Allow Version('') and map it to the empty tuple (#25953)

lib/spack/spack/test/versions.py

@@ -614,3 +614,17 @@ def test_empty_version_range_raises():
         assert VersionRange('2', '1.0')
     with pytest.raises(ValueError):
         assert ver('2:1.0')
+
+
+def test_version_empty_slice():
+    """Check an empty slice to confirm get "empty" version instead of
+       an IndexError (#25953).
+    """
+    assert Version('1.')[1:] == Version('')
+
+
+def test_version_wrong_idx_type():
+    """Ensure exception raised if attempt to use non-integer index."""
+    v = Version('1.1')
+    with pytest.raises(TypeError):
+        v['0:']

lib/spack/spack/version.py

@@ -177,7 +177,7 @@ def __init__(self, string):
         string = string.strip()
         self.string = string
 
-        if not VALID_VERSION.match(string):
+        if string and not VALID_VERSION.match(string):
             raise ValueError("Bad characters in version string: %s" % string)
 
         # An object that can lookup git commits to compare them to versions
@@ -347,9 +347,12 @@ def __getitem__(self, idx):
                 string_arg.append(str(token))
                 string_arg.append(str(sep))
 
-            string_arg.pop()  # We don't need the last separator
-            string_arg = ''.join(string_arg)
-            return cls(string_arg)
+            if string_arg:
+                string_arg.pop()  # We don't need the last separator
+                string_arg = ''.join(string_arg)
+                return cls(string_arg)
+            else:
+                return Version('')
 
         message = '{cls.__name__} indices must be integers'
         raise TypeError(message.format(cls=cls))