feat: support PEP 771

pyproject_metadata/__init__.py

@@ -225,6 +225,7 @@ class StandardMetadata:
     optional_dependencies: dict[str, list[Requirement]] = dataclasses.field(
         default_factory=dict
     )
+    default_optional_dependency_keys: list[str] | None = None
     entrypoints: dict[str, dict[str, str]] = dataclasses.field(default_factory=dict)
     authors: list[tuple[str, str | None]] = dataclasses.field(default_factory=list)
     maintainers: list[tuple[str, str | None]] = dataclasses.field(default_factory=list)
@@ -263,6 +264,8 @@ def auto_metadata_version(self) -> str:
         if self.metadata_version is not None:
             return self.metadata_version
 
+        if self.default_optional_dependency_keys is not None:
+            return "2.6"
         if isinstance(self.license, str) or self.license_files is not None:
             return "2.4"
         if self.dynamic_metadata:
@@ -397,6 +400,9 @@ def from_pyproject(  # noqa: C901
                 requires_python=requires_python,
                 dependencies=pyproject.get_dependencies(project),
                 optional_dependencies=pyproject.get_optional_dependencies(project),
+                default_optional_dependency_keys=pyproject.get_default_optional_dependency_keys(
+                    project
+                ),
                 entrypoints=pyproject.get_entrypoints(project),
                 authors=pyproject.ensure_people(
                     project.get("authors", []), "project.authors"
@@ -527,6 +533,14 @@ def validate(self, *, warn: bool = True) -> None:  # noqa: C901
             msg = "{key} is supported only when emitting metadata version >= 2.4"
             errors.config_error(msg, key="project.license-files")
 
+        if (
+            self.default_optional_dependency_keys is not None
+            and self.auto_metadata_version
+            in constants.PRE_DEFAULT_EXTRAS_METADATA_VERSIONS
+        ):
+            msg = "{key} is supported only when emitting metadata version >= 2.6"
+            errors.config_error(msg, key="project.default-optional-dependency-keys")
+
         for name in self.urls:
             if len(name) > 32:
                 msg = "{key} names cannot be more than 32 characters long"
@@ -595,6 +609,9 @@ def _write_metadata(  # noqa: C901
                 smart_message["Requires-Dist"] = str(
                     _build_extra_req(norm_extra, requirement)
                 )
+        for default_extra in self.default_optional_dependency_keys or []:
+            norm_extra = default_extra.replace(".", "-").replace("_", "-").lower()
+            smart_message["Default-Extra"] = norm_extra
         if self.readme:
             if self.readme.content_type:
                 smart_message["Description-Content-Type"] = self.readme.content_type

pyproject_metadata/constants.py

@@ -15,6 +15,7 @@
     "KNOWN_MULTIUSE",
     "KNOWN_PROJECT_FIELDS",
     "KNOWN_TOPLEVEL_FIELDS",
+    "PRE_DEFAULT_EXTRAS_METADATA_VERSIONS",
     "PRE_SPDX_METADATA_VERSIONS",
     "PROJECT_TO_METADATA",
 ]
@@ -24,8 +25,9 @@ def __dir__() -> list[str]:
     return __all__
 
 
-KNOWN_METADATA_VERSIONS = {"2.1", "2.2", "2.3", "2.4"}
+KNOWN_METADATA_VERSIONS = {"2.1", "2.2", "2.3", "2.4", "2.5", "2.6"}
 PRE_SPDX_METADATA_VERSIONS = {"2.1", "2.2", "2.3"}
+PRE_DEFAULT_EXTRAS_METADATA_VERSIONS = {"2.1", "2.2", "2.3", "2.4", "2.5"}
 
