perf: don't clear the entire dependency cache when backtracking (pyth…

…on-poetry#7950)

(cherry picked from commit f54864e)

src/poetry/mixology/version_solver.py

@@ -39,15 +39,20 @@ class DependencyCache:
     """
 
     def __init__(self, provider: Provider) -> None:
-        self.provider = provider
-        self.cache: dict[
-            tuple[str, str | None, str | None, str | None, str | None],
-            list[DependencyPackage],
-        ] = {}
+        self._provider = provider
+        self._cache: dict[
+            int,
+            dict[
+                tuple[str, str | None, str | None, str | None, str | None],
+                list[DependencyPackage],
+            ],
+        ] = collections.defaultdict(dict)
 
         self.search_for = functools.lru_cache(maxsize=128)(self._search_for)
 
-    def _search_for(self, dependency: Dependency) -> list[DependencyPackage]:
+    def _search_for(
+        self, dependency: Dependency, level: int
+    ) -> list[DependencyPackage]:
         key = (
             dependency.complete_name,
             dependency.source_type,
@@ -56,12 +61,17 @@ def _search_for(self, dependency: Dependency) -> list[DependencyPackage]:
             dependency.source_subdirectory,
         )
 
-        packages = self.cache.get(key)
-
-        if packages:
-            packages = [
-                p for p in packages if dependency.constraint.allows(p.package.version)
-            ]
+        for check_level in range(level, -1, -1):
+            packages = self._cache[check_level].get(key)
+            if packages is not None:
+                packages = [
+                    p
+                    for p in packages
+                    if dependency.constraint.allows(p.package.version)
+                ]
+                break
+        else:
+            packages = None
 
         # provider.search_for() normally does not include pre-release packages
         # (unless requested), but will include them if there are no other
@@ -71,14 +81,14 @@ def _search_for(self, dependency: Dependency) -> list[DependencyPackage]:
         # nothing, we need to call provider.search_for() again as it may return
         # additional results this time.
         if not packages:
-            packages = self.provider.search_for(dependency)
-
-        self.cache[key] = packages
+            packages = self._provider.search_for(dependency)
 
+        self._cache[level][key] = packages
         return packages
 
-    def clear(self) -> None:
-        self.cache.clear()
+    def clear_level(self, level: int) -> None:
+        self.search_for.cache_clear()
+        self._cache.pop(level, None)
 
 
 class VersionSolver:
@@ -318,9 +328,9 @@ def _resolve_conflict(self, incompatibility: Incompatibility) -> Incompatibility
                     self._solution.decision_level, previous_satisfier_level, -1
                 ):
                     self._contradicted_incompatibilities.pop(level, None)
+                    self._dependency_cache.clear_level(level)
 
                 self._solution.backtrack(previous_satisfier_level)
-                self._dependency_cache.clear()
                 if new_incompatibility:
                     self._add_incompatibility(incompatibility)
 
@@ -418,7 +428,11 @@ def _get_min(dependency: Dependency) -> tuple[bool, int, int]:
                 if locked:
                     return is_specific_marker, Preference.LOCKED, 1
 
-            num_packages = len(self._dependency_cache.search_for(dependency))
+            num_packages = len(
+                self._dependency_cache.search_for(
+                    dependency, self._solution.decision_level
+                )
+            )
 
             if num_packages < 2:
                 preference = Preference.NO_CHOICE
@@ -435,7 +449,9 @@ def _get_min(dependency: Dependency) -> tuple[bool, int, int]:
 
         locked = self._provider.get_locked(dependency)
         if locked is None:
-            packages = self._dependency_cache.search_for(dependency)
+            packages = self._dependency_cache.search_for(
+                dependency, self._solution.decision_level
+            )
             package = next(iter(packages), None)
 
             if package is None:

tests/mixology/version_solver/test_dependency_cache.py

@@ -2,6 +2,7 @@
 
 from copy import deepcopy
 from typing import TYPE_CHECKING
+from unittest import mock
 
 from poetry.factory import Factory
 from poetry.mixology.version_solver import DependencyCache
@@ -32,14 +33,14 @@ def test_solver_dependency_cache_respects_source_type(
     cache.search_for.cache_clear()
 
