fix(notify): search freedesktop icon layout and rank by effective size

The hicolor fallback scanned <theme>/apps/<size>, but freedesktop themes
use <size>/apps, so hicolor never resolved. Both layouts are now
searched, and rasters are ranked by effective pixel size (N@2x is 2N)
with a deterministic name tie-break.

2 files changed, 170 insertions, 14 deletions

diff --git a/internal/notify/icons.go b/internal/notify/icons.go
index b874581..d68c171 100644
--- a/internal/notify/icons.go
+++ b/internal/notify/icons.go
@@ -95,22 +95,12 @@ func lookupThemeIcon(name, theme string) string {
 	return ""
 }
 
-// findInTheme prefers scalable then the largest raster under apps/.
+// findInTheme prefers scalable, then the largest raster. It searches both the
+// KDE/Papirus apps/<size> layout and the freedesktop <size>/apps layout.
 func findInTheme(base, name string) string {
-	sizes := []string{"scalable"}
-	matches, _ := filepath.Glob(filepath.Join(base, "apps", "[0-9]*"))
-	for _, m := range matches {
-		sizes = append(sizes, filepath.Base(m))
-	}
-	numeric := sizes[1:]
-	sort.Slice(numeric, func(i, j int) bool {
-		a, _ := strconv.Atoi(strings.TrimSuffix(numeric[i], "@2x"))
-		b, _ := strconv.Atoi(strings.TrimSuffix(numeric[j], "@2x"))
-		return a > b
-	})
-	for _, size := range sizes {
+	for _, dir := range themeSizeDirs(base) {
 		for _, ext := range []string{"svg", "png", "xpm"} {
-			p := filepath.Join(base, "apps", size, name+"."+ext)
+			p := filepath.Join(dir, name+"."+ext)
 			if fileExists(p) {
 				return p
 			}
@@ -119,6 +109,84 @@ func findInTheme(base, name string) string {
 	return ""
 }
 
