feat: support METADATA 2.1+ json format

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

pyproject_metadata/__init__.py

@@ -41,6 +41,7 @@
 
 __version__ = '0.9.0b4'
 
+
 __all__ = [
     'ConfigurationError',
     'ConfigurationWarning',
@@ -110,6 +111,38 @@ def __setitem__(self, name: str, value: str | None) -> None:
             return
         self.message[name] = value
 
+    def set_payload(self, payload: str) -> None:
+        self.message.set_payload(payload)
+
+
+@dataclasses.dataclass
+class _JSonMessageSetter:
+    """
+    This provides an API to build a JSON message output. Line breaks are
+    preserved this way.
+    """
+
+    data: dict[str, str | list[str]]
+
+    def __setitem__(self, name: str, value: str | None) -> None:
+        name = name.lower()
+        key = name.replace('-', '_')
+
+        if value is None:
+            return
+
+        if name == 'keywords':
+            self.data[key] = value.split(',')
+        elif name in constants.KNOWN_MULTIUSE:
+            entry = self.data.get(key, [])
+            assert isinstance(entry, list)
+            entry.append(value)
+        else:
+            self.data[key] = value
+
+    def set_payload(self, payload: str) -> None:
+        self['description'] = payload
+
 
 class RFC822Policy(email.policy.EmailPolicy):
     """
@@ -365,13 +398,20 @@ def from_pyproject(
 
     def as_rfc822(self) -> RFC822Message:
         message = RFC822Message()
-        self.write_to_rfc822(message)
+        smart_message = _SmartMessageSetter(message)
+        self._write_metadata(smart_message)
         return message
 
-    def write_to_rfc822(self, message: email.message.Message) -> None:  # noqa: C901, PLR0912
-        self.validate(warn=False)
+    def as_json(self) -> dict[str, str | list[str]]:
+        message: dict[str, str | list[str]] = {}
+        smart_message = _JSonMessageSetter(message)
+        self._write_metadata(smart_message)
+        return message
 
-        smart_message = _SmartMessageSetter(message)
+    def _write_metadata(  # noqa: PLR0912 C901
+        self, smart_message: _SmartMessageSetter | _JSonMessageSetter
+    ) -> None:
+        self.validate(warn=False)
 
         smart_message['Metadata-Version'] = self.auto_metadata_version
         smart_message['Name'] = self.name
@@ -422,7 +462,7 @@ def write_to_rfc822(self, message: email.message.Message) -> None:  # noqa: C901
         if self.readme:
             if self.readme.content_type:
                 smart_message['Description-Content-Type'] = self.readme.content_type
-            message.set_payload(self.readme.text)
+            smart_message.set_payload(self.readme.text)
         # Core Metadata 2.2
         if self.auto_metadata_version != '2.1':
             for field in self.dynamic_metadata:

pyproject_metadata/constants.py

@@ -2,14 +2,15 @@
 
 
 __all__ = [
+    'KNOWN_BUILD_SYSTEM_FIELDS',
+    'KNOWN_METADATA_FIELDS',
     'KNOWN_METADATA_VERSIONS',
     'KNOWN_METADATA_VERSIONS',
+    'KNOWN_MULTIUSE',
+    'KNOWN_PROJECT_FIELDS',
+    'KNOWN_TOPLEVEL_FIELDS',
     'PRE_SPDX_METADATA_VERSIONS',
     'PROJECT_TO_METADATA',
-    'KNOWN_TOPLEVEL_FIELDS',
-    'KNOWN_BUILD_SYSTEM_FIELDS',
-    'KNOWN_PROJECT_FIELDS',
-    'KNOWN_METADATA_FIELDS',
 ]
 
 
@@ -51,8 +52,8 @@ def __dir__() -> list[str]:
     'classifier',
     'description',
     'description-content-type',
-    'download-url',  # Not specified via pyproject standards 'dynamic',  # Can't be in dynamic
-    'dynamic',
+    'download-urL',  # Not specified via pyproject standards
+    'dynamic',  # Can't be in dynamic
     'home-page',  # Not specified via pyproject standards
     'keywords',
     'license',
@@ -63,11 +64,11 @@ def __dir__() -> list[str]:
     'metadata-version',
     'name',  # Can't be in dynamic
     'obsoletes',  # Deprecated
-    'obsoletes-dist',  # Rarly used
+    'obsoletes-dist',  # Rarely used
     'platform',  # Not specified via pyproject standards
     'project-url',
     'provides',  # Deprecated
-    'provides-dist',  # Rarly used
+    'provides-dist',  # Rarely used
     'provides-extra',
     'requires',  # Deprecated
     'requires-dist',
@@ -77,3 +78,20 @@ def __dir__() -> list[str]:
     'supported-platform',  # Not specified via pyproject standards
     'version',  # Can't be in dynamic
 }
+
+KNOWN_MULTIUSE = {
+    'dynamic',
+    'platform',
+    'provides-extra',
+    'supported-platform',
+    'license-file',
+    'classifier',
+    'requires-dist',
+    'requires-external',
+    'project-url',
+    'provides-dist',
+    'obsoletes-dist',
+    'requires',  # Deprecated
+    'obsoletes',  # Deprecated
+    'provides',  # Deprecated
+}

tests/test_standard_metadata.py

@@ -847,6 +847,31 @@ def test_readme_content_type_unknown(monkeypatch: pytest.MonkeyPatch) -> None:
         pyproject_metadata.StandardMetadata.from_pyproject(tomllib.load(f))
 
 
+def test_as_json(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.chdir(DIR / 'packages/full-metadata')
+
+    with open('pyproject.toml', 'rb') as f:
+        metadata = pyproject_metadata.StandardMetadata.from_pyproject(tomllib.load(f))
+    core_metadata = metadata.as_json()
+
+    assert core_metadata == {
+        'author': 'Example!',
+        'author_email': 'Unknown <example@example.com>',
+        'description': 'some readme 👋\n',
+        'description_content_type': 'text/markdown',
+        'home_page': 'example.com',
+        'keywords': ['trampolim', 'is', 'interesting'],
+        'license': 'some license text',
+        'maintainer': '',
+        'maintainer_email': 'Other Example <other@example.com>',
+        'metadata_version': '2.1',
+        'name': 'full_metadata',
+        'requires_python': '>=3.8',
+        'summary': 'A package with all the metadata :)',
+        'version': '3.2.1',
+    }
+
+
 def test_as_rfc822(monkeypatch: pytest.MonkeyPatch) -> None:
     monkeypatch.chdir(DIR / 'packages/full-metadata')