chore: make Candidate a dataclass

Convert the `Candidate` class to an immutable dataclass.

Instead of an URL to the metadata file, a candidate object now only
holds an `has_metadata` flag. The metadata URL is always
`self.url + 'metadata'`.

`extras` is now a sorted tuple instead of `Iterable[str] | None`. This
simplifies the logic, too.

Signed-off-by: Christian Heimes <cheimes@redhat.com>

Author: tiran

src/fromager/candidate.py

@@ -1,3 +1,4 @@
+import dataclasses
 import logging
 import typing
 from email.message import EmailMessage, Message
@@ -22,37 +23,47 @@
     Metadata = Message
 
 
+@dataclasses.dataclass(frozen=True, order=True, slots=True, repr=False, kw_only=True)
 class Candidate:
-    def __init__(
-        self,
-        name: str,
-        version: Version,
-        url: str,
-        extras: typing.Iterable[str] | None = None,
-        is_sdist: bool | None = None,
-        build_tag: BuildTag = (),
-        metadata_url: str | None = None,
-    ):
-        self.name = canonicalize_name(name)
-        self.version = version
-        self.url = url
-        self.extras = extras
-        self.is_sdist = is_sdist
-        self.build_tag = build_tag
-        self.metadata_url = metadata_url
-
-        self._metadata: Metadata | None = None
-        self._dependencies: list[Requirement] | None = None
+    name: str
+    version: Version
+    url: str
+    is_sdist: bool | None = dataclasses.field(default=None)
+    extras: tuple[str, ...] = dataclasses.field(default=(), compare=False)
+    build_tag: BuildTag = dataclasses.field(default=(), compare=False)
+    has_metadata: bool = dataclasses.field(default=False, compare=False)
+
+    _metadata: Metadata | None = dataclasses.field(
+        default=None, init=False, compare=False
+    )
+    _dependencies: list[Requirement] | None = dataclasses.field(
+        default=None, init=False, compare=False
+    )
+
+    def __post_init__(self):
+        # force normalized name
+        object.__setattr__(self, "name", canonicalize_name(self.name))
 
     def __repr__(self) -> str:
         if not self.extras:
             return f"<{self.name}=={self.version}>"
         return f"<{self.name}[{','.join(self.extras)}]=={self.version}>"
 
+    @property
+    def metadata_url(self) -> str | None:
+        """PEP 658: metadata is available at {url}.metadata"""
+        if self.has_metadata:
+            return self.url + ".metadata"
+        return None
+
     @property
     def metadata(self) -> Metadata:
         if self._metadata is None:
-            self._metadata = get_metadata_for_wheel(self.url, self.metadata_url)
+            if not self.has_metadata:
+                raise ValueError(f"{self.url} does not have metadata")
+            metadata = get_metadata_for_wheel(self.url, self.metadata_url)
+            object.__setattr__(self, "_metadata", metadata)
+        assert self._metadata
         return self._metadata
 
     def _get_dependencies(self) -> typing.Iterable[Requirement]:
@@ -71,7 +82,9 @@ def _get_dependencies(self) -> typing.Iterable[Requirement]:
     @property
     def dependencies(self) -> list[Requirement]:
         if self._dependencies is None:
-            self._dependencies = list(self._get_dependencies())
+            dependencies = list(self._get_dependencies())
+            object.__setattr__(self, "_dependencies", dependencies)
+        assert self._dependencies
         return self._dependencies
 
     @property

src/fromager/resolver.py

@@ -339,13 +339,13 @@ def get_project_from_pypi(
                 continue
 
         c = Candidate(
-            name,
-            version,
+            name=name,
+            version=version,
             url=dp.url,
-            extras=extras,
+            extras=tuple(sorted(extras)),
             is_sdist=is_sdist,
             build_tag=build_tag,
-            metadata_url=dp.metadata_url if dp.has_metadata else None,
+            has_metadata=bool(dp.has_metadata),
         )
         if DEBUG_RESOLVER:
             logger.debug("candidate %s (%s) %s", dp.filename, c, dp.url)
@@ -723,7 +723,7 @@ def find_candidates(self, identifier) -> Candidates:
                     continue
                 assert isinstance(version, Version)
                 version = version
-            candidates.append(Candidate(identifier, version, url=url))
+            candidates.append(Candidate(name=identifier, version=version, url=url))
         return candidates
 
 

tests/test_pep658_support.py

@@ -16,7 +16,7 @@ def test_candidate_with_metadata_url(self):
             name="test-package",
             version=Version("1.0.0"),
             url="https://example.com/test-package-1.0.0-py3-none-any.whl",
-            metadata_url="https://example.com/test-package-1.0.0-py3-none-any.whl.metadata",
+            has_metadata=True,
         )
 
         assert (
@@ -132,12 +132,15 @@ def test_candidate_repr_with_metadata_url(self):
             name="test-package",
             version=Version("1.0.0"),
             url="https://example.com/test-package-1.0.0-py3-none-any.whl",
-            metadata_url="https://example.com/test-package-1.0.0-py3-none-any.whl.metadata",
+            has_metadata=True,
         )
 
         # The candidate should have the metadata URL attribute
         assert hasattr(candidate, "metadata_url")
-        assert candidate.metadata_url is not None
+        assert (
+            candidate.metadata_url
+            == "https://example.com/test-package-1.0.0-py3-none-any.whl.metadata"
+        )
 
     def test_metadata_url_construction(self):
         """Test that metadata URLs are constructed correctly."""
@@ -157,7 +160,7 @@ def test_pep658_integration_with_resolver(self):
             name="test-package",
             version=Version("1.0.0"),
             url="https://example.com/test.whl",
-            metadata_url="https://example.com/test.whl.metadata",
+            has_metadata=True,
         )
 
         candidate_without_metadata = Candidate(
@@ -166,6 +169,11 @@ def test_pep658_integration_with_resolver(self):
             url="https://example.com/test.whl",
         )
 
+        assert (
+            candidate_with_metadata.metadata_url
+            == "https://example.com/test.whl.metadata"
+        )
+
         # Verify PEP 658 metadata URL handling
         assert (
             candidate_with_metadata.metadata_url