User not defined in PostReceive#process_project_changes

When Gitlab::GitPostReceive#changes_refs is empty
user would not get defined and nil would be passed
to PostReceive#after_project_changes_hooks which would
then throw an error.

app/workers/post_receive.rb

@@ -29,14 +29,11 @@ class PostReceive
   def process_project_changes(post_received)
     changes = []
     refs = Set.new
+    @user = post_received.identify
 
     post_received.changes_refs do |oldrev, newrev, ref|
       @user ||= post_received.identify(newrev)
-
-      unless @user
-        log("Triggered hook for non-existing user \"#{post_received.identifier}\"")
-        return false # rubocop:disable Cop/AvoidReturnFromBlocks
-      end
+      break unless @user
 
       if Gitlab::Git.tag_ref?(ref)
         GitTagPushService.new(post_received.project, @user, oldrev: oldrev, newrev: newrev, ref: ref).execute
@@ -48,6 +45,11 @@ class PostReceive
       refs << ref
     end
 
+    unless @user
+      log("Triggered hook for non-existing user \"#{post_received.identifier}\"")
+      return false
+    end
+
     after_project_changes_hooks(post_received, @user, refs.to_a, changes)
   end
 

changelogs/unreleased/51335-fail-early-when-user-cannot-be-identified.yml

+---
+title: If user was not found, service hooks won't run on post receive background job
+merge_request: 22519
+author:
+type: fixed

lib/gitlab/git_post_receive.rb

@@ -11,7 +11,7 @@ module Gitlab
       @changes = deserialize_changes(changes)
     end
 
-    def identify(revision)
+    def identify(revision = nil)
       super(identifier, project, revision)
     end
 

spec/workers/post_receive_spec.rb

@@ -6,7 +6,7 @@ describe PostReceive do
   let(:base64_changes) { Base64.encode64(wrongly_encoded_changes) }
   let(:gl_repository) { "project-#{project.id}" }
   let(:key) { create(:key, user: project.owner) }
-  let(:key_id) { key.shell_id }
+  let!(:key_id) { key.shell_id }
 
   let(:project) do
     create(:project, :repository, auto_cancel_pending_pipelines: 'disabled')
@@ -31,6 +31,17 @@ describe PostReceive do
   end
 
   describe "#process_project_changes" do
+    context 'empty changes' do
+      it "does not call any PushService but runs after project hooks" do
+        expect(GitPushService).not_to receive(:new)
+        expect(GitTagPushService).not_to receive(:new)
+        expect_next_instance_of(SystemHooksService) { |service| expect(service).to receive(:execute_hooks) }
+
+        described_class.new.perform(gl_repository, key_id, "")
+      end
+    end
+
+    context 'with changes' do
       before do
         allow_any_instance_of(Gitlab::GitPostReceive).to receive(:identify).and_return(project.owner)
       end
@@ -38,7 +49,7 @@ describe PostReceive do
       context "branches" do
         let(:changes) { "123456 789012 refs/heads/tést" }
 
-      it "calls GitTagPushService" do
+        it "calls GitPushService" do
           expect_any_instance_of(GitPushService).to receive(:execute).and_return(true)
           expect_any_instance_of(GitTagPushService).not_to receive(:execute)
           described_class.new.perform(gl_repository, key_id, base64_changes)
@@ -113,6 +124,7 @@ describe PostReceive do
         end
       end
     end
+  end
 
   describe '#process_wiki_changes' do
     let(:gl_repository) { "wiki-#{project.id}" }