add resolve_to_specific_version

dbt/semver.py

@@ -242,9 +242,18 @@ def is_exact(self):
 
 
 def reduce_versions(*args):
-    version_specifiers = [
-        VersionSpecifier.from_version_string(version_string)
-        for version_string in args]
+    version_specifiers = []
+
+    for version in args:
+        if isinstance(version, UnboundedVersionSpecifier):
+            continue
+
+        elif isinstance(version, VersionSpecifier):
+            version_specifiers.append(version)
+
+        else:
+            version_specifiers.append(
+                VersionSpecifier.from_version_string(version))
 
     for version_specifier in version_specifiers:
         if not isinstance(version_specifier, VersionSpecifier):
@@ -271,3 +280,19 @@ def versions_compatible(*args):
         return True
     except VersionsNotCompatibleException as e:
         return False
+
+def resolve_to_specific_version(requested_range, available_versions):
+    max_version = None
+    max_version_string = None
+
+    for version_string in available_versions:
+        version = VersionSpecifier.from_version_string(version_string)
+
+        if(versions_compatible(version,
+                               requested_range.start,
+                               requested_range.end) and
+           (max_version is None or max_version.compare(version) < 0)):
+            max_version = version
+            max_version_string = version_string
+
+    return max_version_string

test/unit/test_semver.py

@@ -3,7 +3,8 @@
 
 from dbt.exceptions import VersionsNotCompatibleException
 from dbt.semver import VersionSpecifier, UnboundedVersionSpecifier, \
-    VersionRange, reduce_versions, versions_compatible
+    VersionRange, reduce_versions, versions_compatible, \
+    resolve_to_specific_version
 
 def create_range(start_version_string, end_version_string):
     start = UnboundedVersionSpecifier()
@@ -100,3 +101,34 @@ def test__reduce_versions(self):
         self.assertInvalidVersionSet(['<=0.0.3', '>0.0.3'])
         self.assertInvalidVersionSet(['<0.0.3', '>=0.0.3'])
         self.assertInvalidVersionSet(['<0.0.3', '>0.0.3'])
+
+    def test__resolve_to_specific_version(self):
+        self.assertEqual(
+            resolve_to_specific_version(
+                create_range('>0.0.1', None),
+                ['0.0.1', '0.0.2']),
+            '0.0.2')
+
+        self.assertEqual(
+            resolve_to_specific_version(
+                create_range('>=0.0.2', None),
+                ['0.0.1', '0.0.2']),
+            '0.0.2')
+
+        self.assertEqual(
+            resolve_to_specific_version(
+                create_range('>=0.0.3', None),
+                ['0.0.1', '0.0.2']),
+            None)
+
+        self.assertEqual(
+            resolve_to_specific_version(
+                create_range('>=0.0.3', '<0.0.5'),
+                ['0.0.3', '0.0.4', '0.0.5']),
+            '0.0.4')
+
+        self.assertEqual(
+            resolve_to_specific_version(
+                create_range(None, '<=0.0.5'),
+                ['0.0.3', '0.1.4', '0.0.5']),
+            '0.0.5')