Changing the way baseline formatters are indicated

This commit adds a decorator for formatters to use to indicate
that they are able to display baseline results.  A formatter
should add @accepts_baseline before the report function to show
that it is capable of displaying candidate results.

Change-Id: I5532d4b322b7df9dbca8a2275bf6e273d2801a3a

bandit/bandit.py

@@ -107,6 +107,11 @@ def main():
     os.environ['XDG_CONFIG_DIRS'] = '/etc:/usr/local/etc'
     extension_mgr = _init_extensions()
 
+    baseline_formatters = [f.name for f in filter(lambda x:
+                                                  hasattr(x.plugin,
+                                                          '_accepts_baseline'),
+                                                  extension_mgr.formatters)]
+
     # now do normal startup
     parser = argparse.ArgumentParser(
         description='Bandit - a Python source code analyzer.',
@@ -184,6 +189,8 @@ def main():
     parser.add_argument(
         '-b', '--baseline', dest='baseline', action='store',
         default=None, help='Path to a baseline report, in JSON format. '
+                           'Note: baseline reports must be output in one of '
+                           'the following formats: ' + str(baseline_formatters)
     )
     parser.set_defaults(debug=False)
     parser.set_defaults(verbose=False)
@@ -228,6 +235,11 @@ def main():
             logger.warn("Could not open baseline report: %s", args.baseline)
             sys.exit(2)
 
+        if args.output_format not in baseline_formatters:
+            logger.warn('Baseline must be used with one of the following '
+                        'formats: ' + str(baseline_formatters))
+            sys.exit(2)
+
     if args.output_format != "json":
         logger.info("using config: %s", config_file)
         logger.info("running on Python %d.%d.%d", sys.version_info.major,

bandit/core/test_properties.py

@@ -102,3 +102,21 @@ def takes_config(*args):
     else:
         name = args[0]
         return _takes_config
+
+
+def accepts_baseline(*args):
+    """Decorator to indicate formatter accepts baseline results
+
+    Use of this decorator before a formatter indicates that it is able to deal
+    with baseline results.  Specifically this means it has a way to display
+    candidate results and know when it should do so.
+    """
+    def wrapper(func):
+        if not hasattr(func, '_accepts_baseline'):
+            func._accepts_baseline = True
+
+        logger.debug('accepts_baseline() decorator executed on %s',
+                     func.__name__)
+
+        return func
+    return wrapper(args[0])