Add an initial implementation of "morph tag"

In order to make releases and freeze system branches entirely, we
need to be able to 100% petrify a system branch (that is, resolve
ALL refs into SHA1s) and tag this state to be able to check it out
again later.

This is essentially what "morph tag" does. It takes a tag name
and an arbitrary amount of arguments to "git tag", petrifies all
morphologies of the current system branch behind the scenes, creates
a dangling commit and attaches an annotated tag to it.

Petrifying in this case means that all refs used for chunks are
resolved into commit SHA1s. For stratum and system morphologies,
the refs are replaced by the name of the tag that's being created.

The "tag" command also supports tagging when stratum morphologies
are spread across multiple repositories. In this case, it will
include all statum morphologies from other repos in the tag commi
in the branch root repo. The references to these morphologies are
updated so that they point to the branch root repo and the tag
being created.

This commit also adds a few tests for "morph tag" to verify that
all this works.

1 files changed, 13 insertions, 0 deletions

diff --git a/morphlib/git.py b/morphlib/git.py
index 7985b815..a37b6675 100644
--- a/morphlib/git.py
+++ b/morphlib/git.py
@@ -170,6 +170,19 @@ def get_user_name(runcmd):
             '    git config --global user.email "me@example.com"\n')
 
 
+def get_user_email(runcmd):
+    '''Get user.email configuration setting. Complain if none was found.'''
+    if 'GIT_AUTHOR_EMAIL' in os.environ:
+        return os.environ['GIT_AUTHOR_EMAIL'].strip()
+    try:
+        return runcmd(['git', 'config', 'user.email']).strip()
+    except cliapp.AppException:
+        raise cliapp.AppException(
+            'No git user info found. Please set your identity, using: \n'
+            '    git config --global user.email "My Name"\n'
+            '    git config --global user.email "me@example.com"\n')
+
+
 def set_remote(runcmd, gitdir, name, url):
     '''Set remote with name 'name' use a given url at gitdir'''
     return runcmd(['git', 'remote', 'set-url', name, url], cwd=gitdir)