utils/types: toggle_set: add "~~" semantics

Add support for "~~" special value that indicates that, when merging
into another set, all values from that set should in fact be dropped.
Apart from the unique merge semantics, "~~" just like any other "~"
value.

wa/commands/run.py

@@ -92,7 +92,7 @@ class RunCommand(Command):
         self.logger.debug('Version: {}'.format(get_wa_version()))
         self.logger.debug('Command Line: {}'.format(' '.join(sys.argv)))
 
-        disabled_augmentations = toggle_set(["~{}".format(i)
+        disabled_augmentations = toggle_set([i != '~~' and "~{}".format(i) or i
                                            for i in args.augmentations_to_disable])
         config.jobs_config.disable_augmentations(disabled_augmentations)
         config.jobs_config.only_run_ids(args.only_run_ids)

wa/framework/configuration/core.py

@@ -957,6 +957,8 @@ class JobGenerator(object):
 
     def disable_augmentations(self, augmentations):
         for entry in augmentations:
+            if entry == '~~':
+                continue
             if entry.startswith('~'):
                 entry = entry[1:]
             try:

wa/framework/configuration/parsers.py

@@ -306,7 +306,10 @@ def _construct_valid_entry(raw, seen_ids, prefix, jobs_config):
             workload_entry[name] = value
 
     if "augmentations" in workload_entry:
-        jobs_config.update_augmentations(workload_entry["augmentations"])
+        if '~~' in workload_entry['augmentations']:
+            msg = '"~~" can only be specfied in top-level config, and not for individual workloads/sections'
+            raise ConfigError(msg)
+        jobs_config.update_augmentations(workload_entry['augmentations'])
 
     # error if there are unknown workload_entry
     if raw:

wa/utils/types.py

@@ -370,6 +370,9 @@ class toggle_set(set):
 
     @staticmethod
     def merge(source, dest):
+        if '~~' in dest:
+            dest.remove('~~')
+            return dest
         for item in source:
             if item not in dest:
                 #Disable previously enabled item