Added feature: package extensions

- packages can be "extended" by others
- allows extension to be symlinked into extendee's prefix.
- used for python modules.
  - first module: py-setuptools

lib/spack/llnl/util/filesystem.py

@@ -24,7 +24,8 @@
 ##############################################################################
 __all__ = ['set_install_permissions', 'install', 'expand_user', 'working_dir',
            'touch', 'mkdirp', 'force_remove', 'join_path', 'ancestor',
-           'can_access', 'filter_file', 'change_sed_delimiter', 'is_exe']
+           'can_access', 'filter_file', 'change_sed_delimiter', 'is_exe',
+           'check_link_tree', 'merge_link_tree', 'unmerge_link_tree']
 
 import os
 import sys
@@ -222,3 +223,82 @@ def ancestor(dir, n=1):
 def can_access(file_name):
     """True if we have read/write access to the file."""
     return os.access(file_name, os.R_OK|os.W_OK)
+
+
+def traverse_link_tree(src_root, dest_root, follow_nonexisting=True, **kwargs):
+    # Yield directories before or after their contents.
+    order  = kwargs.get('order', 'pre')
+    if order not in ('pre', 'post'):
+        raise ValueError("Order must be 'pre' or 'post'.")
+
+    # List of relative paths to ignore under the src root.
+    ignore = kwargs.get('ignore', None)
+    if isinstance(ignore, basestring):
+        ignore = (ignore,)
+
+    for dirpath, dirnames, filenames in os.walk(src_root):
+        rel_path  = dirpath[len(src_root):]
+        rel_path = rel_path.lstrip(os.path.sep)
+        dest_dirpath = os.path.join(dest_root, rel_path)
+
+        # Don't descend into ignored directories
+        if ignore and dest_dirpath in ignore:
+            return
+
+        # Don't descend into dirs in dest that do not exist in src.
+        if not follow_nonexisting:
+            dirnames[:] = [
+                d for d in dirnames
+                if os.path.exists(os.path.join(dest_dirpath, d))]
+
+        # preorder yields directories before children
+        if order == 'pre':
+            yield (dirpath, dest_dirpath)
+
+        for name in filenames:
+            src_file  = os.path.join(dirpath, name)
+            dest_file = os.path.join(dest_dirpath, name)
+
+            # Ignore particular paths inside the install root.
+            src_relpath = src_file[len(src_root):]
+            src_relpath = src_relpath.lstrip(os.path.sep)
+            if ignore and src_relpath in ignore:
+                continue
+
+            yield (src_file, dest_file)
+
+        # postorder yields directories after children
+        if order == 'post':
+            yield (dirpath, dest_dirpath)
+
+
+
+def check_link_tree(src_root, dest_root, **kwargs):
+    for src, dest in traverse_link_tree(src_root, dest_root, False, **kwargs):
+        if os.path.exists(dest) and not os.path.isdir(dest):
+            return dest
+    return None
+
+
+def merge_link_tree(src_root, dest_root, **kwargs):
+    kwargs['order'] = 'pre'
+    for src, dest in traverse_link_tree(src_root, dest_root, **kwargs):
+        if os.path.isdir(src):
+            mkdirp(dest)
+        else:
+            assert(not os.path.exists(dest))
+            os.symlink(src, dest)
+
+
+def unmerge_link_tree(src_root, dest_root, **kwargs):
+    kwargs['order'] = 'post'
+    for src, dest in traverse_link_tree(src_root, dest_root, **kwargs):
+        if os.path.isdir(dest):
+            if not os.listdir(dest):
+                # TODO: what if empty directories were present pre-merge?
+                shutil.rmtree(dest, ignore_errors=True)
+
+        elif os.path.exists(dest):
+            if not os.path.islink(dest):
+                raise ValueError("%s is not a link tree!" % dest)
+            os.remove(dest)