static_folder can be a pathlib.Path

CHANGES.rst

@@ -13,6 +13,8 @@ Unreleased
 -   Support View and MethodView instances with async handlers. :issue:`4112`
 -   Enhance typing of ``app.errorhandler`` decorator. :issue:`4095`
 -   Fix registering a blueprint twice with differing names. :issue:`4124`
+-   Fix the type of ``static_folder`` to accept ``pathlib.Path``.
+    :issue:`4150`
 
 
 Version 2.0.1

src/flask/app.py

@@ -389,7 +389,7 @@ class Flask(Scaffold):
         self,
         import_name: str,
         static_url_path: t.Optional[str] = None,
-        static_folder: t.Optional[str] = "static",
+        static_folder: t.Optional[t.Union[str, os.PathLike]] = "static",
         static_host: t.Optional[str] = None,
         host_matching: bool = False,
         subdomain_matching: bool = False,

src/flask/blueprints.py

@@ -1,3 +1,4 @@
+import os
 import typing as t
 from collections import defaultdict
 from functools import update_wrapper
@@ -175,7 +176,7 @@ class Blueprint(Scaffold):
         self,
         name: str,
         import_name: str,
-        static_folder: t.Optional[str] = None,
+        static_folder: t.Optional[t.Union[str, os.PathLike]] = None,
         static_url_path: t.Optional[str] = None,
         template_folder: t.Optional[str] = None,
         url_prefix: t.Optional[str] = None,

src/flask/scaffold.py

@@ -92,7 +92,7 @@ class Scaffold:
     def __init__(
         self,
         import_name: str,
-        static_folder: t.Optional[str] = None,
+        static_folder: t.Optional[t.Union[str, os.PathLike]] = None,
         static_url_path: t.Optional[str] = None,
         template_folder: t.Optional[str] = None,
         root_path: t.Optional[str] = None,
@@ -101,7 +101,7 @@ class Scaffold:
         #: to. Do not change this once it is set by the constructor.
         self.import_name = import_name
 
-        self.static_folder = static_folder
+        self.static_folder = static_folder  # type: ignore
         self.static_url_path = static_url_path
 
         #: The path to the templates folder, relative to
@@ -257,7 +257,7 @@ class Scaffold:
             return None
 
     @static_folder.setter
-    def static_folder(self, value: t.Optional[str]) -> None:
+    def static_folder(self, value: t.Optional[t.Union[str, os.PathLike]]) -> None:
         if value is not None:
             value = os.fspath(value).rstrip(r"\/")