Add deprecation warning for project.license as a table in pyproject.toml

Author: abravalheri

setuptools/config/_apply_pyprojecttoml.py

@@ -203,6 +203,14 @@ def _license(dist: Distribution, val: str | dict, root_dir: StrPath | None):
     if isinstance(val, str):
         _set_config(dist, "license_expression", _static.Str(val))
     else:
+        pypa_guides = "guides/writing-pyproject-toml/#license"
+        SetuptoolsDeprecationWarning.emit(
+            "`project.license` as a TOML table is deprecated",
+            "Please use a simple string containing a SPDX expression for "
+            "`project.license`. You can also use `project.license-files`.",
+            see_url=f"https://packaging.python.org/en/latest/{pypa_guides}",
+            due_date=(2026, 2, 18),  # Introduced on 2025-02-18
+        )
         if "file" in val:
             # XXX: Is it completely safe to assume static?
             value = expand.read_files([val["file"]], root_dir)