Make --debugfile argument optional.

* src/main.c (long_options): Make the argument optional, to allow
setting debug file back to stderr.
(main): Make --debugfile order-dependent.
(usage): Document this.
* doc/m4.texinfo (Debugging options): Likewise.
* NEWS: Likewise.
* tests/options.at (--debugfile): Enhance test.
(--safer): Adjust to new semantics.

Signed-off-by: Eric Blake <ebb9@byu.net>
(cherry picked from commit c59c67993219ec04965b1347b44a7e3d09ff425c)

5 files changed, 77 insertions, 28 deletions

diff --git a/ChangeLog b/ChangeLog
index 11e31b2d..c042e0c7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,15 @@
+2008-12-23  Eric Blake  <ebb9@byu.net>
+
+	Make --debugfile argument optional.
+	* src/main.c (long_options): Make the argument optional, to allow
+	setting debug file back to stderr.
+	(main): Make --debugfile order-dependent.
+	(usage): Document this.
+	* doc/m4.texinfo (Debugging options): Likewise.
+	* NEWS: Likewise.
+	* tests/options.at (--debugfile): Enhance test.
+	(--safer): Adjust to new semantics.
+
 2008-12-22  Eric Blake  <ebb9@byu.net>
 
 	Use @var correctly.
diff --git a/NEWS b/NEWS
index 618a8f2b..2e9a8c24 100644
--- a/NEWS
+++ b/NEWS
@@ -251,24 +251,12 @@ promoted to 2.0.
    `-d-V' to disable prior debug settings from the command line, similar to
    using the builtin `debugmode' without arguments.  The option
    `--debugmode' is added as an alias for `-d'.  The new flag `d' is added
-   to control whether dereferncing an undefined macro causes a warning;
+   to control whether dereferencing an undefined macro causes a warning;
    this flag is enabled by default if neither `-d' nor `-E' are specified.
    When given the empty string, the mode is treated as `+adeq' instead of
    `aeq'.  Also, the position of `-d' with respect to files on the command
    line is now significant.
 
-** New `-g'/`--gnu' command-line option overrides `-G'/`--traditional'.
-   For now, the environment variable POSIXLY_CORRECT has no effect on M4
-   behavior; but a future release of M4 will behave as though --traditional
-   is implied if POSIXLY_CORRECT is set (this future change is necessary,
-   because in the current release, there is no way to disable GNU
-   extensions that conflict with POSIX without the use of a non-POSIX
-   command-line argument).  Clients of M4 that want to use GNU extensions,
-   even when POSIXLY_CORRECT is set, should start using the -g command-line
-   argument, even though it is currently a no-op if -G did not appear
-   earlier in the command line, so that the client will not break in the
-   face of an upgraded m4 and a POSIXLY_CORRECT execution environment.
-
 ** A new predefined text macro, `__m4_version__', expands to the unquoted
    version number of M4, if GNU extensions are enabled.  While you should
    generally favor feature tests over version number checks, this macro can
@@ -334,6 +322,23 @@ contains the following beta features that were deemed worth deferring until
 
 ** A number of portability improvements inherited from gnulib.
 
+* Noteworthy changes in Version 1.4.13 (2008-12-??) [stable]
+  Released by Eric Blake, based on git version 1.4.12.*
+
+** The manual is now distributed under the terms of FDL 1.3.
+
+** The `divert' and `undivert' builtins have been made more efficient
+   when using temporary files for large diversions.
+
+** The command line option `--debugfile', introduced in 1.4.7, now
+   treats its argument as optional, in order to allow setting the debug
+   output back to stderr when used without an argument; and order is now
+   significant with respect to command line files.  You must therefore use
+   `m4 --debugfile=trace file', not `m4 file --debugfile trace'.  This
+   change does not affect the deprecated `-o'/`--error-output' option.
+
+** A number of portability improvements inherited from gnulib.
+
 * Noteworthy changes in Version 1.4.12 (2008-10-10) [stable]
   Released by Eric Blake, based on git version 1.4.11.*
 
diff --git a/doc/m4.texinfo b/doc/m4.texinfo
index a2eda21a..121300f6 100644
--- a/doc/m4.texinfo
+++ b/doc/m4.texinfo
@@ -856,7 +856,7 @@ redefining the same @var{name} adds another definition to its stack.
 Short for @option{--syncoutput=1}, turning on synchronization lines
 (sometimes called @dfn{synclines}).
 
