Exercise mode UUID serialization and grading crash fixes (#1108)

src/haz3lcore/tiles/Id.re

@@ -59,9 +59,20 @@ type t = Uuidm.t;
 let mk: unit => t = Uuidm.v4_gen(Random.State.make_self_init());
 
 let compare: (t, t) => int = Uuidm.compare;
-let pp: (Format.formatter, t) => unit = Uuidm.pp;
 let to_string: (~upper: bool=?, t) => string = Uuidm.to_string;
 let of_string: (~pos: int=?, string) => option(t) = Uuidm.of_string;
+let pp: (Format.formatter, t) => unit =
+  (f, id) =>
+    Format.fprintf(
+      f,
+      "Option.get(Haz3lcore.Id.of_string(\"%s\"))",
+      to_string(id),
+    );
+let show = id =>
+  Format.sprintf(
+    "Option.get(Haz3lcore.Id.of_string(\"%s\"))",
+    to_string(id),
+  );
 
 [@deriving (sexp, yojson)]
 type binding('v) = (t, 'v);

src/haz3lweb/Grading.re

@@ -389,7 +389,12 @@ module ImplGradingReport = {
 
   let individual_reports = (~inject, ~report) => {
     switch (report.test_results) {
-    | Some(test_results) =>
+    | Some(test_results)
+        when
+          List.length(test_results.test_map)
+          == List.length(report.hinted_results) =>
+      /* NOTE: This condition will be false when evaluation crashes,
+       * for example due to a stack overflow, which may occur in normal operation  */
       div(
         report.hinted_results
         |> List.mapi((i, (status, hint)) =>
@@ -402,7 +407,7 @@ module ImplGradingReport = {
              )
            ),
       )
-    | None => div([])
+    | _ => div([])
     };
   };