Handle multi-line default values in olso-config-generator

The oslo.config file format permits multi-line values for options,
however all the lines except for the first one need to be indented.

Right now oslo-config-generator fails to take that into account, and
instead outputs the formatted value as is, adding a comment character
only to the first line, and not commenting out or indenting the
subsequent lines.

This patch tries to fix that by adding a comment character and some
indentation to every newline in the formatted value.

Change-Id: I33381c8cfb59901ce6dfc07bd662f2edb56531dd
Closes-bug: #1689594

oslo_config/generator.py

@@ -311,7 +311,7 @@ class _OptFormatter(object):
             defaults = _format_defaults(opt)
         for default_str in defaults:
             if default_str:
-                default_str = ' ' + default_str
+                default_str = ' ' + default_str.replace('\n', '\n#    ')
             if minimal:
                 lines.append('%s =%s\n' % (opt.dest, default_str))
             else:

oslo_config/tests/test_generator.py

@@ -122,6 +122,9 @@ class GeneratorTestCase(base.BaseTestCase):
         'str_opt_with_space': cfg.StrOpt('str_opt',
                                          default='  foo bar  ',
                                          help='a string with spaces'),
+        'str_opt_multiline': cfg.StrOpt('str_opt',
+                                        default='foo\nbar\nbaz',
+                                        help='a string with newlines'),
         'bool_opt': cfg.BoolOpt('bool_opt',
                                 default=False,
                                 help='a boolean'),
@@ -528,6 +531,19 @@ class GeneratorTestCase(base.BaseTestCase):
 
 # a string with spaces (string value)
 #str_opt = "  foo bar  "
+''')),
+        ('str_opt_multiline',
+         dict(opts=[('test', [(None, [opts['str_opt_multiline']])])],
+              expected='''[DEFAULT]
+
+#
+# From test
+#
+
+# a string with newlines (string value)
+#str_opt = foo
+#    bar
+#    baz
 ''')),
         ('bool_opt',
          dict(opts=[('test', [(None, [opts['bool_opt']])])],