 PROJECT_TO_METADATA = {
     "authors": frozenset(["Author", "Author-Email"]),
@@ -41,6 +43,7 @@ def __dir__() -> list[str]:
     "maintainers": frozenset(["Maintainer", "Maintainer-Email"]),
     "name": frozenset(["Name"]),
     "optional-dependencies": frozenset(["Provides-Extra", "Requires-Dist"]),
+    "default-optional-dependency-keys": frozenset(["Default-Extra"]),
     "readme": frozenset(["Description", "Description-Content-Type"]),
     "requires-python": frozenset(["Requires-Python"]),
     "scripts": frozenset(),
@@ -76,6 +79,7 @@ def __dir__() -> list[str]:
     "provides",  # Deprecated
     "provides-dist",  # Rarely used
     "provides-extra",
+    "default-extra",
     "requires",  # Deprecated
     "requires-dist",
     "requires-external",  # Not specified via pyproject standards
@@ -89,6 +93,7 @@ def __dir__() -> list[str]:
     "dynamic",
     "platform",
     "provides-extra",
+    "default-extra",
     "supported-platform",
     "license-file",
     "classifier",

pyproject_metadata/project_table.py

@@ -54,6 +54,7 @@ class LicenseTable(TypedDict, total=False):
 Dynamic = Literal[
     "authors",
     "classifiers",
+    "default-optional-dependency-keys",
     "dependencies",
     "description",
     "dynamic",
@@ -82,6 +83,7 @@ class LicenseTable(TypedDict, total=False):
         "requires-python": str,
         "dependencies": List[str],
         "optional-dependencies": Dict[str, List[str]],
+        "default-optional-dependency-keys": List[str],
         "entry-points": Dict[str, Dict[str, str]],
         "authors": List[ContactTable],
         "maintainers": List[ContactTable],

pyproject_metadata/pyproject.py

@@ -374,6 +374,36 @@ def get_optional_dependencies(
                     return {}
         return dict(requirements_dict)
 
+    def get_default_optional_dependency_keys(
+        self, project: ProjectTable
+    ) -> list[str] | None:
+        """Get the default extras, or None if none provided"""
+
+        default_extras = project.get("default-optional-dependency-keys")
+        if default_extras is None:
+            return None
+
+        default_extra_list = self.ensure_list(
+            default_extras, key="project.default-optional-dependency-keys"
+        )
+        if default_extra_list is None:
+            return None
+
+        missing_keys = {
+            extra.replace(".", "-").replace("_", "-").lower()
+            for extra in default_extra_list
+        } - {
+            extra.replace(".", "-").replace("_", "-").lower()
+            for extra in self.get_optional_dependencies(project)
+        }
+        if missing_keys:
+            msg = 'Field {key} contains keys not in "project.optional-dependencies": {values!r}'
+            self.config_error(
+                msg, key="project.default-optional-dependency-keys", values=missing_keys
+            )
+
+        return default_extra_list
+
     def get_entrypoints(self, project: ProjectTable) -> dict[str, dict[str, str]]:
         """Get the entrypoints from the project table."""
 

tests/packages/default_extra/pyproject.toml

@@ -0,0 +1,14 @@
+[project]
+name = "default_extras"
+version = "0.1.2"
+default-optional-dependency-keys = [
+    "backend1",
+    "backend2",
+    "backend3"
+]
+
+[project.optional-dependencies]
+backend1 = ["a"]
+backend2 = ["b"]
+backend3 = ["c"]
+backend4 = ["d"]

