Implement a fallback character request `.fchar'.

* src/roff/troff/charinfo.h (charinfo): New flag `fallback'.
(is_fallback): New inline function.
* src/roff/troff/input.cc (do_define_character): New function.
(define_character): Call `do_define_character'.
(define_fallback_character): New function.
(init_input_requests): Add `fchar'.
(charinfo::charinfo): Updated.
(charinfo::set_macro): New argument to set `fallback' flag.
* src/roff/troff/node.cc (make_glyph_node, make_node,
node::add_char): Check `fallback' flag.
* NEWS, man/groff_diff.man, man/groff_man: Updated.

7 files changed, 77 insertions, 10 deletions

diff --git a/ChangeLog b/ChangeLog
index beb72f2c..65481a38 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,19 @@
+2001-12-19  Werner LEMBERG  <wl@gnu.org>
+
+	Implement a fallback character request `.fchar'.
+
+	* src/roff/troff/charinfo.h (charinfo): New flag `fallback'.
+	(is_fallback): New inline function.
+	* src/roff/troff/input.cc (do_define_character): New function.
+	(define_character): Call `do_define_character'.
+	(define_fallback_character): New function.
+	(init_input_requests): Add `fchar'.
+	(charinfo::charinfo): Updated.
+	(charinfo::set_macro): New argument to set `fallback' flag.
+	* src/roff/troff/node.cc (make_glyph_node, make_node,
+	node::add_char): Check `fallback' flag.
+	* NEWS, man/groff_diff.man, man/groff_man: Updated.
+
 2001-12-16  Werner LEMBERG  <wl@gnu.org>
 
 	* groff.texinfo: Document exact search algorithm for glyphs.
diff --git a/NEWS b/NEWS
index 4313ef73..ae01a9c6 100644
--- a/NEWS
+++ b/NEWS
@@ -40,7 +40,14 @@ o It is now possible to have whitespace between the first and second dot (or
     ..
 
 o `.fn' is a new string-valued register which returns the (internal) real
-  font name; style and families are properly concatenated.
+  font name; styles and families are properly concatenated.
+
+o The new request `fchar' can be used to provide fallback characters.  Its
+  syntax is the same as the `char' request; the only difference is that a
+  character defined with `.char' hides the glyph with the same name in the
+  current font, whereas a character defined with `.fchar' is checked only if
+  the particular glyph isn't found in the current font.  This test happens
+  before checking special fonts.
 
 o A new escape sequence `\O' is available (mainly for internal use with
   grohtml).  Please see groff_diff.man and groff.texinfo for more details.
diff --git a/man/groff.man b/man/groff.man
index a64e9f0e..b845985a 100644
--- a/man/groff.man
+++ b/man/groff.man
@@ -987,7 +987,7 @@ to
 .REQ .char c anything
 Define character
 .argument c
-to string
+as string
 .argument anything .
 .
 .REQ .chop object
@@ -1171,12 +1171,19 @@ Disable field mechanism.
 Set field delimiter to
 .argument a
 and pad character to space.
+.
 .REQ .fc a b
 Set field delimiter to
 .argument a
 and pad character to
 .argument b .
 .
+.REQ .fchar c anything
+Define fallback character
+.argument c
+as string
+.argument anything .
+.
 .REQ .fi
 Fill output lines.
 .
diff --git a/man/groff_diff.man b/man/groff_diff.man
index fe3ae95b..644639e1 100644
--- a/man/groff_diff.man
+++ b/man/groff_diff.man
@@ -1088,6 +1088,22 @@ See the description of the
 request for more information on font families.
 .
 .TP
+.BI .fchar\  c\ string
+Define fallback character
+.I c
+to be
+.IR string .
+The syntax of this request is the same as the
+.B char
+request; the only difference is that a character defined with
+.B char
+hides the glyph with the same name in the current font, whereas a character
+defined with
+.B fchar
+is checked only if the particular glyph isn't found in the current font.
+This test happens before checking special fonts.
+.
+.TP
 .BI .fspecial\  f\ s1\ s2\|.\|.\|.
 When the current font is
 .IR f ,
diff --git a/src/roff/troff/charinfo.h b/src/roff/troff/charinfo.h
index a4ecd574..048d6266 100644
--- a/src/roff/troff/charinfo.h
+++ b/src/roff/troff/charinfo.h
@@ -1,5 +1,5 @@
 // -*- C++ -*-
-/* Copyright (C) 1989, 1990, 1991, 1992 Free Software Foundation, Inc.
+/* Copyright (C) 1989, 1990, 1991, 1992, 2001 Free Software Foundation, Inc.
      Written by James Clark (jjc@jclark.com)
 
