From 8663ecf31c51e5bf7fef194bb15aed0b038fb8fc Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Mon, 2 Jul 2018 12:25:39 +0200
Subject: Add ability to suppress auto-synchronization via BDEP_SYNC envvar

If BDEP_SYNC is set, auto-synchronization will only be performed if its
value is true or 1.

So to suppress, run:

$ BDEP_SYNC=0 b
---
 bdep/sync.cli | 10 ++++++++--
 bdep/sync.cxx | 12 ++++++++++--
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/bdep/sync.cli b/bdep/sync.cli
index fd5a375..bf0fbb5 100644
--- a/bdep/sync.cli
+++ b/bdep/sync.cli
@@ -224,8 +224,14 @@ namespace bdep
 
   "\h|ENVIRONMENT|
 
-   To avoid recursive re-synchronization, the \cb{sync} command maintains the
-   \cb{BDEP_SYNCED_CONFIGS} environment variable. It contains a
+   The \cb{BDEP_SYNC} environment variable can be used to suppress automatic
+   synchronization on build system invocation. If set, auto-synchronization
+   will only be performed if the variable's value is \cb{true} or \cb{1}. The
+   ability to suppress auto-synchronization can be useful when you don't have
+   usable \cb{bdep} and/or \cb{bpkg}.
+
+   To avoid recursive re-synchronization, the \cb{sync} command also maintains
+   the \cb{BDEP_SYNCED_CONFIGS} environment variable. It contains a
    space-separated, \cb{\"}-quoted list of configuration paths that have been
    or are being synchronized by the current \cb{bdep} invocation chain. The
    \cb{sync} command examines this variable and silently ignores
diff --git a/bdep/sync.cxx b/bdep/sync.cxx
index 8cfdc7a..1620555 100644
--- a/bdep/sync.cxx
+++ b/bdep/sync.cxx
@@ -436,14 +436,22 @@ namespace bdep
             // if! $null($cfgs)
             //   cfgs = [dir_paths] $regex.split($cfgs, ' *"([^"]*)" *', '\1')
             //
+            // Also note that we try to avoid setting any variables in order
+            // not to pollute the configuration's root scope.
+            //
             os << "# Created automatically by bdep."                   << endl
                << "#"                                                  << endl
                << "if ($build.meta_operation != 'info'      && \\"     << endl
                << "    $build.meta_operation != 'configure' && \\"     << endl
                << "    $build.meta_operation != 'disfigure')"          << endl
-               << "  run '" << argv0 << "' sync --hook=1 "             <<
+               << "{"                                                  << endl
+               << "  if ($getenv('BDEP_SYNC') == [null] || \\"         << endl
+               << "      $getenv('BDEP_SYNC') == true   || \\"         << endl
+               << "      $getenv('BDEP_SYNC') == 1)"                   << endl
+               << "    run '" << argv0 << "' sync --hook=1 "           <<
               "--verbose $build.verbosity "                            <<
-              "--config \"$out_root\""                                 << endl;
+              "--config \"$out_root\""                                 << endl
+               << "}"                                                  << endl;
 
             os.close ();
           }
-- 
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