fix mypy errors; add mypy precommit hooks (#5237)

.pre-commit-config.yaml

@@ -19,6 +19,12 @@ repos:
           - flake8-string-format
     repo: https://gitlab.com/pycqa/flake8
     rev: 3.8.4
+  - hooks:
+      -  id: mypy
+         language_version: python3
+         files: ^dvc/
+    repo: https://github.com/pre-commit/mirrors-mypy
+    rev: 'v0.790'
   - repo: local
     hooks:
     - id: pylint

dvc/repo/add.py

@@ -1,5 +1,6 @@
 import logging
 import os
+from typing import TYPE_CHECKING
 
 import colorama
 
@@ -14,20 +15,29 @@ from ..repo.scm_context import scm_context
 from ..utils import LARGE_DIR_SIZE, glob_targets, resolve_paths
 from . import locked
 
+if TYPE_CHECKING:
+    from dvc.types import TargetType
+
+
 logger = logging.getLogger(__name__)
 
 
 @locked
 @scm_context
 def add(
-    repo, targets, recursive=False, no_commit=False, fname=None, **kwargs,
+    repo,
+    targets: "TargetType",
+    recursive=False,
+    no_commit=False,
+    fname=None,
+    **kwargs,
 ):
+    from dvc.utils.collections import ensure_list
+
     if recursive and fname:
         raise RecursiveAddingWhileUsingFilename()
 
-    if isinstance(targets, str):
-        targets = [targets]
-
+    targets = ensure_list(targets)
     link_failures = []
     stages_list = []
     num_targets = len(targets)

dvc/repo/params/show.py

@@ -14,6 +14,7 @@ from dvc.utils.serialize import LOADERS, ParseError
 if TYPE_CHECKING:
     from dvc.output.base import BaseOutput
     from dvc.repo import Repo
+    from dvc.types import DvcPath
 
 logger = logging.getLogger(__name__)
 
@@ -26,7 +27,7 @@ def _is_params(dep: "BaseOutput"):
     return isinstance(dep, ParamsDependency)
 
 
-def _collect_configs(repo: "Repo", rev, targets=None) -> List[PathInfo]:
+def _collect_configs(repo: "Repo", rev, targets=None) -> List["DvcPath"]:
     params, path_infos = collect(
         repo,
         targets=targets or [],

dvc/repo/plots/__init__.py

@@ -50,9 +50,10 @@ class Plots:
         Data parsing is postponed, since it's affected by props.
         """
         from dvc.tree.repo import RepoTree
+        from dvc.utils.collections import ensure_list
 
-        targets = [targets] if isinstance(targets, str) else targets or []
-        data = {}
+        targets = ensure_list(targets)
+        data: Dict[str, Dict] = {}
         for rev in self.repo.brancher(revs=revs):
             # .brancher() adds unwanted workspace
             if revs is not None and rev not in revs:
@@ -121,18 +122,18 @@ class Plots:
 
     def show(
         self,
-        targets=None,
+        targets: List[str] = None,
         revs=None,
         props=None,
         templates=None,
         recursive=False,
     ):
+        from dvc.utils.collections import ensure_list
 
         data = self.collect(targets, revs, recursive)
 
         # If any mentioned plot doesn't have any data then that's an error
-        targets = [targets] if isinstance(targets, str) else targets or []
-        for target in targets:
+        for target in ensure_list(targets):
             rpath = relpath(target, self.repo.root_dir)
             if not any(
                 "data" in rev_data[key]

dvc/stage/__init__.py

@@ -37,6 +37,7 @@ from .utils import (
 logger = logging.getLogger(__name__)
 # Disallow all punctuation characters except hyphen and underscore
 INVALID_STAGENAME_CHARS = set(string.punctuation) - {"_", "-"}
+Env = Dict[str, str]
 
 
 def loads_from(cls, repo, path, wdir, data):
@@ -252,8 +253,8 @@ class Stage(params.StageParams):
         return any(out.checkpoint for out in self.outs)
 
     @property
-    def env(self) -> Dict[str, str]:
-        env = {}
+    def env(self) -> Env:
+        env: Env = {}
         for out in self.outs:
             if any(out.env.keys() and env.keys()):
                 raise DvcException("Duplicated env variable")

dvc/types.py

@@ -1,4 +1,4 @@
-from typing import TYPE_CHECKING, Optional, Union
+from typing import TYPE_CHECKING, List, Optional, Union
 
 from dvc.path_info import PathInfo, URLInfo
 
@@ -10,3 +10,4 @@ DvcPath = Union[PathInfo, URLInfo]
 AnyPath = Union[str, DvcPath, StrPath]
 
 OptStr = Optional[str]
+TargetType = Union[List[str], str]

dvc/utils/collections.py

@@ -1,5 +1,6 @@
 import os
 from collections.abc import Mapping
+from typing import Iterable, List, Union
 
 from pygtrie import StringTrie as _StringTrie
 
@@ -57,3 +58,11 @@ def apply_diff(src, dest):
                 src.__class__.__name__, dest.__class__.__name__
             )
         )
+
+
+def ensure_list(item: Union[Iterable[str], str, None]) -> List[str]:
+    if item is None:
+        return []
+    if isinstance(item, str):
+        return [item]
+    return list(item)

setup.cfg

@@ -40,5 +40,5 @@ check_untyped_defs = False
 # Warnings
 warn_no_return=True
 warn_redundant_casts=True
-warn_unused_ignores=True
 warn_unreachable = True
+files = dvc