Expose web_url to Compare API endpoint

Changelog: added

doc/api/repositories.md

@@ -200,7 +200,8 @@ Example response:
     "deleted_file": false
   }],
   "compare_timeout": false,
-  "compare_same_ref": false
+  "compare_same_ref": false,
+  "web_url": "https://gitlab.example.com/thedude/gitlab-foss/-/compare/ae73cb07c9eeaf35924a10f713b364d32b2dd34f...0b4bc9a49b562e85de7cc9e834518ea6828729b9"
 }
 ```
 

lib/api/entities/compare.rb

@@ -20,6 +20,10 @@ module API
       end
 
       expose :same, as: :compare_same_ref
+
+      expose :web_url do |compare, _|
+        Gitlab::UrlBuilder.build(compare)
+      end
     end
   end
 end

spec/requests/api/repositories_spec.rb

@@ -354,6 +354,7 @@ RSpec.describe API::Repositories do
         expect(response).to have_gitlab_http_status(:ok)
         expect(json_response['commits']).to be_present
         expect(json_response['diffs']).to be_present
+        expect(json_response['web_url']).to be_present
       end
 
       it "compares branches with explicit merge-base mode" do
@@ -365,6 +366,7 @@ RSpec.describe API::Repositories do
         expect(response).to have_gitlab_http_status(:ok)
         expect(json_response['commits']).to be_present
         expect(json_response['diffs']).to be_present
+        expect(json_response['web_url']).to be_present
       end
 
       it "compares branches with explicit straight mode" do
@@ -376,6 +378,7 @@ RSpec.describe API::Repositories do
         expect(response).to have_gitlab_http_status(:ok)
         expect(json_response['commits']).to be_present
         expect(json_response['diffs']).to be_present
+        expect(json_response['web_url']).to be_present
       end
 
       it "compares tags" do
@@ -384,6 +387,7 @@ RSpec.describe API::Repositories do
         expect(response).to have_gitlab_http_status(:ok)
         expect(json_response['commits']).to be_present
         expect(json_response['diffs']).to be_present
+        expect(json_response['web_url']).to be_present
       end
 
       it "compares commits" do
@@ -393,6 +397,7 @@ RSpec.describe API::Repositories do
         expect(json_response['commits']).to be_empty
         expect(json_response['diffs']).to be_empty
         expect(json_response['compare_same_ref']).to be_falsey
+        expect(json_response['web_url']).to be_present
       end
 
       it "compares commits in reverse order" do
@@ -401,6 +406,7 @@ RSpec.describe API::Repositories do
         expect(response).to have_gitlab_http_status(:ok)
         expect(json_response['commits']).to be_present
         expect(json_response['diffs']).to be_present
+        expect(json_response['web_url']).to be_present
       end
 
       it "compare commits between different projects with non-forked relation" do