spaces_pending >= length) {
         length*=2; buf=xrealloc(buf, length);
       }