Fix import of symlinks outside of path with modutils (#546)

Makes load_module_from_file able to import files within the path that
are just a symlink to a file outside of the path.
modutils is using realpath at the moment which will resolve the symlink
and don't allow the import as the file is detected outside of the
available paths. By checking both abspath and realpath this patches add
support for such scenarios.

1 files changed, 49 insertions, 12 deletions

diff --git a/astroid/modutils.py b/astroid/modutils.py
index 83d0ba74..4d8dfec0 100644
--- a/astroid/modutils.py
+++ b/astroid/modutils.py
@@ -285,26 +285,63 @@ def check_modpath_has_init(path, mod_path):
     return True
 
 
+def _get_relative_base_path(filename, path_to_check):
+    """Extracts the relative mod path of the file to import from
+
+    Check if a file is within the passed in path and if so, returns the
+    relative mod path from the one passed in.
+
+    If the filename is no in path_to_check, returns None
+
+    Note this function will look for both abs and realpath of the file,
+    this allows to find the relative base path even if the file is a
+    symlink of a file in the passed in path
+
+    Examples:
+        _get_relative_base_path("/a/b/c/d.py", "/a/b") ->  ["c","d"]
+        _get_relative_base_path("/a/b/c/d.py", "/dev") ->  None
+    """
+    importable_path = None
+    path_to_check = os.path.normcase(path_to_check)
+    abs_filename = os.path.abspath(filename)
+    if os.path.normcase(abs_filename).startswith(path_to_check):
+        importable_path = abs_filename
+
+    real_filename = os.path.realpath(filename)
+    if os.path.normcase(real_filename).startswith(path_to_check):
+        importable_path = real_filename
+
+    if importable_path:
+        base_path = os.path.splitext(importable_path)[0]
+        relative_base_path = base_path[len(path_to_check):]
+        return [pkg for pkg in relative_base_path.split(os.sep) if pkg]
+
+    return None
+
+
 def modpath_from_file_with_callback(filename, extrapath=None, is_package_cb=None):
-    filename = _path_from_filename(filename)
-    filename = os.path.realpath(os.path.expanduser(filename))
-    base = os.path.splitext(filename)[0]
+    filename = os.path.expanduser(_path_from_filename(filename))
 
     if extrapath is not None:
         for path_ in six.moves.map(_canonicalize_path, extrapath):
             path = os.path.abspath(path_)
-            if path and os.path.normcase(base[:len(path)]) == os.path.normcase(path):
-                submodpath = [pkg for pkg in base[len(path):].split(os.sep)
-                              if pkg]
-                if is_package_cb(path, submodpath[:-1]):
-                    return extrapath[path_].split('.') + submodpath
+            if not path:
+                continue
+            submodpath = _get_relative_base_path(filename, path)
+            if not submodpath:
+                continue
+            if is_package_cb(path, submodpath[:-1]):
+                return extrapath[path_].split('.') + submodpath
 
     for path in six.moves.map(_canonicalize_path, sys.path):
         path = _cache_normalize_path(path)
-        if path and os.path.normcase(base).startswith(path):
-            modpath = [pkg for pkg in base[len(path):].split(os.sep) if pkg]
-            if is_package_cb(path, modpath[:-1]):
-                return modpath
+        if not path:
+            continue
+        modpath = _get_relative_base_path(filename, path)
+        if not modpath:
+            continue
+        if is_package_cb(path, modpath[:-1]):
+            return modpath
 
     raise ImportError('Unable to find module for %s in %s' % (
         filename, ', \n'.join(sys.path)))