manifest: Only display XML help on XML manifest

Some of the help text is only related to the XML formatted manifest,
so only display that text if that is the current format.

Signed-off-by: Shawn O. Pearce <sop@google.com>

subcmds/manifest.py

@@ -18,13 +18,22 @@ import sys
 
 from command import PagedCommand
 
+def _doc(name):
+  r = os.path.dirname(__file__)
+  r = os.path.dirname(r)
+  fd = open(os.path.join(r, 'docs', 'manifest_xml.txt'))
+  try:
+    return fd.read()
+  finally:
+    fd.close()
+
 class Manifest(PagedCommand):
   common = False
   helpSummary = "Manifest inspection utility"
   helpUsage = """
 %prog [-o {-|NAME.xml} [-r]]
 """
-  _helpDescription = """
+  _xmlHelp = """
 
 With the -o option, exports the current manifest for inspection.
 The manifest and (if present) local_manifest.xml are combined
@@ -35,13 +44,9 @@ in a Git repository for use during future 'repo init' invocations.
 
   @property
   def helpDescription(self):
-    help = self._helpDescription + '\n'
-    r = os.path.dirname(__file__)
-    r = os.path.dirname(r)
-    fd = open(os.path.join(r, 'docs', 'manifest-format.txt'))
-    for line in fd:
-      help += line
-    fd.close()
+    help = ''
+    if isinstance(self.manifest, XmlManifest):
+      help += self._xmlHelp + '\n' + _doc('manifest_xml.txt')
     return help
 
   def _Options(self, p):