MDL-49814 quiz: make question dependency clear in the nav

mod/quiz/attemptlib.php

@@ -2145,6 +2145,11 @@ abstract class quiz_nav_panel_base {
             $button->currentpage = $this->showall || $button->page == $this->page;
             $button->flagged     = $qa->is_flagged();
             $button->url         = $this->get_question_url($slot);
+            if ($this->attemptobj->is_blocked_by_previous_question($slot)) {
+                $button->url = null;
+                $button->stateclass = 'blocked';
+                $button->statestring = get_string('questiondependsonprevious', 'quiz');
+            }
             $buttons[] = $button;
         }
 

mod/quiz/styles.css

@@ -125,6 +125,11 @@ body.jsenabled .questionflagcheckbox {
 .path-mod-quiz.dir-rtl  .qnbutton {
     float: right;
 }
+.path-mod-quiz .qnbutton:visited:hover,
+.path-mod-quiz .qnbutton:link:hover {
+    text-decoration: underline;
+}
+
 .path-mod-quiz .qnbutton .trafficlight,
 .path-mod-quiz .qnbutton .thispageholder {
     display: block;
@@ -146,6 +151,7 @@ body.jsenabled .questionflagcheckbox {
     background: url([[pix:quiz|navflagged]]) no-repeat top right;
 }
 
+.path-mod-quiz .qnbutton.blocked,
 .path-mod-quiz .qnbutton.notyetanswered,
 .path-mod-quiz .qnbutton.requiresgrading,
 .path-mod-quiz .qnbutton.invalidanswer {
@@ -164,18 +170,14 @@ body.jsenabled .questionflagcheckbox {
 .path-mod-quiz .qnbutton.incorrect {
     background-color: #fcc;
 }
+.path-mod-quiz .qnbutton.blocked {
+    color: #999;
+}
 .path-mod-quiz .qnbutton.notanswered .trafficlight,
 .path-mod-quiz .qnbutton.incorrect .trafficlight {
     border-top: 3px solid #800;
 }
 
-.path-mod-quiz .qnbutton.free:hover {
-    text-decoration: underline;
-}
-.path-mod-quiz .qnbutton.free span {
-    cursor: pointer;
-}
-
 .path-mod-quiz .othernav {
     clear: both;
     margin: 0.5em 0;

mod/quiz/tests/behat/attempt_require_previous.feature

@@ -51,6 +51,8 @@ Feature: Attemp a quiz where some questions require that the previous question h
     And I should see "First question"
     And I should see "This question cannot be attempted until the previous question has been completed."
     And I should not see "Second question"
+    And "Question 1" "link" should exist
+    And "Question 2" "link" should not exist
 
   @javascript
   Scenario: A question requires the previous one becomes available when the first one is answered
@@ -76,6 +78,8 @@ Feature: Attemp a quiz where some questions require that the previous question h
     Then I should see "First question"
     And I should not see "This question cannot be attempted until the previous question has been completed."
     And I should see "Second question"
+    And "Question 1" "link" should exist
+    And "Question 2" "link" should exist
 
   @javascript
   Scenario: After quiz submitted, all questions show on the review page