manifest: support optional --manifest-name

Still use the repo manifest by default as before, but gives us
the option of overriding it to support e.g.: using a subset of
the full manifest.

Change-Id: Ia42cd1cb3a0a58929d31bb01c9724e9d31f68730
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/256372
Reviewed-by: Mike Frysinger <vapier@google.com>
Tested-by: Sean McAllister <smcallis@google.com>

subcmds/manifest.py

@@ -25,7 +25,7 @@ class Manifest(PagedCommand):
   common = False
   helpSummary = "Manifest inspection utility"
   helpUsage = """
-%prog [-o {-|NAME.xml} [-r]]
+%prog [-o {-|NAME.xml}] [-m MANIFEST.xml] [-r]
 """
   _helpDescription = """
 
@@ -50,6 +50,8 @@ in a Git repository for use during future 'repo init' invocations.
     p.add_option('-r', '--revision-as-HEAD',
                  dest='peg_rev', action='store_true',
                  help='Save revisions as current HEAD')
+    p.add_option('-m', '--manifest-name',
+                 help='temporary manifest to use for this sync', metavar='NAME.xml')
     p.add_option('--suppress-upstream-revision', dest='peg_rev_upstream',
                  default=True, action='store_false',
                  help='If in -r mode, do not write the upstream field.  '
@@ -62,6 +64,10 @@ in a Git repository for use during future 'repo init' invocations.
                  metavar='-|NAME.xml')
 
   def _Output(self, opt):
+    # If alternate manifest is specified, override the manifest file that we're using.
+    if opt.manifest_name:
+      self.manifest.Override(opt.manifest_name, False)
+
     if opt.output_file == '-':
       fd = sys.stdout
     else: