Only use "master" as default branch if not set

So far we've used "master" as default branch when we encounter a project
configuration that doesn't have a default branch set. The problem here
is, that later project stanzas that do define a default branch won't
have any effect.

To fix this, we will only fall back on using "master" in the project
metadata if none of the project definitions declares a default branch.

Change-Id: Iddd5ef906c2bdbcc472615ffe25033c4ca961df7

tests/fixtures/layouts/default-branch.yaml

@@ -0,0 +1,40 @@
+- pipeline:
+    name: check
+    manager: independent
+    trigger:
+      gerrit:
+        - event: patchset-created
+    success:
+      gerrit:
+        Verified: 1
+    failure:
+      gerrit:
+        Verified: -1
+
+- project:
+    name: '^org/regex-default.*'
+
+- project:
+    name: '^org/regex-override.*'
+    default-branch: regex
+
+- project:
+    name: org/project-default
+
+- project:
+    # This should be the default
+    name: org/regex-default-project-empty
+
+- project:
+    # This should be 'develop' because the regex doesn't specify
+    name: org/regex-default-project-develop
+    default-branch: develop
+
+- project:
+    # This should be 'regex' because of the regex
+    name: org/regex-override-project-empty
+
+- project:
+    # This should be 'develop' because it is more specific than the regex
+    name: org/regex-override-project-develop
+    default-branch: develop

tests/unit/test_configloader.py

@@ -1249,3 +1249,26 @@ class TestMergeMode(ZuulTestCase):
     def test_default_merge_mode_github(self):
         self._test_default_merge_mode(model.MERGER_MERGE,
                                       'github.com')
+
+
+class TestDefaultBranch(ZuulTestCase):
+    config_file = 'zuul-connections-gerrit-and-github.conf'
+
+    @simple_layout('layouts/default-branch.yaml')
+    def test_default_branch(self):
+        layout = self.scheds.first.sched.abide.tenants.get('tenant-one').layout
+        md = layout.getProjectMetadata(
+            'review.example.com/org/project-default')
+        self.assertEqual('master', md.default_branch)
+        md = layout.getProjectMetadata(
+            'review.example.com/org/regex-default-project-empty')
+        self.assertEqual('master', md.default_branch)
+        md = layout.getProjectMetadata(
+            'review.example.com/org/regex-default-project-develop')
+        self.assertEqual('develop', md.default_branch)
+        md = layout.getProjectMetadata(
+            'review.example.com/org/regex-override-project-empty')
+        self.assertEqual('regex', md.default_branch)
+        md = layout.getProjectMetadata(
+            'review.example.com/org/regex-override-project-develop')
+        self.assertEqual('develop', md.default_branch)

tests/unit/test_web.py

@@ -856,7 +856,7 @@ class TestWeb(BaseTestWeb):
                                        'path': 'zuul.yaml',
                                        'project': 'common-config'},
                     'templates': [],
-                    'default_branch': 'master',
+                    'default_branch': None,
                     'queue_name': 'integrated',
                     'merge_mode': None,
                     'pipelines': [{

zuul/configloader.py

@@ -1253,7 +1253,7 @@ class ProjectParser(object):
         if mode is not None:
             project_config.merge_mode = model.MERGER_MAP[mode]
 
-        default_branch = conf.get('default-branch', 'master')
+        default_branch = conf.get('default-branch')
         project_config.default_branch = default_branch
 
         project_config.queue_name = conf.get('queue', None)

zuul/model.py

@@ -7306,9 +7306,20 @@ class ProjectMetadata:
 
     def __init__(self):
         self.merge_mode = None
-        self.default_branch = None
+        self._default_branch = None
         self.queue_name = None
 
+    def isDefaultBranchSet(self):
+        return self._default_branch is not None
+
+    @property
+    def default_branch(self):
+        return self._default_branch or "master"
+
+    @default_branch.setter
+    def default_branch(self, default_branch):
+        self._default_branch = default_branch
+
     def toDict(self):
         return {
             'merge_mode': self.merge_mode,
@@ -7946,7 +7957,7 @@ class Layout(object):
         md = self.project_metadata[project_config.name]
         if md.merge_mode is None and project_config.merge_mode is not None:
             md.merge_mode = project_config.merge_mode
-        if (md.default_branch is None and
+        if (not md.isDefaultBranchSet() and
             project_config.default_branch is not None):
             md.default_branch = project_config.default_branch
         if (