Merge ~twom/launchpad:git-page-default-branch into launchpad:master

[Tom Wardill]

Add a default branch to the Git Merge Proposal page.

The target branch needs manually filling in, but most of the time you want to merge to the equivalent of 'master', or whatever is set as the default branch on that repository.

This change populates the box with the ref path with one of (choosing in order from):
* The default branch of the target repository
* The default branch of the source repository
* Nothing

[Colin Watson (cjwatson)]

review: Needs Fixing

09ef3cf... by Tom Wardill on 2020-02-26

Use setupWidgets for more code reuse

[Colin Watson (cjwatson)]

review: Approve

6a9a70b... by Tom Wardill on 2020-02-26

Variable name and test assertion

diff --git a/lib/lp/code/browser/gitref.py b/lib/lp/code/browser/gitref.py
index 84bfc25..edbb0bf 100644
--- a/lib/lp/code/browser/gitref.py
+++ b/lib/lp/code/browser/gitref.py
@@ -279,6 +279,17 @@ class GitRefRegisterMergeProposalView(LaunchpadFormView):
             raise NotFound(self.context, '+register-merge')
         super(GitRefRegisterMergeProposalView, self).initialize()
 
+    def setUpWidgets(self, context=None):
+        super(GitRefRegisterMergeProposalView, self).setUpWidgets(
+            context=context)
+        term = next(
+            iter(self.widgets['target_git_repository'].vocabulary),
+            None)
+        # If we have a target, and the user hasn't entered a value.
+        if term and not self.widgets['target_git_path'].hasInput():
+            self.widgets['target_git_path'].setRenderedValue(
+                term.value.default_branch)
+
     @action('Propose Merge', name='register',
             failure=LaunchpadFormView.ajax_failure_handler)
     def register_action(self, action, data):
diff --git a/lib/lp/code/browser/tests/test_branchmergeproposal.py b/lib/lp/code/browser/tests/test_branchmergeproposal.py
index 8180bc0..bf5bdb3 100644
--- a/lib/lp/code/browser/tests/test_branchmergeproposal.py
+++ b/lib/lp/code/browser/tests/test_branchmergeproposal.py
@@ -862,6 +862,26 @@ class TestRegisterBranchMergeProposalViewGit(
         values.update(extras)
         return values
 
+    def test_default_branch(self):
+        with admin_logged_in():
+            target_branch = self._makeTargetBranch(target_default=True)
+        removeSecurityProxy(
+            target_branch.repository)._default_branch = target_branch.path
+        view = self._createView()
+        self.assertEqual(
+            target_branch.repository.default_branch,
+            view.widgets['target_git_path']._getCurrentValue())
+
+    def test_default_branch_no_default_set(self):
+        with admin_logged_in():
+            self._makeTargetBranch(target_default=True)
+        view = self._createView()
+        self.assertIsNone(view.widgets['target_git_path']._getCurrentValue())
+
+    def test_default_branch_no_target(self):
+        view = self._createView()
+        self.assertIsNone(view.widgets['target_git_path']._getCurrentValue())
+
     def test_register_ajax_request_with_confirmation(self):
         # Ajax submits return json data containing info about what the visible
         # repositories are if they are not all visible to the reviewer.