Recalculate form fields when page is turned (#3920)

Attempt to work around jr:choice-name() performance issues by reclalculating
fields one more time on form load, and on every page change.  If choice-name()s
only reference fields on different pages, or vice versa, then maybe they will
become usable.

Issue: #3870

Gruntfile.js

@@ -252,10 +252,6 @@ module.exports = function(grunt) {
             // https://github.com/medic/medic-webapp/issues/2797
             'patch node_modules/pouchdb-adapter-idb/lib/index.js < patches/pouchdb-ignore-safari-check.patch',
 
-            // patch enketo to support cascading of jr:choice-name() update results
-            // https://github.com/medic/medic-webapp/issues/3804
-            'patch node_modules/enketo-core/src/js/output.js < patches/3804_jr-choice-name.patch',
-
             // patch enketo's bootstrap-datepicker dependency so that sass compiles properly
             'patch node_modules/enketo-core/src/widget/date/datepicker-extended.scss < patches/enketo-datepicker-extended-sass-import.patch',
           ];

static/js/services/enketo.js

@@ -258,6 +258,7 @@ angular.module('inboxServices').service('Enketo',
         window.history.replaceState({ enketo_page_number: 0 }, '');
         overrideNavigationButtons(form, wrapper);
         addPopStateHandler(form, wrapper);
+        forceRecalculate(form);
 
         return form;
       });
@@ -272,6 +273,7 @@ angular.module('inboxServices').service('Enketo',
               if(typeof newPageIndex === 'number') {
                 window.history.pushState({ enketo_page_number: newPageIndex }, '');
               }
+              forceRecalculate(form);
             });
           return false;
         });
@@ -280,6 +282,7 @@ angular.module('inboxServices').service('Enketo',
         .off('.pagemode')
         .on('click.pagemode', function() {
           window.history.back();
+          forceRecalculate(form);
           return false;
         });
     };
@@ -464,6 +467,10 @@ angular.module('inboxServices').service('Enketo',
       });
     };
 
+    var forceRecalculate = function(form) {
+      form.calc.update();
+    };
+
     this.save = function(formInternalId, form, docId) {
       return $q.resolve(form.validate())
         .then(function(valid) {

tests/karma/unit/services/enketo.js

@@ -91,7 +91,8 @@ describe('Enketo service', function() {
 
     window.EnketoForm = EnketoForm;
     EnketoForm.returns({
-      init: enketoInit
+      init: enketoInit,
+      calc: { update: function() {} }
     });
 
     XmlForm.returns(KarmaUtils.mockPromise(null, { id: 'abc' }));