commandserver: enable logging when server process started

This allows us to keep track of server events before client connects to
the server.

Tests will be added later. Currently there's no log() call to check if
things are working well.

mercurial/commandserver.py

@@ -208,15 +208,10 b' class server(object):'
     def __init__(self, ui, repo, fin, fout):
         self.cwd = encoding.getcwd()
 
-        # developer config: cmdserver.log
-        logpath = ui.config("cmdserver", "log")
-        if logpath:
+        if ui.config("cmdserver", "log") == '-':
             global logfile
-            if logpath == '-':
-                # write log on a special 'd' (debug) channel
+            # switch log stream to the 'd' (debug) channel
                 logfile = channeledoutput(fout, 'd')
-            else:
-                logfile = open(logpath, 'a')
 
         if repo:
             # the ui here is really the repo ui so take its baseui so we don't
@@ -361,6 +356,24 b' class server(object):'
 
         return 0
 
+def setuplogging(ui):
+    """Set up server logging facility
+
+    If cmdserver.log is '-', log messages will be sent to the 'd' channel
+    while a client is connected. Otherwise, messages will be written to
+    the stderr of the server process.
+    """
+    # developer config: cmdserver.log
+    logpath = ui.config(b'cmdserver', b'log')
+    if not logpath:
+        return
+
+    global logfile
+    if logpath == b'-':
+        logfile = ui.ferr
+    else:
+        logfile = open(logpath, 'ab')
+
 class pipeservice(object):
     def __init__(self, ui, repo, opts):
         self.ui = ui

mercurial/server.py

@@ -155,9 +155,11 b' def runservice(opts, parentfn=None, init'
 def _createcmdservice(ui, repo, opts):
     mode = opts['cmdserver']
     try:
-        return _cmdservicemap[mode](ui, repo, opts)
+        servicefn = _cmdservicemap[mode]
     except KeyError:
         raise error.Abort(_('unknown mode %s') % mode)
+    commandserver.setuplogging(ui)
+    return servicefn(ui, repo, opts)
 
 def _createhgwebservice(ui, repo, opts):
     # this way we can check if something was given in the command-line