     # ensure cache was never hit for both calls
-    cache.search_for(dependency_pypi)
-    cache.search_for(dependency_git)
+    cache.search_for(dependency_pypi, 0)
+    cache.search_for(dependency_git, 0)
     assert not cache.search_for.cache_info().hits
 
     # increase test coverage by searching for copies
     # (when searching for the exact same object, __eq__ is never called)
-    packages_pypi = cache.search_for(deepcopy(dependency_pypi))
-    packages_git = cache.search_for(deepcopy(dependency_git))
+    packages_pypi = cache.search_for(deepcopy(dependency_pypi), 0)
+    packages_git = cache.search_for(deepcopy(dependency_git), 0)
 
     assert cache.search_for.cache_info().hits == 2
     assert cache.search_for.cache_info().currsize == 2
@@ -60,6 +61,44 @@ def test_solver_dependency_cache_respects_source_type(
     assert package_git.package.source_resolved_reference == MOCK_DEFAULT_GIT_REVISION
 
 
+def test_solver_dependency_cache_pulls_from_prior_level_cache(
+    root: ProjectPackage, provider: Provider, repo: Repository
+) -> None:
+    dependency_pypi = Factory.create_dependency("demo", ">=0.1.0")
+    root.add_dependency(dependency_pypi)
+    add_to_repo(repo, "demo", "1.0.0")
+
+    wrapped_provider = mock.Mock(wraps=provider)
+    cache = DependencyCache(wrapped_provider)
+    cache.search_for.cache_clear()
+
+    # On first call, provider.search_for() should be called and the level-0
+    # cache populated.
+    cache.search_for(dependency_pypi, 0)
+    assert len(wrapped_provider.search_for.mock_calls) == 1
+    assert ("demo", None, None, None, None) in cache._cache[0]
+    assert cache.search_for.cache_info().hits == 0
+    assert cache.search_for.cache_info().misses == 1
+
+    # On second call at level 1, provider.search_for() should not be called
+    # again and the level-1 cache should be populated from the level-0 cache.
+    cache.search_for(dependency_pypi, 1)
+    assert len(wrapped_provider.search_for.mock_calls) == 1
+    assert ("demo", None, None, None, None) in cache._cache[1]
+    assert cache._cache[0] == cache._cache[1]
+    assert cache.search_for.cache_info().hits == 0
+    assert cache.search_for.cache_info().misses == 2
+
+    # Clearing the level 1 cache should invalidate the lru_cache on
+    # cache.search_for and wipe out the level 1 cache while preserving the
+    # level 0 cache.
+    cache.clear_level(1)
+    assert set(cache._cache.keys()) == {0}
+    assert ("demo", None, None, None, None) in cache._cache[0]
+    assert cache.search_for.cache_info().hits == 0
+    assert cache.search_for.cache_info().misses == 0
+
+
 def test_solver_dependency_cache_respects_subdirectories(
     root: ProjectPackage, provider: Provider, repo: Repository
 ) -> None:
@@ -87,14 +126,14 @@ def test_solver_dependency_cache_respects_subdirectories(
     cache.search_for.cache_clear()
 
     # ensure cache was never hit for both calls
-    cache.search_for(dependency_one)
-    cache.search_for(dependency_one_copy)
+    cache.search_for(dependency_one, 0)
+    cache.search_for(dependency_one_copy, 0)
     assert not cache.search_for.cache_info().hits
 
     # increase test coverage by searching for copies
     # (when searching for the exact same object, __eq__ is never called)
-    packages_one = cache.search_for(deepcopy(dependency_one))
-    packages_one_copy = cache.search_for(deepcopy(dependency_one_copy))
+    packages_one = cache.search_for(deepcopy(dependency_one), 0)
+    packages_one_copy = cache.search_for(deepcopy(dependency_one_copy), 0)
 
     assert cache.search_for.cache_info().hits == 2
     assert cache.search_for.cache_info().currsize == 2