Fixed #29529 -- FilePathField path parameter now accepts a callable.

django/db/models/fields/__init__.py

@@ -1712,7 +1712,7 @@ def get_prep_value(self, value):
 
     def formfield(self, **kwargs):
         return super().formfield(**{
-            'path': self.path,
+            'path': self.path() if callable(self.path) else self.path,
             'match': self.match,
             'recursive': self.recursive,
             'form_class': forms.FilePathField,

docs/ref/models/fields.txt

@@ -868,6 +868,19 @@ directory on the filesystem. Has three special arguments, of which the first is
     Required. The absolute filesystem path to a directory from which this
     :class:`FilePathField` should get its choices. Example: ``"/home/images"``.
 
+    A callable (such as a function) can also be passed to dynamically set the
+    path at runtime::
+
+         def generate_path():
+            return os.path.join(settings.LOCAL_FILE_DIR, '/images')
+
+         file = models.FilePathField(path=generate_path)
+
+    .. versionchanged:: 3.0
+
+         Older versions don't allow passing a callable.
+
+
 .. attribute:: FilePathField.match
 
     Optional. A regular expression, as a string, that :class:`FilePathField`

tests/model_fields/test_filepathfield.py

@@ -0,0 +1,26 @@
+import os.path
+
+from django.db.models import FilePathField
+from django.test import TestCase
+
+PATH = os.path.dirname(os.path.abspath(__file__))
+
+
+def generate_path():
+    return PATH
+
+
+class FilePathFieldTests(TestCase):
+
+    def test_string(self):
+        fp = FilePathField(path=PATH)
+        self.assertEqual(PATH, fp.path)
+
+    def test_callable(self):
+        fp = FilePathField(path=generate_path)
+        self.assertEqual(PATH, fp.path())
+
+    def test_formfield(self):
+        fp = FilePathField(path=generate_path)
+        formfield = fp.formfield()
+        self.assertEqual(formfield.path, PATH)