Fix diff commenting results just after changing view35695-comment-appears-in-a-wrong-place-after-changing-diff-view-to-inline

When you change the diff view (inline / side-by-side), we set a cookie based on
that new view. When you add a comment, we choose the style to use in the
response based on that cookie.

However, when you have just changed diff style, the request cookie will contain
the old value, so we should use the view param instead.

3 files changed, 20 insertions, 3 deletions

diff --git a/app/helpers/diff_helper.rb b/app/helpers/diff_helper.rb
index 926502bf239..91ddd73fac1 100644
--- a/app/helpers/diff_helper.rb
+++ b/app/helpers/diff_helper.rb
@@ -15,7 +15,7 @@ module DiffHelper
   def diff_view
     @diff_view ||= begin
       diff_views = %w(inline parallel)
-      diff_view = cookies[:diff_view]
+      diff_view = params[:view] || cookies[:diff_view]
       diff_view = diff_views.first unless diff_views.include?(diff_view)
       diff_view.to_sym
     end
diff --git a/changelogs/unreleased/35695-comment-appears-in-a-wrong-place-after-changing-diff-view-to-inline.yml b/changelogs/unreleased/35695-comment-appears-in-a-wrong-place-after-changing-diff-view-to-inline.yml
new file mode 100644
index 00000000000..1c9ad20bc95
--- /dev/null
+++ b/changelogs/unreleased/35695-comment-appears-in-a-wrong-place-after-changing-diff-view-to-inline.yml
@@ -0,0 +1,4 @@
+---
+title: Fix display of new diff comments after changing b between diff views
+merge_request:
+author:
diff --git a/spec/helpers/diff_helper_spec.rb b/spec/helpers/diff_helper_spec.rb
index 0d909e6e140..060c112e20d 100644
--- a/spec/helpers/diff_helper_spec.rb
+++ b/spec/helpers/diff_helper_spec.rb
@@ -12,19 +12,32 @@ describe DiffHelper do
   let(:diff_file) { Gitlab::Diff::File.new(diff, diff_refs: diff_refs, repository: repository) }
 
   describe 'diff_view' do
+    it 'uses the view param over the cookie' do
+      controller.params[:view] = 'parallel'
+      helper.request.cookies[:diff_view] = 'inline'
+
+      expect(helper.diff_view).to eq :parallel
+    end
+
+    it 'returns the default value when the view param is invalid' do
+      controller.params[:view] = 'invalid'
+
+      expect(helper.diff_view).to eq :inline
+    end
+
     it 'returns a valid value when cookie is set' do
       helper.request.cookies[:diff_view] = 'parallel'
 
       expect(helper.diff_view).to eq :parallel
     end
 
-    it 'returns a default value when cookie is invalid' do
+    it 'returns the default value when cookie is invalid' do
       helper.request.cookies[:diff_view] = 'invalid'
 
       expect(helper.diff_view).to eq :inline
     end
 
-    it 'returns a default value when cookie is nil' do
+    it 'returns the default value when cookie is nil' do
       expect(helper.request.cookies).to be_empty
 
       expect(helper.diff_view).to eq :inline