Remove unused data from discussions endpoint

We don't need a series of attributes to render diff files on
discussions.json request. Therefore this MR removes lots of unnecessary
attributes from the request, mainly the highlighted diff lines, which
are pretty expensive.

5 files changed, 85 insertions, 43 deletions

diff --git a/spec/javascripts/diffs/mock_data/diff_discussions.js b/spec/javascripts/diffs/mock_data/diff_discussions.js
index 5ffe5a366ba..44313caba29 100644
--- a/spec/javascripts/diffs/mock_data/diff_discussions.js
+++ b/spec/javascripts/diffs/mock_data/diff_discussions.js
@@ -489,8 +489,6 @@ export default {
   diff_discussion: true,
   truncated_diff_lines:
     '<tr class="line_holder new" id="">\n<td class="diff-line-num new old_line" data-linenumber="1">\n \n</td>\n<td class="diff-line-num new new_line" data-linenumber="1">\n1\n</td>\n<td class="line_content new noteable_line"><span id="LC1" class="line" lang="plaintext">  - Bad dates</span>\n</td>\n</tr>\n<tr class="line_holder new" id="">\n<td class="diff-line-num new old_line" data-linenumber="1">\n \n</td>\n<td class="diff-line-num new new_line" data-linenumber="2">\n2\n</td>\n<td class="line_content new noteable_line"><span id="LC2" class="line" lang="plaintext"></span>\n</td>\n</tr>\n',
-  image_diff_html:
-    '<div class="image js-replaced-image" data="">\n<div class="two-up view">\n<div class="wrap">\n<div class="frame deleted">\n<img alt="CHANGELOG" src="http://localhost:3000/gitlab-org/gitlab-test/raw/e63f41fe459e62e1228fcef60d7189127aeba95a/CHANGELOG" />\n</div>\n<p class="image-info hide">\n<span class="meta-filesize">22.3 KB</span>\n|\n<strong>W:</strong>\n<span class="meta-width"></span>\n|\n<strong>H:</strong>\n<span class="meta-height"></span>\n</p>\n</div>\n<div class="wrap">\n<div class="added frame js-image-frame" data-note-type="DiffNote" data-position="{&quot;base_sha&quot;:&quot;e63f41fe459e62e1228fcef60d7189127aeba95a&quot;,&quot;start_sha&quot;:&quot;d9eaefe5a676b820c57ff18cf5b68316025f7962&quot;,&quot;head_sha&quot;:&quot;c48ee0d1bf3b30453f5b32250ce03134beaa6d13&quot;,&quot;old_path&quot;:&quot;CHANGELOG&quot;,&quot;new_path&quot;:&quot;CHANGELOG&quot;,&quot;position_type&quot;:&quot;text&quot;,&quot;old_line&quot;:null,&quot;new_line&quot;:2}">\n<img alt="CHANGELOG" draggable="false" src="http://localhost:3000/gitlab-org/gitlab-test/raw/c48ee0d1bf3b30453f5b32250ce03134beaa6d13/CHANGELOG" />\n</div>\n\n<p class="image-info hide">\n<span class="meta-filesize">22.3 