Merge branch 'fix-gh-rate-limit' into 'master'

Fix GitHub client requests when rate limit is disabled

## What does this MR do?

GitHub Rate Limit API returns 404 when the rate limit is disabled. In this case we just want to return gracefully instead of spitting out an error.

## Are there points in the code the reviewer needs to double check?

No.

## Why was this MR needed?

GitHub importer fails when rate limit is disabled in GitHub Enterprise.

## What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ee/issues/697

## Does this MR meet the acceptance criteria?

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

See merge request !5191

CHANGELOG

@@ -80,6 +80,7 @@ v 8.10.0 (unreleased)
   - Add reminder to not paste private SSH keys !4399 (Ingo Blechschmidt)
   - Remove duplicate `description` field in `MergeRequest` entities (Ben Boeckel)
   - Style of import project buttons were fixed in the new project page. !5183 (rdemirbay)
+  - Fix GitHub client requests when rate limit is disabled
 
 v 8.9.6 (unreleased)
   - Fix importing of events under notes for GitLab projects

lib/gitlab/github_import/client.rb

@@ -78,10 +78,21 @@ module Gitlab
 
       def rate_limit
         api.rate_limit!
+      # GitHub Rate Limit API returns 404 when the rate limit is
+      # disabled. In this case we just want to return gracefully
+      # instead of spitting out an error.
+      rescue Octokit::NotFound
+        nil
+      end
+
+      def has_rate_limit?
+        return @has_rate_limit if defined?(@has_rate_limit)
+
+        @has_rate_limit = rate_limit.present?
       end
 
       def rate_limit_exceed?
-        rate_limit.remaining <= GITHUB_SAFE_REMAINING_REQUESTS
+        has_rate_limit? && rate_limit.remaining <= GITHUB_SAFE_REMAINING_REQUESTS
       end
 
       def rate_limit_sleep_time

spec/lib/gitlab/github_import/client_spec.rb

@@ -61,4 +61,11 @@ describe Gitlab::GithubImport::Client, lib: true do
       expect(client.api.api_endpoint).to eq 'https://github.company.com/'
     end
   end
+
+  it 'does not raise error when rate limit is disabled' do
+    stub_request(:get, /api.github.com/)
+    allow(client.api).to receive(:rate_limit!).and_raise(Octokit::NotFound)
+
+    expect { client.issues }.not_to raise_error
+  end
 end