layouts: Make selection testable

From now on, all the parameters for loading layout are handled inside a single pure function, which makes them possible to test.

As a side benefit, the old preference order function composed of a mess of nested procedures is gone.

src/data.rs

@@ -69,8 +69,12 @@ pub mod c {
         let overlay_str = as_str(&overlay)
                 .expect("Bad overlay name")
                 .expect("Empty overlay name");
+        let overlay_str = match overlay_str {
+            "" => None,
+            other => Some(other),
+        };
 
-        let (kind, layout) = load_layout_data_with_fallback(&name, type_, variant, &overlay_str);
+        let (kind, layout) = load_layout_data_with_fallback(&name, type_, variant, overlay_str);
         let layout = ::layout::Layout::new(layout, kind);
         Box::into_raw(Box::new(layout))
     }
@@ -113,97 +117,156 @@ impl fmt::Display for DataSource {
     }
 }
 
-type LayoutSource = (ArrangementKind, DataSource);
+/* All functions in this family carry around ArrangementKind,
+ * because it's not guaranteed to be preserved,
+ * and the resulting layout needs to know which version was loaded.
+ * See `squeek_layout_get_kind`.
+ * Possible TODO: since this is used only in styling,
+ * and makes the below code nastier than needed, maybe it should go.
+ */
 
-/// 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
-/// The `purpose` argument is not ContentPurpose,
-/// but rather ContentPurpose and overlay in one.
-fn list_layout_sources(
-    name: &str,
-    kind: ArrangementKind,
-    purpose: &str,
-    keyboards_path: Option<PathBuf>,
-) -> Vec<LayoutSource> {
-    // Just a simplification of often called code.
-    let add_by_name = |
-        mut ret: Vec<LayoutSource>,
-        purpose: &str,
-        name: &str,
-        kind: &ArrangementKind,
-    | -> Vec<LayoutSource> {
-        let name = if purpose == "" { name.into() }
-            else { format!("{}/{}", purpose, name) };
-
-        if let Some(path) = keyboards_path.clone() {
-            ret.push((
-                kind.clone(),
-                DataSource::File(
-                    path.join(name.clone())
-                        .with_extension("yaml")
-                )
-            ))
-        }
-
-        ret.push((
-            kind.clone(),
-            DataSource::Resource(name)
-        ));
-        ret
+/// Returns ordered names treating `name` as the base name,
+/// ignoring any `+` inside.
+fn _get_arrangement_names(name: &str, arrangement: ArrangementKind)
+    -> Vec<(ArrangementKind, String)>
+{
+    let name_with_arrangement = match arrangement {    
+        ArrangementKind::Base => name.into(),
+        ArrangementKind::Wide => format!("{}_wide", name),
     };
-
-    // Another grouping.
-    let add_by_kind = |ret, purpose: &str, name: &str, kind| {
-        let ret = match kind {
-            &ArrangementKind::Base => ret,
-            kind => add_by_name(
-                ret,
-                purpose,
-                &name_with_arrangement(name.into(), kind),
-                kind,
-            ),
-        };
-
-        add_by_name(ret, purpose, name, &ArrangementKind::Base)
-    };
-
-    fn name_with_arrangement(
-        name: String,
-        kind: &ArrangementKind,
-    ) -> String {
-        match kind {    
-            ArrangementKind::Base => name,
-            ArrangementKind::Wide => name + "_wide",
-        }
+    
+    let mut ret = Vec::new();
+    if name_with_arrangement != name {
+        ret.push((arrangement, name_with_arrangement));
     }
+    ret.push((ArrangementKind::Base, name.into()));
+    ret
+}
 
-    let ret = Vec::new();
-
-    // Name as given takes priority.
-    let ret = add_by_kind(ret, purpose, name, &kind);
-
-    // Then try non-alternative name if applicable (`us` for `us+colemak`).
-    let ret = {
+/// Returns names accounting for any `+` in the `name`,
+/// including the fallback to the default layout.
+fn get_preferred_names(name: &str, kind: ArrangementKind)
+    -> Vec<(ArrangementKind, String)>
+{
+    let mut ret = _get_arrangement_names(name, kind);
+    
+    let base_name_preferences = {
         let mut parts = name.splitn(2, '+');
         match parts.next() {
             Some(base) => {
-                // The name is already equal to base, so it was already added.
-                if base == name { ret }
-                else {
-                    add_by_kind(ret, purpose, base, &kind)
+                // The name is already equal to base, so nothing to add
+                if base == name {
+                    vec![]
+                } else {
+                    _get_arrangement_names(base, kind)
                 }
             },
             // The layout's base name starts with a "+". Weird but OK.
             None => {
                 log_print!(logging::Level::Surprise, "Base layout name is empty: {}", name);
-                ret
+                vec![]
             }
         }
     };
+    
+    ret.extend(base_name_preferences.into_iter());
+    let fallback_names = _get_arrangement_names(FALLBACK_LAYOUT_NAME, kind);
+    ret.extend(fallback_names.into_iter());
+    ret
+}
 
