#4392·mamba

Long path support not enabled on AppVeyor with 2.9

Author: QuLogicCreated Aug 22, 2026Updated Aug 25, 2026

Troubleshooting docs

My problem is not solved in the Troubleshooting docs

Anaconda default channels

I do NOT use the Anaconda default channels (pkgs/* etc.)

How did you install Mamba?

Micromamba

Search tried in issue tracker

long path

Latest version of Mamba

My problem is not solved with the latest version

Tried in Conda?

I didn't try

Describe your issue

Since about two weeks ago, the AppVeyor job on the Matplotlib repo has been failing. Looking back into the history, the last passing build has been with micromamba 2.8.1, and the first failure was with 2.9.0.

The path of the file that breaks (in the log below) is slightly over 260 characters, so this points toward long path support. I see some related issues mentioned for 2.9.0 (#4275 and #4342).

Within the logs, for the passing build, we see:

Windows long-path support enabled.

but in the failing build, we have:

warning libmamba Windows version found:10.0.17763 - Not setting long path registry key;Windows version must be at least 10 with the fall 2016 "Anniversary update" or newer.

AFAICT, there has been no changes to AppVeyor build images, so this points to some regression in how micromamba detects and enables long path support, possibly from #4342.

mamba info / micromamba info

bash

libmamba version : 2.9.0
     micromamba version : 2.9.0
           curl version : libcurl/8.21.0 Schannel zlib/1.3.2 libpsl/0.23.0 libssh2/1.11.1 WinLDAP
     libarchive version : libarchive 3.8.9 zlib/1.3.2 bz2lib/1.0.8 libzstd/1.5.7 cng/2.0 libb2/bundled
       envs directories : C:\Users\appveyor\AppData\Roaming\mamba\envs
          package cache : C:\Users\appveyor\AppData\Roaming\mamba\pkgs
                          C:\Users\appveyor\.mamba\pkgs
                          C:\Users\appveyor\AppData\Roaming\.mamba\pkgs
            environment : base
           env location : C:\Users\appveyor\AppData\Roaming\mamba
      user config files : C:\Users\appveyor\.mambarc
 populated config files : C:\Users\appveyor\.condarc
       virtual packages : __win=10.0.17763=0
                          __archspec=1=x86_64_v3
               channels : https://conda.anaconda.org/conda-forge/noarch
                          https://conda.anaconda.org/conda-forge/win-64
       base environment : C:\Users\appveyor\AppData\Roaming\mamba
               platform : win-64

Logs

bash

...
Linking debugpy-1.8.21-py312ha1a9051_0
warning  libmamba Invalid package cache, file 'C:\Users\appveyor\AppData\Roaming\mamba\pkgs\https\conda.anaconda.org\conda-forge\win-64\debugpy-1.8.21-py312ha1a9051_0\Lib\site-packages\debugpy\_vendored\pydevd\_pydevd_bundle\_debug_adapter\__pycache__\__main__pydevd_gen_debug_adapter_protocol.cpython-312.pyc' is missing
error    libmamba Cannot find a valid extracted directory cache for 'debugpy-1.8.21-py312ha1a9051_0.conda'
critical libmamba Package cache error.

environment.yml

yaml

name: mpl-dev
channels:
  - conda-forge
dependencies:
  # runtime dependencies
  - cairocffi
  - c-compiler
  - cxx-compiler
  - contourpy>=1.2.1
  - cycler>=0.12.0
  - fonttools>=4.28.2
  - importlib-resources>=3.2.0
  - kiwisolver>=1.3.1
  - pybind11>=2.13.2
  - meson-python>=0.13.1
  - numpy>=2.0
  - pillow>=9
  - pkg-config
  - pygobject
  - pyparsing>=3
  - pyqt
  - python>=3.12
  - python-dateutil>=2.1
  - setuptools_scm<10
  - wxpython
  # building documentation
  - colour-science
  - graphviz
  - ipython
  - ipywidgets
  - numpydoc>=1.0
  - packaging>=20
  - pydata-sphinx-theme=0.18.0  # required by mpl-sphinx-theme=3.11
  - pyyaml
  - sphinx>=3.0.0,!=6.1.2
  - sphinx-copybutton
  - sphinx-gallery>=0.12.0
  - joblib  # needed for sphinx-gallery[parallel]
  - sphinx-design
  - sphinx-tags>=0.4.0
  - pystemmer
  - pikepdf
  - pip
  - pip:
      - mpl-sphinx-theme~=3.11.0
      - sphinxcontrib-svg2pdfconverter>=1.1.0
      - sphinxcontrib-video>=0.2.1
  # testing
  - black<26
  - coverage
  - gtk4
  - ipykernel
  - nbconvert[execute]!=6.0.0,!=6.0.1,!=7.3.0,!=7.3.1
  - nbformat!=5.0.0,!=5.0.1
  - pandas!=0.25.0
  - psutil
  - prek
  - pydocstyle>=5.1.0
  - pytest!=4.6.0,!=5.4.0,!=8.1.0
  - pytest-cov
  - pytest-rerunfailures
  - pytest-timeout
  - pytest-xdist
  - tornado
  - pytz
  - ruff
  - tox

~/.condarc

yaml

Source: mamba-org/mamba

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