Make Path and .path() expand users and environment variables.

Fixes #3

CHANGES.rst

@@ -16,6 +16,11 @@ Changes
 
 - Drop support for ``python setup.py test``.
 
+- Make ``zope.configuration.fields.Path`` and
+  ``zope.configuration.config.ConfigurationContext`` expand
+  environment variables and expand user home directories in paths. See
+  `issue <https://github.com/zopefoundation/zope.configuration/issues/3>`_.
+
 - Fix resolving names from a Python 2 package whose ``__init__.py`` has
   unicode elements in ``__all__``.
 

docs/api/fields.rst

@@ -203,6 +203,16 @@
       >>> n.split(os.sep)
       ['', 'a', 'b']
 
+   Environment variables are expanded:
+
+   .. doctest::
+
+      >>> os.environ['path-test'] = '42'
+      >>> with_env = os.path.join(os.sep, u'a', u'${path-test}')
+      >>> n = field.fromUnicode(with_env)
+      >>> n.split(os.sep)
+      ['', 'a', '42']
+
    Now try a relative path:
 
    .. doctest::
@@ -212,6 +222,21 @@
       >>> n.split(os.sep)
       ['', 'faux', 'context', 'a', 'b']
 
+   The current user is expanded (these are implicitly relative paths):
+
+   .. doctest::
+
+      >>> old_home = os.environ.get('HOME')
+      >>> os.environ['HOME'] = os.path.join(os.sep, 'HOME')
+      >>> n = field.fromUnicode('~')
+      >>> n.split(os.sep)
+      ['', 'HOME']
+      >>> if old_home:
+      ...    os.environ['HOME'] = old_home
+      ... else:
+      ...    del os.environ['HOME']
+
+
 .. autoclass:: Bool
    :members:
    :member-order: bysource

src/zope/configuration/config.py

@@ -31,6 +31,7 @@
 from zope.configuration.interfaces import IGroupingContext
 from zope.configuration.fields import GlobalInterface
 from zope.configuration.fields import GlobalObject
+from zope.configuration.fields import PathProcessor
 from zope.configuration._compat import builtins
 from zope.configuration._compat import reraise
 from zope.configuration._compat import string_types
@@ -185,9 +186,9 @@ def resolve(self, dottedname):
     def path(self, filename):
         """ Compute package-relative paths.
         """
-        filename = os.path.normpath(filename)
+        filename, needs_processing = PathProcessor.expand(filename)
 
-        if os.path.isabs(filename):
+        if not needs_processing:
             return filename
 
         # Got a relative path, combine with base path.

src/zope/configuration/fields.py

@@ -120,19 +120,42 @@ def fromUnicode(self, u):
 
         return values
 
+class PathProcessor(object):
+    # Internal helper for manipulations on paths
+
+    @classmethod
+    def expand(cls, filename):
+        # Perform the expansions we want to have done. Returns a
+        # tuple: (path, needs_processing) If the second value is true,
+        # further processing should be done (the path isn't fully
+        # resolved); if false, the path should be used as is
+
+        filename = filename.strip()
+        # expanding a ~ at the front should generally result
+        # in an absolute path.
+        filename = os.path.expanduser(filename)
+        filename = os.path.expandvars(filename)
+        if os.path.isabs(filename):
+            return os.path.normpath(filename), False
+        return filename, True
+
 
 @implementer(IFromUnicode)
 class Path(Text):
     """A file path name, which may be input as a relative path
 
     Input paths are converted to absolute paths and normalized.
+
+    .. versionchanged:: 4.2.0
+        Start expanding home directories and environment variables.
     """
-    def fromUnicode(self, u):
-        u = u.strip()
-        if os.path.isabs(u):
-            return os.path.normpath(u)
 
-        return self.context.path(u)
+    def fromUnicode(self, value):
+        filename, needs_processing = PathProcessor.expand(value)
+        if needs_processing:
+            filename = self.context.path(filename)
+
+        return filename
 
 
 @implementer(IFromUnicode)

src/zope/configuration/interfaces.py

@@ -64,6 +64,12 @@ def path(filename):
         If the filename is relative to the package, then the returned
         name will include the package path, otherwise, the original
         file name is returned.
+
+        Environment variables in the path are expanded, and if the path
+        begins with the username marker (~), that is expanded as well.
+
+        .. versionchanged:: 4.2.0
+            Start expanding home directories and environment variables.
         """
 
     def checkDuplicate(filename):

src/zope/configuration/tests/test_config.py

@@ -163,6 +163,31 @@ class stub:
         c.package = stub()
         self.assertTrue(os.path.isabs(c.path('y/z')))
 
+    def test_path_expand_filenames(self):
+        import os
+        c = self._makeOne()
+        os.environ['path-test'] = '42'
+        try:
+            path = c.path(os.path.join(os.sep, '${path-test}'))
+            self.assertEqual(path, os.path.join(os.sep, '42'))
+        finally:
+            del os.environ['path-test']
+
+    def test_path_expand_user(self):
+        import os
+        c = self._makeOne()
+        old_home = os.environ.get('HOME')
+        # HOME should be absolute
+        os.environ['HOME'] = os.path.join(os.sep, 'HOME')
+        try:
+            path = c.path('~')
+            self.assertEqual(path, os.path.join(os.sep, 'HOME'))
+        finally: # pragma: no cover
+            if old_home:
+                os.environ['HOME'] = old_home
+            else:
+                del os.environ['HOME']
+
     def test_checkDuplicate_miss(self):
         import os
         c = self._makeOne()