Fix select spark version in staging (#388)

## Changes
In staging, there are some spark versions that do not have a patch
version. We fall back to a different pattern with no patch component for
these. Additionally, we check if the builds are equal to one another
(which allows us to avoid comparing one < the other in the case where
they are both None).

Closes #352 and #378.

## Tests
<!-- 
How is this tested? Please see the checklist below and also describe any
other relevant tests
-->

- [x] Added a unit test with a format that was previously not supported.
- [x] Hand-wrote an example using select_spark_versions(). This failed
on `main` but passed on my branch when targeting a staging workspace.

databricks/sdk/mixins/compute.py

@@ -21,9 +21,9 @@ class SemVer:
     build: Optional[str] = None
 
     # official https://semver.org/ recommendation: https://regex101.com/r/Ly7O1x/
-    # with addition of "x" wildcards for minor/patch versions
+    # with addition of "x" wildcards for minor/patch versions. Also, patch version may be omitted.
     _pattern = re.compile(r"^"
-                          r"(?P<major>0|[1-9]\d*)\.(?P<minor>x|0|[1-9]\d*)\.(?P<patch>x|0|[1-9x]\d*)"
+                          r"(?P<major>0|[1-9]\d*)\.(?P<minor>x|0|[1-9]\d*)(\.(?P<patch>x|0|[1-9x]\d*))?"
                           r"(?:-(?P<pre_release>(?:0|[1-9]\d*|\d*[a-zA-Z-][0-9a-zA-Z-]*)"
                           r"(?:\.(?:0|[1-9]\d*|\d*[a-zA-Z-][0-9a-zA-Z-]*))*))?"
                           r"(?:\+(?P<build>[0-9a-zA-Z-]+(?:\.[0-9a-zA-Z-]+)*))?$")
@@ -40,10 +40,13 @@ def parse(cls, v: str) -> 'SemVer':
         # patch and/or minor versions may be wildcards.
         # for now, we're converting wildcards to zeroes.
         minor = m.group('minor')
-        patch = m.group('patch')
+        try:
+            patch = m.group('patch')
+        except IndexError:
+            patch = 0
         return SemVer(major=int(m.group('major')),
                       minor=0 if minor == 'x' else int(minor),
-                      patch=0 if patch == 'x' else int(patch),
+                      patch=0 if patch == 'x' or patch is None else int(patch),
                       pre_release=m.group('pre_release'),
                       build=m.group('build'))
 
@@ -58,7 +61,9 @@ def __lt__(self, other: 'SemVer'):
             return self.patch < other.patch
         if self.pre_release != other.pre_release:
             return self.pre_release < other.pre_release
-        return self.build < other.build
+        if self.build != other.build:
+            return self.build < other.build
+        return False
 
 
 class ClustersExt(compute.ClustersAPI):

tests/test_compute_mixins.py

@@ -3,10 +3,12 @@
 from databricks.sdk.mixins.compute import SemVer
 
 
-@pytest.mark.parametrize("given,expected", [('v0.0.4', SemVer(0, 0, 4)), ('v1.2.3', SemVer(1, 2, 3)),
-                                            ('v12.1.x', SemVer(12, 1, 0)), ('v10.20.30', SemVer(10, 20, 30)),
-                                            ('v1.1.2+meta', SemVer(1, 1, 2, build='meta')),
-                                            ('v1.0.0-alpha', SemVer(1, 0, 0, pre_release='alpha'))])
+@pytest.mark.parametrize("given,expected",
+                         [('v0.0.4', SemVer(0, 0, 4)), ('v1.2.3', SemVer(1, 2, 3)),
+                          ('v12.1.x', SemVer(12, 1, 0)), ('v10.20.30', SemVer(10, 20, 30)),
+                          ('v1.1.2+meta', SemVer(1, 1, 2, build='meta')),
+                          ('v1.0.0-alpha', SemVer(1, 0, 0, pre_release='alpha')),
+                          ('8.x-snapshot-scala2.12', SemVer(8, 0, 0, pre_release='snapshot-scala2.12')), ])
 def test_parse_semver(given, expected):
     assert SemVer.parse(given) == expected