only override config values from command line if they are actually set

If we set defaults for the query configuration options and then pass
the namespace created by parsing the command line options to the
config object it cannot tell the difference between values set on the
command line and defaults. That means we may override settings in the
configuration file with defaults from the command line parser.

This change sets all of the defaults for command line options to None
as a sentinel value and then updates the Config class to ignore
command line option values of None. It also adds tests to verify that
we get the expected override behavior with boolean and string options.

Change-Id: I1c9ce668b5e5c372d1c861bcae6e6de05a8ebc0c
Signed-off-by: Doug Hellmann <doug@doughellmann.com>

releasenotes/notes/fix-cli-option-handling-a13652d14507f2d7.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    Fix an issue with the way command line options and configuration
+    settings interact so that the settings in the configuration file
+    are used properly when command line arguments for those options
+    are not provided.

reno/config.py

@@ -275,9 +275,11 @@ class Config(object):
         arg_values = {
             o.name: getattr(parsed_args, o.name)
             for o in _OPTIONS
-            if hasattr(parsed_args, o.name)
+            if getattr(parsed_args, o.name, None) is not None
         }
-        self.override(**arg_values)
+        if arg_values:
+            LOG.info('[config] updating from command line options')
+            self.override(**arg_values)
 
     @property
     def reporoot(self):

reno/main.py

@@ -32,7 +32,7 @@ _query_args = [
           help='the branch to scan, defaults to the current')),
     (('--collapse-pre-releases',),
      dict(action='store_true',
-          default=config.Config.get_default('collapse_pre_releases'),
+          default=None,
           help='combine pre-releases with their final release')),
     (('--no-collapse-pre-releases',),
      dict(action='store_false',
@@ -42,12 +42,12 @@ _query_args = [
      dict(default=None,
           help='stop when this version is reached in the history')),
     (('--ignore-cache',),
-     dict(default=False,
+     dict(default=None,
           action='store_true',
           help='if there is a cache file present, do not use it')),
     (('--stop-at-branch-base',),
      dict(action='store_true',
-          default=True,
+          default=None,
           dest='stop_at_branch_base',
           help='stop scanning when the branch meets master')),
     (('--no-stop-at-branch-base',),

reno/tests/test_config.py

@@ -126,7 +126,7 @@ collapse_pre_releases: false
         }
         self.assertEqual(expected, actual)
 
-    def test_override_from_parsed_args(self):
+    def test_override_from_parsed_args_boolean_false(self):
         c = self._run_override_from_parsed_args([
             '--no-collapse-pre-releases',
         ])
@@ -138,6 +138,30 @@ collapse_pre_releases: false
         expected['collapse_pre_releases'] = False
         self.assertEqual(expected, actual)
 
+    def test_override_from_parsed_args_boolean_true(self):
+        c = self._run_override_from_parsed_args([
+            '--collapse-pre-releases',
+        ])
+        actual = c.options
+        expected = {
+            o.name: o.default
+            for o in config._OPTIONS
+        }
+        expected['collapse_pre_releases'] = True
+        self.assertEqual(expected, actual)
+
+    def test_override_from_parsed_args_string(self):
+        c = self._run_override_from_parsed_args([
+            '--earliest-version', '1.2.3',
+        ])
+        actual = c.options
+        expected = {
+            o.name: o.default
+            for o in config._OPTIONS
+        }
+        expected['earliest_version'] = '1.2.3'
+        self.assertEqual(expected, actual)
+
     def test_override_from_parsed_args_ignore_non_options(self):
         parser = argparse.ArgumentParser()
         main._build_query_arg_group(parser)