Merge branch '19820-safer-diffs' into 'master'

Collapsed diffs lines/size don't accumulate to overflow diffs.

## What does this MR do?

Reduce the number of lines that we highlight on big diffs to try to reduce the degradation introduced by  !4990 as you can see on the issue description #19820 .

We collapse any files after the diff is over the number of safe files (100), or over the safe lines (500) or over the safe number of bytes (5KB x 100 files).

We still need to bump the gitlab_git and point this branch to the new gitlab_git version.

## What are the relevant issue numbers?

Closes #19820 
Closes #19885

## 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 [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)


See merge request !5306

1 files changed, 42 insertions, 1 deletions

diff --git a/spec/features/expand_collapse_diffs_spec.rb b/spec/features/expand_collapse_diffs_spec.rb
index 78bc888f2a6..688f68d3cff 100644
--- a/spec/features/expand_collapse_diffs_spec.rb
+++ b/spec/features/expand_collapse_diffs_spec.rb
@@ -3,10 +3,11 @@ require 'spec_helper'
 feature 'Expand and collapse diffs', js: true, feature: true do
   include WaitForAjax
 
+  let(:branch) { 'expand-collapse-diffs' }
+
   before do
     login_as :admin
     project = create(:project)
-    branch = 'expand-collapse-diffs'
 
     # Ensure that undiffable.md is in .gitattributes
     project.repository.copy_gitattributes(branch)
@@ -167,6 +168,46 @@ feature 'Expand and collapse diffs', js: true, feature: true do
     end
   end
 
+  context 'visiting a commit without collapsed diffs' do
+    let(:branch) { 'feature' }
+
+    it 'does not show Expand all button' do
+      expect(page).not_to have_link('Expand all')
+    end
+  end
+
+  context 'visiting a commit with more than safe files' do
+    let(:branch) { 'expand-collapse-files' }
+
+    # safe-files -> 100 | safe-lines -> 5000 | commit-files -> 105
+    it 'does collapsing from the safe number of files to the end on small files' do
+      expect(page).to have_link('Expand all')
+
+      expect(page).to have_selector('.diff-content', count: 105)
+      expect(page).to have_selector('.diff-collapsed', count: 5)
+
+      %w(file-95.txt file-96.txt file-97.txt file-98.txt file-99.txt).each do |filename|
+        expect(find("[data-blob-diff-path*='#{filename}']")).to have_selector('.diff-collapsed')
+      end
+    end
+  end
+
+  context 'visiting a commit with more than safe lines' do
+    let(:branch) { 'expand-collapse-lines' }
+
+    # safe-files -> 100 | safe-lines -> 5000 | commit_files -> 8 (each 1250 lines)
+    it 'does collapsing from the safe number of lines to the end' do
+      expect(page).to have_link('Expand all')
+
+      expect(page).to have_selector('.diff-content', count: 6)
+      expect(page).to have_selector('.diff-collapsed', count: 2)
+
+      %w(file-4.txt file-5.txt).each do |filename|
+        expect(find("[data-blob-diff-path*='#{filename}']")).to have_selector('.diff-collapsed')
+      end
+    end
+  end
+
   context 'expanding all diffs' do
     before do
       click_link('Expand all')