🐛 Exclude 5.0rc1 when <5 is requested (#139)

src/pipgrip/libs/mixology/range.py

@@ -31,6 +31,7 @@
 #
 # SPDX-License-Identifier: BSD-3-Clause
 # flake8: noqa:A002,A003
+from copy import deepcopy
 from typing import Any, NoReturn, Optional
 from typing import Union as _Union
 
@@ -315,6 +316,21 @@ def is_strictly_lower(self, other):  # type: (Range) -> bool
         return not self.include_max or not other.include_min
 
     def is_strictly_higher(self, other):  # type: (Range) -> bool
+        if (
+            self.is_single_version()
+            and self.max is not None
+            and other.max is not None
+            and self.max.is_prerelease()
+            and not other.max.is_prerelease()
+            and not other.include_max
+            and self.max.equals_without_prerelease(other.max)
+        ):
+            # in pip, `<5`, `<5.0`, `<5.0.0` are shorthand for `<5.0.0-alpha.0`.
+            # e.g. `pip install --pre django<5.0` will not install django==5.0rc1
+            # although technically 5.0rc1 < 5.0 according to semver.
+            # mimic this behaviour here (check 5.0rc1 against <5.0.0-alpha.0)
+            other = deepcopy(other)
+            other._max = other.max.first_prerelease
         return other.is_strictly_lower(self)
 
     def is_adjacent_to(self, other):  # type: (Range) -> bool

tests/tests_mixology/test_basic_graph.py

@@ -95,3 +95,30 @@ def test_circular_dependency(source):
     source.add("bar", "1.0.0", deps={"foo": "1.0.0"})
 
     check_solver_result(source, {"foo": "1.0.0", "bar": "1.0.0"})
+
+
+def test_prerelease_lte(source):
+    source.root_dep("foo", "<=5")
+
+    source.add("foo", "4.1.1")
+    source.add("foo", "5.0rc1")
+
+    check_solver_result(source, {"foo": "5.0rc1"})
+
+
+def test_prerelease_lt(source):
+    source.root_dep("foo", "<5")
+
+    source.add("foo", "4.1.1")
+    source.add("foo", "5.0rc1")
+
+    check_solver_result(source, {"foo": "4.1.1"})
+
+
+def test_prerelease_gte(source):
+    source.root_dep("foo", ">=5.0.0a0")
+
+    source.add("foo", "4.1.1")
+    source.add("foo", "5.0rc1")
+
+    check_solver_result(source, {"foo": "5.0rc1"})

tests/tests_mixology/test_unsolvable.py

@@ -48,6 +48,21 @@ def test_no_version_matching_constraint(source):
     )
 
 
+def test_prerelease(source):
+    source.root_dep("foo", "<5")
+
+    source.add("foo", "5.0rc1")
+    source.add("foo", "5.0")
+
+    check_solver_result(
+        source,
+        error=(
+            "Because root depends on foo (<5) "
+            "which doesn't match any versions, version solving failed."
+        ),
+    )
+
+
 def test_no_version_that_matches_combined_constraints(source):
     source.root_dep("foo", "1.0.0")
     source.root_dep("bar", "1.0.0")