+// sizeDir is one candidate icon directory inside a theme.
+type sizeDir struct {
+	path     string
+	scalable bool
+	size     int
+	name     string
+}
+
+// themeSizeDirs lists a theme's candidate directories, scalable first, then
+// rasters by effective pixel size descending, name as a deterministic
+// tie-break. Both icon layouts are covered.
+func themeSizeDirs(base string) []string {
+	var found []sizeDir
+	add := func(name, path string) {
+		if name == "scalable" {
+			found = append(found, sizeDir{path: path, scalable: true, name: name})
+			return
+		}
+		if n, ok := pixelSize(name); ok {
+			found = append(found, sizeDir{path: path, size: n, name: name})
+		}
+	}
+	// KDE/Papirus: apps/<size>/
+	if entries, err := os.ReadDir(filepath.Join(base, "apps")); err == nil {
+		for _, e := range entries {
+			if e.IsDir() {
+				add(e.Name(), filepath.Join(base, "apps", e.Name()))
+			}
+		}
+	}
+	// freedesktop: <size>/apps/
+	if entries, err := os.ReadDir(base); err == nil {
+		for _, e := range entries {
+			if !e.IsDir() {
+				continue
+			}
+			apps := filepath.Join(base, e.Name(), "apps")
+			if info, err := os.Stat(apps); err == nil && info.IsDir() {
+				add(e.Name(), apps)
+			}
+		}
+	}
+	sort.Slice(found, func(i, j int) bool {
+		a, b := found[i], found[j]
+		if a.scalable != b.scalable {
+			return a.scalable
+		}
+		if a.size != b.size {
+			return a.size > b.size
+		}
+		return a.name < b.name
+	})
+	dirs := make([]string, len(found))
+	for i, d := range found {
+		dirs[i] = d.path
+	}
+	return dirs
+}
+
+// pixelSize turns a size directory name into its effective pixel size. "48"
+// and "48x48" styles are recognised, and a trailing @2x doubles the size.
+func pixelSize(name string) (int, bool) {
+	s := name
+	mult := 1
+	if strings.HasSuffix(s, "@2x") {
+		s = strings.TrimSuffix(s, "@2x")
+		mult = 2
+	}
+	if i := strings.IndexByte(s, 'x'); i >= 0 {
+		s = s[:i]
+	}
+	n, err := strconv.Atoi(s)
+	if err != nil {
+		return 0, false
+	}
+	return n * mult, true
+}
+
 func inheritsOf(base string) string {
 	v := iniValue(filepath.Join(base, "index.theme"), "Inherits")
 	if i := strings.IndexByte(v, ','); i >= 0 {
diff --git a/internal/notify/icons_test.go b/internal/notify/icons_test.go
index 527b330..9a6824a 100644
--- a/internal/notify/icons_test.go
+++ b/internal/notify/icons_test.go
@@ -68,3 +68,91 @@ func TestResolveIconThemeName(t *testing.T) {
 		t.Fatalf("missing name must be empty, got %q", got)
 	}
 }
+
+// iconEnv builds a throwaway XDG tree, points qt6ct at theme, and returns the
+// root. HOME, XDG_DATA_HOME and XDG_DATA_DIRS are restored after the test.
+func iconEnv(t *testing.T, theme string) string {
+	t.Helper()
+	root := t.TempDir()
+	home := filepath.Join(root, "home")
+	if err := os.MkdirAll(filepath.Join(home, ".config", "qt6ct"), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(home, ".config", "qt6ct", "qt6ct.conf"), []byte("icon_theme="+theme+"\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	t.Setenv("XDG_DATA_HOME", root)
+	t.Setenv("XDG_DATA_DIRS", "")
+	t.Setenv("HOME", home)
+	return root
+}
+
+// putIcon creates a placeholder icon file, and its parents.
+func putIcon(t *testing.T, path string) {
+	t.Helper()
+	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(path, []byte("<svg/>"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+}
+
+// writeIndex writes a theme's index.theme with a single Inherits value.
+func writeIndex(t *testing.T, dir, inherits string) {
+	t.Helper()
+	if err := os.MkdirAll(dir, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(dir, "index.theme"), []byte("[Icon Theme]\nInherits="+inherits+"\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestResolveIconFreedesktopLayout(t *testing.T) {
+	root := iconEnv(t, "Flat")
+	putIcon(t, filepath.Join(root, "icons", "Flat", "scalable", "apps", "firefox.svg"))
+	putIcon(t, filepath.Join(root, "icons", "Flat", "48x48", "apps", "firefox.png"))
+	want := filepath.Join(root, "icons", "Flat", "scalable", "apps", "firefox.svg")
+	if got := ResolveIcon("firefox"); got != want {
+		t.Fatalf("freedesktop scalable: got %q want %q", got, want)
+	}
+
+	root = iconEnv(t, "Grid")
+	putIcon(t, filepath.Join(root, "icons", "Grid", "48x48", "apps", "gimp.png"))
+	want = filepath.Join(root, "icons", "Grid", "48x48", "apps", "gimp.png")
+	if got := ResolveIcon("gimp"); got != want {
+		t.Fatalf("freedesktop raster: got %q want %q", got, want)
+	}
+}
+
+func TestResolveIconSizePreference(t *testing.T) {
+	root := iconEnv(t, "Sized")
+	base := filepath.Join(root, "icons", "Sized")
+	putIcon(t, filepath.Join(base, "apps", "48", "app.png"))
+	putIcon(t, filepath.Join(base, "apps", "32@2x", "app.png"))
+	want := filepath.Join(base, "apps", "32@2x", "app.png")
+	if got := ResolveIcon("app"); got != want {
+		t.Fatalf("@2x beats plain 48 (64px vs 48px): got %q want %q", got, want)
+	}
+
+	root = iconEnv(t, "Tied")
+	base = filepath.Join(root, "icons", "Tied")
+	putIcon(t, filepath.Join(base, "32x32@2x", "apps", "app.png"))
+	putIcon(t, filepath.Join(base, "64x64", "apps", "app.png"))
+	want = filepath.Join(base, "32x32@2x", "apps", "app.png")
+	if got := ResolveIcon("app"); got != want {
+		t.Fatalf("equal 64px must break ties deterministically: got %q want %q", got, want)
+	}
+}
+
+func TestResolveIconInheritsCycle(t *testing.T) {
+	root := iconEnv(t, "LoopA")
+	writeIndex(t, filepath.Join(root, "icons", "LoopA"), "LoopB")
+	writeIndex(t, filepath.Join(root, "icons", "LoopB"), "LoopA")
+	putIcon(t, filepath.Join(root, "icons", "hicolor", "48x48", "apps", "app.png"))
+	want := filepath.Join(root, "icons", "hicolor", "48x48", "apps", "app.png")
+	if got := ResolveIcon("app"); got != want {
+		t.Fatalf("cycle must terminate and fall through to hicolor: got %q want %q", got, want)
+	}
+}