Harmonize containing branch matcher for tags

Perform a `re.match()` instead of `re.fullmatch()` for the containing
branches for tag triggered items. Requiring a full match is unexpected
for users.

Change-Id: Icd8c258b0dfc36df8c94d9cb5edb3125804b9bc4

tests/unit/test_change_matcher.py

@@ -71,6 +71,13 @@ class TestBranchMatcher(BaseTestMatcher):
         self.change.ref = 'baz'
         self.assertFalse(self.matcher.matches(self.change))
 
+    def test_containing_branch_partial_match(self):
+        self.change = model.Tag(self.project)
+        self.change.ref = 'refs/tags/1.0'
+        self.matcher = cm.BranchMatcher(ZuulRegex('^release-'))
+        self.change.containing_branches = ["release-1.0", "master"]
+        self.assertTrue(self.matcher.matches(self.change))
+
 
 class TestAbstractMatcherCollection(BaseTestMatcher):
 

tools/releasenotes/notes/harmonize-containing-branch-matcher-d0ba4ee8881cd3c1.yaml

@@ -0,0 +1,6 @@
+---
+upgrade:
+  - |
+    The branch matcher for containing branches of a tag will now perform a
+    normal regex match instead of requiring a full-match. This was done to
+    harmonize the matching behavior between the different change-types.

zuul/change_matcher.py

@@ -88,7 +88,7 @@ class BranchMatcher(AbstractChangeMatcher):
                     if self._regex == branch:
                         return True
                 else:
-                    if self.regex.fullmatch(branch):
+                    if self.regex.match(branch):
                         return True
         return False