chore: Enable type checking in meltano.core.schedule_service (melta…

…no#6831)

Co-authored-by: Will Da Silva <will@willdasilva.xyz>

noxfile.py

@@ -94,6 +94,7 @@ def mypy(session: Session) -> None:
     session.install(
         "mypy",
         "sqlalchemy2-stubs",
+        "types-croniter",
         "types-requests",
     )
     session.run("mypy", *args)

pyproject.toml

@@ -96,6 +96,7 @@ pyupgrade = "^2.29.1"
 requests-mock = "^1.6.0"
 setproctitle = "^1.3" # Used by pytest-xdist to aid with handling resource intensive processes.
 tox = "^3.24.4"
+types-croniter = "^1.3.2"
 types-requests = "^2.28.9"
 wemake-python-styleguide = "^0.16.1"
 
@@ -144,7 +145,9 @@ show_missing = true
 skip_covered = true
 precision = 2
 exclude_lines = [
+    "pragma: no cover",
     "if TYPE_CHECKING:",
+    "\\.\\.\\.",
 ]
 
 [tool.commitizen]
@@ -204,7 +207,6 @@ module = [
   "meltano.core.project_plugins_service",
   "meltano.core.project_settings_service",
   "meltano.core.schedule",
-  "meltano.core.schedule_service",
   "meltano.core.select_service",
   "meltano.core.setting",
   "meltano.core.setting_definition",

src/meltano/core/schedule.py

@@ -23,7 +23,7 @@ class Schedule(NameEq, Canonical):  # noqa: WPS230
 
     def __init__(
         self,
-        name: str | None = None,
+        name: str,
         extractor: str | None = None,
         loader: str | None = None,
         transform: str | None = None,

src/meltano/core/schedule_service.py

@@ -174,7 +174,7 @@ def default_start_date(self, session, extractor: str) -> datetime:
         extractor_plugin = self.plugins_service.find_plugin(
             extractor, plugin_type=PluginType.EXTRACTORS
         )
-        start_date = None
+        start_date: str | datetime | date | None = None
         try:
             settings_service = PluginSettingsService(
                 self.project, extractor_plugin, plugins_service=self.plugins_service

src/meltano/core/utils/__init__.py

@@ -9,12 +9,13 @@
 import math
 import os
 import re
+import sys
 import traceback
 from collections import OrderedDict
 from copy import deepcopy
 from datetime import date, datetime, time
 from pathlib import Path
-from typing import Any, Callable, Iterable, TypeVar
+from typing import Any, Callable, Iterable, TypeVar, overload
 
 import flatten_dict
 from requests.auth import HTTPBasicAuth
@@ -35,6 +36,11 @@
 except AttributeError:
     asyncio_all_tasks = asyncio.Task.all_tasks
 
+if sys.version_info >= (3, 8):
+    from typing import Protocol
+else:
+    from typing_extensions import Protocol
+
 
 class NotFound(Exception):
     """Occurs when an element is not found."""
@@ -290,7 +296,22 @@ def truthy(val: str) -> bool:
     return str(val).lower() in TRUTHY
 
 
-def coerce_datetime(d: date | datetime) -> datetime | None:
+@overload
+def coerce_datetime(d: None) -> None:
+    ...  # noqa: WPS428
+
+
+@overload
+def coerce_datetime(d: datetime) -> datetime:
+    ...  # noqa: WPS428
+
+
+@overload
+def coerce_datetime(d: date) -> datetime:
+    ...  # noqa: WPS428
+
+
+def coerce_datetime(d):
     """Add a `time` component to `d` if it is missing.
 
     Args:
@@ -308,7 +329,17 @@ def coerce_datetime(d: date | datetime) -> datetime | None:
     return datetime.combine(d, time())
 
 
-def iso8601_datetime(d: str) -> datetime | None:
+@overload
+def iso8601_datetime(d: None) -> None:
+    ...  # noqa: WPS428
+
+
+@overload
+def iso8601_datetime(d: str) -> datetime:
+    ...  # noqa: WPS428
+
+
+def iso8601_datetime(d):
     if d is None:
         return None
 
@@ -328,7 +359,15 @@ def iso8601_datetime(d: str) -> datetime | None:
     raise ValueError(f"{d} is not a valid UTC date.")
 
 
-def find_named(xs: Iterable[dict], name: str, obj_type: type = None) -> dict:
+class _GetItemProtocol(Protocol):
+    def __getitem__(self, key: str) -> str:
+        ...  # noqa: WPS428
+
+
+_G = TypeVar("_G", bound=_GetItemProtocol)
+
+
+def find_named(xs: Iterable[_G], name: str, obj_type: type = None) -> _G:
     """Find an object by its 'name' key.
 
     Args: