[PATCH] dispatch: do not construct repo for chgserver

[Jun Wu]

# HG changeset patch
# User Jun Wu <quark at fb.com>
# Date 1455890329 0
#      Fri Feb 19 13:58:49 2016 +0000
# Node ID 4668ead485adb2d83dc4399d4e2ce619e70751c7
# Parent  6c3ab048228f9b1760bf0b6baa307a4ec361c638
dispatch: do not construct repo for chgserver

chgserver is designed to be able to serve multiple repos from one server
process. It does not need a repo object but still needs to read repo config
to get the final [extensions] config to know what extensions it should load.

While constructing a repo object (running reposetup) should not have bad side
effects, it hurts performance a bit and there are some bad extensions having
global side effects like wrapping ui in reposetup.

This patch adds special handling logic in dispatch.py to detect the chgserver
case and skip repo object construction. It is not ideal but relatively
reasonable comparing to other hacks like a global flag or monkey patching.

diff --git a/mercurial/dispatch.py b/mercurial/dispatch.py
--- a/mercurial/dispatch.py
+++ b/mercurial/dispatch.py
@@ -873,9 +873,17 @@
     elif not cmd:
         return commands.help_(ui, 'shortlist')
 
+    norepocmd = cmd in commands.norepo.split()
+    norepo = norepocmd
+    cmdserver = _earlygetopt(['--cmdserver'], fullargs)
+    # chgserver does not need repo object. one chgserver is designed to serve
+    # multiple repos with same sensitive configs ([extensions], etc.)
+    if cmdserver[:1] == ['chgunix'] and fullargs[:1] == ['serve']:
+        norepo = True
+
     repo = None
     cmdpats = args[:]
-    if cmd not in commands.norepo.split():
+    if not norepo:
         # use the repo from the request only if we don't have -R
         if not rpath and not cwd:
             repo = req.repo
@@ -914,7 +922,7 @@
             if options['hidden']:
                 repo = repo.unfiltered()
         args.insert(0, repo)
-    elif rpath:
+    elif rpath and norepocmd:
         ui.warn(_("warning: --repository ignored\n"))
 
     msg = ' '.join(' ' in a and repr(a) or a for a in fullargs)