+++ This bug was initially created as a clone of Bug #1662632 +++

The error message seems like exactly the same as bug #1662632, but that's marked fixed. So I'm filing another one, as I am experiencing this on latest mozilla-central.

My log output below:

Would you like to run a few configuration steps to ensure Git is
optimally configured? (Yn): y
================================================================================
Ensuring https://github.com/glandium/git-cinnabar.git is up to date at /home/freddy/.mozbuild/git-cinnabar
warning: Pulling without specifying how to reconcile divergent branches is
discouraged. You can squelch this message by running one of the following
commands sometime before your next pull:

  git config pull.rebase false  # merge (the default strategy)
  git config pull.rebase true   # rebase
  git config pull.ff only       # fast-forward only

You can replace "git config" with "git config --global" to set a default
preference for all repositories. You can also pass --rebase, --no-rebase,
or --ff-only on the command line to override the configured default per
invocation.

remote: Enumerating objects: 9, done.
remote: Counting objects: 100% (9/9), done.
remote: Compressing objects: 100% (3/3), done.
remote: Total 9 (delta 6), reused 9 (delta 6), pack-reused 0
Unpacking objects: 100% (9/9), 1.15 KiB | 167.00 KiB/s, done.
From https://github.com/glandium/git-cinnabar
 + 80a327c...26e9c46 try        -> origin/try  (forced update)
Fetching submodule git-core
From git://git.kernel.org/pub/scm/git/git
   e9b77c84a0..d4a392452e  master      -> origin/master
   40977abb40..fa9743e501  next        -> origin/next
 + 2f034f2290...836cbb00d9 seen        -> origin/seen  (forced update)
   de4ebe0460..1b1372cb2f  todo        -> origin/todo
 * [new tag]               v2.29.0-rc1 -> v2.29.0-rc1
 * [new tag]               v2.29.0-rc0 -> v2.29.0-rc0
Already up to date.
Your branch is up to date with 'origin/master'.
================================================================================
Downloading from https://community-tc.services.mozilla.com/api/index/v1/task/project.git-cinnabar.helper.e7e446b707ce7a9a3bdf50a8233bc8237c421f06.linux.x86_64/artifacts/public/git-cinnabar-helper...
 100%
Error running mach:

    ['bootstrap']

The error occurred in code that was called by the mach command. This is either
a bug in the called code itself or in the way that mach is calling it.
You can invoke |./mach busted| to check if this issue is already on file. If it
isn't, please use |./mach busted file bootstrap| to report it. If |./mach busted| is
misbehaving, you can also inspect the dependencies of bug 1543241.

If filing a bug, please include the full output of mach, including this error
message.

The details of the failure are as follows:

UnboundLocalError: local variable 'have_clone' referenced before assignment

  File "/home/freddy/gecko-tip/python/mozboot/mozboot/mach_commands.py", line 45, in bootstrap
    bootstrapper.bootstrap()
  File "/home/freddy/gecko-tip/python/mozboot/mozboot/bootstrap.py", line 486, in bootstrap
    have_clone,
Sentry is attempting to send 0 pending error messages
Waiting up to 2 seconds
Press Ctrl-C to quit

Set release status flags based on info from the regressing bug 1647792

That bug was indeed fixed, and the string have_clone doesn't even exist anywhere in the entire source tree any more. Are you sure you're at an up-to-date mozilla-central? Does the problem persist after a mach clobber python?

Resolving in the absence of any additional information about this.