Respond 404 when repo does not exist

changelogs/unreleased/mk-fix-error-code-for-repo-does-not-exist.yml

+---
+title: Return a 404 instead of 403 if the repository does not exist on disk
+merge_request: 17341
+author:
+type: fixed

lib/gitlab/git_access.rb

@@ -199,7 +199,7 @@ module Gitlab
     def check_repository_existence!
       unless repository.exists?
-        raise UnauthorizedError, ERROR_MESSAGES[:no_repo]
+        raise NotFoundError, ERROR_MESSAGES[:no_repo]
       end
     end

spec/lib/gitlab/git_access_spec.rb

@@ -534,6 +534,19 @@ describe Gitlab::GitAccess do
       expect { pull_access_check }.to raise_unauthorized('Your account has been blocked.')
     end
+    context 'when the project repository does not exist' do
+      it 'returns not found' do
+        project.add_guest(user)
+        repo = project.repository
+        FileUtils.rm_rf(repo.path)
+
+        # Sanity check for rm_rf
+        expect(repo.exists?).to eq(false)
+
+        expect { pull_access_check }.to raise_error(Gitlab::GitAccess::NotFoundError, 'A repository for this project does not exist yet.')
+      end
+    end
+
     describe 'without access to project' do
       context 'pull code' do
         it { expect { pull_access_check }.to raise_not_found }

spec/lib/gitlab/git_access_wiki_spec.rb

@@ -57,7 +57,7 @@ describe Gitlab::GitAccessWiki do
           # Sanity check for rm_rf
           expect(wiki_repo.exists?).to eq(false)
-          expect { subject }.to raise_error(Gitlab::GitAccess::UnauthorizedError, 'A repository for this project does not exist yet.')
+          expect { subject }.to raise_error(Gitlab::GitAccess::NotFoundError, 'A repository for this project does not exist yet.')
         end
       end
     end

spec/requests/git_http_spec.rb

@@ -597,7 +597,7 @@ describe 'Git HTTP requests' do
         context "when a gitlab ci token is provided" do
           let(:project) { create(:project, :repository) }
           let(:build) { create(:ci_build, :running) }
-          let(:other_project) { create(:project) }
+          let(:other_project) { create(:project, :repository) }
           before do
             build.update!(project: project) # can't associate it on factory create
@@ -648,10 +648,10 @@ describe 'Git HTTP requests' do
               context 'when the repo does not exist' do
                 let(:project) { create(:project) }
-                it 'rejects pulls with 403 Forbidden' do
+                it 'rejects pulls with 404 Not Found' do
                   clone_get path, env
-                  expect(response).to have_gitlab_http_status(:forbidden)
+                  expect(response).to have_gitlab_http_status(:not_found)
                   expect(response.body).to eq(git_access_error(:no_repo))
                 end
               end