morph petrify: Avoid petrifying chunks that have already been edited

This change causes 'morph petrify' to avoid petrifying any chunk whose
ref matches the current system branch, because it makes no sense to
petrify something that is also being edited. It also improves efficiency
slightly and adds warning where different systems point to different
refs of the same stratum.

A non-obvious effect of this is that if you try to petrify 'master',
many of the chunks won't get petrified because they are built from
'master'. However, petrifying master makes no sense so I'm not sure
that we need to worry.

1 files changed, 39 insertions, 18 deletions

diff --git a/morphlib/plugins/branch_and_merge_plugin.py b/morphlib/plugins/branch_and_merge_plugin.py
index 384f0550..050410d4 100644
--- a/morphlib/plugins/branch_and_merge_plugin.py
+++ b/morphlib/plugins/branch_and_merge_plugin.py
@@ -722,7 +722,8 @@ class BranchAndMergePlugin(cliapp.Plugin):
         Strata refs are not petrified, because they must all be edited to set
         the new chunk refs, which requires branching them all for the current
         branch - so they will not be updated outside of the user's control in
-        any case.
+        any case. Chunks that have already been edited on the current branch
+        are also not petrified.
 
         '''
 
@@ -733,9 +734,11 @@ class BranchAndMergePlugin(cliapp.Plugin):
         branch, branch_path = self.deduce_system_branch()
         root_repo = self.get_branch_config(branch_path, 'branch.root')
         root_repo_dir = self.find_repository(branch_path, root_repo)
-
         self.lrc, self.rrc = morphlib.util.new_repo_caches(self.app)
 
+        # We must first get the full set of strata. One same stratum may be
+        # in multiple systems and each system may use a different ref.
+        strata = {}
         for f in glob.glob(os.path.join(root_repo_dir, '*.morph')):
             name = os.path.basename(f)[:-len('.morph')]
             morphology = self.load_morphology(root_repo_dir, name)
@@ -743,24 +746,42 @@ class BranchAndMergePlugin(cliapp.Plugin):
                 continue
 
             for stratum_info in morphology['strata']:
-                repo_dir = self.edit_stratum(
-                    branch, branch_path, root_repo, root_repo_dir,
-                    stratum_info)
-
-                stratum = self.load_morphology(repo_dir, stratum_info['morph'])
-
-                for chunk_info in stratum['chunks']:
-                    if 'unpetrify-ref' not in chunk_info:
-                        commit_sha1, tree_sha1 = self.app.resolve_ref(
-                            self.lrc, self.rrc, chunk_info['repo'],
-                            chunk_info['ref'],
-                            update=not self.app.settings['no-git-update'])
-                        chunk_info['unpetrify-ref'] = chunk_info['ref']
-                        chunk_info['ref'] = commit_sha1
-                self.save_morphology(repo_dir, stratum_info['morph'], stratum)
-
+                key = (stratum_info['repo'], stratum_info['morph'])
+                if key in strata:
+                    original_ref = strata[key]
+                    if stratum_info['ref'] == branch:
+                        strata[key] = branch
+                    elif stratum_info['ref'] != original_ref:
+                        if original_ref != branch:
+                            self.app.output.write(
+                                'WARNING: not merging any differences from '
+                                'ref %s into %s of stratum %s\n' %
+                                (stratum_info['ref'], original_ref,
+                                 stratum_info['morph']))
+                        stratum_info['ref'] = branch
+                else:
+                    strata[key] = stratum_info['ref']
+                    stratum_info['ref'] = branch
             self.save_morphology(root_repo_dir, name, morphology)
 
+        for (repo, morph), ref in strata.iteritems():
+            repo_dir = self.edit_stratum(
+                branch, branch_path, root_repo, root_repo_dir,
+                { 'repo': repo, 'ref': ref, 'morph': morph})
+
+            stratum = self.load_morphology(repo_dir, morph)
+
+            for chunk_info in stratum['chunks']:
+                if chunk_info['ref'] != branch and \
+                        'unpetrify-ref' not in chunk_info:
+                    commit_sha1, tree_sha1 = self.app.resolve_ref(
+                        self.lrc, self.rrc, chunk_info['repo'],
+                        chunk_info['ref'],
+                        update=not self.app.settings['no-git-update'])
+                    chunk_info['unpetrify-ref'] = chunk_info['ref']
+                    chunk_info['ref'] = commit_sha1
+            self.save_morphology(repo_dir, morph, stratum)
+
         self.print_changelog('The following changes were made but have not '
                              'been comitted')