Ensure file referenced by 'readme' in pyproject.toml is added to sdist

1 files changed, 9 insertions, 3 deletions

diff --git a/setuptools/config/_apply_pyprojecttoml.py b/setuptools/config/_apply_pyprojecttoml.py
index 8af55616..22388e4f 100644
--- a/setuptools/config/_apply_pyprojecttoml.py
+++ b/setuptools/config/_apply_pyprojecttoml.py
@@ -16,7 +16,7 @@ from functools import partial, reduce
 from itertools import chain
 from types import MappingProxyType
 from typing import (TYPE_CHECKING, Any, Callable, Dict, List, Optional, Set, Tuple,
-                    Type, Union)
+                    Type, Union, cast)
 
 from setuptools._deprecation_warning import SetuptoolsDeprecationWarning
 
@@ -142,16 +142,22 @@ def _long_description(dist: "Distribution", val: _DictOrStr, root_dir: _Path):
     from setuptools.config import expand
 
     if isinstance(val, str):
-        text = expand.read_files(val, root_dir)
+        file: Union[str, list] = val
+        text = expand.read_files(file, root_dir)
         ctype = _guess_content_type(val)
     else:
-        text = val.get("text") or expand.read_files(val.get("file", []), root_dir)
+        file = val.get("file") or []
+        text = val.get("text") or expand.read_files(file, root_dir)
         ctype = val["content-type"]
 
     _set_config(dist, "long_description", text)
+
     if ctype:
         _set_config(dist, "long_description_content_type", ctype)
 
+    if file:
+        dist._referenced_files.add(cast(str, file))
+
 
 def _license(dist: "Distribution", val: dict, root_dir: _Path):
     from setuptools.config import expand