add VersionMap helper

Resolves #489

src/fromager/versionmap.py

@@ -0,0 +1,38 @@
+"""VersionMap interface for managing package settings in plugins."""
+
+import typing
+
+from packaging.requirements import Requirement
+from packaging.version import Version
+
+
+class VersionMap:
+    def __init__(self, initial_content: dict | None = None) -> None:
+        self._content: dict[Version, typing.Any] = {}
+        for k, v in (initial_content or {}).items():
+            self.add(k, v)
+
+    def add(self, key: Version | str, value: typing.Any) -> None:
+        if not isinstance(key, Version):
+            key = Version(key)
+        self._content[key] = value
+
+    def versions(self) -> typing.Iterable[Version]:
+        # return the values sorted highest to lowest
+        return reversed(sorted(self._content.keys()))
+
+    def lookup(
+        self,
+        req: Requirement,
+        constraint: Requirement | None = None,
+        allow_prerelease: bool = False,
+    ) -> typing.Any:
+        for version in self.versions():
+            if not req.specifier.contains(version, prereleases=allow_prerelease):
+                continue
+            if constraint and not constraint.specifier.contains(
+                version, prereleases=allow_prerelease
+            ):
+                continue
+            return self._content[version]
+        raise ValueError(f"No version matched {req} with constraint {constraint}")

tests/test_versionmap.py

@@ -0,0 +1,79 @@
+import pytest
+from packaging.requirements import Requirement
+from packaging.version import Version
+
+from fromager.versionmap import VersionMap
+
+
+def test_initialize():
+    m = VersionMap(
+        {
+            "1.2": "value for 1.2",
+            Version("1.3"): "value for 1.3",
+            "1.0": "value for 1.0",
+        }
+    )
+    assert list(m.versions()) == [Version("1.3"), Version("1.2"), Version("1.0")]
+
+
+def test_lookup():
+    m = VersionMap(
+        {
+            "1.2": "value for 1.2",
+            Version("1.3"): "value for 1.3",
+            "1.0": "value for 1.0",
+        }
+    )
+    assert m.lookup(Requirement("pkg")) == "value for 1.3"
+    assert m.lookup(Requirement("pkg>1.0")) == "value for 1.3"
+    assert m.lookup(Requirement("pkg<1.3")) == "value for 1.2"
+
+
+def test_prerelease():
+    m = VersionMap(
+        {
+            Version("0.4.1b0"): "value for 0.4.1b",
+            "1.2": "value for 1.2",
+            Version("1.3"): "value for 1.3",
+            "1.0": "value for 1.0",
+            "1.5.0a0": "value for 1.5.0a0",
+        }
+    )
+    assert m.lookup(Requirement("pkg")) == "value for 1.3"
+    assert m.lookup(Requirement("pkg>1.0")) == "value for 1.3"
+    assert m.lookup(Requirement("pkg<1.3")) == "value for 1.2"
+    assert m.lookup(Requirement("pkg"), allow_prerelease=True) == "value for 1.5.0a0"
+    with pytest.raises(ValueError):
+        assert (
+            m.lookup(Requirement("pkg"), Requirement("pkg<1.0")) == "value for 0.4.1b"
+        )
+    assert (
+        m.lookup(Requirement("pkg"), Requirement("pkg<1.0"), allow_prerelease=True)
+        == "value for 0.4.1b"
+    )
+
+
+def test_with_constraint():
+    m = VersionMap(
+        {
+            "1.2": "value for 1.2",
+            Version("1.3"): "value for 1.3",
+            "1.0": "value for 1.0",
+        }
+    )
+    assert m.lookup(Requirement("pkg"), Requirement("pkg<1.3")) == "value for 1.2"
+    assert m.lookup(Requirement("pkg>1.0"), Requirement("pkg==1.2")) == "value for 1.2"
+
+
+def test_no_match():
+    m = VersionMap(
+        {
+            "1.2": "value for 1.2",
+            Version("1.3"): "value for 1.3",
+            "1.0": "value for 1.0",
+        }
+    )
+    with pytest.raises(ValueError):
+        m.lookup(Requirement("pkg"), Requirement("pkg<1.0"))
+    with pytest.raises(ValueError):
+        m.lookup(Requirement("pkg>1.0"), Requirement("pkg<1.0"))