Validate vers qualifier

setup.cfg

@@ -41,6 +41,7 @@ package_dir = =src
 include_package_data = true
 zip_safe = false
 install_requires =
+    univers>=30.12.1
 
 [options.packages.find]
 where = src

src/packageurl/__init__.py

@@ -43,6 +43,8 @@
 
     AnyStr = Union[str, bytes]
 
+from univers.version_range import VersionRange
+
 # Python 3
 basestring = (bytes, str)
 
@@ -221,6 +223,9 @@ def normalize_qualifiers(
         if key[0] in string.digits:
             raise ValueError(f"A qualifier key cannot start with a number: {key!r}")
 
+    if vers := qualifiers_map.get("vers"):
+        VersionRange.from_string(vers, validate=True)
+
     qualifiers_map = dict(sorted(qualifiers_map.items()))
 
     if not encode:

tests/test_packageurl.py

@@ -29,6 +29,8 @@
 import re
 import unittest
 
+import pytest
+
 from packageurl import PackageURL
 from packageurl import normalize
 from packageurl import normalize_qualifiers
@@ -374,3 +376,13 @@ def test_encoding_stuff_with_colons_correctly() -> None:
         p.to_string()
         == "pkg:nuget/an:odd:space/libiconv:%20character%20set%20conversion%20library@1.9?package-id=e11a609df352e292"
     )
+
+
+def test_vers_validation_ok():
+    url = PackageURL.from_string("pkg:pypi/requests?vers=vers:pypi/>=2.0")
+    assert url.qualifiers["vers"] == "vers:pypi/>=2.0"
+
+
+def test_vers_validation_fails():
+    with pytest.raises(ValueError, match="must start with the 'vers:' URI scheme."):
+        PackageURL.from_string("pkg:pypi/requests?vers=>=2.0")