branch-1_4 changeword cleanup

[Eric Blake]

I know changeword is on its last leg, but:

changeword() currently has the (not so) cool effect of crippling the input 
engine (I'm not sure if it is because every character you type adds to the ever-
growing potential macro name, or because no character is recognized as being a 
potential macro); there is no way to recover once you type it.  I also think it 
is good that changeword is currently a no-op without arguments, (since not all 
m4 compilations have it, you should have to explicitly request it with 
arguments), but it might as well be blind rather than warning and expanding to 
void.  So here's a TODO item, done.

2006-07-13  Eric Blake  <address@hidden>

        * src/input.c (input_init): Simplify.
        (set_word_regexp): Treat empty string as default, since empty
        regexp would disable word parsing.
        * src/m4.c (user_word_regexp): Default to empty string.
        * src/builtin.c (builtin_tab): Make changeword blind.
        * NEWS: Document this.
        * TODO: Knock off completed items.

Index: TODO
===================================================================
RCS file: /sources/m4/m4/TODO,v
retrieving revision 1.1.1.1
diff -u -r1.1.1.1 TODO
--- TODO        17 Feb 2000 03:03:19 -0000      1.1.1.1
+++ TODO        13 Jul 2006 21:59:54 -0000
@@ -1,11 +1,10 @@
 TODO file for GNU m4
 
-Tell <address@hidden> if you feel like volunteering for any
+Tell <address@hidden> if you feel like volunteering for any
 of these ideas, listed more or less in decreasing order of priority.
 
 * Features or problems
   - Update documentation from accumulated mail about it
-  - Changeword without arguments should restore default behavior
   - Study synclines at the very beginning of each diverted sequence
   - Make eval work on bignums - the 32 bits limit is artificial
        From Krste Asanovic <address@hidden>, 1993-03-20
@@ -13,8 +12,6 @@
 * Optimization and clean up
   - Check for memory leaks and uninitialized reads
        From Vern Paxson <address@hidden> on 1993-12-06
-  - Simplify format/ecvt code, together with HAVE_EFGCVT
-  - Finalize the stdarg vs varargs thing
   - Profile GNU m4 and speed it up
        From David J. MacKenzie <address@hidden>, 1993-01-20
 
@@ -31,9 +28,6 @@
        GNU m4 is lousy regarding NULs in streams (this would require
        maintaining the string lengths, and avoiding strlen, strcpy,
        etc.). 
-  - Clean up the obstack.[ch] code
-  - Use rx.[ch] instead of regex.[ch]
-       From Hal Peterson <address@hidden>, 1994-04-22
 
 Local Variables:
 mode: outline
Index: NEWS
===================================================================
RCS file: /sources/m4/m4/NEWS,v
retrieving revision 1.1.1.1.2.36
diff -u -r1.1.1.1.2.36 NEWS
--- NEWS        13 Jul 2006 21:16:41 -0000      1.1.1.1.2.36
+++ NEWS        13 Jul 2006 21:59:54 -0000
@@ -45,6 +45,8 @@
 * The ifdef, divert, m4exit, substr, and translit macros now correctly
   ignore extra arguments.
 * The popdef and undefine macros now correctly accept multiple arguments.
+* Although changeword is on its last leg, if enabled, it now reverts to the
+  default (faster) regexp when passed the empty string.
 
 Version 1.4.4b - 17 June 2006, by Eric Blake  (CVS version 1.4.4a)
 
Index: src/builtin.c
===================================================================
RCS file: /sources/m4/m4/src/Attic/builtin.c,v
retrieving revision 1.1.1.1.2.22
diff -u -r1.1.1.1.2.22 builtin.c
--- src/builtin.c       13 Jul 2006 21:16:42 -0000      1.1.1.1.2.22
+++ src/builtin.c       13 Jul 2006 21:59:54 -0000
@@ -101,7 +101,7 @@
   { "changecom",       FALSE,  FALSE,  FALSE,  m4_changecom },
   { "changequote",     FALSE,  FALSE,  FALSE,  m4_changequote },
 #ifdef ENABLE_CHANGEWORD
-  { "changeword",      TRUE,   FALSE,  FALSE,  m4_changeword },
+  { "changeword",      TRUE,   FALSE,  TRUE,   m4_changeword },
 #endif
   { "debugmode",       TRUE,   FALSE,  FALSE,  m4_debugmode },
   { "debugfile",       TRUE,   FALSE,  FALSE,  m4_debugfile },
Index: src/input.c
===================================================================
RCS file: /sources/m4/m4/src/Attic/input.c,v
retrieving revision 1.1.1.1.2.8
diff -u -r1.1.1.1.2.8 input.c
--- src/input.c 23 Jun 2006 13:06:10 -0000      1.1.1.1.2.8
+++ src/input.c 13 Jul 2006 21:59:55 -0000
@@ -593,10 +593,7 @@
   ecomm.length = strlen (ecomm.string);
 
 #ifdef ENABLE_CHANGEWORD
-  if (user_word_regexp)
-    set_word_regexp (user_word_regexp);
-  else
-    set_word_regexp (DEFAULT_WORD_REGEXP);
+  set_word_regexp (user_word_regexp);
 #endif
 }
 
@@ -649,7 +646,7 @@
   const char *msg;
   struct re_pattern_buffer new_word_regexp;
 
-  if (!strcmp (regexp, DEFAULT_WORD_REGEXP))
+  if (!*regexp || !strcmp (regexp, DEFAULT_WORD_REGEXP))
     {
       default_word_regexp = TRUE;
       return;
Index: src/m4.c
===================================================================
RCS file: /sources/m4/m4/src/Attic/m4.c,v
retrieving revision 1.1.1.1.2.16
diff -u -r1.1.1.1.2.16 m4.c
--- src/m4.c    12 Jul 2006 13:14:51 -0000      1.1.1.1.2.16
+++ src/m4.c    13 Jul 2006 21:59:55 -0000
@@ -58,7 +58,7 @@
 
 #ifdef ENABLE_CHANGEWORD
 /* User provided regexp for describing m4 words.  */
-const char *user_word_regexp = NULL;
+const char *user_word_regexp = "";
 #endif
 
 /* Name of frozen file to digest after initialization.  */
Index: doc/m4.texinfo
===================================================================
RCS file: /sources/m4/m4/doc/m4.texinfo,v
retrieving revision 1.1.1.1.2.40
diff -u -r1.1.1.1.2.40 m4.texinfo
--- doc/m4.texinfo      13 Jul 2006 21:16:41 -0000      1.1.1.1.2.40
+++ doc/m4.texinfo      13 Jul 2006 22:05:25 -0000
@@ -2445,7 +2445,9 @@
 
 You should note that using @code{changeword} will slow @code{m4} down
 by a factor of about seven, once it is changed to something other
-than the default regular expression.
+than the default regular expression.  You can invoke @code{changeword}
+with the empty string to restore the default word definition, and regain
+the parsing speed.
+
+The builtin macro @code{changeword} is recognized only when given
+arguments.
 
 @node M4wrap
 @section Saving input