[core/theme] Fix detection of "best matching theme"

Previous code accepted the "first" hit in a theme - particularly, if a
module is called "A" and a *different* module "B" uses "A" as state, a
widget of module B with state A would be themed as *module* A, wrongly.

Essentially, made sure that the last (most specific) themeing "wins".

fixes #647

bumblebee_status/core/theme.py

@@ -35,8 +35,7 @@ def merge_replace(value, new_value, key):
     if not isinstance(value, dict):
         return new_value
     if isinstance(new_value, dict):
-        util.algorithm.merge(value, new_value)
-        return value
+        return util.algorithm.merge(new_value, value)
     # right now, merging needs explicit pango support :(
     if "pango" in value:
         value["pango"]["full_text"] = new_value

tests/core/test_theme.py

@@ -4,6 +4,13 @@ import types
 import core.theme
 import core.event
 import core.widget
+import core.module
+
+
+class TestModule(core.module.Module):
+    def __init__(self, widgets, config=core.config.Config([]), theme=None):
+        super().__init__(config, theme, widgets)
+        self.name = "test"
 
 
 class theme(unittest.TestCase):
@@ -23,6 +30,10 @@ class theme(unittest.TestCase):
         self.walTheme = {"colors": ["wal"]}
         self.cycleValueTheme = {"defaults": {"fg": ["red", "green", "blue"]}}
         self.stateTheme = {"warning": {"fg": "yellow"}, "critical": {"fg": "red"}}
+        self.overlayTheme = {
+            "load": {"prefix": "a"},
+            "test": {"load": {"prefix": "b"}, "prefix": "x"},
+        }
 
     def test_invalid_theme(self):
         with self.assertRaises(RuntimeError):
@@ -114,5 +125,21 @@ class theme(unittest.TestCase):
         widget.state = types.MethodType(lambda self: ["critical"], widget)
         self.assertEqual(self.stateTheme["critical"]["fg"], theme.get("fg", widget))
 
+    def test_overlay(self):
+        widget = core.widget.Widget()
+        module = TestModule(widget)
+        theme = core.theme.Theme(raw_data=self.overlayTheme)
+
+        self.assertEqual(
+            self.overlayTheme[module.name]["prefix"], theme.get("prefix", widget)
+        )
+
+        widget.state = types.MethodType(lambda self: ["load"], widget)
+
+        self.assertEqual(
+            self.overlayTheme[module.name]["load"]["prefix"],
+            theme.get("prefix", widget),
+        )
+
 
 # vim: tabstop=8 expandtab shiftwidth=4 softtabstop=4