Fix Gitaly N+1 calls with listing issues/MRs via API

In GitLab 9.0,
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/9661 removed the
`subscribed` flag from the API when the user requested a list of issues
or merge requests since calculating this value triggers extensive
Markdown processing.

In GitLab 12.0 via a4fbf39e, we accidentally reintroduced this
performance regression by changing `IssueBasic` to `Issue` in
`entities.rb`. This showed up as a Gitaly N+1 issue since the Markdown
processing would attempt to extract a commit if it detected a regex that
matched a commit.

We restore the prior behavior by once again removing the `subscribed`
flag for the bulk list of issues and merge requests and add a test to
ensure they aren't reintroduced.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/66202

3 files changed, 13 insertions, 0 deletions

diff --git a/spec/requests/api/issues/get_group_issues_spec.rb b/spec/requests/api/issues/get_group_issues_spec.rb
index 5916bb11516..c487471e4a1 100644
--- a/spec/requests/api/issues/get_group_issues_spec.rb
+++ b/spec/requests/api/issues/get_group_issues_spec.rb
@@ -342,6 +342,14 @@ describe API::Issues do
         group_project.add_reporter(user)
       end
 
+      it 'exposes known attributes' do
+        get api(base_url, admin)
+
+        expect(response).to have_gitlab_http_status(200)
+        expect(json_response.last.keys).to include(*%w(id iid project_id title description))
+        expect(json_response.last).not_to have_key('subscribed')
+      end
+
       it 'returns all group issues (including opened and closed)' do
         get api(base_url, admin)
 
diff --git a/spec/requests/api/issues/get_project_issues_spec.rb b/spec/requests/api/issues/get_project_issues_spec.rb
index f7ca6fd1e0a..521d6b88734 100644
--- a/spec/requests/api/issues/get_project_issues_spec.rb
+++ b/spec/requests/api/issues/get_project_issues_spec.rb
@@ -575,6 +575,7 @@ describe API::Issues do
       expect(json_response['assignee']).to be_a Hash
       expect(json_response['author']).to be_a Hash
       expect(json_response['confidential']).to be_falsy
+      expect(json_response['subscribed']).to be_truthy
     end
 
     it 'exposes the closed_at attribute' do
diff --git a/spec/requests/api/issues/issues_spec.rb b/spec/requests/api/issues/issues_spec.rb
index d195f54be11..27cf66629fe 100644
--- a/spec/requests/api/issues/issues_spec.rb
+++ b/spec/requests/api/issues/issues_spec.rb
@@ -216,6 +216,10 @@ describe API::Issues do
         expect_paginated_array_response([issue.id, closed_issue.id])
         expect(json_response.first['title']).to eq(issue.title)
         expect(json_response.last).to have_key('web_url')
+        # Calculating the value of subscribed field triggers Markdown
+        # processing. We can't do that for multiple issues / merge
+        # requests in a single API request.
+        expect(json_response.last).not_to have_key('subscribed')
       end
 
       it 'returns an array of closed issues' do