Return custom error if pkg directory is not found

src/command/pack.rs

@@ -9,7 +9,15 @@ pub fn pack(path: Option<String>, log: &Logger) -> result::Result<(), Error> {
     let crate_path = set_crate_path(path);
 
     info!(&log, "Packing up the npm package...");
-    npm::npm_pack(&crate_path)?;
+    match npm::npm_pack(&crate_path) {
+        Ok(r) => r,
+        Err(Error::Io { .. }) => {
+            return Err(Error::DirNotFound {
+                message: "Unable to find the pkg directory".to_owned(),
+            });
+        }
+        Err(e) => return Err(e),
+    };
     #[cfg(not(target_os = "windows"))]
     info!(&log, "Your package is located at {}/pkg", &crate_path);
     #[cfg(target_os = "windows")]

src/error.rs

@@ -17,6 +17,8 @@ pub enum Error {
     Cli { message: String, stderr: String },
     #[fail(display = "{}", message)]
     CrateConfig { message: String },
+    #[fail(display = "{}", message)]
+    DirNotFound { message: String },
 }
 
 impl Error {
@@ -45,6 +47,7 @@ impl Error {
             Error::CrateConfig { message: _ } => {
                 "There was a crate configuration error. Details:\n\n"
             }
+            Error::DirNotFound { message: _ } => "Unable to find the directory\n\n",
         }.to_string()
     }
 }