-@item --syncoutput@r{[}=STATE@r{]}
+@item --syncoutput@r{[}=@var{state}@r{]}
 @cindex synchronization lines
 @cindex location, input
 @cindex input location
@@ -1024,15 +1024,18 @@ len(`123')
 @result{}3
 @end example
 
-@item --debugfile=@var{file}
+@item --debugfile@r{[}=@var{file}@r{]}
 @itemx -o @var{file}
 @itemx --error-output=@var{file}
 Redirect debug and trace output to the named @var{file}.  Warnings,
 error messages, and the output of @code{errprint} and @code{dumpdef},
-are still printed to standard error.  If this option is not given, debug
-output goes to standard error; if @var{file} is the empty string, debug
-output is discarded.  @xref{Debugfile}, for more details.  The
-spellings @option{-o} and @option{--error-output} are misleading and
+are still printed to standard error.  If these options are not used, or
+if @var{file} is unspecified (only possible for @option{--debugfile}),
+debug output goes to standard error; if @var{file} is the empty string,
+debug output is discarded.  @xref{Debugfile}, for more details.  The
+option @option{--debugfile} may be given more than once, and order is
+significant with respect to file names.  The spellings @option{-o} and
+@option{--error-output} are misleading and
 inconsistent with other @acronym{GNU} tools; using those spellings will
 evoke a warning, and they may be withdrawn or change semantics in a
 future release.
diff --git a/src/main.c b/src/main.c
index b8900417..f8ab98ea 100644
--- a/src/main.c
+++ b/src/main.c
@@ -94,7 +94,7 @@ Operation modes:\n\
   -b, --batch                  buffer output, process interrupts\n\
   -c, --discard-comments       do not copy comments to the output\n\
   -E, --fatal-warnings         once: warnings become errors, twice: stop\n\
-                               execution at first error\n\
+                                 execution at first error\n\
   -i, --interactive            unbuffer output, ignore interrupts\n\
   -P, --prefix-builtins        force a `m4_' prefix to all builtins\n\
   -Q, --quiet, --silent        suppress some warnings for builtins\n\
@@ -112,10 +112,10 @@ SPEC is any one of:\n\
       xprintf (_("\
 Dynamic loading features:\n\
   -M, --module-directory=DIR   add DIR to module search path before\n\
-                               `%s'\n\
+                                 %s\n\
   -m, --load-module=MODULE     load dynamic MODULE\n\
       --unload-module=MODULE   unload dynamic MODULE\n\
-"), PKGLIBEXECDIR);
+"), quotearg_style (locale_quoting_style, PKGLIBEXECDIR));
       puts ("");
       fputs (_("\
 Preprocessor features:\n\
@@ -129,7 +129,7 @@ Preprocessor features:\n\
   -p, --pushdef=NAME[=VALUE]   pushdef NAME as having VALUE, or empty\n\
   -s, --synclines              short for --syncoutput=1\n\
       --syncoutput[=STATE]     set generation of `#line NUM \"FILE\"' lines\n\
-                               to STATE (0=off, 1=on, default 0 if omitted)\n\
+                                 to STATE (0=off, 1=on, default 0)\n\
   -U, --undefine=NAME          undefine NAME\n\
 "), stdout);
       puts ("");
@@ -150,7 +150,8 @@ Frozen state files:\n\
 Debugging:\n\
   -d, --debug[=[-|+]FLAGS], --debugmode[=[-|+]FLAGS]\n\
                                set debug level (no FLAGS implies `+adeq')\n\
-      --debugfile=FILE         redirect debug and trace output\n\
+      --debugfile[=FILE]       redirect debug and trace output to FILE\n\
+                                 (default stderr, discard if empty string)\n\
   -l, --debuglen=NUM           restrict macro tracing size\n\
   -t, --trace=NAME, --traceon=NAME\n\
                                trace NAME when it is defined\n\
@@ -253,7 +254,7 @@ static const struct option long_options[] =
   {"warnings", no_argument, NULL, 'W'},
 
