repo: raise exception if root_dir is not a directory path (#3295)

* repo: throw if root_dir in Repo.__init__() is not a directory path

When Repo is instantiated with invalid urls such as 'http://github.com/iterative/dvc.git',
it does os.path.realpath which is not intelligent enough and just concatenates with current
working directory, which is then traversed outward. It might happen that the outward folder
is a dvc directory which is not really what we want.

So, a check for root to be a directory is added. Otherwise, NotDvcRepoError is thrown with
a custom message.

* repo: set message from raise for NotDvcRepoError

dvc/exceptions.py

@@ -112,18 +112,7 @@ def __init__(self, path):
 
 
 class NotDvcRepoError(DvcException):
-    """Thrown if a directory is not a DVC repo.
-
-    Args:
-        root (str): path to the directory.
-    """
-
-    def __init__(self, root):
-        msg = (
-            "you are not inside of a DVC repository "
-            "(checked up to mount point '{}')"
-        )
-        super().__init__(msg.format(root))
+    """Thrown if a directory is not a DVC repo"""
 
 
 class DvcParserError(DvcException):

dvc/repo/__init__.py

@@ -129,19 +129,24 @@ def __repr__(self):
 
     @classmethod
     def find_root(cls, root=None):
-        if root is None:
-            root = os.getcwd()
-        else:
-            root = os.path.abspath(os.path.realpath(root))
+        root_dir = os.path.realpath(root or os.curdir)
+
+        if not os.path.isdir(root_dir):
+            raise NotDvcRepoError("directory '{}' does not exist".format(root))
 
         while True:
-            dvc_dir = os.path.join(root, cls.DVC_DIR)
+            dvc_dir = os.path.join(root_dir, cls.DVC_DIR)
             if os.path.isdir(dvc_dir):
-                return root
-            if os.path.ismount(root):
+                return root_dir
+            if os.path.ismount(root_dir):
                 break
-            root = os.path.dirname(root)
-        raise NotDvcRepoError(root)
+            root_dir = os.path.dirname(root_dir)
+
+        message = (
+            "you are not inside of a DVC repository "
+            "(checked up to mount point '{}')"
+        ).format(root_dir)
+        raise NotDvcRepoError(message)
 
     @classmethod
     def find_dvc_dir(cls, root=None):