From f7e02d76ec22bda2a0dfcd24f44a4df8544fae02 Mon Sep 17 00:00:00 2001
From: Sam Thursfield <sam.thursfield@codethink.co.uk>
Date: Thu, 13 Sep 2012 13:25:44 +0100
Subject: morph merge: Don't make a merge commit if only the refs changed

'git commit' fails if there are no changes in any case.
---
 morphlib/git.py                             | 11 +++++++++++
 morphlib/plugins/branch_and_merge_plugin.py | 13 ++++++++++---
 tests.branching/merge.script                |  2 ++
 tests.branching/merge.stdout                |  2 +-
 4 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/morphlib/git.py b/morphlib/git.py
index 9ab98ad0..5862ef9b 100644
--- a/morphlib/git.py
+++ b/morphlib/git.py
@@ -196,6 +196,17 @@ def checkout_ref(runcmd, gitdir, ref):
     '''Checks out a specific ref/SHA1 in a git working tree.'''
     runcmd(['git', 'checkout', ref], cwd=gitdir)
 
+
+def index_has_changes(runcmd, gitdir):
+    '''Returns True if there are no staged changes to commit'''
+    try:
+        runcmd(['git', 'diff-index', '--cached', '--quiet',
+                '--ignore-submodules', 'HEAD'], cwd=gitdir)
+    except cliapp.AppException:
+        return True
+    return False
+
+
 def reset_workdir(runcmd, gitdir):
     '''Removes any differences between the current commit '''
     '''and the status of the working directory'''
diff --git a/morphlib/plugins/branch_and_merge_plugin.py b/morphlib/plugins/branch_and_merge_plugin.py
index c81c95c8..75935b72 100644
--- a/morphlib/plugins/branch_and_merge_plugin.py
+++ b/morphlib/plugins/branch_and_merge_plugin.py
@@ -685,6 +685,8 @@ class BranchAndMergePlugin(cliapp.Plugin):
                 merge_chunk(old_ci, ci)
             if changed:
                 self.save_morphology(to_repo, si['morph'], stratum)
+                self.app.runcmd(['git', 'add', si['morph'] + '.morph'],
+                                cwd=to_repo)
 
         from_root_dir = self.find_repository(from_branch_dir, root_repo)
         to_root_dir = self.find_repository(to_branch_dir, root_repo)
@@ -718,11 +720,16 @@ class BranchAndMergePlugin(cliapp.Plugin):
                     merge_stratum(old_si, si)
                 if changed:
                     self.save_morphology(to_root_dir, name, morphology)
+                    self.app.runcmd(['git', 'add', f], cwd=to_root_dir)
 
         for repo_dir in dirty_repos:
-            msg = "Merge system branch '%s'" % from_branch
-            self.app.runcmd(['git', 'commit', '--all', '--message=%s' % msg],
-                            cwd=repo_dir)
+            # Repo will often turn out to not be dirty: if the changes we
+            # merged only updated refs to the system branch, we will have
+            # changed them back again so that the index will now be empty.
+            if morphlib.git.index_has_changes(self.app.runcmd, repo_dir):
+                msg = "Merge system branch '%s'" % from_branch
+                self.app.runcmd(['git', 'commit', '--all', '-m%s' % msg],
+                                cwd=repo_dir)
 
     def build(self, args):
         if len(args) != 1:
diff --git a/tests.branching/merge.script b/tests.branching/merge.script
index d8a28cb3..21a30116 100755
--- a/tests.branching/merge.script
+++ b/tests.branching/merge.script
@@ -49,6 +49,8 @@ git status --short # make sure all changes are committed
 cd ../baserock:morphs
 ! grep "\"ref\": \"baserock/newbranch\"" *.morph
 
+# The only change here was the branch refs, which have now been
+# changed back - so there should not be any new commits.
 echo "Commit message for baserock:morphs"
 git cat-file commit HEAD | tail -n 1
 
diff --git a/tests.branching/merge.stdout b/tests.branching/merge.stdout
index e5127734..6806f75a 100644
--- a/tests.branching/merge.stdout
+++ b/tests.branching/merge.stdout
@@ -1,5 +1,5 @@
 Commit message for baserock:morphs
-Merge system branch 'baserock/newbranch'
+initial
 
 Commit message for baserock:hello
 Merge system branch 'baserock/newbranch'
-- 
cgit v1.2.1