avoid special-casing the python version requirement in download.py

Author: cosmicexplorer

src/pip/_internal/commands/download.py

@@ -81,13 +81,12 @@ def as_json(self) -> Dict[str, Any]:
 
 @dataclass
 class DownloadInfos:
-    # python_version: Optional[Requirement] = None
-    python_version: Optional[str] = None
+    implicit_requirements: List[Requirement] = field(default_factory=list)
     resolution: Dict[str, RequirementDownloadInfo] = field(default_factory=dict)
 
     def as_json(self) -> Dict[str, Any]:
         return {
-            "python_version": self.python_version and str(self.python_version),
+            "implicit_requirements": [str(req) for req in self.implicit_requirements],
             "resolution": {
                 name: info.as_json() for name, info in self.resolution.items()
             },
@@ -241,8 +240,9 @@ def run(self, options: Values, args: List[str]) -> int:
         for candidate in requirement_set.candidates.mapping.values():
             # This will occur for the python version requirement, for example.
             if candidate.name not in requirement_set.requirements:
-                # download_infos.python_version = candidate.as_requirement()
-                download_infos.python_version = str(candidate)
+                download_infos.implicit_requirements.append(
+                    candidate.as_serializable_requirement()
+                )
                 continue
             req = requirement_set.requirements[candidate.name]
             assert req.name is not None
@@ -251,7 +251,7 @@ def run(self, options: Values, args: List[str]) -> int:
             download_infos.resolution[
                 req.name
             ] = RequirementDownloadInfo.from_req_and_link(
-                req=candidate.as_requirement(),
+                req=candidate.as_serializable_requirement(),
                 link=req.link,
             )
 

src/pip/_internal/metadata/base.py

@@ -101,6 +101,9 @@ def __repr__(self) -> str:
     def __str__(self) -> str:
         return f"{self.raw_name} {self.version}"
 
+    def as_serializable_requirement(self) -> Requirement:
+        raise NotImplementedError()
+
     @property
     def location(self) -> Optional[str]:
         """Where the distribution is loaded from.

src/pip/_internal/metadata/pkg_resources.py

@@ -120,6 +120,9 @@ def from_wheel(cls, wheel: Wheel, name: str) -> "Distribution":
         )
         return cls(dist)
 
+    def as_serializable_requirement(self) -> Requirement:
+        return self._dist.as_requirement()
+
     @property
     def location(self) -> Optional[str]:
         return self._dist.location

src/pip/_internal/resolution/resolvelib/base.py

@@ -61,34 +61,34 @@ def is_satisfied_by(self, candidate: "Candidate") -> bool:
         return self.specifier.contains(candidate.version, prereleases=True)
 
 
-class Requirement:
-    @property
+class Requirement(metaclass=abc.ABCMeta):
+    @abc.abstractproperty
     def project_name(self) -> NormalizedName:
         """The "project name" of a requirement.
 
         This is different from ``name`` if this requirement contains extras,
         in which case ``name`` would contain the ``[...]`` part, while this
         refers to the name of the project.
         """
-        raise NotImplementedError("Subclass should override")
 
-    @property
+    @abc.abstractproperty
     def name(self) -> str:
         """The name identifying this requirement in the resolver.
 
         This is different from ``project_name`` if this requirement contains
         extras, where ``project_name`` would not contain the ``[...]`` part.
         """
-        raise NotImplementedError("Subclass should override")
 
     def is_satisfied_by(self, candidate: "Candidate") -> bool:
         return False
 
+    @abc.abstractmethod
     def get_candidate_lookup(self) -> CandidateLookup:
-        raise NotImplementedError("Subclass should override")
+        ...
 
+    @abc.abstractmethod
     def format_for_error(self) -> str:
-        raise NotImplementedError("Subclass should override")
+        ...
 
 
 def _match_link(link: Link, candidate: "Candidate") -> bool:
@@ -120,7 +120,7 @@ def version(self) -> CandidateVersion:
         ...
 
     @abc.abstractmethod
-    def as_requirement(self) -> PkgRequirement:
+    def as_serializable_requirement(self) -> PkgRequirement:
         ...
 
     @abc.abstractproperty

src/pip/_internal/resolution/resolvelib/candidates.py

@@ -35,6 +35,9 @@
 
 # Avoid conflicting with the PyPI package "Python".
 REQUIRES_PYTHON_IDENTIFIER = cast(NormalizedName, "<Python from Requires-Python>")
+# Avoid clashing with any package on PyPI, but remain parseable as a Requirement. This
+# should only be used for .as_serializable_requirement().
+REQUIRES_PYTHON_SERIALIZABLE_IDENTIFIER = cast(NormalizedName, "Requires-Python")
 
 
 def as_base_candidate(candidate: Candidate) -> Optional[BaseCandidate]:
@@ -160,7 +163,7 @@ def __init__(
     def __str__(self) -> str:
         return f"{self.name} {self.version}"
 
-    def as_requirement(self) -> PkgRequirement:
+    def as_serializable_requirement(self) -> PkgRequirement:
         return produce_exact_version_requirement(self.name, str(self.version))
 
     def __repr__(self) -> str:
@@ -371,6 +374,9 @@ def name(self) -> str:
     def version(self) -> CandidateVersion:
         return self.dist.version
 
+    def as_serializable_requirement(self) -> PkgRequirement:
+        return self.dist.as_serializable_requirement()
+
     @property
     def is_editable(self) -> bool:
         return self.dist.editable
@@ -453,6 +459,9 @@ def name(self) -> str:
     def version(self) -> CandidateVersion:
         return self.base.version
 
+    def as_serializable_requirement(self) -> PkgRequirement:
+        return self.base.as_serializable_requirement()
+
     def format_for_error(self) -> str:
         return "{} [{}]".format(
             self.base.format_for_error(), ", ".join(sorted(self.extras))
@@ -535,9 +544,10 @@ def name(self) -> str:
     def version(self) -> CandidateVersion:
         return self._version
 
-    def as_requirement(self) -> PkgRequirement:
-        raise NotImplementedError("FIXME!!!")
-        # return produce_exact_version_requirement(self.name, str(self.version))
+    def as_serializable_requirement(self) -> PkgRequirement:
+        return produce_exact_version_requirement(
+            REQUIRES_PYTHON_SERIALIZABLE_IDENTIFIER, str(self.version)
+        )
 
     @property
     def is_editable(self) -> bool: