Merge branch 'issue-description-scroll-fix' into 'master'

Trigger autosize update after template selection

## What does this MR do?

Triggers an autosize update after selecting an issue template.

The autosize plugin doesn't react to value changes and therefore doesn't automatically update when the user selects the template. This merge request adds it so that it detects if the editor the template selector is a jQuery object (not Ace editor) & then triggers the autosize event to allow the user to scroll the textarea.

## Screenshots (if relevant)

![resize](/uploads/1ab04b4202309b13f1178e04c0953112/resize.gif)

## What are the relevant issue numbers?

Closes #21982

See merge request !6282

CHANGELOG

@@ -37,6 +37,7 @@ v 8.12.0 (unreleased)
   - Request only the LDAP attributes we need !6187
   - Center build stage columns in pipeline overview (ClemMakesApps)
   - Rename behaviour to behavior in bug issue template for consistency (ClemMakesApps)
+  - Fix bug stopping issue description being scrollable after selecting issue template
   - Remove suggested colors hover underline (ClemMakesApps)
   - Shorten task status phrase (ClemMakesApps)
   - Fix project visibility level fields on settings

app/assets/javascripts/blob/template_selector.js

@@ -13,6 +13,9 @@
       this.buildDropdown();
       this.bindEvents();
       this.onFilenameUpdate();
+
+      this.autosizeUpdateEvent = document.createEvent('Event');
+      this.autosizeUpdateEvent.initEvent('autosize:update', true, false);
     }
 
     TemplateSelector.prototype.buildDropdown = function() {
@@ -72,6 +75,10 @@
     TemplateSelector.prototype.requestFileSuccess = function(file, skipFocus) {
       this.editor.setValue(file.content, 1);
       if (!skipFocus) this.editor.focus();
+
+      if (this.editor instanceof jQuery) {
+        this.editor.get(0).dispatchEvent(this.autosizeUpdateEvent);
+      }
     };
 
     TemplateSelector.prototype.startLoadingSpinner = function() {

spec/features/projects/issuable_templates_spec.rb

@@ -13,10 +13,12 @@ feature 'issuable templates', feature: true, js: true do
 
   context 'user creates an issue using templates' do
     let(:template_content) { 'this is a test "bug" template' }
+    let(:longtemplate_content) { %Q(this\n\n\n\n\nis\n\n\n\n\na\n\n\n\n\nbug\n\n\n\n\ntemplate) }
     let(:issue) { create(:issue, author: user, assignee: user, project: project) }
 
     background do
       project.repository.commit_file(user, '.gitlab/issue_templates/bug.md', template_content, 'added issue template', 'master', false)
+      project.repository.commit_file(user, '.gitlab/issue_templates/test.md', longtemplate_content, 'added issue template', 'master', false)
       visit edit_namespace_project_issue_path project.namespace, project, issue
       fill_in :'issue[title]', with: 'test issue title'
     end
@@ -27,6 +29,17 @@ feature 'issuable templates', feature: true, js: true do
       preview_template
       save_changes
     end
+
+    it 'updates height of markdown textarea' do
+      start_height = page.evaluate_script('$(".markdown-area").outerHeight()')
+
+      select_template 'test'
+      wait_for_ajax
+
+      end_height = page.evaluate_script('$(".markdown-area").outerHeight()')
+      
+      expect(end_height).not_to eq(start_height)
+    end
   end
 
   context 'user creates a merge request using templates' do