Merge branch 'preventdefault-disabled-buttons' into 'master'

Prevent default disabled buttons and links.

## What does this MR do?
Prevents default action for disabled buttons and links. If the element has `.btn` and `.disabled` at the same time, its default action will be prevented.

## Are there points in the code the reviewer needs to double check?
Yes. Is there a better way to do that?

## Why was this MR needed?
Right now we can click disabled links and it cause some troubles like in #18079.

## What are the relevant issue numbers?
Fixes #18079

## Screenshots (if relevant)
![disabled-click](/uploads/48b58ce130f843e530e62632bcc27436/disabled-click.gif)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- [x] Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !4658

CHANGELOG

@@ -77,6 +77,7 @@ v 8.9.0 (unreleased)
   - RepositoryCheck::SingleRepositoryWorker public and private methods are now instrumented
   - Improve issuables APIs performance when accessing notes !4471
   - External links now open in a new tab
+  - Prevent default actions of disabled buttons and links
   - Markdown editor now correctly resets the input value on edit cancellation !4175
   - Toggling a task list item in a issue/mr description does not creates a Todo for mentions
   - Improved UX of date pickers on issue & milestone forms

app/assets/javascripts/application.js.coffee

@@ -125,6 +125,7 @@ window.onload = ->
     setTimeout shiftWindow, 100
 
 $ ->
+  gl.utils.preventDisabledButtons()
   bootstrapBreakpoint = bp.getBreakpointSize()
 
   $(".nicescroll").niceScroll(cursoropacitymax: '0.4', cursorcolor: '#FFF', cursorborder: "1px solid #FFF")

app/assets/javascripts/lib/common_utils.js.coffee

@@ -32,5 +32,12 @@
       .attr    'title', newTitle
       .tooltip 'fixTitle'
 
+  gl.utils.preventDisabledButtons = ->
+
+    $('.btn').click (e) ->
+      if $(this).hasClass 'disabled'
+        e.preventDefault()
+        e.stopImmediatePropagation()
+        return false
 
 ) window

spec/javascripts/application_spec.js.coffee

+#= require lib/common_utils
+
+describe 'Application', ->
+  describe 'disable buttons', ->
+    fixture.preload('application.html')
+
+    beforeEach ->
+      fixture.load('application.html')
+
+    it 'should prevent default action for disabled buttons', ->
+
+      gl.utils.preventDisabledButtons()
+
+      isClicked = false
+      $button   = $ '#test-button'
+
+      $button.click -> isClicked = true
+      $button.trigger 'click'
+
+      expect(isClicked).toBe false
+
+
+    it 'should be on the same page if a disabled link clicked', ->
+
+      locationBeforeLinkClick = window.location.href
+      gl.utils.preventDisabledButtons()
+
+      $('#test-link').click()
+
+      expect(window.location.href).toBe locationBeforeLinkClick

spec/javascripts/fixtures/application.html.haml

+%a#test-link.btn.disabled{:href => "/foo"} Test link
+%button#test-button.btn.disabled Test Button