Fixed repo abandon to give better messages.

The main fix is to give an error message if nothing was actually
abandoned.  See <http://crosbug.com/6041>.

The secondary fix is to list projects where the abandon happened.
This could be done in a separate CL or dropped altogether if requested.

TEST=manual

$ repo abandon dougabc; echo $?
Abandon dougabc: 100% (127/127), done.
Abandoned in 2 project(s):
  chromite
  src/platform/init
0

$ repo abandon dougabc; echo $?
Abandon dougabc: 100% (127/127), done.
error: no project has branch dougabc
1

$ repo abandon dougabc; echo $?
Abandon dougabc: 100% (127/127), done.
error: chromite/: cannot abandon dougabc
1

Change-Id: I79520cc3279291acadc1a24ca34a761e9de04ed4

project.py

@@ -1204,13 +1204,19 @@ class Project(object):
 
   def AbandonBranch(self, name):
     """Destroy a local topic branch.
+
+    Args:
+      name: The name of the branch to abandon.
+
+    Returns:
+      True if the abandon succeeded; False if it didn't; None if the branch
+      didn't exist.
     """
     rev = R_HEADS + name
     all = self.bare_ref.all
     if rev not in all:
-      # Doesn't exist; assume already abandoned.
-      #
-      return True
+      # Doesn't exist
+      return None
 
     head = self.work_git.GetHead()
     if head == rev:

subcmds/abandon.py

@@ -41,21 +41,30 @@ It is equivalent to "git branch -D <branchname>".
 
     nb = args[0]
     err = []
+    success = []
     all = self.GetProjects(args[1:])
 
     pm = Progress('Abandon %s' % nb, len(all))
     for project in all:
       pm.update()
-      if not project.AbandonBranch(nb):
-        err.append(project)
+
+      status = project.AbandonBranch(nb)
+      if status is not None:
+        if status:
+          success.append(project)
+        else:
+          err.append(project)
     pm.end()
 
     if err:
-      if len(err) == len(all):
-        print >>sys.stderr, 'error: no project has branch %s' % nb
-      else:
-        for p in err:
-          print >>sys.stderr,\
-            "error: %s/: cannot abandon %s" \
-            % (p.relpath, nb)
+      for p in err:
+        print >>sys.stderr,\
+          "error: %s/: cannot abandon %s" \
+          % (p.relpath, nb)
       sys.exit(1)
+    elif not success:
+      print >>sys.stderr, 'error: no project has branch %s' % nb
+      sys.exit(1)
+    else:
+      print >>sys.stderr, 'Abandoned in %d project(s):\n  %s' % (
+            len(success), '\n  '.join(p.relpath for p in success))