Convert more record classes to dataclasses (#12659)

- Removes BestCandidateResult's iter_all() and iter_applicable()
  methods as they were redundant
- Removes ParsedLine's is_requirement attribute as it was awkward to use
  (to please mypy, you would need to add asserts on .requirement)
- Removes ParsedRequirement's defaults as they conflict with slots (Python
  3.10 dataclasses have a built-in workaround that we can't use yet...)

Author: ichard26

news/c33bb4df-d6ab-4d9b-8113-55c27a237dfd.trivial.rst

@@ -334,44 +334,30 @@ class CandidatePreferences:
     allow_all_prereleases: bool = False
 
 
+@dataclass(frozen=True)
 class BestCandidateResult:
     """A collection of candidates, returned by `PackageFinder.find_best_candidate`.
 
     This class is only intended to be instantiated by CandidateEvaluator's
     `compute_best_candidate()` method.
-    """
-
-    def __init__(
-        self,
-        candidates: List[InstallationCandidate],
-        applicable_candidates: List[InstallationCandidate],
-        best_candidate: Optional[InstallationCandidate],
-    ) -> None:
-        """
-        :param candidates: A sequence of all available candidates found.
-        :param applicable_candidates: The applicable candidates.
-        :param best_candidate: The most preferred candidate found, or None
-            if no applicable candidates were found.
-        """
-        assert set(applicable_candidates) <= set(candidates)
-
-        if best_candidate is None:
-            assert not applicable_candidates
-        else:
-            assert best_candidate in applicable_candidates
 
-        self._applicable_candidates = applicable_candidates
-        self._candidates = candidates
+    :param all_candidates: A sequence of all available candidates found.
+    :param applicable_candidates: The applicable candidates.
+    :param best_candidate: The most preferred candidate found, or None
+        if no applicable candidates were found.
+    """
 
-        self.best_candidate = best_candidate
+    all_candidates: List[InstallationCandidate]
+    applicable_candidates: List[InstallationCandidate]
+    best_candidate: Optional[InstallationCandidate]
 
-    def iter_all(self) -> Iterable[InstallationCandidate]:
-        """Iterate through all candidates."""
-        return iter(self._candidates)
+    def __post_init__(self) -> None:
+        assert set(self.applicable_candidates) <= set(self.all_candidates)
 
-    def iter_applicable(self) -> Iterable[InstallationCandidate]:
-        """Iterate through the applicable candidates."""
-        return iter(self._applicable_candidates)
+        if self.best_candidate is None:
+            assert not self.applicable_candidates
+        else:
+            assert self.best_candidate in self.applicable_candidates
 
 
 class CandidateEvaluator:
@@ -929,7 +915,7 @@ def _format_versions(cand_iter: Iterable[InstallationCandidate]) -> str:
                 "Could not find a version that satisfies the requirement %s "
                 "(from versions: %s)",
                 req,
-                _format_versions(best_candidate_result.iter_all()),
+                _format_versions(best_candidate_result.all_candidates),
             )
 
             raise DistributionNotFound(f"No matching distribution found for {req}")
@@ -963,15 +949,15 @@ def _should_install_candidate(
             logger.debug(
                 "Using version %s (newest of versions: %s)",
                 best_candidate.version,
-                _format_versions(best_candidate_result.iter_applicable()),
+                _format_versions(best_candidate_result.applicable_candidates),
             )
             return best_candidate
 
         # We have an existing version, and its the best version
         logger.debug(
             "Installed version (%s) is most up-to-date (past versions: %s)",
             installed_version,
-            _format_versions(best_candidate_result.iter_applicable()),
+            _format_versions(best_candidate_result.applicable_candidates),
         )
         raise BestVersionAlreadyInstalled
 

src/pip/_internal/index/package_finder.py

@@ -1,9 +1,10 @@
 import collections
 import logging
 import os
+from dataclasses import dataclass, field
 from typing import Container, Dict, Generator, Iterable, List, NamedTuple, Optional, Set
 
-from pip._vendor.packaging.utils import canonicalize_name
+from pip._vendor.packaging.utils import NormalizedName, canonicalize_name
 from pip._vendor.packaging.version import InvalidVersion
 
 from pip._internal.exceptions import BadCommand, InstallationError
@@ -220,19 +221,16 @@ def _get_editable_info(dist: BaseDistribution) -> _EditableInfo:
     )
 
 
+@dataclass(frozen=True)
 class FrozenRequirement:
-    def __init__(
-        self,
-        name: str,
-        req: str,
-        editable: bool,
-        comments: Iterable[str] = (),
-    ) -> None:
-        self.name = name
-        self.canonical_name = canonicalize_name(name)
-        self.req = req
-        self.editable = editable
-        self.comments = comments
+    name: str
+    req: str
+    editable: bool
+    comments: Iterable[str] = field(default_factory=tuple)
+
+    @property
+    def canonical_name(self) -> NormalizedName:
+        return canonicalize_name(self.name)
 
