mandoc: Use TIOCGWINSZ to reduce the default -Owidth during interactive

[schwarze@mandoc.bsd.lv]

Log Message:
-----------
Use TIOCGWINSZ to reduce the default -Owidth during interactive use
on terminals narrower than 79 columns and the default -Oindent on
terminals narrower than 66 columns.
Requested by and feedback from pirofti@;
mpi@ and juanfra@ also like the general direction.

Modified Files:
--------------
    mandoc:
        main.c
        mandoc.1

Revision Data
-------------
Index: main.c
===================================================================
RCS file: /home/cvs/mandoc/mandoc/main.c,v
retrieving revision 1.303
retrieving revision 1.304
diff -Lmain.c -Lmain.c -u -p -r1.303 -r1.304
--- main.c
+++ main.c
@@ -1,7 +1,7 @@
 /*	$Id$ */
 /*
  * Copyright (c) 2008-2012 Kristaps Dzonsons <kristaps@bsd.lv>
- * Copyright (c) 2010-2012, 2014-2017 Ingo Schwarze <schwarze@openbsd.org>
+ * Copyright (c) 2010-2012, 2014-2018 Ingo Schwarze <schwarze@openbsd.org>
  * Copyright (c) 2010 Joerg Sonnenberger <joerg@netbsd.org>
  *
  * Permission to use, copy, modify, and distribute this software for any
@@ -19,7 +19,9 @@
 #include "config.h"
 
 #include <sys/types.h>
+#include <sys/ioctl.h>
 #include <sys/param.h>	/* MACHINE */
+#include <sys/termios.h>
 #include <sys/wait.h>
 
 #include <assert.h>
@@ -120,6 +122,7 @@ main(int argc, char *argv[])
 	struct manconf	 conf;
 	struct mansearch search;
 	struct curparse	 curp;
+	struct winsize	 ws;
 	struct tag_files *tag_files;
 	struct manpage	*res, *resp;
 	const char	*progname, *sec, *thisarg;
@@ -315,6 +318,15 @@ main(int argc, char *argv[])
 	    outmode == OUTMODE_LST ||
 	    !isatty(STDOUT_FILENO))
 		use_pager = 0;
+
+	if (use_pager &&
+	    (conf.output.width == 0 || conf.output.indent == 0) &&
+	    ioctl(STDOUT_FILENO, TIOCGWINSZ, &ws) != -1) {
+		if (conf.output.width == 0 && ws.ws_col < 79)
+			conf.output.width = ws.ws_col - 1;
+		if (conf.output.indent == 0 && ws.ws_col < 66)
+			conf.output.indent = 3;
+	}
 
 #if HAVE_PLEDGE
 	if (!use_pager)
Index: mandoc.1
===================================================================
RCS file: /home/cvs/mandoc/mandoc/mandoc.1,v
retrieving revision 1.222
retrieving revision 1.223
diff -Lmandoc.1 -Lmandoc.1 -u -p -r1.222 -r1.223
--- mandoc.1
+++ mandoc.1
@@ -299,9 +299,6 @@ The special characters documented in
 .Xr mandoc_char 7
 are rendered best-effort in an ASCII equivalent.
 .Pp
-Output width is limited to 78 visible columns unless literal input lines
-exceed this limit.
-.Pp
 The following
 .Fl O
 arguments are accepted:
@@ -315,6 +312,8 @@ and seven for
 .Xr man 7 .
 Increasing this is not recommended; it may result in degraded formatting,
 for example overfull lines or ugly line breaks.
+When output is to a pager on a terminal that is less than 66 columns
+wide, the default is reduced to three columns.
 .It Cm mdoc
 Format
 .Xr man 7
@@ -331,7 +330,12 @@ output formats in the same way as the
 source it was generated from.
 .It Cm width Ns = Ns Ar width
 The output width is set to
-.Ar width .
+.Ar width
+instead of the default of 78.
+When output is to a pager on a terminal that is less than 79 columns
+wide, the default is reduced to one less than the terminal width.
+In any case, lines that are output in literal mode are never wrapped
+and may exceed the output width.
 .El
 .Ss HTML Output
 Output produced by
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