add link_to_if helper on target_branch link on Merge Request show page for case of deleted target branch

add spec on #24507 bug description

add changelog entry

fix changelog

remove unnecessary js:true from specs

change spec title

add test for link to target branch before deletions

renamed spec about state of target branch link before and after deletion

some fixes into spec

3 files changed, 46 insertions, 1 deletions

diff --git a/app/views/projects/merge_requests/_show.html.haml b/app/views/projects/merge_requests/_show.html.haml
index 0e2975bd551..896f10104fa 100644
--- a/app/views/projects/merge_requests/_show.html.haml
+++ b/app/views/projects/merge_requests/_show.html.haml
@@ -31,7 +31,7 @@
         %span.label-branch= source_branch_with_namespace(@merge_request)
         %span into
         %span.label-branch
-          = link_to @merge_request.target_branch, namespace_project_commits_path(@project.namespace, @project, @merge_request.target_branch)
+          = link_to_if @merge_request.target_branch_exists?, @merge_request.target_branch, namespace_project_commits_path(@project.namespace, @project, @merge_request.target_branch)
         - if @merge_request.open? && @merge_request.diverged_from_target_branch?
           %span (#{pluralize(@merge_request.diverged_commits_count, 'commit')} behind)
 
diff --git a/changelogs/unreleased/24507_remove_deleted_branch_link_in_merge_request.yml b/changelogs/unreleased/24507_remove_deleted_branch_link_in_merge_request.yml
new file mode 100644
index 00000000000..34999480d4a
--- /dev/null
+++ b/changelogs/unreleased/24507_remove_deleted_branch_link_in_merge_request.yml
@@ -0,0 +1,4 @@
+---
+title: 'Remove unnecessary target branch link from MR page in case of deleted target branch'
+merge_request: 7916
+author: Rydkin Maxim
diff --git a/spec/features/merge_requests/target_branch_spec.rb b/spec/features/merge_requests/target_branch_spec.rb
new file mode 100644
index 00000000000..b6134540273
--- /dev/null
+++ b/spec/features/merge_requests/target_branch_spec.rb
@@ -0,0 +1,41 @@
+require 'spec_helper'
+
+describe 'Target branch', feature: true do
+  let(:user) { create(:user) }
+  let(:merge_request) { create(:merge_request) }
+  let(:project) { merge_request.project }
+
+  def path_to_merge_request
+    namespace_project_merge_request_path(
+      project.namespace,
+      project, merge_request
+    )
+  end
+
+  before do
+    login_as user
+    project.team << [user, :master]
+  end
+
+  it 'shows link to target branch' do
+    visit path_to_merge_request
+    expect(page).to have_link('feature', href: namespace_project_commits_path(project.namespace, project, merge_request.target_branch))
+  end
+
+  context 'when branch was deleted' do
+    before do
+      DeleteBranchService.new(project, user).execute('feature')
+      visit path_to_merge_request
+    end
+
+    it 'shows a message about missing target branch' do
+      expect(page).to have_content(
+        'Target branch feature does not exist'
+      )
+    end
+
+    it 'does not show link to target branch' do
+      expect(page).not_to have_link('feature')
+    end
+  end
+end