exceptions: use semantic exceptions (#3430)

dvc/exceptions.py

@@ -325,3 +325,7 @@ class RemoteCacheRequiredError(DvcException):
                 format_link("https://man.dvc.org/config#cache"),
             )
         )
+
+
+class IsADirectoryError(DvcException):
+    """Raised when a file operation is requested on a directory."""

dvc/repo/__init__.py

@@ -10,6 +10,7 @@ from funcy import cached_property, cat, first
 from dvc.config import Config
 from dvc.exceptions import (
     FileMissingError,
+    IsADirectoryError,
     NotDvcRepoError,
     OutputNotFoundError,
 )
@@ -476,7 +477,7 @@ class Repo(object):
 
     def _open_cached(self, out, remote=None, mode="r", encoding=None):
         if out.isdir():
-            raise ValueError("Can't open a dir")
+            raise IsADirectoryError("Can't open a dir")
 
         cache_file = self.cache.local.checksum_to_path_info(out.checksum)
         cache_file = fspath_py35(cache_file)

dvc/repo/reproduce.py

@@ -1,6 +1,6 @@
 import logging
 
-from dvc.exceptions import ReproductionError
+from dvc.exceptions import ReproductionError, InvalidArgumentError
 from dvc.repo.scm_context import scm_context
 from . import locked
 from .graph import get_pipeline, get_pipelines
@@ -61,7 +61,9 @@ def reproduce(
     from dvc.stage import Stage
 
     if not target and not all_pipelines:
-        raise ValueError()
+        raise InvalidArgumentError(
+            "Neither target nor all_pipelines are specified."
+        )
 
     interactive = kwargs.get("interactive", False)
     if not interactive: