Workaround for illegal package merging in py-matplotlib/py-basemap (#1964)

* Workaround for illegal package merging in py-matplotlib/py-basemap

# Conflicts:
#	var/spack/repos/builtin/packages/py-basemap/package.py

* flake8

* flake8

* Be conservative: only apply the namespace package fix for Python >= 3.5.2

* flake8

* Bug fix

var/spack/repos/builtin/packages/py-basemap/package.py

@@ -23,6 +23,7 @@
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
 from spack import *
+import os
 
 
 class PyBasemap(Package):
@@ -37,10 +38,83 @@ class PyBasemap(Package):
     extends('python')
     depends_on('py-setuptools', type='build')
     depends_on('py-numpy', type=nolink)
-    depends_on('py-matplotlib+gui', type=nolink)
+    depends_on('py-matplotlib', type=nolink)
     depends_on('pil', type=nolink)
     depends_on("geos")
 
     def install(self, spec, prefix):
         env['GEOS_DIR'] = spec['geos'].prefix
         setup_py('install', '--prefix=%s' % prefix)
+
+        # We are not sure if this fix is needed before Python 3.5.2.
+        # If it is needed, this test should be changed.
+        # See: https://github.com/LLNL/spack/pull/1964
+        if spec['python'].version >= Version('3.5.2'):
+            # Use symlinks to join the two mpl_toolkits/ directories into
+            # one, inside of basemap.  This is because Basemap tries to
+            # "add to" an existing package in Matplotlib, which is only
+            # legal Python for "Implicit Namespace Packages":
+            #     https://www.python.org/dev/peps/pep-0420/
+            #     https://github.com/Homebrew/homebrew-python/issues/112
+            # In practice, Python will see only the basemap version of
+            # mpl_toolkits
+            path_m = find_package_dir(
+                spec['py-matplotlib'].prefix, 'mpl_toolkits')
+            path_b = find_package_dir(spec.prefix, 'mpl_toolkits')
+            link_dir(path_m, path_b)
+
+
+def find_package_dir(spack_package_root, name):
+
+    """Finds directory with a specific name, somewhere inside a Spack
+    package.
+
+    spack_package_root:
+        Root directory to start searching
+    oldname:
+        Original name of package (not fully qualified, just the leaf)
+    newname:
+        What to rename it to
+
+    """
+    for root, dirs, files in os.walk(spack_package_root):
+        path = os.path.join(root, name)
+
+        # Make sure it's a directory
+        if not os.path.isdir(path):
+            continue
+
+        # Make sure it's really a package
+        if not os.path.exists(os.path.join(path, '__init__.py')):
+            continue
+
+        return path
+
+    return None
+
+
+def link_dir(src_root, dest_root, link=os.symlink):
+    """Link all files in src_root into directory dest_root"""
+
+    for src_path, dirnames, filenames in os.walk(src_root):
+        if not filenames:
+            continue        # avoid explicitly making empty dirs
+
+        # Avoid internal Python stuff
+        src_leaf = os.path.split(src_path)[1]
+        if src_leaf.startswith('__'):
+            continue
+
+        # Make sure the destination directory exists
+        dest_path = os.path.join(dest_root, src_path[len(src_root) + 1:])
+        try:
+            os.makedirs(dest_path)
+        except:
+            pass
+
+        # Link all files from src to dest directory
+        for fname in filenames:
+            src = os.path.join(src_path, fname)
+            dst = os.path.join(dest_path, fname)
+            if not os.path.exists(dst):
+                link(src, dst)