Improve error handling

[harold]

Hi, first, thanks for Oz, having great and powerful viz in Clojure is a good thing and I appreciate your efforts.

Using (oz/start-plot-server!)

I had a spec like:

{:data {:vaules data}
 :mark :bar
 :encoding {:x {:bin true
                :field k
                :type :quantitative}
            :y {:aggregate :count
                :type :quantitative}}}

data and k were good...

And when I did (oz/view!) the webpage disappeared (went completely blank) and this was in the console:

It took me just a minute to figure out that :vaules was misspelled, but having a nicer error in this case would be great.

Thanks again, and keep up the good work.

[metasoarous]

Hi @harold. Thanks for reporting this issue, and for the kind feedback.

I fully agree; There's definitely a need for some improved error handling. A few others have hit this wall as well. I've changed the issue title to reflect this.

Thanks again

[harold]

Ok, it looks like one possible path forward is to do what the vega editor does:

https://github.com/vega/editor/blob/master/src/utils/validate.ts

Which uses ajv, which appears to be available from cljsjs: https://github.com/cljsjs/packages/tree/master/ajv

Not sure if the schema is accessible from the vega-lite package in use, but it could likely be acquired from somewhere.

In this case, the errors are still pretty unhelpful:

Additionally, something like this in the implementation of oz.core may be helpful:

diff --git a/src/cljs/oz/core.cljs b/src/cljs/oz/core.cljs
index 13508c8..b8cb087 100644
--- a/src/cljs/oz/core.cljs
+++ b/src/cljs/oz/core.cljs
@@ -26,7 +26,12 @@
      (let [spec (clj->js spec)
            opts {:renderer "canvas"
                  :mode "vega-lite"}
-           vega-spec (. js/vl (compile spec))]
+           vega-spec (try
+                       (. js/vl (compile spec))
+                       (catch js/Error e
+                         (println "Compile failed, JSON spec was:")
+                         (log spec)
+                         (throw e)))]
        (log "Vega-lite translates to:")
        (log vega-spec)
        (-> (js/vegaEmbed elem spec (clj->js opts))
@@ -86,5 +91,3 @@
                (reduce merge (rest x))]
               x))
     spec))

I kind of wanted to print the spec as JSON with (js/JSON.stringify spec nil 2) so I could paste it right into the vega editor --- but that's not really tenable if there is nontrivial data.

[metasoarous]

That seems pretty reasonable. I could be wrong, but I believe vl does expose the schema.

Thanks again