-    add_by_kind(ret, purpose, FALLBACK_LAYOUT_NAME.into(), &kind)
+/// Includes the subdirectory before the forward slash.
+type LayoutPath = String;
 
+// This is only used inside iter_fallbacks_with_meta.
+// Placed at the top scope
+// because `use LayoutPurpose::*;`
+// complains about "not in scope" otherwise.
+// This seems to be a Rust 2015 edition problem.
+/// Helper for determining where to look up the layout.
+enum LayoutPurpose<'a> {
+    Default,
+    Special(&'a str),
+}
+
+/// Returns the directory string
+/// where the layout should be looked up, including the slash.
+fn get_directory_string(
+    content_purpose: ContentPurpose,
+    overlay: Option<&str>) -> String
+{
+    use self::LayoutPurpose::*;
+
+    let layout_purpose = match overlay {
+        None => match content_purpose {
+            ContentPurpose::Number => Special("number"),
+            ContentPurpose::Digits => Special("number"),
+            ContentPurpose::Phone => Special("number"),
+            ContentPurpose::Terminal => Special("terminal"),
+            _ => Default,
+        },
+        Some(overlay) => Special(overlay),
+    };
+
+    // For intuitiveness,
+    // default purpose layouts are stored in the root directory,
+    // as they correspond to typical text
+    // and are seen the most often.
+    match layout_purpose {
+        Default => "".into(),
+        Special(purpose) => format!("{}/", purpose),
+    }
+}
+
+/// Returns an iterator over all fallback paths.
+fn to_layout_paths(
+    name_fallbacks: Vec<(ArrangementKind, String)>,
+    content_purpose: ContentPurpose,
+    overlay: Option<&str>,
+) -> impl Iterator<Item=(ArrangementKind, LayoutPath)> {
+    let prepend_directory = get_directory_string(content_purpose, overlay);
+
+    name_fallbacks.into_iter()
+        .map(move |(arrangement, name)|
+            (arrangement, format!("{}{}", prepend_directory, name))
+        )
+}
+
+type LayoutSource = (ArrangementKind, DataSource);
+
+fn to_layout_sources(
+    layout_paths: impl Iterator<Item=(ArrangementKind, LayoutPath)>,
+    filesystem_path: Option<PathBuf>,
+) -> impl Iterator<Item=LayoutSource> {
+    layout_paths.flat_map(move |(arrangement, layout_path)| {
+        let mut sources = Vec::new();
+        if let Some(path) = &filesystem_path {
+            sources.push((
+                arrangement,
+                DataSource::File(
+                    path.join(&layout_path)
+                        .with_extension("yaml")
+                )
+            ));
+        };
+        sources.push((arrangement, DataSource::Resource(layout_path.clone())));
+        sources.into_iter()
+    })
+}
+
+/// Returns possible sources, with first as the most preferred one.
+/// Trying order: native lang of the right kind, native base,
+/// fallback lang of the right kind, fallback base
+fn iter_layout_sources(
+    name: &str,
+    arrangement: ArrangementKind,
+    purpose: ContentPurpose,
+    ui_overlay: Option<&str>,
+    layout_storage: Option<PathBuf>,
+) -> impl Iterator<Item=LayoutSource> {
+    let names = get_preferred_names(name, arrangement);
+    let paths = to_layout_paths(names, purpose, ui_overlay);
+    to_layout_sources(paths, layout_storage)
 }
 
 fn load_layout_data(source: DataSource)
@@ -231,7 +294,7 @@ fn load_layout_data_with_fallback(
     name: &str,
     kind: ArrangementKind,
     purpose: ContentPurpose,
-    overlay: &str,
+    overlay: Option<&str>,
 ) -> (ArrangementKind, ::layout::LayoutData) {
 
     // Build the path to the right keyboard layout subdirectory
@@ -239,18 +302,7 @@ fn load_layout_data_with_fallback(
         .map(PathBuf::from)
         .or_else(|| xdg::data_path("squeekboard/keyboards"));
 
-    let layout_purpose = match overlay {
-        "" => match purpose {
-            ContentPurpose::Number => "number",
-            ContentPurpose::Digits => "number",
-            ContentPurpose::Phone => "number",
-            ContentPurpose::Terminal => "terminal",
-            _ => "",
-        },
-        overlay => overlay,
-    };
-
-    for (kind, source) in list_layout_sources(&name, kind, layout_purpose, path) {
+    for (kind, source) in iter_layout_sources(&name, kind, purpose, overlay, path) {
         let layout = load_layout_data(source.clone());
         match layout {
             Err(e) => match (e, source) {
@@ -982,11 +1034,11 @@ mod tests {
     
