Homebrew-cask: QGIS fails to install

[englishm]

$ brew cask install qgis
==> Satisfying dependencies
==> Installing Formula dependencies from Homebrew
matplotlib ... already installed
==> Installing Cask dependencies: gdal-framework
gdal-framework ...
already installed
complete
==> Downloading http://www.kyngchaos.com/files/software/qgis/QGIS-2.12.0-1.dmg
Already downloaded: /Library/Caches/Homebrew/qgis-2.12.0-1.dmg
==> Running installer for qgis; your password may be necessary.
==> Package installers may write to any location; options such as --appdir are ignored.
Password:
==> installer: Error - QGIS requires the Matplotlib python module (kyngchaos build).
Error: Command failed to execute!

==> Failed command:
["/usr/bin/sudo", "-E", "--", "/usr/sbin/installer", "-pkg", "#<Pathname:/opt/homebrew-cask/Caskroom/qgis/2.12.0-1/Install QGIS.pkg>", "-target", "/"]

==> Output of failed command:


==> Exit status of failed command:
#<Process::Status: pid 5199 exit 1>

$ brew info matplotlib
homebrew/python/matplotlib: stable 1.4.3, HEAD
http://matplotlib.org
/usr/local/Cellar/matplotlib/1.4.3 (2996 files, 78M) *
  Built from source
From: https://github.com/Homebrew/homebrew-python/blob/master/matplotlib.rb
==> Dependencies
Build: pkg-config ✔
Required: freetype ✔, libpng ✔, homebrew/python/numpy ✔
Optional: ghostscript ✘, homebrew/dupes/tcl-tk ✘, gtk+3 ✘, pygtk ✘, pyside ✘, pyqt ✘, pyqt5 ✘
==> Options
--with-cairo
    Build with cairo backend support
--with-ghostscript
    Build with ghostscript support
--with-gtk+3
    Build with gtk+3 support
--with-pygtk
    Build with pygtk backend support (python2 only)
--with-pyqt
    Build with pyqt support
--with-pyqt5
    Build with pyqt5 support
--with-pyside
    Build with pyside support
--with-python3
    Build with python3 support
--with-tcl-tk
    Build with tcl-tk support
--with-tex
    Build with tex support
--without-python
    Build without python2 support
--HEAD
    Install HEAD version
==> Caveats
If you want to use the `wxagg` backend, do `brew install wxpython`.
This can be done even after the matplotlib install.
If you use system python (that comes - depending on the OS X version -
with older versions of numpy, scipy and matplotlib), you may need to
ensure that the brewed packages come earlier in Python's sys.path with:
  mkdir -p /Users/username/Library/Python/2.7/lib/python/site-packages
  echo 'import sys; sys.path.insert(1, "/usr/local/lib/python2.7/site-packages")' >> /Users/username/Library/Python/2.7/lib/python/site-packages/homebrew.pth

$ brew doctor
Your system is ready to brew.

This is on El Capitan, but it looks like the issue is that QGIS expects a particular distribution of matplotlib that differs from what homebrew/python currently provides. I'm not familiar enough with the homebrew/python packaging/distribution situation to effectively troubleshoot this at the moment. It looks like the qgis formula used to depend on a casked version of matplotlib, but switched to a formula-provided version with #14043. It has also been updated since that change with #14881.

[englishm]

This may just be a bug with the QGIS installer having a hardcoded path. A possible (untested) workaround appears to be creating a symlink:

ln -s /System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python /Library/Python/2.7/site-packages/matplotlib-override

( via http://gis.stackexchange.com/a/163512 )

[englishm]

I'd be curious to know if either @scarnecchia or @MatzFan have encountered this issue.

[englishm]

Update: after creating the symlink, brew cask install qgis completed successfully.

$ sudo ln -s /System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python /Library/Python/2.7/site-packages/matplotlib-override
Password:
$ brew cask install qgis
==> Satisfying dependencies
==> Installing Formula dependencies from Homebrew
matplotlib ... already installed
==> Installing Cask dependencies: gdal-framework
gdal-framework ...
already installed
complete
==> Downloading http://www.kyngchaos.com/files/software/qgis/QGIS-2.12.0-1.dmg
Already downloaded: /Library/Caches/Homebrew/qgis-2.12.0-1.dmg
==> Running installer for qgis; your password may be necessary.
==> Package installers may write to any location; options such as --appdir are ignored.


==> installer: Package name is QGIS
==> installer: Installing at base path /
==> installer: The install was successful.
🍺  qgis staged at '/opt/homebrew-cask/Caskroom/qgis/2.12.0-1' (6 files, 182M)

This seems less than ideal, but does appear to work.
I'll let the maintainers decide whether or not to consider this issue closed.
Thanks! :smile:

[adidalal]

Depending on the severity, we can either add a caveat, or actually execute that command automatically after install, something along the lines of

  # Symlink matplotlib so that QGIS's hardcoded path requirement is satisfied
  # Original discussion: https://github.com/caskroom/homebrew-cask/issues/15131
  postflight do
    system '/usr/bin/sudo', '-E', '--', '/bin/ln', '-s', '--', '/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python', '/Library/Python/2.7/site-packages/matplotlib-override'
  end

Is this command always required for a working install? (in which case the postflight stanza shown above would be more appropriate)

[englishm]

My limited experience (documented above) is that the QGIS installer will not even run without the symlink. Would a postflight stanza execute before or after the package installer runs? I think it would need to run beforehand to be effective. I'm also wary of creating such symlinks without a user's explicit permission.

I'd personally be more comfortable with a caveat, but are there many other examples of caveats for dependency workarounds or do they primarily address runtime issues after the software is installed?

[adidalal]

That could be done as a preflight stanza, which would be run before the install.

The caveat would look like:

caveats <<-EOS.undent
  #{token} requires matplotlib in a specific location. Please run the following to finish install:

    sudo ln -s /System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python /Library/Python/2.7/site-packages/matplotlib-override
EOS

I'll wait for some feedback from some of the other maintainers before we make a decision. Thanks for the detailed reporting.

cc @vitorgalvao thoughts?

[vitorgalvao]

I'm also wary of creating such symlinks without a user's explicit permission.

Bingo.

I'd personally be more comfortable with a caveat

And that is exactly what we should do in this case.

This may just be a bug with the QGIS installer having a hardcoded path.

Ideally, this should be fixed upstream (at which point we’ll remove the caveat).

[adidalal]

Fixed by https://github.com/caskroom/homebrew-cask/pull/15173