Show 'too many changes' message for merge request

app/helpers/diff_helper.rb

@@ -165,4 +165,10 @@ module DiffHelper
     link_to "#{hide_whitespace? ? 'Show' : 'Hide'} whitespace changes", url, class: options[:class]
   end
+
+  def render_overflow_warning?(diff_files)
+    diffs = @merge_request_diff.presence || diff_files
+
+    diffs.overflow?
+  end
 end

app/models/merge_request_diff.rb

@@ -234,28 +234,28 @@ class MergeRequestDiff < ActiveRecord::Base
   # and save it as array of hashes in st_diffs db field
   def save_diffs
     new_attributes = {}
-    new_diffs = []
     if commits.size.zero?
       new_attributes[:state] = :empty
     else
       diff_collection = compare.diffs(Commit.max_diff_options)
-
-      if diff_collection.overflow?
-        # Set our state to 'overflow' to make the #empty? and #collected?
-        # methods (generated by StateMachine) return false.
-        new_attributes[:state] = :overflow
-      end
-
-      new_attributes[:real_size] = diff_collection.real_size
+      new_attributes[:real_size] = compare.diffs.real_size
       if diff_collection.any?
         new_diffs = dump_diffs(diff_collection)
         new_attributes[:state] = :collected
       end
+
+      new_attributes[:st_diffs] = new_diffs || []
+
+      # Set our state to 'overflow' to make the #empty? and #collected?
+      # methods (generated by StateMachine) return false.
+      #
+      # This attribution has to come at the end of the method so 'overflow'
+      # state does not get overridden by 'collected'.
+      new_attributes[:state] = :overflow if diff_collection.overflow?
     end
-    new_attributes[:st_diffs] = new_diffs
     update_columns_serialized(new_attributes)
   end

app/views/devise/shared/_signup_box.html.haml

@@ -15,7 +15,7 @@
       .form-group
         = f.label :email
         = f.email_field :email, class: "form-control middle", required: true, title: "Please provide a valid email address."
-      %div.form-group
+      .form-group
         = f.label :email_confirmation
         = f.email_field :email_confirmation, class: "form-control middle", required: true, title: "Please retype the email address."
       .form-group.append-bottom-20#password-strength

app/views/projects/diffs/_diffs.html.haml

@@ -18,8 +18,8 @@
       = parallel_diff_btn
   = render 'projects/diffs/stats', diff_files: diff_files
-- if diff_files.overflow?
-  = render 'projects/diffs/warning', diff_files: diff_files
+- if render_overflow_warning?(diff_files)
+  = render 'projects/diffs/warning', diff_files: diffs
 .files{ data: { can_create_note: can_create_note } }
   - diff_files.each_with_index do |diff_file|

app/views/projects/merge_requests/show/_diffs.html.haml

-- if @merge_request_diff.collected?
+- if @merge_request_diff.collected? || @merge_request_diff.overflow?
   = render 'projects/merge_requests/show/versions'
   = render "projects/diffs/diffs", diffs: @diffs
 - elsif @merge_request_diff.empty?
   .nothing-here-block Nothing to merge from #{@merge_request.source_branch} into #{@merge_request.target_branch}
-- else
-  .alert.alert-warning
-    %h4
-      Changes view for this comparison is extremely large.
-    %p
-      You can
-      = link_to "download it", merge_request_path(@merge_request, format: :diff), class: "vlink"
-      instead.

changelogs/unreleased/issue_25017.yml

+---
+title: Show 'too many changes' message for created merge requests when they are too large
+merge_request:
+author:

spec/features/merge_requests/diffs_spec.rb

@@ -22,4 +22,18 @@ feature 'Diffs URL', js: true, feature: true do
       expect(page).to have_css('.diffs.tab-pane.active')
     end
   end
+
+  context 'when merge request has overflow' do
+    it 'displays warning' do
+      allow_any_instance_of(MergeRequestDiff).to receive(:overflow?).and_return(true)
+      allow(Commit).to receive(:max_diff_options).and_return(max_files: 20, max_lines: 20)
+
+      visit diffs_namespace_project_merge_request_path(@project.namespace, @project, @merge_request)
+
+      page.within('.alert') do
+        expect(page).to have_text("Too many changes to show. Plain diff Email patch To preserve
+          performance only 3 of 3+ files are displayed.")
+      end
+    end
+  end
 end

spec/models/merge_request_diff_spec.rb

@@ -76,6 +76,32 @@ describe MergeRequestDiff, models: true do
     end
   end
+  describe '#save_diffs' do
+    it 'saves collected state' do
+      mr_diff = create(:merge_request).merge_request_diff
+
+      expect(mr_diff.collected?).to be_truthy
+    end
+
+    it 'saves overflow state' do
+      allow(Commit).to receive(:max_diff_options)
+        .and_return(max_lines: 0, max_files: 0)
+
+      mr_diff = create(:merge_request).merge_request_diff
+
+      expect(mr_diff.overflow?).to be_truthy
+    end
+
+    it 'saves empty state' do
+      allow_any_instance_of(MergeRequestDiff).to receive(:commits)
+        .and_return([])
+
+      mr_diff = create(:merge_request).merge_request_diff
+
+      expect(mr_diff.empty?).to be_truthy
+    end
+  end
+
   describe '#commits_sha' do
     it 'returns all commits SHA using serialized commits' do
       subject.st_commits = [