[PATCH] ui: remove urllib2 from being imported early

[Kyle Lippincott]

# HG changeset patch
# User Kyle Lippincott <spectral at google.com>
# Date 1486897598 28800
#      Sun Feb 12 03:06:38 2017 -0800
# Node ID 1f3234760225170767d10bfcd9cc5b2431b65471
# Parent  72f25e17af9d6a206ea374c30f229ae9513f3f23
ui: remove urllib2 from being imported early

Before this change, urllib2 was brought in when constructing the ui object, and
that added ~5ms on my Linux workstation to the hg startup time for every
command, bringing the time for 'HGRCPATH=/dev/null hg root' from 46ms to 40ms.

Now, we construct a single proxy object per initial ui creation (so that if the
ui is copied they share the object), but defer the actual instantiation of it
and the import of urllib2 until it's needed.

diff -r 72f25e17af9d -r 1f3234760225 mercurial/ui.py
--- a/mercurial/ui.py	Mon Feb 13 02:31:56 2017 -0800
+++ b/mercurial/ui.py	Sun Feb 12 03:06:38 2017 -0800
@@ -94,6 +94,24 @@
 # pager =""",
 }
 
+
+class httppasswordmgrdbproxy(object):
+    """Delays loading urllib2 until it's needed."""
+    def __init__(self):
+        self._mgr = None
+
+    def _get_mgr(self):
+        if self._mgr is None:
+            self._mgr = urlreq.httppasswordmgrwithdefaultrealm()
+        return self._mgr
+
+    def add_password(self, *args, **kwargs):
+        return self._get_mgr().add_password(*args, **kwargs)
+
+    def find_user_password(self, *args, **kwargs):
+        return self._get_mgr().find_user_password(*args, **kwargs)
+
+
 class ui(object):
     def __init__(self, src=None):
         """Create a fresh new ui object if no src given
@@ -145,7 +163,7 @@
             # shared read-only environment
             self.environ = encoding.environ
 
-            self.httppasswordmgrdb = urlreq.httppasswordmgrwithdefaultrealm()
+            self.httppasswordmgrdb = httppasswordmgrdbproxy()
 
         allowed = self.configlist('experimental', 'exportableenviron')
         if '*' in allowed:
@@ -172,7 +190,7 @@
         """Clear internal state that shouldn't persist across commands"""
         if self._progbar:
             self._progbar.resetstate()  # reset last-print time of progress bar
-        self.httppasswordmgrdb = urlreq.httppasswordmgrwithdefaultrealm()
+        self.httppasswordmgrdb = httppasswordmgrdbproxy()
 
     def formatter(self, topic, opts):
         return formatter.formatter(self, topic, opts)