Add extension to push shell variables to server side hg

Summary:
Create an extension that allows shell variables to be passed to the
server via command line option. When pushing with the following command:

 hg push --pushvars "DEBUG=1"

will make HG_SCM_DEBUG=1 available to the hooks. Note the prepending of HG_SCM_

Test Plan: Run run_tests

Reviewers: pyd, rmcelroy, durham

Reviewed By: durham

Differential Revision: https://phabricator.fb.com/D1991994

Tasks: 4841351

Signature: t1:1991994:1430417209:9a05fb11f9ecdeab3a1d89cf331014dafe7d959f

pushvars.py

@@ -0,0 +1,67 @@
+# pushvars.py - enable pushing environment variables to the server
+#
+# Copyright 2015 Facebook, Inc.
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+#
+# When we want to modify how a hook works or to disable it, we
+# can send environment variables that the hooks can read. The
+# environment variables are prepended with HG_USERVAR_ and are thus
+# not a security vulnerability. For example:
+#
+# hg push --pushvars="BYPASS_REVIEWERS=true" --pushvars="DEBUG=1"
+#
+# will result in both HG_USERVAR_BYPASS_REVIEWERS and HG_USERVAR_DEBUG
+# available to the hook environment.
+
+from mercurial import bundle2, cmdutil, exchange, extensions, hg
+from mercurial import util, error, commands
+from mercurial.i18n import _
+import errno, urllib
+
+cmdtable = {}
+command = cmdutil.command(cmdtable)
+
+@exchange.b2partsgenerator('pushvars')
+def _getbundlesendvars(pushop, bundler):
+    '''send shellvars via bundle2'''
+    if getattr(pushop.repo, '_shellvars', ()):
+        part = bundler.newpart('pushvars')
+        for entry in pushop.repo._shellvars:
+            try:
+                key, value = entry.split('=', 1)
+            except Exception, e:
+                raise util.Abort(
+                    _('passed in variable needs to be of form var= or var=val. '
+                      'Instead, this was given "%s"' % entry))
+            part.addparam(key, value, mandatory=False)
+
+# Ugly hack suggested by pyd to ensure pushvars part comes before
+# hook part. Pyd has a fix for this in in he works.
+exchange.b2partsgenorder.insert(0, exchange.b2partsgenorder.pop())
+
+# Eventually, this will be used when we update to an  Hg that supports this.
+#@exchange.b2partsgenerator('pushvars', idx=0)
+
+@bundle2.parthandler('pushvars')
+def bundle2getvars(op, part):
+    '''unbundle a bundle2 containing shellvars on the server'''
+    tr = op.gettransaction()
+    for key, value in part.advisoryparams:
+        key = key.upper()
+        # We want pushed variables to have USERVAR_ prepended so we know
+        # they came from the pushvar extension.
+        key = "USERVAR_" + key
+        tr.hookargs[key] = value
+
+def push(orig, ui, repo, *args, **opts):
+  repo._shellvars = opts['pushvars']
+  try:
+    return orig(ui, repo, *args, **opts)
+  finally:
+    del repo._shellvars
+
+def extsetup(ui):
+    entry = extensions.wrapcommand(commands.table, 'push', push)
+    entry[1].append(('', 'pushvars', [], "variables that can be sent to the server"))

tests/test-pushvars.t

@@ -0,0 +1,58 @@
+  $ extpath=$(dirname $TESTDIR)
+  $ cat > $TESTTMP/pretxnchangegroup.sh << EOF
+  > #!/bin/bash
+  > env | grep -E "^HG_USERVAR_DEBUG"
+  > env | grep -E "^HG_USERVAR_BYPASS_REVIEW"
+  > exit 0
+  > EOF
+  $ chmod +x $TESTTMP/pretxnchangegroup.sh
+  $ cp $extpath/pushvars.py $TESTTMP # use $TESTTMP substitution in message
+  $ cat >> $HGRCPATH << EOF
+  > [extensions]
+  > pushvars=$TESTTMP/pushvars.py
+  > [hooks]
+  > pretxnchangegroup = $TESTTMP/pretxnchangegroup.sh
+  > [experimental]
+  > bundle2-exp = true
+  > EOF
+
+  $ hg init repo
+  $ hg clone -q repo child
+  $ cd child
+
+Test pushing vars to repo
+
+  $ echo b > a
+  $ hg commit -Aqm a
+  $ hg push --pushvars "DEBUG=1" --pushvars "BYPASS_REVIEW=true"
+  pushing to $TESTTMP/repo
+  searching for changes
+  HG_USERVAR_DEBUG=1
+  HG_USERVAR_BYPASS_REVIEW=true
+  remote: adding changesets
+  remote: adding manifests
+  remote: adding file changes
+  remote: added 1 changesets with 1 changes to 1 files
+
+Test pushing var with empty right-hand side
+
+  $ echo b >> a
+  $ hg commit -Aqm a
+  $ hg push --pushvars "DEBUG="
+  pushing to $TESTTMP/repo
+  searching for changes
+  HG_USERVAR_DEBUG=
+  remote: adding changesets
+  remote: adding manifests
+  remote: adding file changes
+  remote: added 1 changesets with 1 changes to 1 files
+
+Test pushing bad vars
+
+  $ echo b >> a
+  $ hg commit -Aqm b
+  $ hg push --pushvars "DEBUG"
+  pushing to $TESTTMP/repo
+  searching for changes
+  abort: passed in variable needs to be of form var= or var=val. Instead, this was given "DEBUG"
+  [255]