Preserve dynamic metadata for empty dependencies

newsfragments/5120.bugfix.rst

@@ -0,0 +1 @@
+Preserved ``Dynamic: requires-dist`` in generated core metadata when ``dependencies`` is listed as dynamic and the resolved dependency list is empty.

setuptools/_core_metadata.py

@@ -211,8 +211,11 @@ def write_field(key, value):
     self._write_list(file, 'License-File', safe_license_files)
     _write_requirements(self, file)
 
+    dynamic_fields = set(getattr(self, "_setuptools_dynamic", ()))
     for field, attr in _POSSIBLE_DYNAMIC_FIELDS.items():
-        if (val := getattr(self, attr, None)) and not is_static(val):
+        if field in dynamic_fields:
+            write_field('Dynamic', field)
+        elif (val := getattr(self, attr, None)) and not is_static(val):
             write_field('Dynamic', field)
 
     long_description = self.get_long_description()

setuptools/config/_apply_pyprojecttoml.py

@@ -73,6 +73,7 @@ def _apply_project_table(dist: Distribution, config: dict, root_dir: StrPath):
 
     project_table = {k: _static.attempt_conversion(v) for k, v in orig_config.items()}
     _handle_missing_dynamic(dist, project_table)
+    _handle_dynamic_metadata(dist, project_table)
     _unify_entry_points(project_table)
 
     for field, value in project_table.items():
@@ -137,6 +138,14 @@ def _handle_missing_dynamic(dist: Distribution, project_table: dict):
                 project_table[field] = _RESET_PREVIOUSLY_DEFINED.get(field)
 
 
+def _handle_dynamic_metadata(dist: Distribution, project_table: dict):
+    dynamic = set(project_table.get("dynamic", []))
+    if "dependencies" in dynamic:
+        metadata_dynamic = set(getattr(dist.metadata, "_setuptools_dynamic", ()))
+        metadata_dynamic.add("requires-dist")
+        dist.metadata._setuptools_dynamic = metadata_dynamic
+
+
 def json_compatible_key(key: str) -> str:
     """As defined in :pep:`566#json-compatible-metadata`"""
     return key.lower().replace("-", "_")

setuptools/tests/config/test_apply_pyprojecttoml.py

@@ -646,6 +646,22 @@ def test_listed_in_dynamic(self, tmp_path, attr, field, value):
         dist_value = _some_attrgetter(f"metadata.{attr}", attr)(dist)
         assert dist_value == value
 
+    def test_empty_dynamic_dependencies_in_metadata(self, tmp_path):
+        pyproject = self.pyproject(tmp_path, ["dependencies"])
+        dist = makedist(tmp_path, install_requires=[])
+        dist = pyprojecttoml.apply_configuration(dist, pyproject)
+        metadata = core_metadata(dist)
+        assert "Dynamic: requires-dist\n" in metadata
+        assert "Requires-Dist:" not in metadata
+
+    def test_empty_static_dependencies_not_dynamic_in_metadata(self, tmp_path):
+        extra = "dependencies = []\n"
+        pyproject = self.pyproject(tmp_path, [], extra)
+        dist = pyprojecttoml.apply_configuration(makedist(tmp_path), pyproject)
+        metadata = core_metadata(dist)
+        assert "Dynamic:" not in metadata
+        assert "Requires-Dist:" not in metadata
+
     def test_license_files_exempt_from_dynamic(self, monkeypatch, tmp_path):
         """
         license-file is currently not considered in the context of dynamic.