Full log:

./mach bootstrap               

Note on Artifact Mode:

Artifact builds download prebuilt C++ components rather than building
them locally. Artifact builds are faster!

Artifact builds are recommended for people working on Firefox or
Firefox for Android frontends, or the GeckoView Java API. They are unsuitable
for those working on C++ code. For more information see:
https://developer.mozilla.org/en-US/docs/Artifact_builds.

Please choose the version of Firefox you want to build:
  1. Firefox for Desktop Artifact Mode
  2. Firefox for Desktop
  3. GeckoView/Firefox for Android Artifact Mode
  4. GeckoView/Firefox for Android
Your choice: 4
Your version of Python 3 (3.7.3) is new enough.
Your version of Python 2 (2.7.17) is new enough.
created virtual environment CPython3.7.3.final.0-64 in 162ms
  creator CPython3macOsFramework(dest=/Users/asferro/.mozbuild/_virtualenvs/mach, clear=False, global=False)
  seeder FromAppData(download=False, pip=bundle, setuptools=bundle, wheel=bundle, via=copy, app_data_dir=/Users/asferro/Library/Application Support/virtualenv)
    added seed packages: pip==20.2.2, setuptools==49.6.0, wheel==0.35.1
  activators BashActivator,CShellActivator,FishActivator,PowerShellActivator,PythonActivator,XonshActivator
running build_ext
copying build/lib.macosx-10.14-x86_64-3.7/psutil/_psutil_osx.cpython-37m-darwin.so -> psutil
copying build/lib.macosx-10.14-x86_64-3.7/psutil/_psutil_posix.cpython-37m-darwin.so -> psutil

Error processing command. Ignoring because optional. (optional:packages.txt:comm/build/virtualenv_packages.txt)
Collecting zstandard<=0.13.0,>=0.9.0
  Using cached zstandard-0.13.0-cp37-cp37m-macosx_10_6_intel.whl (879 kB)
Installing collected packages: zstandard
Successfully installed zstandard-0.13.0
WARNING: You are using pip version 20.2.2; however, version 20.2.3 is available.
You should consider upgrading via the '/Users/asferro/.mozbuild/_virtualenvs/mach/bin/python -m pip install --upgrade pip' command.
Collecting glean_sdk~=32.3.1
  Using cached glean_sdk-32.3.2-cp36-abi3-macosx_10_7_x86_64.whl (789 kB)
Collecting cffi>=1
  Using cached cffi-1.14.3-2-cp37-cp37m-macosx_10_9_x86_64.whl (176 kB)
Collecting glean-parser==1.28.3
  Using cached glean_parser-1.28.3-py3-none-any.whl (56 kB)
Collecting pycparser
  Using cached pycparser-2.20-py2.py3-none-any.whl (112 kB)
Collecting appdirs>=1.4
  Using cached appdirs-1.4.4-py2.py3-none-any.whl (9.6 kB)
Collecting jsonschema>=3.0.2
  Using cached jsonschema-3.2.0-py2.py3-none-any.whl (56 kB)
Collecting yamllint>=1.18.0
  Using cached yamllint-1.25.0-py2.py3-none-any.whl (60 kB)
Collecting Jinja2>=2.10.1
  Using cached Jinja2-2.11.2-py2.py3-none-any.whl (125 kB)
Collecting Click>=7
  Using cached click-7.1.2-py2.py3-none-any.whl (82 kB)
Collecting diskcache>=4
  Using cached diskcache-5.0.3-py3-none-any.whl (43 kB)
Processing /Users/asferro/Library/Caches/pip/wheels/a7/c1/ea/cf5bd31012e735dc1dfea3131a2d5eae7978b251083d6247bd/PyYAML-5.3.1-cp37-cp37m-macosx_10_15_x86_64.whl
Collecting six>=1.11.0
  Using cached six-1.15.0-py2.py3-none-any.whl (10 kB)
Requirement already satisfied: setuptools in /Users/asferro/.mozbuild/_virtualenvs/mach/lib/python3.7/site-packages (from jsonschema>=3.0.2->glean-parser==1.28.3->glean_sdk~=32.3.1) (49.6.0)
Collecting importlib-metadata; python_version < "3.8"
  Using cached importlib_metadata-2.0.0-py2.py3-none-any.whl (31 kB)
Processing /Users/asferro/Library/Caches/pip/wheels/a5/52/bf/71258a1d7b3c8cbe1ee53f9314c6f65f20385481eaee573cc5/pyrsistent-0.17.3-cp37-cp37m-macosx_10_14_x86_64.whl
Collecting attrs>=17.4.0
  Using cached attrs-20.2.0-py2.py3-none-any.whl (48 kB)
Collecting pathspec>=0.5.3
  Using cached pathspec-0.8.0-py2.py3-none-any.whl (28 kB)
Collecting MarkupSafe>=0.23
  Using cached MarkupSafe-1.1.1-cp37-cp37m-macosx_10_6_intel.whl (18 kB)
Collecting zipp>=0.5
  Using cached zipp-3.3.0-py3-none-any.whl (5.3 kB)
Installing collected packages: pycparser, cffi, appdirs, six, zipp, importlib-metadata, pyrsistent, attrs, jsonschema, pathspec, PyYAML, yamllint, MarkupSafe, Jinja2, Click, diskcache, glean-parser, glean-sdk
Successfully installed Click-7.1.2 Jinja2-2.11.2 MarkupSafe-1.1.1 PyYAML-5.3.1 appdirs-1.4.4 attrs-20.2.0 cffi-1.14.3 diskcache-5.0.3 glean-parser-1.28.3 glean-sdk-32.3.2 importlib-metadata-2.0.0 jsonschema-3.2.0 pathspec-0.8.0 pycparser-2.20 pyrsistent-0.17.3 six-1.15.0 yamllint-1.25.0 zipp-3.3.0
WARNING: You are using pip version 20.2.2; however, version 20.2.3 is available.
You should consider upgrading via the '/Users/asferro/.mozbuild/_virtualenvs/mach/bin/python -m pip install --upgrade pip' command.
Python 3 mach environment created.
created virtual environment CPython2.7.17.final.0-64 in 252ms
  creator CPython2macOsFramework(dest=/Users/asferro/.mozbuild/_virtualenvs/mach_py2, clear=False, global=False)
  seeder FromAppData(download=False, pip=bundle, wheel=bundle, setuptools=bundle, via=copy, app_data_dir=/Users/asferro/Library/Application Support/virtualenv)
    added seed packages: pip==20.2.2, setuptools==44.1.1, wheel==0.35.1
  activators PythonActivator,CShellActivator,FishActivator,PowerShellActivator,BashActivator
running build_ext
copying build/lib.macosx-10.15-x86_64-2.7/psutil/_psutil_osx.so -> psutil
copying build/lib.macosx-10.15-x86_64-2.7/psutil/_psutil_posix.so -> psutil