 This file is part of groff.
@@ -33,6 +33,7 @@ class charinfo {
   char not_found;
   char transparent_translate;	// non-zero means translation applies to
 				// to transparent throughput
+  char fallback;
 public:
   enum { 
     ENDS_SENTENCE = 1,
@@ -68,12 +69,13 @@ public:
   void set_flags(unsigned char);
   void set_special_translation(int, int);
   int get_special_translation(int = 0);
-  macro *set_macro(macro *);
+  macro *set_macro(macro *, int = 0);
   macro *get_macro();
   int first_time_not_found();
   void set_number(int);
   int get_number();
   int numbered();
+  int is_fallback();
   symbol *get_symbol();
 };
 
@@ -116,6 +118,11 @@ inline int charinfo::numbered()
   return flags & NUMBERED;
 }
 
+inline int charinfo::is_fallback()
+{
+  return fallback;
+}
+
 inline charinfo *charinfo::get_translation(int transparent_throughput)
 {
   return (transparent_throughput && !transparent_translate
diff --git a/src/roff/troff/input.cc b/src/roff/troff/input.cc
index 1baeea24..26846577 100644
--- a/src/roff/troff/input.cc
+++ b/src/roff/troff/input.cc
@@ -3579,7 +3579,7 @@ void append_string()
   do_define_string(1);
 }
 
-void define_character()
+void do_define_character(int fallback)
 {
   node *n;
   int c;
@@ -3613,12 +3613,22 @@ void define_character()
       m->append((unsigned char)c);
     c = get_copy(&n);
   }
-  m = ci->set_macro(m);
+  m = ci->set_macro(m, fallback);
   if (m)
     delete m;
   tok.next();
 }
 
+void define_character()
+{
+  do_define_character(0);
+}
+
+void define_fallback_character()
+{
+  do_define_character(1);
+}
+
 static void remove_character()
 {
   tok.skip();
@@ -6708,6 +6718,7 @@ void init_input_requests()
   init_request("rd", read_request);
   init_request("cp", compatible);
   init_request("char", define_character);
+  init_request("fchar", define_fallback_character);
   init_request("rchar", remove_character);
   init_request("hcode", hyphenation_code);
   init_request("while", while_request);
@@ -7125,7 +7136,7 @@ int charinfo::next_index = 0;
 charinfo::charinfo(symbol s)
 : translation(0), mac(0), special_translation(TRANSLATE_NONE),
   hyphenation_code(0), flags(0), ascii_code(0), not_found(0),
-  transparent_translate(1), nm(s)
+  transparent_translate(1), fallback(0), nm(s)
 {
   index = next_index++;
 }
@@ -7154,10 +7165,11 @@ void charinfo::set_ascii_code(unsigned char c)
   ascii_code = c;
 }
 
-macro *charinfo::set_macro(macro *m)
+macro *charinfo::set_macro(macro *m, int f)
 {
   macro *tem = mac;
   mac = m;
+  fallback = f;
   return tem;
 }
 
diff --git a/src/roff/troff/node.cc b/src/roff/troff/node.cc
index b1bd80dd..68df49bf 100644
--- a/src/roff/troff/node.cc
+++ b/src/roff/troff/node.cc
@@ -4389,6 +4389,8 @@ node *make_glyph_node(charinfo *s, environment *env, int no_error_message = 0)
   int fn = fontno;
   int found = font_table[fontno]->contains(s);
   if (!found) {
+    if (s->is_fallback())
+      return make_composite_node(s, env);
     if (s->numbered()) {
       if (!no_error_message)
 	warning(WARN_CHAR, "can't find numbered character %1",
@@ -4467,7 +4469,7 @@ node *make_node(charinfo *ci, environment *env)
   if (tem)
     ci = tem;
   macro *mac = ci->get_macro();
-  if (mac)
+  if (mac && !ci->is_fallback())
     return make_composite_node(ci, env);
   else
     return make_glyph_node(ci, env);
@@ -4513,7 +4515,7 @@ node *node::add_char(charinfo *ci, environment *env,
   if (tem)
     ci = tem;
   macro *mac = ci->get_macro();
-  if (mac) {
+  if (mac && !ci->is_fallback()) {
     res = make_composite_node(ci, env);
     if (res) {
       res->next = this;