Merge branch 'append-issue-template' into 'master'

Append issue template to existing description

## What does this MR do?

When selecting an issue template after entering a description, append the template and leave the original content intact.

## Are there points in the code the reviewer needs to double check?

Not that I'm aware of.

## Why was this MR needed?

The issue template shouldn't override the issue content without warning.

## Screenshots

![](https://i.imgur.com/E16X2tc.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
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [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`
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/21733

See merge request !6149

4 files changed, 47 insertions, 16 deletions

diff --git a/CHANGELOG b/CHANGELOG
index 395ee8d3980..1b8854930b7 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -27,6 +27,7 @@ v 8.13.0 (unreleased)
   - Only update issuable labels if they have been changed
   - Take filters in account in issuable counters. !6496
   - Use custom Ruby images to test builds (registry.dev.gitlab.org/gitlab/gitlab-build-images:*)
+  - Append issue template to existing description !6149 (Joseph Frazier)
   - Revoke button in Applications Settings underlines on hover.
   - Add missing values to linter !6276 (Katarzyna Kobierska Ula Budziszewska)
   - Fix Long commit messages overflow viewport in file tree
diff --git a/app/assets/javascripts/blob/template_selector.js b/app/assets/javascripts/blob/template_selector.js
index 95352164d76..6d41442cdfc 100644
--- a/app/assets/javascripts/blob/template_selector.js
+++ b/app/assets/javascripts/blob/template_selector.js
@@ -72,9 +72,17 @@
     // To be implemented on the extending class
     // e.g.
     // Api.gitignoreText item.name, @requestFileSuccess.bind(@)
-    TemplateSelector.prototype.requestFileSuccess = function(file, skipFocus) {
-      this.editor.setValue(file.content, 1);
-      if (!skipFocus) this.editor.focus();
+    TemplateSelector.prototype.requestFileSuccess = function(file, opts) {
+      var oldValue = this.editor.getValue();
+      var newValue = file.content;
+      if (opts == null) {
+        opts = {};
+      }
+      if (opts.append && oldValue.length && oldValue !== newValue) {
+        newValue = oldValue + '\n\n' + newValue;
+      }
+      this.editor.setValue(newValue, 1);
+      if (!opts.skipFocus) this.editor.focus();
 
       if (this.editor instanceof jQuery) {
         this.editor.get(0).dispatchEvent(this.autosizeUpdateEvent);
diff --git a/app/assets/javascripts/templates/issuable_template_selector.js.es6 b/app/assets/javascripts/templates/issuable_template_selector.js.es6
index c32ddf80219..017008c8438 100644
--- a/app/assets/javascripts/templates/issuable_template_selector.js.es6
+++ b/app/assets/javascripts/templates/issuable_template_selector.js.es6
@@ -16,7 +16,7 @@
       if (initialQuery.name) this.requestFile(initialQuery);
 
       $('.reset-template', this.dropdown.parent()).on('click', () => {
-        if (this.currentTemplate) this.setInputValueToTemplateContent();
+        if (this.currentTemplate) this.setInputValueToTemplateContent(false);
       });
     }
 
@@ -26,22 +26,24 @@
         this.currentTemplate = currentTemplate;
         if (err) return; // Error handled by global AJAX error handler
         this.stopLoadingSpinner();
-        this.setInputValueToTemplateContent();
+        this.setInputValueToTemplateContent(true);
       });
       return;
     }
 
-    setInputValueToTemplateContent() {
+    setInputValueToTemplateContent(append) {
       // `this.requestFileSuccess` sets the value of the description input field
-      // to the content of the template selected.
+      // to the content of the template selected. If `append` is true, the
+      // template content will be appended to the previous value of the field,
+      // separated by a blank line if the previous value is non-empty.
       if (this.titleInput.val() === '') {
         // If the title has not yet been set, focus the title input and
-        // skip focusing the description input by setting `true` as the 2nd
-        // argument to `requestFileSuccess`.
-        this.requestFileSuccess(this.currentTemplate, true);
+        // skip focusing the description input by setting `true` as the
+        // `skipFocus` option to `requestFileSuccess`.
+        this.requestFileSuccess(this.currentTemplate, {skipFocus: true, append});
         this.titleInput.focus();
       } else {
-        this.requestFileSuccess(this.currentTemplate);
+        this.requestFileSuccess(this.currentTemplate, {skipFocus: false, append});
       }
       return;
     }
diff --git a/spec/features/projects/issuable_templates_spec.rb b/spec/features/projects/issuable_templates_spec.rb
index f76c4fe8b57..cd79c4f512d 100644
--- a/spec/features/projects/issuable_templates_spec.rb
+++ b/spec/features/projects/issuable_templates_spec.rb
@@ -26,7 +26,7 @@ feature 'issuable templates', feature: true, js: true do
     scenario 'user selects "bug" template' do
       select_template 'bug'
       wait_for_ajax
-      preview_template
+      preview_template(template_content)
       save_changes
     end
 
@@ -42,6 +42,26 @@ feature 'issuable templates', feature: true, js: true do
     end
   end
 
+  context 'user creates an issue using templates, with a prior description' do
+    let(:prior_description) { 'test issue description' }
+    let(:template_content) { 'this is a test "bug" template' }
+    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)
+      visit edit_namespace_project_issue_path project.namespace, project, issue
+      fill_in :'issue[title]', with: 'test issue title'
+      fill_in :'issue[description]', with: prior_description
+    end
+
+    scenario 'user selects "bug" template' do
+      select_template 'bug'
+      wait_for_ajax
+      preview_template("#{prior_description}\n\n#{template_content}")
+      save_changes
+    end
+  end
+
   context 'user creates a merge request using templates' do
     let(:template_content) { 'this is a test "feature-proposal" template' }
     let(:merge_request) { create(:merge_request, :with_diffs, source_project: project) }
@@ -55,7 +75,7 @@ feature 'issuable templates', feature: true, js: true do
     scenario 'user selects "feature-proposal" template' do
       select_template 'feature-proposal'
       wait_for_ajax
-      preview_template
+      preview_template(template_content)
       save_changes
     end
   end
@@ -82,16 +102,16 @@ feature 'issuable templates', feature: true, js: true do
         scenario 'user selects template' do
           select_template 'feature-proposal'
           wait_for_ajax
-          preview_template
+          preview_template(template_content)
           save_changes
         end
       end
     end
   end
 
-  def preview_template
+  def preview_template(expected_content)
     click_link 'Preview'
-    expect(page).to have_content template_content
+    expect(page).to have_content expected_content
   end
 
   def save_changes