data: Made data flow in fallback clearer

src/data.rs

@@ -97,6 +97,8 @@ impl fmt::Display for DataSource {
     }
 }
 
+type LayoutSource = (ArrangementKind, DataSource);
+
 /// Lists possible sources, with 0 as the most preferred one
 /// Trying order: native lang of the right kind, native base,
 /// fallback lang of the right kind, fallback base
@@ -104,19 +106,12 @@ fn list_layout_sources(
     name: &str,
     kind: ArrangementKind,
     keyboards_path: Option<PathBuf>,
-) -> Vec<(ArrangementKind, DataSource)> {
-    let mut ret = Vec::new();
-    {
-        fn name_with_arrangement(name: String, kind: &ArrangementKind)
-            -> String
-        {
-            match kind {    
-                ArrangementKind::Base => name,
-                ArrangementKind::Wide => name + "_wide",
-            }
-        }
-
-        let mut add_by_name = |name: &str, kind: &ArrangementKind| {
+) -> Vec<LayoutSource> {
+    let add_by_name = |
+        mut ret: Vec<LayoutSource>,
+        name: &str,
+        kind: &ArrangementKind,
+    | -> Vec<LayoutSource> {
         if let Some(path) = keyboards_path.clone() {
             ret.push((
                 kind.clone(),
@@ -130,28 +125,43 @@ fn list_layout_sources(
             kind.clone(),
             DataSource::Resource(name.into())
         ));
+        ret
     };
 
-        match &kind {
-            ArrangementKind::Base => {},
+    let ret = {
+        fn name_with_arrangement(name: String, kind: &ArrangementKind)
+            -> String
+        {
+            match kind {    
+                ArrangementKind::Base => name,
+                ArrangementKind::Wide => name + "_wide",
+            }
+        }
+
+        let ret = Vec::new();
+
+        let ret = match &kind {
+            ArrangementKind::Base => ret,
             kind => add_by_name(
+                ret,
                 &name_with_arrangement(name.into(), &kind),
                 &kind,
             ),
         };
 
-        add_by_name(name, &ArrangementKind::Base);
+        let ret = add_by_name(ret, name, &ArrangementKind::Base);
 
-        match &kind {
-            ArrangementKind::Base => {},
+        let ret = match &kind {
+            ArrangementKind::Base => ret,
             kind => add_by_name(
+                ret,
                 &name_with_arrangement(FALLBACK_LAYOUT_NAME.into(), &kind),
                 &kind,
             ),
         };
 
-        add_by_name(FALLBACK_LAYOUT_NAME, &ArrangementKind::Base);
-    }
+        add_by_name(ret, FALLBACK_LAYOUT_NAME, &ArrangementKind::Base)
+    };
     ret
 }