   {"arglength", required_argument, NULL, ARGLENGTH_OPTION},
-  {"debugfile", required_argument, NULL, DEBUGFILE_OPTION},
+  {"debugfile", optional_argument, NULL, DEBUGFILE_OPTION},
   {"hashsize", required_argument, NULL, HASHSIZE_OPTION},
   {"error-output", required_argument, NULL, ERROR_OUTPUT_OPTION},
   {"import-environment", no_argument, NULL, IMPORT_ENVIRONMENT_OPTION},
@@ -564,6 +565,15 @@ main (int argc, char *const *argv, char *const *envp)
 	  m4_set_max_debug_arg_length_opt (context, size);
 	  break;
 
+	case DEBUGFILE_OPTION:
+	  /* Staggered handling of '--debugfile', since it is useful
+	     prior to first file and prior to reloading, but other
+	     uses must also have effect between files.  */
+	  if (seen_file || frozen_file_to_read)
+	    goto defer;
+	  debugfile = optarg;
+	  break;
+
 	case 'o':
 	case ERROR_OUTPUT_OPTION:
 	  /* FIXME: -o is inconsistent with other tools' use of
@@ -573,8 +583,6 @@ main (int argc, char *const *argv, char *const *envp)
 	     after 2.1.	 */
 	  error (0, 0, _("Warning: `%s' is deprecated, use `%s' instead"),
 		 optchar == 'o' ? "-o" : "--error-output", "--debugfile");
-	  /* fall through */
-	case DEBUGFILE_OPTION:
 	  /* Don't call m4_debug_set_output here, as it has side effects.  */
 	  debugfile = optarg;
 	  break;
@@ -710,6 +718,13 @@ main (int argc, char *const *argv, char *const *envp)
 	  process_file (context, arg);
 	  break;
 
+	case DEBUGFILE_OPTION:
+	  if (!m4_debug_set_output (context, NULL, arg))
+	    m4_error (context, 0, errno, NULL, _("cannot set debug file %s"),
+		      quotearg_style (locale_quoting_style,
+				      arg ? arg : _("stderr")));
+	  break;
+
 	case POPDEF_OPTION:
 	  {
 	    size_t len = strlen (arg);
diff --git a/tests/options.at b/tests/options.at
index dce43f87..48e5b036 100644
--- a/tests/options.at
+++ b/tests/options.at
@@ -312,6 +312,20 @@ AT_CHECK_M4([--debugfile=trace4 -dV in], [0], [[foo
 ]])
 AT_CHECK([cat trace4], [0], [expout])
 
+dnl check that order matters
+AT_DATA([in1], [[bar
+]])
+AT_DATA([in2], [[errprint(`hi
+')dnl
+bar
+]])
+AT_CHECK_M4([-Dbar=hello -tbar --debugfile= in1 --debugfile in2], [0],
+[[hello
+hello
+]], [[hi
+m4trace: -1- bar -> `hello'
+]])
+
 AT_CLEANUP
 
 
@@ -746,7 +760,7 @@ debugfile(`trace2')
 define(`foo', `2')foo
 ]])
 
-AT_CHECK_M4([--safer --debugfile trace1 -t foo in], [1],
+AT_CHECK_M4([--safer --debugfile=trace1 -t foo in], [1],
 [[1
 
 2