proposal for version mismatch

[Eric Blake]

Would this patch be okay to apply to branch-1_4?  It will help people playing 
with m4 2.0 to more easily recognize when 1.4.6 can't parse a frozen file 
generated by 2.0.

2006-07-18  Eric Blake  <address@hidden>

        * src/m4.h (EXIT_MISMATCH): Define.
        * src/freeze.c (reload_frozen_state): Detect version mismatch, by
        exiting with status 63.
        * src/m4.c (usage): Document this.
        * doc/m4.texinfo (Invoking m4, Using frozen files): Likewise.
        * NEWS: Likewise.

Index: NEWS
===================================================================
RCS file: /sources/m4/m4/NEWS,v
retrieving revision 1.1.1.1.2.41
diff -u -r1.1.1.1.2.41 NEWS
--- NEWS        17 Jul 2006 17:09:53 -0000      1.1.1.1.2.41
+++ NEWS        18 Jul 2006 15:21:35 -0000
@@ -7,6 +7,8 @@
 * Fix buffer overrun in regexp and patsubst macros when handed a trailing
   backslash in the replacement text.
 * The format macro now understands %F, %g, and %G.
+* When loading frozen files, m4 now exits with status 63 if version
+  mismatch is detected.
 
 Version 1.4.5 - 15 July 2006, by Eric Blake  (CVS version 1.4.4c)
 
Index: doc/m4.texinfo
===================================================================
RCS file: /sources/m4/m4/doc/m4.texinfo,v
retrieving revision 1.1.1.1.2.48
diff -u -r1.1.1.1.2.48 m4.texinfo
--- doc/m4.texinfo      17 Jul 2006 17:09:53 -0000      1.1.1.1.2.48
+++ doc/m4.texinfo      18 Jul 2006 15:21:36 -0000
@@ -593,7 +593,9 @@
 argument collection or a quoted string.
 
 If none of the input files invoked @code{m4exit} (@pxref{M4exit}), the
-exit status of @code{m4} will be 0 for success, and 1 for failure.
+exit status of @code{m4} will be 0 for success, 1 for general failure
+(such as problems with reading an input file), and 63 for version
+mismatch (@pxref{Using frozen files}).
 
 If you need to read a file whose name starts with a @file{-}, you can
 specify it as @samp{./-file}, or use @option{--} to mark the end of
@@ -4016,6 +4018,11 @@
 It is looked up the same way as an @code{include} file (@pxref{Search
 Path}).
 
+If the frozen file was generated with a newer version of @code{m4} and
+contains directives that an older @code{m4} cannot parse, attempting to
+load the frozen file with option @option{-R} will cause @code{m4} to
+exit with status 63 to indicate version mismatch.
+
 @node Frozen file format
 @section Frozen file format
 @cindex frozen file format
Index: src/freeze.c
===================================================================
RCS file: /sources/m4/m4/src/freeze.c,v
retrieving revision 1.1.1.1.2.9
diff -u -r1.1.1.1.2.9 freeze.c
--- src/freeze.c        7 Jul 2006 03:37:26 -0000       1.1.1.1.2.9
+++ src/freeze.c        18 Jul 2006 15:21:36 -0000
@@ -234,8 +234,14 @@
   GET_DIRECTIVE;
   VALIDATE ('V');
   GET_CHARACTER;
-  VALIDATE ('1');
-  GET_CHARACTER;
+  GET_NUMBER (number[0]);
+  if (number[0] > 1)
+    M4ERROR ((EXIT_MISMATCH, 0,
+              "frozen file version %d greater than max supported of 1",
+             number[0]));
+  else if (number[0] < 1)
+    M4ERROR ((EXIT_FAILURE, 0,
+              "ill-formed frozen file, version directive expected"));
   VALIDATE ('\n');
 
   GET_DIRECTIVE;
Index: src/m4.c
===================================================================
RCS file: /sources/m4/m4/src/Attic/m4.c,v
retrieving revision 1.1.1.1.2.18
diff -u -r1.1.1.1.2.18 m4.c
--- src/m4.c    15 Jul 2006 22:08:58 -0000      1.1.1.1.2.18
+++ src/m4.c    18 Jul 2006 15:21:36 -0000
@@ -217,8 +217,8 @@
 ", stdout);
       fputs ("\
 \n\
-Exit status is 0 for success, 1 for failure, or whatever value was passed\n\
-to the m4exit macro.\n\
+Exit status is 0 for success, 1 for failure, 63 for frozen file version\n\
+mismatch, or whatever value was passed to the m4exit macro.\n\
 ", stdout);
     }
   exit (status);
Index: src/m4.h
===================================================================
RCS file: /sources/m4/m4/src/m4.h,v
retrieving revision 1.1.1.1.2.16
diff -u -r1.1.1.1.2.16 m4.h
--- src/m4.h    11 Jul 2006 12:17:11 -0000      1.1.1.1.2.16
+++ src/m4.h    18 Jul 2006 15:21:36 -0000
@@ -73,6 +73,9 @@
 #if ! HAVE_MKSTEMP
 int mkstemp (char *);
 #endif
+
+/* Used for version mismatch, when -R detects a frozen file it can't parse.  */
+#define EXIT_MISMATCH 63
 
 /* Various declarations.  */