Error processing command. Ignoring because optional. (optional:packages.txt:comm/build/virtualenv_packages.txt)
DEPRECATION: Python 2.7 reached the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 is no longer maintained. pip 21.0 will drop support for Python 2.7 in January 2021. More details about Python 2 support in pip can be found at https://pip.pypa.io/en/latest/development/release-process/#python-2-support
Collecting zstandard<=0.13.0,>=0.9.0
  Using cached zstandard-0.13.0-cp27-cp27m-macosx_10_6_intel.whl (879 kB)
Installing collected packages: zstandard
Successfully installed zstandard-0.13.0
WARNING: You are using pip version 20.2.2; however, version 20.2.3 is available.
You should consider upgrading via the '/Users/asferro/.mozbuild/_virtualenvs/mach_py2/bin/python -m pip install --upgrade pip' command.
Python 2 mach environment created.

Looks like you have Homebrew installed. We will install all required packages via Homebrew.

Checking if we need to fetch /usr/local/Homebrew...
Checking if we need to fetch /usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask...
Checking if we need to fetch /usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask-versions...
Checking if we need to fetch /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core...
Checking if we need to fetch /usr/local/Homebrew/Library/Taps/homebrew/homebrew-services...
Fetching /usr/local/Homebrew...
Fetching /usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask...
remote: Enumerating objects: 12, done.
remote: Counting objects: 100% (12/12), done.
remote: Compressing objects: 100% (6/6), done.
remote: Total 8 (delta 6), reused 2 (delta 2), pack-reused 0
Unpacking objects: 100% (8/8), 1.65 KiB | 105.00 KiB/s, done.
From https://github.com/Homebrew/homebrew-cask
   aa10062c59..867dfe7b16  master     -> origin/master
Updating /usr/local/Homebrew...
Branch 'master' set up to track remote branch 'master' from 'origin'.
Switched to and reset branch 'master'
Your branch is up to date with 'origin/master'.
Switched to and reset branch 'stable'
Current branch stable is up to date.

Updating /usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask...
Successfully rebased and updated refs/heads/master.

Updated 1 tap (homebrew/cask).
==> Updated Casks
element                                                           obsidian
Warning: Calling brew cask list is deprecated! Use brew list --cask instead.
Warning: Calling brew cask outdated is deprecated! Use brew outdated --cask instead.
Your version of Java (/Library/Java/JavaVirtualMachines/adoptopenjdk-8.jdk/Contents/Home/bin/java) is at least 1.8 (1.8).

