Implement single-level merging of “args” dictionaries

docs/source/configuration/reference.rst

@@ -256,11 +256,16 @@ common configuration key <config-common-default_top_theme>`.
     A dict where keys are segment names or strings ``{module}.{name}``. Used to 
     specify default values for various keys:
     :ref:`after <config-themes-seg-after>`,
-    :ref:`args <config-themes-seg-args>` (only for function segments),
     :ref:`before <config-themes-seg-before>`,
     :ref:`contents <config-themes-seg-contents>` (only for string segments
     if :ref:`name <config-themes-seg-name>` is defined),
     :ref:`display <config-themes-seg-display>`.
+
+    Key :ref:`args <config-themes-seg-args>` (only for function and 
+    segments_list segments) is handled specially: unlike other values it is 
+    merged with all other values, except that a single ``{module}.{name}`` key 
+    if found prevents merging all ``{name}`` values.
+
     When using :ref:`local themes <config-ext-local_themes>` values of these 
     keys are first searched in the segment description, then in ``segment_data`` 
     key of a local theme, then in ``segment_data`` key of a :ref:`default theme 
@@ -289,8 +294,8 @@ common configuration key <config-common-default_top_theme>`.
     Each segment dictionary has the following options:
 
     ``type``
-        The segment type. Can be one of ``function`` (default), ``string`` 
-        or ``filler``:
+        The segment type. Can be one of ``function`` (default), ``string``, 
+        ``filler`` or ``segments_list``:
 
         ``function``
             The segment contents is the return value of the function defined 

powerline/config_files/themes/shell/__main__.json

@@ -5,7 +5,7 @@
 				"only_if_ssh": true
 			}
 		},
-		"cwd": {
+		"powerline.segments.common.cwd": {
 			"args": {
 				"dir_limit_depth": 3
 			}

powerline/segment.py

@@ -6,20 +6,52 @@ from powerline.lib.file_watcher import create_file_watcher
 import sys
 
 
-def get_segment_key(segment, theme_configs, key, module=None, default=None):
+def list_segment_key_values(segment, theme_configs, key, module=None, default=None):
 	try:
-		return segment[key]
+		yield segment[key]
 	except KeyError:
-		if 'name' in segment:
-			name = segment['name']
-			for theme_config in theme_configs:
-				if 'segment_data' in theme_config:
-					for segment_key in ((module + '.' + name, name) if module else (name,)):
-						try:
-							return theme_config['segment_data'][segment_key][key]
-						except KeyError:
-							pass
-	return default
+		pass
+	try:
+		name = segment['name']
+	except KeyError:
+		pass
+	else:
+		found_module_key = False
+		for theme_config in theme_configs:
+			try:
+				segment_data = theme_config['segment_data']
+			except KeyError:
+				pass
+			else:
+				if module:
+					try:
+						yield segment_data[module + '.' + name][key]
+						found_module_key = True
+					except KeyError:
+						pass
+				if not found_module_key:
+					try:
+						yield segment_data[name][key]
+					except KeyError:
+						pass
+	yield default
+
+
+def get_segment_key(merge, *args, **kwargs):
+	if merge:
+		ret = None
+		for value in list_segment_key_values(*args, **kwargs):
+			if ret is None:
+				ret = value
+			elif isinstance(ret, dict) and isinstance(value, dict):
+				old_ret = ret
+				ret = value.copy()
+				ret.update(old_ret)
+			else:
+				return ret
+		return ret
+	else:
+		return next(list_segment_key_values(*args, **kwargs))
 
 
 def get_function(data, segment):
@@ -33,7 +65,7 @@ def get_function(data, segment):
 
 
 def get_string(data, segment):
-	return data['get_key'](segment, None, 'contents'), None, None
+	return data['get_key'](False, segment, None, 'contents'), None, None
 
 
 def get_filler(data, segment):
@@ -129,8 +161,8 @@ def gen_segment_getter(pl, ext, common_config, theme_configs, default_module=Non
 		'path': common_config['paths'],
 	}
 
-	def get_key(segment, module, key, default=None):
-		return get_segment_key(segment, theme_configs, key, module, default)
+	def get_key(merge, segment, module, key, default=None):
+		return get_segment_key(merge, segment, theme_configs, key, module, default)
 	data['get_key'] = get_key
 
 	def get(segment, side):
@@ -146,7 +178,7 @@ def gen_segment_getter(pl, ext, common_config, theme_configs, default_module=Non
 			pl.exception('Failed to generate segment from {0!r}: {1}', segment, str(e), prefix='segment_generator')
 			return None
 
-		if not get_key(segment, module, 'display', True):
+		if not get_key(False, segment, module, 'display', True):
 			return None
 
 		if segment_type == 'function':
@@ -155,7 +187,7 @@ def gen_segment_getter(pl, ext, common_config, theme_configs, default_module=Non
 			highlight_group = segment.get('highlight_group') or segment.get('name')
 
 		if segment_type in ('function', 'segment_list'):
-			args = dict(((str(k), v) for k, v in get_key(segment, module, 'args', {}).items()))
+			args = dict(((str(k), v) for k, v in get_key(True, segment, module, 'args', {}).items()))
 
 		if segment_type == 'segment_list':
 			# Handle startup and shutdown of _contents_func?
@@ -219,8 +251,8 @@ def gen_segment_getter(pl, ext, common_config, theme_configs, default_module=Non
 			'type': segment_type,
 			'highlight_group': highlight_group,
 			'divider_highlight_group': None,
-			'before': get_key(segment, module, 'before', ''),
-			'after': get_key(segment, module, 'after', ''),
+			'before': get_key(False, segment, module, 'before', ''),
+			'after': get_key(False, segment, module, 'after', ''),
 			'contents_func': contents_func,
 			'contents': contents,
 			'priority': segment.get('priority', None),