Rework git caches to be bare mirrors of the repos.

This reworks the code for managing and using the git caches in morph to treat
the caches as bare repositories which are mirrors of where we clone from.  In
addition we correctly prune the branches during updates, so that we don't end
up accumulating pointless branches over and over.  This is even more important
with branch-and-merge generating temporary build refs for things.

1 files changed, 49 insertions, 2 deletions

diff --git a/morphlib/git.py b/morphlib/git.py
index d8169c93..9ab98ad0 100644
--- a/morphlib/git.py
+++ b/morphlib/git.py
@@ -154,8 +154,42 @@ def set_remote(runcmd, gitdir, name, url):
 
 
 def copy_repository(runcmd, repo, destdir):
-    '''Copies a cached repository into a directory using cp.'''
-    return runcmd(['cp', '-a', os.path.join(repo, '.git'), destdir])
+    '''Copies a cached repository into a directory using cp.
+
+    This also fixes up the repository afterwards, so that it can contain
+    code etc.  It does not leave any given branch ready for use.
+
+    '''
+    runcmd(['cp', '-a', repo, os.path.join(destdir, '.git')])
+    # core.bare should be false so that git believes work trees are possible
+    runcmd(['git', 'config', 'core.bare', 'false'], cwd=destdir)
+    # we do not want the origin remote to behave as a mirror for pulls
+    runcmd(['git', 'config', '--unset', 'remote.origin.mirror'], cwd=destdir)
+    # we want a traditional refs/heads -> refs/remotes/origin ref mapping
+    runcmd(['git', 'config', 'remote.origin.fetch',
+            '+refs/heads/*:refs/remotes/origin/*'], cwd=destdir)
+    # set the origin url to the cached repo so that we can quickly clean up
+    runcmd(['git', 'config', 'remote.origin.url', repo], cwd=destdir)
+    # by packing the refs, we can then edit then en-masse easily
+    runcmd(['git', 'pack-refs', '--all', '--prune'], cwd=destdir)
+    # turn refs/heads/* into refs/remotes/origin/* in the packed refs
+    # so that the new copy behaves more like a traditional clone.
+    logging.debug("Adjusting packed refs for %s" % destdir)
+    with open(os.path.join(destdir, ".git", "packed-refs"), "r") as ref_fh:
+        pack_lines = ref_fh.read().split("\n")
+    with open(os.path.join(destdir, ".git", "packed-refs"), "w") as ref_fh:
+        ref_fh.write(pack_lines.pop(0) + "\n")
+        for refline in pack_lines:
+            if ' refs/remotes/' in refline:
+                continue
+            if ' refs/heads/' in refline:
+                sha, ref = refline[:40], refline[41:]
+                if ref.startswith("refs/heads/"):
+                    ref = "refs/remotes/origin/" + ref[11:]
+                refline = "%s %s" % (sha, ref)
+            ref_fh.write("%s\n" % (refline))
+    # Finally run a remote update to clear up the refs ready for use.
+    runcmd(['git', 'remote', 'update', 'origin', '--prune'], cwd=destdir)
 
 
 def checkout_ref(runcmd, gitdir, ref):
@@ -167,3 +201,16 @@ def reset_workdir(runcmd, gitdir):
     '''and the status of the working directory'''
     runcmd(['git', 'clean', '-fxd'], cwd=gitdir)
     runcmd(['git', 'reset', '--hard', 'HEAD'], cwd=gitdir)
+
+
+def clone_into(runcmd, srcpath, targetpath, ref=None):
+    '''Clones a repo in srcpath into targetpath, optionally directly at ref.'''
+    if ref is None:
+        runcmd(['git', 'clone', srcpath, targetpath])
+    else:
+        runcmd(['git', 'clone', '-b', ref, srcpath, targetpath])
+
+def find_first_ref(runcmd, gitdir, ref):
+    '''Find the *first* ref match and returns its sha1.'''
+    return runcmd(['git', 'show-ref', ref],
+                  cwd=gitdir).split("\n")[0].split(" ")[0]