Handle further git exceptions in do_attach()

This improves validation of attach arguments. Previously, the command:
    git bz attach 741345
would result in the crash:
    fatal: ambiguous argument '741345': unknown revision or path not in
        the working tree.
    Use '--' to separate paths from revisions, like this:
    'git <command> [<revision>...] -- [<file>...]'
    Traceback (most recent call last):
      File "/home/philip/.local/bin/git-bz", line 2472, in <module>
        do_attach(*args)
      File "/home/philip/.local/bin/git-bz", line 1830, in do_attach
        commits = get_commits(commit_or_revision_range)
      File "/home/philip/.local/bin/git-bz", line 233, in get_commits
        commits = rev_list_commits(commit_or_revision_range)
      File "/home/philip/.local/bin/git-bz", line 205, in
        rev_list_commits
        output = git.rev_list(*args, **kwargs_copy)
      File "/home/philip/.local/bin/git-bz", line 192, in f
        return git_run(command, *args, **kwargs)
      File "/home/philip/.local/bin/git-bz", line 174, in git_run
        raise CalledProcessError(process.returncode, " ".join(to_run))
    subprocess.CalledProcessError: Command 'git rev-list
        --pretty=format:%s 741345' returned non-zero exit status 128

Now it prints an error gracefully.

https://bugzilla.gnome.org/show_bug.cgi?id=742371

1 files changed, 6 insertions, 1 deletions

diff --git a/git-bz b/git-bz
index 7b0fe69..01f37d9 100755
--- a/git-bz
+++ b/git-bz
@@ -245,7 +245,12 @@ def get_commits(commit_or_revision_range):
         commits = rev_list_commits(rev, max_count='1')
     except CalledProcessError:
         # If not, assume the argument is a range
-        commits = rev_list_commits(commit_or_revision_range)
+        try:
+            commits = rev_list_commits(commit_or_revision_range)
+        except CalledProcessError:
+            # If not again, the argument must be invalid — perhaps the user has
+            # accidentally specified a bug number but not a revision.
+            commits = []
 
     if len(commits) == 0:
         die("'%s' does not name any commits. Use HEAD to specify just the last commit" %