add Wrapper for WMCore configuration (#5112)

* add Wrapper for WMCore configuration

* Create WMCoreConfigWrapper.py

Co-authored-by: Stefano Belforte <[email protected]>

src/python/CRABClient/WMCoreConfigWrapper.py

@@ -0,0 +1,36 @@
+"""
+This is a temporary file used to help transitioning to a
+CRABClient which has no dependency on WMCore. Its only purpose
+is to allow users to keep having this line in crabConfig.py:
+from WMCore.Configuration import Configuration
+instead of :
+from CRABClient.Configuration import Configuration
+
+File is meant to be renamed and moved by the CRABClient build procedure  
+(crab-build.file in cmsdist)or an ad hoc setup script in case a developer wants
+to run using source from GH, so that python discovers it as
+WMCore.Configuration. When executed, the code oi here prints a simple warning
+asking the user to update the configuration and calls
+CRABClient.Configuration. In CRABClient.Configuration we have
+a modified (and frozen) version of WMCore.Configuration which
+runs in both python2 and python3 without requiring external
+dependencies which are not available in CMSSW_8 or earlier, e.g. "future"
+"""
+
+from CRABClient.Configuration import Configuration as Config
+from CRABClient.ClientUtilities import colors
+
+import logging
+logger = logging.getLogger("CRAB3.all")
+
+class Configuration(Config):
+    def __init__(self):
+        msg = ''
+        msg += '%sWarning: CRABClient does not depend on WMCore anymore.\n' % (colors.RED)
+        msg += 'Please update your config file to use configuration from CRABClient instead.\n'
+        msg += 'Change inside that file it from "from WMCore.Configuration import Configuration"\n'
+        msg += 'to "from CRABClient.Configuration import Configuration%s\n"' % (colors.NORMAL)
+        msg += 'Support for old style "from WMCore.Configuration import ..." will be remove in future versions of CRAB'
+        logger.info(msg)
+        Config.__init__(self)
+