Add custom missing mandatory UFO path error types & missing mandatory UFO path checks

src/error.rs

@@ -19,7 +19,6 @@ pub enum Error {
     MissingDefaultLayer,
     MissingLayer(String),
     DuplicateLayer(String),
-    MissingLayerContents,
     InvalidColor(InvalidColorString),
     DuplicateGlyph {
         layer: String,
@@ -44,6 +43,8 @@ pub enum Error {
     ExpectedPositiveValue,
     #[cfg(feature = "kurbo")]
     ConvertContour(ErrorKind),
+    MissingFile(String),
+    MissingUFODir(String),
 }
 
 /// An error representing a failure to validate UFO groups.
@@ -160,9 +161,6 @@ impl std::fmt::Display for Error {
             Error::MissingDefaultLayer => write!(f, "Missing default ('glyphs') layer."),
             Error::DuplicateLayer(name) => write!(f, "Layer name '{}' already exists.", name),
             Error::MissingLayer(name) => write!(f, "Layer name '{}' does not exist.", name),
-            Error::MissingLayerContents => {
-                write!(f, "Missing required 'layercontents.plist' file.")
-            }
             Error::DuplicateGlyph { layer, glyph } => {
                 write!(f, "Glyph named '{}' already exists in layer '{}'", glyph, layer)
             }
@@ -194,6 +192,12 @@ impl std::fmt::Display for Error {
             Error::ExpectedPositiveValue => {
                 write!(f, "PositiveIntegerOrFloat expects a positive value.")
             }
+            Error::MissingFile(path) => {
+                write!(f, "missing required {} file", path)
+            }
+            Error::MissingUFODir(path) => {
+                write!(f, "{} directory was not found", path)
+            }
             #[cfg(feature = "kurbo")]
             Error::ConvertContour(cause) => write!(f, "Failed to convert contour: '{}'", cause),
         }

src/font.rs

@@ -118,6 +118,10 @@ impl Font {
     }
 
     fn load_impl(path: &Path, request: DataRequest) -> Result<Font, Error> {
+        if !path.exists() {
+            return Err(Error::MissingUFODir(path.display().to_string()));
+        }
+
         let meta_path = path.join(METAINFO_FILE);
         let mut meta: MetaInfo = plist::from_file(meta_path)?;
 
@@ -393,7 +397,7 @@ fn load_layers(
 ) -> Result<LayerSet, Error> {
     let layercontents_path = ufo_path.join(LAYER_CONTENTS_FILE);
     if meta.format_version == FormatVersion::V3 && !layercontents_path.exists() {
-        return Err(Error::MissingLayerContents);
+        return Err(Error::MissingFile(layercontents_path.display().to_string()));
     }
     LayerSet::load(ufo_path, glyph_names)
 }
@@ -438,6 +442,17 @@ mod tests {
         assert_eq!(font_obj.features.unwrap(), "# this is the feature from lightWide\n");
     }
 
+    #[test]
+    fn loading_invalid_ufo_dir_path() {
+        let path = "totally/bogus/filepath/font.ufo";
+        let font_load_res = Font::load(path);
+        match font_load_res {
+            Ok(_) => panic!("unxpected Ok result"),
+            Err(Error::MissingUFODir(_)) => (), // expected value
+            _ => panic!("incorrect error type returned"),
+        }
+    }
+
     #[test]
     fn data_request() {
         let path = "testdata/mutatorSans/MutatorSansLightWide.ufo";