Crash when editable field with calculate is used in relevance expression

[grzesiek2010]

Problem description

https://console.firebase.google.com/u/0/project/api-project-322300403941/crashlytics/app/android:org.odk.collect.android/issues/85177cf7b388af8b6ec086cd77c7cc05?time=last-seven-days&versions=v1.28.2%20(3943)&sessionEventKey=5F88045E02020001727F5A1D764EC4D0_1462203208677627982

Fatal Exception: java.lang.ArrayIndexOutOfBoundsException: length=2; index=2
       at org.odk.collect.android.activities.FormEntryActivity.saveAnswersForCurrentScreen(FormEntryActivity.java:1129)
       at org.odk.collect.android.activities.FormEntryActivity.updateFieldListQuestions(FormEntryActivity.java:2714)
       at org.odk.collect.android.activities.FormEntryActivity.access$1900(FormEntryActivity.java:200)
       at org.odk.collect.android.activities.FormEntryActivity$10.run(FormEntryActivity.java:2681)
       at android.app.Activity.runOnUiThread(Activity.java:6972)
       at org.odk.collect.android.activities.FormEntryActivity.widgetValueChanged(FormEntryActivity.java:2678)
       at org.odk.collect.android.formentry.ODKView.widgetValueChanged(ODKView.java:621)
       at org.odk.collect.android.widgets.QuestionWidget.widgetValueChanged(QuestionWidget.java:499)
       at org.odk.collect.android.widgets.items.SelectOneWidget.onItemClicked(SelectOneWidget.java:103)
       at org.odk.collect.android.formentry.questions.AudioVideoImageTextLabel.lambda$setTextView$0(AudioVideoImageTextLabel.java:118)
       at org.odk.collect.android.formentry.questions.-$$Lambda$AudioVideoImageTextLabel$MqCYJ2yJoQ6DnhH04sxqp-kc3wc.onClick(-.java:2)

Steps to reproduce the problem

crashOnFieldList.xlsx

[lognaturel]

In this case, the value of ${name} used to compute relevance is briefly the user-provided value but as soon as there's a recalculation round, it goes back to the computed value. But recalculation gets triggered by the user typing into middleName which by that point is no longer relevant.

This is really a form design issue -- calculate should not be used on an editable field. https://xlsform.org/en/#trigger would be the right thing to use in this case to set the value of fullName only when name is edited. We should make sure that works.

Good find, @grzesiek2010. I'm not yet sure what the action to take is. We should make it clearer in the docs that calculate is not appropriate on an editable field. Ideally, this wouldn't crash, but I'm not sure what it should do. Probably throw an error dialog that says it's a form design issue?

The problem occurs on v1.27.3 as well but we don't see it in crash logs. Presumably someone published a faulty form definition recently and that's why we see so many of these crashes on v1.28.x.

[lognaturel]

Addressed by #4750.