SchemaRetreiver: typecheck dataset examples individually (#324)

In certain cases, the dataset can fail to typecheck as a whole
because there are examples with newer functions or wrong parameters.
This can occur if a device has been updated recently (in the last
3 hours), or can occur for a builtin device if Genie or the platform
layers have not been updated yet.
In that case, we should ignore and log the error, and let as many
examples through as we can.

Fixes stanford-oval/thingpedia-common-devices#286
and will probably help with stanford-oval/almond-gnome#40

lib/schema.ts

@@ -543,7 +543,6 @@ export default class SchemaRetriever {
                 this._classCache.dataset.set(kind, result[kind] = new Dataset(null, kind, []));
         } else {
             const parsed = Grammar.parse(code) as Library;
-            await parsed.typecheck(this, true);
 
             const examples = new Map<string, Example[]>();
 
@@ -554,6 +553,17 @@ export default class SchemaRetriever {
             // on disk
             for (const dataset of parsed.datasets) {
                 for (const example of dataset.examples) {
+                    // typecheck each example individually, and ignore those that do not
+                    // typecheck
+                    // this can occur if the dataset we retrieved from Thingpedia is newer
+                    // than the cached manifest and includes new functions or a parameter change
+                    try {
+                        await example.typecheck(this, true);
+                    } catch(e) {
+                        console.log(`Failed to load dataset example ${example.id}: ${e.message}`);
+                        continue;
+                    }
+
                     const devices = new Set<string>();
                     for (const [, prim] of example.iteratePrimitives(false))
                         devices.add(prim.selector.kind);