commands: config: error out if value is unset

This makes sense, and matches git config's behavior too. Stay silent
by default, but log.dbg() what happened.

Add a test case, too.

Signed-off-by: Marti Bolivar <marti.bolivar@nordicsemi.no>

src/west/commands/config.py

@@ -10,7 +10,7 @@ import configparser
 from west import log
 from west import configuration
 from west.configuration import ConfigFile
-from west.commands import WestCommand
+from west.commands import WestCommand, CommandError
 
 CONFIG_DESCRIPTION = '''\
 West configuration file handling.
@@ -125,6 +125,9 @@ class Config(WestCommand):
             value = config_settings.get(section, key, fallback=None)
             if value is not None:
                 log.inf(value)
+            else:
+                log.dbg('{} is unset'.format(args.name))
+                raise CommandError(returncode=1)
         else:
             if configfile == ConfigFile.ALL:
                 # No file given, thus writing defaults to LOCAL

tests/test_config.py

@@ -270,3 +270,10 @@ def test_config_missing_key():
         cmd('config pytest')
         assert str(e) == 'west config: error: missing key, please invoke ' \
             'as: west config <section>.<key>\n'
+
+def test_unset_config():
+    # Getting unset configuration options should raise an error.
+    # With verbose output, the exact missing option should be printed.
+    with pytest.raises(subprocess.CalledProcessError) as e:
+        cmd('-v config pytest.missing')
+        assert 'pytest.missing is unset' in str(e)