     /// First fallback should be to builtin, not to FALLBACK_LAYOUT_NAME
     #[test]
-    fn fallbacks_order() {
-        let sources = list_layout_sources("nb", ArrangementKind::Base, "", None);
+    fn test_fallback_basic_builtin() {
+        let sources = iter_layout_sources("nb", ArrangementKind::Base, ContentPurpose::Normal, None, None);
         
         assert_eq!(
-            sources,
+            sources.collect::<Vec<_>>(),
             vec!(
                 (ArrangementKind::Base, DataSource::Resource("nb".into())),
                 (
@@ -996,14 +1048,36 @@ mod tests {
             )
         );
     }
+    
+    /// Prefer loading from file system before builtin.
+    #[test]
+    fn test_preferences_order_path() {
+        let sources = iter_layout_sources("nb", ArrangementKind::Base, ContentPurpose::Normal, None, Some(".".into()));
+        
+        assert_eq!(
+            sources.collect::<Vec<_>>(),
+            vec!(
+                (ArrangementKind::Base, DataSource::File("./nb.yaml".into())),
+                (ArrangementKind::Base, DataSource::Resource("nb".into())),
+                (
+                    ArrangementKind::Base,
+                    DataSource::File("./us.yaml".into())
+                ),
+                (
+                    ArrangementKind::Base,
+                    DataSource::Resource("us".into())
+                ),
+            )
+        );
+    }
 
     /// If layout contains a "+", it should reach for what's in front of it too.
     #[test]
-    fn fallbacks_order_base() {
-        let sources = list_layout_sources("nb+aliens", ArrangementKind::Base, "", None);
+    fn test_preferences_order_base() {
+        let sources = iter_layout_sources("nb+aliens", ArrangementKind::Base, ContentPurpose::Normal, None, None);
 
         assert_eq!(
-            sources,
+            sources.collect::<Vec<_>>(),
             vec!(
                 (ArrangementKind::Base, DataSource::Resource("nb+aliens".into())),
                 (ArrangementKind::Base, DataSource::Resource("nb".into())),
@@ -1016,22 +1090,58 @@ mod tests {
     }
 
     #[test]
-    fn fallbacks_terminal_order_base() {
-        let sources = list_layout_sources("nb+aliens", ArrangementKind::Base, "terminal", None);
+    fn test_preferences_order_arrangement() {
+        let sources = iter_layout_sources("nb", ArrangementKind::Wide, ContentPurpose::Normal, None, None);
 
         assert_eq!(
-            sources,
+            sources.collect::<Vec<_>>(),
             vec!(
-                (ArrangementKind::Base, DataSource::Resource("terminal/nb+aliens".into())),
-                (ArrangementKind::Base, DataSource::Resource("terminal/nb".into())),
+                (ArrangementKind::Wide, DataSource::Resource("nb_wide".into())),
+                (ArrangementKind::Base, DataSource::Resource("nb".into())),
+                (
+                    ArrangementKind::Wide,
+                    DataSource::Resource("us_wide".into())
+                ),
                 (
                     ArrangementKind::Base,
-                    DataSource::Resource(format!("terminal/{}", FALLBACK_LAYOUT_NAME))
+                    DataSource::Resource("us".into())
                 ),
             )
         );
     }
-    
+
+    #[test]
+    fn test_preferences_order_overlay() {
+        let sources = iter_layout_sources("nb", ArrangementKind::Base, ContentPurpose::Normal, Some("terminal"), None);
+
+        assert_eq!(
+            sources.collect::<Vec<_>>(),
+            vec!(
+                (ArrangementKind::Base, DataSource::Resource("terminal/nb".into())),
+                (
+                    ArrangementKind::Base,
+                    DataSource::Resource("terminal/us".into())
+                ),
+            )
+        );
+    }
+
+    #[test]
+    fn test_preferences_order_hint() {
+        let sources = iter_layout_sources("nb", ArrangementKind::Base, ContentPurpose::Terminal, None, None);
+
+        assert_eq!(
+            sources.collect::<Vec<_>>(),
+            vec!(
+                (ArrangementKind::Base, DataSource::Resource("terminal/nb".into())),
+                (
+                    ArrangementKind::Base,
+                    DataSource::Resource("terminal/us".into())
+                ),
+            )
+        );
+    }
+
     #[test]
     fn unicode_keysym() {
         let keysym = xkb::keysym_from_name(

src/layout.rs

@@ -600,7 +600,7 @@ impl View {
 }
 
 /// The physical characteristic of layout for the purpose of styling
-#[derive(Clone, PartialEq, Debug)]
+#[derive(Clone, Copy, PartialEq, Debug)]
 pub enum ArrangementKind {
     Base = 0,
     Wide = 1,