Looks like you have the correct version of the Android NDK installed at:
/Users/asferro/.mozbuild/android-ndk-r20


Looks like you have the Android SDK installed at:
/Users/asferro/.mozbuild/android-sdk-macosx
We will install all required Android packages.


We are now installing the following Android packages:
platform-tools
build-tools;29.0.3
platforms;android-29
emulator

You may be prompted to agree to the Android license. You may see some of
output as packages are downloaded and installed.

Warning: File /Users/asferro/.android/repositories.cfg could not be loaded.     
[=======================================] 100% Computing updates...             
Your version of Mercurial (5.5.2) is sufficiently modern.
Your version of Rust (1.44.1) is new enough.
Rust supports aarch64-linux-android, i686-linux-android, thumbv7neon-linux-androideabi, x86_64-apple-darwin, x86_64-linux-android targets.

Mozilla recommends using git-cinnabar to work with mozilla-central (or
mozilla-unified).

Would you like to run a few configuration steps to ensure Git is
optimally configured? (Yn): n

Build system telemetry

Mozilla collects data about local builds in order to make builds faster and
improve developer tooling. To learn more about the data we intend to collect
read here:

  https://firefox-source-docs.mozilla.org/build/buildsystem/telemetry.html

If you have questions, please ask in #build on Matrix:

  https://chat.mozilla.org/#/room/#build:mozilla.org

If you would like to opt out of data collection, select (N) at the prompt.

Would you like to enable build system telemetry? (Yn): n
 0:03.01 Setting up artifact node.tar.xz
 0:03.01 Using artifact from local cache: /Users/asferro/.mozbuild/toolchains/21c8c2e16da12530-node.tar.xz
 0:03.06 rm tree: /Users/asferro/.mozbuild/node
 0:03.45 untarring "/Users/asferro/.mozbuild/node.tar.xz"
 0:02.98 Setting up artifact fix-stacks.tar.xz
 0:02.98 Using artifact from local cache: /Users/asferro/.mozbuild/toolchains/5e762b7042533b5f-fix-stacks.tar.xz
 0:02.98 rm tree: /Users/asferro/.mozbuild/fix-stacks
 0:02.98 untarring "/Users/asferro/.mozbuild/fix-stacks.tar.xz"
 0:03.01 Could not find artifacts for a toolchain build named `macosx64-minidump-stackwalk`. Local commits, dirty/stale files, and other changes in your checkout may cause this error. Make sure you are on a fresh, current checkout of mozilla-central. If you are already, you may be able to avoid this error by running `mach clobber python`. Beware that commands like `mach bootstrap` and `mach artifact` are unlikely to work on any versions of the code besides recent revisions of mozilla-central.
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:

subprocess.CalledProcessError: Command '['/Users/asferro/.mozbuild/_virtualenvs/mach/bin/python', '/Users/asferro/workspace/mozilla-central/mach', 'artifact', 'toolchain', '--bootstrap', '--from-build', 'macosx64-minidump-stackwalk']' returned non-zero exit status 1.

  File "/Users/asferro/workspace/mozilla-central/python/mozboot/mozboot/mach_commands.py", line 45, in bootstrap
    bootstrapper.bootstrap()
  File "/Users/asferro/workspace/mozilla-central/python/mozboot/mozboot/bootstrap.py", line 412, in bootstrap
    self.maybe_install_private_packages_or_exit(state_dir, checkout_root)
  File "/Users/asferro/workspace/mozilla-central/python/mozboot/mozboot/bootstrap.py", line 295, in maybe_install_private_packages_or_exit
    self.instance.ensure_minidump_stackwalk_packages(state_dir, checkout_root)
  File "/Users/asferro/workspace/mozilla-central/python/mozboot/mozboot/osx.py", line 571, in ensure_minidump_stackwalk_packages
    minidump_stackwalk.MACOS_MINIDUMP_STACKWALK)
  File "/Users/asferro/workspace/mozilla-central/python/mozboot/mozboot/base.py", line 375, in install_toolchain_artifact
    subprocess.check_call(cmd, cwd=state_dir)
  File "/Applications/Xcode.app/Contents/Developer/Library/Frameworks/Python3.framework/Versions/3.7/lib/python3.7/subprocess.py", line 347, in check_call
    raise CalledProcessError(retcode, cmd)

Similar problem for me on Linux. Same package.

In my case the issue was that I had made some local changes to some test harness scripts, which messed up the hashes of the dependencies.