catch errors when marking gaps, and when updating correct answer for …

…variable replacements

The marking script for gapfill parts now catches errors encountered
while submitting gaps, and ends marking immediately with an error
message.

After submitting a part, any parts which use it in adaptive marking have
their displayed expected answers updated. If there's an error when
computing the error-carried-forward scope (for example, because another
"must be answered" part hasn't been answered yet), silently give up.

fixes #629

locales/en-GB.json

@@ -244,6 +244,7 @@
     "part.matrix.empty cell": "One or more of the cells in your answer is empty.",
     "part.matrix.size mismatch": "The question author hasn't allowed the student to decide the dimensions of their answer, but the correct answer is {{correct_dimensions}} while the answer input is {{input_dimensions}}",
     "part.gapfill.feedback header": "<strong>{{name}}</strong>",
+    "part.gapfill.error marking gap": "Error marking {{name}}: {{-message}}",
     "part.extension.not implemented": "Part hasn't implemented the <code>{{name}}</code> method.",
     "part.custom.empty setting": "No value given.",
     "part.custom.unrecognised input type": "Unrecognised setting type <code>{{input_type}}</code>",

marking_scripts/gapfill.jme

@@ -28,16 +28,20 @@ gap_order:
 
 gap_feedback (Feedback on each of the gaps):
     map(
-        let(
-            result, submit_part(gaps[gap_number]["path"],answer),
-            gap, gaps[gap_number],
-            name, gap["name"],
-            noFeedbackIcon, not gap["settings"]["showFeedbackIcon"],
-                assert(noFeedbackIcon,
-                    assert(name="" or len(gaps)=1,feedback(translate('part.gapfill.feedback header',["name": name])))
-                );
-                concat_feedback(filter(x["op"]<>"warning",x,result["feedback"]), if(marks>0,result["marks"]/marks,1), noFeedbackIcon);
-                result
+        try(
+            let(
+                result, submit_part(gaps[gap_number]["path"],answer),
+                gap, gaps[gap_number],
+                name, gap["name"],
+                noFeedbackIcon, not gap["settings"]["showFeedbackIcon"],
+                    assert(noFeedbackIcon,
+                        assert(name="" or len(gaps)=1,feedback(translate('part.gapfill.feedback header',["name": name])))
+                    );
+                    concat_feedback(filter(x["op"]<>"warning",x,result["feedback"]), if(marks>0,result["marks"]/marks,1), noFeedbackIcon);
+                    result
+            ),
+            err,
+            fail(translate("part.gapfill.error marking gap",["name": gaps[gap_number]["name"], "message": err]))
         ),
         [gap_number,answer,index],
         zip(gap_order,studentAnswer,list(1..len(gaps)))

runtime/scripts/part.js

@@ -804,8 +804,11 @@ Part.prototype = /** @lends Numbas.parts.Part.prototype */ {
             for(var path in this.errorCarriedForwardBackReferences) {
                 var p2 = this.question.getPart(path);
                 if(p2.settings.variableReplacementStrategy=='alwaysreplace') {
-                    var answer = p2.getCorrectAnswer(p2.errorCarriedForwardScope());
-                    p2.display && p2.display.updateCorrectAnswer(answer);
+                    try {
+                        var answer = p2.getCorrectAnswer(p2.errorCarriedForwardScope());
+                        p2.display && p2.display.updateCorrectAnswer(answer);
+                    } catch(e) {
+                    }
                 }
                 if(p2.answered) {
                     p2.pleaseResubmit();