bundle2: add generic debug output regarding generated bundle

If we are about to hide the detailed debug output, we need some generic debug
message to replace it in a more compact way.

mercurial/bundle2.py

@@ -472,6 +472,12 b' class bundle20(object):'
 
     # methods used to generate the bundle2 stream
     def getchunks(self):
+        if self.ui.debugflag:
+            msg = ['bundle2-output-bundle: "%s",' % self._magicstring]
+            if self._params:
+                msg.append(' (%i params)' % len(self._params))
+            msg.append(' %i parts total\n' % len(self._parts))
+            self.ui.debug(''.join(msg))
         outdebug(self.ui, 'start emission of %s stream' % self._magicstring)
         yield self._magicstring
         param = self._paramchunk()

tests/test-bundle2-format.t

@@ -337,6 +337,7 b' Test debug output'
 bundling debug
 
   $ hg bundle2 --debug --param 'e|! 7/=babar%#==tutu' --param simple ../out.hg2 --config progress.debug=true
+  bundle2-output-bundle: "HG20", (2 params) 0 parts total
   bundle2-output: start emission of HG20 stream
   bundle2-output: bundle parameter: e%7C%21%207/=babar%25%23%3D%3Dtutu simple
   bundle2-output: start of parts
@@ -384,6 +385,7 b' Test part'
 =================
 
   $ hg bundle2 --parts ../parts.hg2 --debug --config progress.debug=true
+  bundle2-output-bundle: "HG20", 7 parts total
   bundle2-output: start emission of HG20 stream
   bundle2-output: bundle parameter: 
   bundle2-output: start of parts
@@ -734,6 +736,7 b' Support for changegroup'
   9520eea781bcca16c1e15acc0ba14335a0e8e5ba
   eea13746799a9e0bfd88f29d3c2e9dc9389f524f
   02de42196ebee42ef284b6780a87cdc96e8eaab6
+  bundle2-output-bundle: "HG20", 1 parts total
   bundle2-output: start emission of HG20 stream
   bundle2-output: bundle parameter: 
   bundle2-output: start of parts