     @classmethod
     def from_dist(cls, dist: BaseDistribution) -> "FrozenRequirement":

src/pip/_internal/operations/freeze.py

@@ -8,6 +8,7 @@
 import re
 import shlex
 import urllib.parse
+from dataclasses import dataclass
 from optparse import Values
 from typing import (
     TYPE_CHECKING,
@@ -84,49 +85,48 @@
 logger = logging.getLogger(__name__)
 
 
+@dataclass(frozen=True)
 class ParsedRequirement:
-    def __init__(
-        self,
-        requirement: str,
-        is_editable: bool,
-        comes_from: str,
-        constraint: bool,
-        options: Optional[Dict[str, Any]] = None,
-        line_source: Optional[str] = None,
-    ) -> None:
-        self.requirement = requirement
-        self.is_editable = is_editable
-        self.comes_from = comes_from
-        self.options = options
-        self.constraint = constraint
-        self.line_source = line_source
+    # TODO: replace this with slots=True when dropping Python 3.9 support.
+    __slots__ = (
+        "requirement",
+        "is_editable",
+        "comes_from",
+        "constraint",
+        "options",
+        "line_source",
+    )
+
+    requirement: str
+    is_editable: bool
+    comes_from: str
+    constraint: bool
+    options: Optional[Dict[str, Any]]
+    line_source: Optional[str]
 
 
+@dataclass(frozen=True)
 class ParsedLine:
-    def __init__(
-        self,
-        filename: str,
-        lineno: int,
-        args: str,
-        opts: Values,
-        constraint: bool,
-    ) -> None:
-        self.filename = filename
-        self.lineno = lineno
-        self.opts = opts
-        self.constraint = constraint
-
-        if args:
-            self.is_requirement = True
-            self.is_editable = False
-            self.requirement = args
-        elif opts.editables:
-            self.is_requirement = True
-            self.is_editable = True
+    __slots__ = ("filename", "lineno", "args", "opts", "constraint")
+
+    filename: str
+    lineno: int
+    args: str
+    opts: Values
+    constraint: bool
+
+    @property
+    def is_editable(self) -> bool:
+        return bool(self.opts.editables)
+
+    @property
+    def requirement(self) -> Optional[str]:
+        if self.args:
+            return self.args
+        elif self.is_editable:
             # We don't support multiple -e on one line
-            self.requirement = opts.editables[0]
-        else:
-            self.is_requirement = False
+            return self.opts.editables[0]
+        return None
 
 
 def parse_requirements(
@@ -179,7 +179,7 @@ def handle_requirement_line(
         line.lineno,
     )
 
-    assert line.is_requirement
+    assert line.requirement is not None
 
     # get the options that apply to requirements
     if line.is_editable:
@@ -301,7 +301,7 @@ def handle_line(
     affect the finder.
     """
 
-    if line.is_requirement:
+    if line.requirement is not None:
         parsed_req = handle_requirement_line(line, options)
         return parsed_req
     else:
@@ -340,7 +340,7 @@ def _parse_and_recurse(
         parsed_files_stack: List[Dict[str, Optional[str]]],
     ) -> Generator[ParsedLine, None, None]:
         for line in self._parse_file(filename, constraint):
-            if not line.is_requirement and (
+            if line.requirement is None and (
                 line.opts.requirements or line.opts.constraints
             ):
                 # parse a nested requirements file

src/pip/_internal/req/req_file.py

@@ -309,7 +309,7 @@ def iter_index_candidate_infos() -> Iterator[IndexCandidateInfo]:
                 specifier=specifier,
                 hashes=hashes,
             )
-            icans = list(result.iter_applicable())
+            icans = result.applicable_candidates
 
             # PEP 592: Yanked releases are ignored unless the specifier
             # explicitly pins a version (via '==' or '===') that can be

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

@@ -467,13 +467,13 @@ def test_compute_best_candidate(self) -> None:
         )
         result = evaluator.compute_best_candidate(candidates)
 
-        assert result._candidates == candidates
+        assert result.all_candidates == candidates
         expected_applicable = candidates[:2]
         assert [str(c.version) for c in expected_applicable] == [
             "1.10",
             "1.11",
         ]
-        assert result._applicable_candidates == expected_applicable
+        assert result.applicable_candidates == expected_applicable
 
         assert result.best_candidate is expected_applicable[1]
 
@@ -490,8 +490,8 @@ def test_compute_best_candidate__none_best(self) -> None:
         )
         result = evaluator.compute_best_candidate(candidates)
 
-        assert result._candidates == candidates
-        assert result._applicable_candidates == []
+        assert result.all_candidates == candidates
+        assert result.applicable_candidates == []
         assert result.best_candidate is None
 
     @pytest.mark.parametrize(