diff: improve RevError message

dvc/scm/base.py

@@ -27,10 +27,7 @@ def __init__(self, url, path):
 
 
 class RevError(SCMError):
-    def __init__(self, url, rev):
-        super().__init__(
-            "failed to access revision '{}' for repo '{}'".format(rev, url)
-        )
+    pass
 
 
 class Base(object):

dvc/scm/git/__init__.py

@@ -94,7 +94,11 @@ def clone(url, to_path, rev=None):
             try:
                 repo.checkout(rev)
             except git.exc.GitCommandError as exc:
-                raise RevError(url, rev) from exc
+                raise RevError(
+                    "failed to access revision '{}' for repo '{}'".format(
+                        rev, url
+                    )
+                ) from exc
 
         return repo
 
@@ -367,8 +371,8 @@ def resolve_rev(self, rev):
 
         try:
             return self.repo.git.rev_parse(rev)
-        except GitCommandError as exc:
-            raise RevError(url=self.root_dir, rev=rev) from exc
+        except GitCommandError:
+            raise RevError("unknown Git revision '{}'".format(rev))
 
     def close(self):
         self.repo.close()

tests/func/test_diff.py

@@ -107,9 +107,7 @@ def test_refs(tmp_dir, scm, dvc):
         ],
     }
 
-    with pytest.raises(
-        DvcException, match=r"failed to access revision 'missing'"
-    ):
+    with pytest.raises(DvcException, match=r"unknown Git revision 'missing'"):
         dvc.diff("missing")