KB</span>\n|\n<strong>W:</strong>\n<span class="meta-width"></span>\n|\n<strong>H:</strong>\n<span class="meta-height"></span>\n</p>\n</div>\n</div>\n<div class="swipe view hide">\n<div class="swipe-frame">\n<div class="frame deleted">\n<img alt="CHANGELOG" src="http://localhost:3000/gitlab-org/gitlab-test/raw/e63f41fe459e62e1228fcef60d7189127aeba95a/CHANGELOG" />\n</div>\n<div class="swipe-wrap">\n<div class="added frame js-image-frame" data-note-type="DiffNote" data-position="{&quot;base_sha&quot;:&quot;e63f41fe459e62e1228fcef60d7189127aeba95a&quot;,&quot;start_sha&quot;:&quot;d9eaefe5a676b820c57ff18cf5b68316025f7962&quot;,&quot;head_sha&quot;:&quot;c48ee0d1bf3b30453f5b32250ce03134beaa6d13&quot;,&quot;old_path&quot;:&quot;CHANGELOG&quot;,&quot;new_path&quot;:&quot;CHANGELOG&quot;,&quot;position_type&quot;:&quot;text&quot;,&quot;old_line&quot;:null,&quot;new_line&quot;:2}">\n<img alt="CHANGELOG" draggable="false" src="http://localhost:3000/gitlab-org/gitlab-test/raw/c48ee0d1bf3b30453f5b32250ce03134beaa6d13/CHANGELOG" />\n</div>\n\n</div>\n<span class="swipe-bar">\n<span class="top-handle"></span>\n<span class="bottom-handle"></span>\n</span>\n</div>\n</div>\n<div class="onion-skin view hide">\n<div class="onion-skin-frame">\n<div class="frame deleted">\n<img alt="CHANGELOG" src="http://localhost:3000/gitlab-org/gitlab-test/raw/e63f41fe459e62e1228fcef60d7189127aeba95a/CHANGELOG" />\n</div>\n<div class="added frame js-image-frame" data-note-type="DiffNote" data-position="{&quot;base_sha&quot;:&quot;e63f41fe459e62e1228fcef60d7189127aeba95a&quot;,&quot;start_sha&quot;:&quot;d9eaefe5a676b820c57ff18cf5b68316025f7962&quot;,&quot;head_sha&quot;:&quot;c48ee0d1bf3b30453f5b32250ce03134beaa6d13&quot;,&quot;old_path&quot;:&quot;CHANGELOG&quot;,&quot;new_path&quot;:&quot;CHANGELOG&quot;,&quot;position_type&quot;:&quot;text&quot;,&quot;old_line&quot;:null,&quot;new_line&quot;:2}">\n<img alt="CHANGELOG" draggable="false" src="http://localhost:3000/gitlab-org/gitlab-test/raw/c48ee0d1bf3b30453f5b32250ce03134beaa6d13/CHANGELOG" />\n</div>\n\n<div class="controls">\n<div class="transparent"></div>\n<div class="drag-track">\n<div class="dragger" style="left: 0px;"></div>\n</div>\n<div class="opaque"></div>\n</div>\n</div>\n</div>\n</div>\n<div class="view-modes hide">\n<ul class="view-modes-menu">\n<li class="two-up" data-mode="two-up">2-up</li>\n<li class="swipe" data-mode="swipe">Swipe</li>\n<li class="onion-skin" data-mode="onion-skin">Onion skin</li>\n</ul>\n</div>\n',
 };
 
