Bug 1210157 - Add a --debug option to bootstrap.py r=nalexander

Add an option to run bootstrap.py with '--debug'. This will print full
tracebacks if the bootstrap process encounters an uncaught exception. It should
be useful for developers who are working on the bootstrap code as well as users
when writing bug reports.

Depends on D39362

Differential Revision: https://phabricator.services.mozilla.com/D39363

--HG--
extra : moz-landing-system : lando

python/mozboot/bin/bootstrap.py

@@ -154,6 +154,9 @@ def main(args):
                       'instead of using the default interactive prompt.')
     parser.add_option('--no-interactive', dest='no_interactive', action='store_true',
                       help='Answer yes to any (Y/n) interactive prompts.')
+    parser.add_option('--debug', dest='debug', action='store_true',
+                      help='Print extra runtime information useful for debugging and '
+                      'bug reports.')
 
     options, leftover = parser.parse_args(args)
 
@@ -165,6 +168,11 @@ def main(args):
             print('Could not load the bootstrap Python environment.\n')
             print('This should never happen. Consider filing a bug.\n')
             print('\n')
+
+            if options.debug:
+                # Raise full tracebacks during debugging and for bug reporting.
+                raise
+
             print(e)
             return 1
         dasboot = cls(choice=options.application_choice, no_interactive=options.no_interactive,