git-debrebase: Implement --help, providing a summary.

Provide a usage message.

I'm not convinced an option summary here is a good idea, mainly there
aren't any really important options.  (-f will be advertised when it
is relevant.)  So I have just summarised the most important operations.

Closes:#904990.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

2 files changed, 17 insertions, 1 deletions

diff --git a/debian/changelog b/debian/changelog
index 4cc32d2..dd97216 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -15,6 +15,8 @@ dgit (6.3~) unstable; urgency=medium
   * git-debrebase(1): Warn against plain git rebase.  (Re#905004.)
   * dgit-maint-debrebase(7): Warn more against plain git rebase.
     Closes:#905004.
+  * git-debrebase: Implement --help, providing a summary.
+    Closes:#904990.
 
  --
 
diff --git a/git-debrebase b/git-debrebase
index 13ca472..b61970c 100755
--- a/git-debrebase
+++ b/git-debrebase
@@ -36,6 +36,18 @@ use Dpkg::Version;
 use File::FnMatch qw(:fnmatch);
 use File::Copy;
 
+our ($usage_message) = <<'END';
+usages:
+  git-debrebase [<options>] [--|-i <git rebase options...>]
+  git-debrebase [<options>] status
+  git-debrebase [<options>] prepush [--prose=...]
+  git-debrebase [<options>] quick|conclude
+  git-debrebase [<options>] new-upstream <new-version> [<details ...>]
+  git-debrebase [<options>] convert-from-gbp [<upstream-commitish>]
+  ...
+See git-debrebase(1), git-debrebase(5), dgit-maint-debrebase(7) (in dgit).
+END
+
 our ($opt_force, $opt_noop_ok, @opt_anchors);
 our ($opt_defaultcmd_interactive);
 
@@ -1826,7 +1838,9 @@ getoptions("bad options\n",
 	       # approach.  '-i=s{0,}' does not work with bundling.
 	       push @$opt_defaultcmd_interactive, @ARGV;
 	       @ARGV=();
-	   });
+	   },
+	   'help' => sub { print $usage_message or die $!; finish 0; },
+	   );
 
 initdebug('git-debrebase ');
 enabledebug if $debuglevel;