 export const imageDiffDiscussions = [
diff --git a/spec/serializers/diff_file_entity_spec.rb b/spec/serializers/diff_file_entity_spec.rb
index 7497b8f27bd..073c13c2cbb 100644
--- a/spec/serializers/diff_file_entity_spec.rb
+++ b/spec/serializers/diff_file_entity_spec.rb
@@ -13,39 +13,6 @@ describe DiffFileEntity do
 
   subject { entity.as_json }
 
-  shared_examples 'diff file entity' do
-    it 'exposes correct attributes' do
-      expect(subject).to include(
-        :submodule, :submodule_link, :submodule_tree_url, :file_path,
-        :deleted_file, :old_path, :new_path, :mode_changed,
-        :a_mode, :b_mode, :text, :old_path_html,
-        :new_path_html, :highlighted_diff_lines, :parallel_diff_lines,
-        :blob, :file_hash, :added_lines, :removed_lines, :diff_refs, :content_sha,
-        :stored_externally, :external_storage, :too_large, :collapsed, :new_file,
-        :context_lines_path
-      )
-    end
-
-    it 'includes viewer' do
-      expect(subject[:viewer].with_indifferent_access)
-          .to match_schema('entities/diff_viewer')
-    end
-
-    # Converted diff files from GitHub import does not contain blob file
-    # and content sha.
-    context 'when diff file does not have a blob and content sha' do
-      it 'exposes some attributes as nil' do
-        allow(diff_file).to receive(:content_sha).and_return(nil)
-        allow(diff_file).to receive(:blob).and_return(nil)
-
-        expect(subject[:context_lines_path]).to be_nil
-        expect(subject[:view_path]).to be_nil
-        expect(subject[:highlighted_diff_lines]).to be_nil
-        expect(subject[:can_modify_blob]).to be_nil
-      end
-    end
-  end
-
   context 'when there is no merge request' do
     it_behaves_like 'diff file entity'
   end
diff --git a/spec/serializers/discussion_diff_file_entity_spec.rb b/spec/serializers/discussion_diff_file_entity_spec.rb
new file mode 100644
index 00000000000..101ac918a98
--- /dev/null
+++ b/spec/serializers/discussion_diff_file_entity_spec.rb
@@ -0,0 +1,39 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe DiscussionDiffFileEntity do
+  include RepoHelpers
+
+  let(:project) { create(:project, :repository) }
+  let(:repository) { project.repository }
+  let(:commit) { project.commit(sample_commit.id) }
+  let(:diff_refs) { commit.diff_refs }
+  let(:diff) { commit.raw_diffs.first }
+  let(:diff_file) { Gitlab::Diff::File.new(diff, diff_refs: diff_refs, repository: repository) }
+  let(:entity) { described_class.new(diff_file, request: {}) }
+
+  subject { entity.as_json }
+
+  context 'when there is no merge request' do
+    it_behaves_like 'diff file discussion entity'
+  end
+
+  context 'when there is a merge request' do
+    let(:user) { create(:user) }
+    let(:request) { EntityRequest.new(project: project, current_user: user) }
+    let(:merge_request) { create(:merge_request, source_project: project, target_project: project) }
+    let(:entity) { described_class.new(diff_file, request: request, merge_request: merge_request) }
+
+    it_behaves_like 'diff file discussion entity'
+
+    it 'exposes additional attributes' do
+      expect(subject).to include(:edit_path)
+    end
+
+    it 'exposes no diff lines' do
+      expect(subject).not_to include(:highlighted_diff_lines,
+                                     :parallel_diff_lines)
+    end
+  end
+end
diff --git a/spec/serializers/discussion_entity_spec.rb b/spec/serializers/discussion_entity_spec.rb
index 0590304e832..138749b0fdf 100644
--- a/spec/serializers/discussion_entity_spec.rb
+++ b/spec/serializers/discussion_entity_spec.rb
@@ -74,13 +74,5 @@ describe DiscussionEntity do
         :active
       )
     end
-
-    context 'when diff file is a image' do
-      it 'exposes image attributes' do
-        allow(discussion).to receive(:on_image?).and_return(true)
-
-        expect(subject.keys).to include(:image_diff_html)
-      end
-    end
   end
 end
diff --git a/spec/support/shared_examples/serializers/diff_file_entity_examples.rb b/spec/support/shared_examples/serializers/diff_file_entity_examples.rb
new file mode 100644
index 00000000000..b8065886c42
--- /dev/null
+++ b/spec/support/shared_examples/serializers/diff_file_entity_examples.rb
@@ -0,0 +1,46 @@
+# frozen_string_literal: true
+
+shared_examples 'diff file base entity' do
+  it 'exposes essential attributes' do
+    expect(subject).to include(:content_sha, :submodule, :submodule_link,
+                               :submodule_tree_url, :old_path_html,
+                               :new_path_html, :blob, :can_modify_blob,
+                               :file_hash, :file_path, :old_path, :new_path,
+                               :collapsed, :text, :diff_refs, :stored_externally,
+                               :external_storage, :renamed_file, :deleted_file,
+                               :mode_changed, :a_mode, :b_mode, :new_file)
+  end
+
+  # Converted diff files from GitHub import does not contain blob file
+  # and content sha.
+  context 'when diff file does not have a blob and content sha' do
+    it 'exposes some attributes as nil' do
+      allow(diff_file).to receive(:content_sha).and_return(nil)
+      allow(diff_file).to receive(:blob).and_return(nil)
+
+      expect(subject[:context_lines_path]).to be_nil
+      expect(subject[:view_path]).to be_nil
+      expect(subject[:highlighted_diff_lines]).to be_nil
+      expect(subject[:can_modify_blob]).to be_nil
+    end
+  end
+end
+
+shared_examples 'diff file entity' do
+  it_behaves_like 'diff file base entity'
+
+  it 'exposes correct attributes' do
+    expect(subject).to include(:too_large, :added_lines, :removed_lines,
+                               :context_lines_path, :highlighted_diff_lines,
+                               :parallel_diff_lines)
+  end
+
+  it 'includes viewer' do
+    expect(subject[:viewer].with_indifferent_access)
+        .to match_schema('entities/diff_viewer')
+  end
+end
+
+shared_examples 'diff file discussion entity' do
+  it_behaves_like 'diff file base entity'
+end