git: update hook, fix post-receive-email

 Add an update hook that prevents merge commits on master.

 Fix the post-receive-email script to work properly with merge commits --
 don't try to report pushes of merges with one email per commit.

 (Since we deny non-fast-forwards, we pretty much need to allow merges on
 other branches, or give up keeping them in the main repo.)

diff --git a/git/post-receive-email b/git/post-receive-email
index 60cce2c..beecf43 100755 (executable)
--- a/git/post-receive-email
+++ b/git/post-receive-email
@@ -346,17 +346,11 @@ generate_update_branch_email()
        # have already had notification emails and is present to show the
        # full detail of the change from rolling back the old revision to
        # the base revision and then forward to the new revision
-       #
-       # For SBCL we skip this for branch updates, since we're getting
-       # one email per commit.
-       if [ "branch" != "$refname_type" ] || [ "update" != "$change_type" ]
-       then
-           for rev in $(git rev-list $oldrev..$newrev)
-           do
-               revtype=$(git cat-file -t "$rev")
-               echo "       via  $rev ($revtype)"
-           done
-       fi
+       for rev in $(git rev-list $oldrev..$newrev)
+       do
+           revtype=$(git cat-file -t "$rev")
+           echo "       via  $rev ($revtype)"
+       done
 
        if [ "$fast_forward" ]; then
                echo "      from  $oldrev ($oldrev_type)"
@@ -715,14 +709,15 @@ else
          # push. We want one per commit. As long as we're
          # in fast-forward-only world, this should do the
          # right thing.
-         if (expr "$oldrev" : '0*$' >/dev/null ||
-             expr "$newrev" : '0*$' >/dev/null ||
-              ! expr "$refname" : "refs/heads/" > /dev/null)
+         if (expr "$oldrev" : '0*$' >/dev/null ||                    # create
+             expr "$newrev" : '0*$' >/dev/null ||                    # delete
+              (! expr "$refname" : "refs/heads/" > /dev/null) ||      # not a branch
+              git rev-parse --verify --quiet "$newrev"^2 > /dev/null) # merge commit
          then
              # Just one email.
              generate_email $oldrev $newrev $refname | send_mail
          else
-             # Branch update, one mail per commit.
+             # Simple branch update, one mail per commit.
              lastrev=$oldrev
              for step in $(git rev-list --reverse $oldrev..$newrev)
              do