tests/test_standard_metadata.py

@@ -420,6 +420,66 @@ def all_errors(request: pytest.FixtureRequest, monkeypatch: pytest.MonkeyPatch)
             ),
             id="Invalid optional-dependencies item",
         ),
+        pytest.param(
+            """
+                [project]
+                name = "test"
+                version = "0.1.0"
+                default-optional-dependency-keys = ["none"]
+                [project.optional-dependencies]
+                test = [
+                    "a",
+                ]
+            """,
+            (
+                'Field "project.default-optional-dependency-keys" contains keys '
+                "not in \"project.optional-dependencies\": {'none'}"
+            ),
+            id="Invalid default-optional-dependency-keys item",
+        ),
+        pytest.param(
+            """
+                [project]
+                name = "test"
+                version = "0.1.0"
+                default-optional-dependency-keys = ["none"]
+            """,
+            (
+                'Field "project.default-optional-dependency-keys" contains keys '
+                "not in \"project.optional-dependencies\": {'none'}"
+            ),
+            id="Invalid default-optional-dependency-keys item without optional-dependencies",
+        ),
+        pytest.param(
+            """
+                [project]
+                name = "test"
+                version = "0.1.0"
+                default-optional-dependency-keys = [1]
+            """,
+            (
+                'Field "project.default-optional-dependency-keys" contains item with invalid '
+                "type, expecting a string (got int)"
+            ),
+            id="Invalid default-optional-dependency-keys item type",
+        ),
+        pytest.param(
+            """
+                [project]
+                name = "test"
+                version = "0.1.0"
+                default-optional-dependency-keys = "test"
+                [project.optional-dependencies]
+                test = [
+                    "a",
+                ]
+            """,
+            (
+                'Field "project.default-optional-dependency-keys" has an invalid type, '
+                "expecting a list of strings (got str)"
+            ),
+            id="Invalid default-optional-dependency-keys not list",
+        ),
         pytest.param(
             """
                 [project]
@@ -943,6 +1003,17 @@ def test_load_multierror(
             "2.3",
             id="license-files with metadata_version 2.3",
         ),
+        pytest.param(
+            """
+                [project]
+                name = "test"
+                version = "0.1.0"
+                default-optional-dependency-keys = []
+            """,
+            '"project.default-optional-dependency-keys" is supported only when emitting metadata version >= 2.6',
+            "2.5",
+            id=" with metadata_version 2.5",
+        ),
     ],
 )
 def test_load_with_metadata_version(
@@ -1183,6 +1254,53 @@ def test_as_rfc822(monkeypatch: pytest.MonkeyPatch) -> None:
     assert core_metadata.get_payload() == "some readme 👋\n"
 
 
+def test_as_json_default_extra(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.chdir(DIR / "packages/default_extra")
+
+    with open("pyproject.toml", "rb") as f:
+        metadata = pyproject_metadata.StandardMetadata.from_pyproject(tomllib.load(f))
+    core_metadata = metadata.as_json()
+    assert core_metadata == {
+        "metadata_version": "2.6",
+        "name": "default_extras",
+        "version": "0.1.2",
+        "default_extra": ["backend1", "backend2", "backend3"],
+        "provides_extra": ["backend1", "backend2", "backend3", "backend4"],
+        "requires_dist": [
+            'a; extra == "backend1"',
+            'b; extra == "backend2"',
+            'c; extra == "backend3"',
+            'd; extra == "backend4"',
+        ],
+    }
+
+
+def test_as_rfc822_default_extra(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.chdir(DIR / "packages/default_extra")
+
+    with open("pyproject.toml", "rb") as f:
+        metadata = pyproject_metadata.StandardMetadata.from_pyproject(tomllib.load(f))
+    core_metadata = metadata.as_rfc822()
+    assert core_metadata.items() == [
+        ("Metadata-Version", "2.6"),
+        ("Name", "default_extras"),
+        ("Version", "0.1.2"),
+        ("Provides-Extra", "backend1"),
+        ("Requires-Dist", 'a; extra == "backend1"'),
+        ("Provides-Extra", "backend2"),
+        ("Requires-Dist", 'b; extra == "backend2"'),
+        ("Provides-Extra", "backend3"),
+        ("Requires-Dist", 'c; extra == "backend3"'),
+        ("Provides-Extra", "backend4"),
+        ("Requires-Dist", 'd; extra == "backend4"'),
+        ("Default-Extra", "backend1"),
+        ("Default-Extra", "backend2"),
+        ("Default-Extra", "backend3"),
+    ]
+
+    assert core_metadata.get_payload() is None
+
+
 def test_as_json_spdx(monkeypatch: pytest.MonkeyPatch) -> None:
     monkeypatch.chdir(DIR / "packages/spdx")