Source code management

Git hosting plus the social layer (commits, branches, tags, merge requests, code review, approvals).

Source

app/models/
├── project.rb
├── repository.rb
├── commit.rb, commits.rb
├── merge_request.rb, merge_requests/
├── branch.rb, ref.rb, ref_matcher.rb
├── protected_branch.rb, protected_tag.rb
├── deploy_key.rb, ssh_key.rb
└── ...
app/services/
├── projects/                     # ~14 service namespaces
├── branches/                     # branch CRUD
├── repositories/                 # archive, language detection
├── merge_requests/               # ~6 namespaces; the largest
├── protected_branches/, protected_tags/, protected_refs/
├── git/                          # git callbacks (post-receive)
├── files/                        # file edits via UI / API
└── commits/, compare_service.rb
app/controllers/projects/
app/controllers/projects/merge_requests/
lib/api/
├── repositories.rb, repository_*.rb
├── branches.rb, tags.rb, commits.rb
├── merge_requests.rb, merge_request_*.rb
└── files.rb
ee/                                # extra MR rules, code owners, etc.

Frontend lives under app/assets/javascripts/{repository,merge_requests,diffs,notes,...}/.

Repository lifecycle

graph LR
    User -->|git push| Shell[GitLab Shell]
    User -->|git push HTTPS| WH[Workhorse]
    Shell -->|gRPC| Gitaly
    WH -->|gRPC| Gitaly
    Gitaly -->|post-receive hook| Internal[Internal API]
    Internal -->|enqueue| PostReceiveWorker
    PostReceiveWorker --> Hooks[Web hooks]
    PostReceiveWorker --> Pipelines[CI pipeline create]
    PostReceiveWorker --> MRs[MR refresh]
    PostReceiveWorker --> Notif[Notifications]

The post-receive flow is in app/services/post_receive_service.rb, with downstream concerns dispatched via the EventStore.

Merge requests

The MR domain is the largest in the codebase:

• Models: app/models/merge_request.rb, merge_requests/, merge_request_diff.rb, merge_request_diff_commit.rb, merge_request_metric.rb, plus EE subscribers.
• Services: app/services/merge_requests/ — create, update, refresh, merge, rebase, squash, conflict resolution, mergeability checks, etc.
• Controllers and views: app/controllers/projects/merge_requests/, app/views/projects/merge_requests/.
• Frontend: app/assets/javascripts/merge_requests/, app/assets/javascripts/diffs/, app/assets/javascripts/notes/, batch_comments/.
• Mergeability: lib/gitlab/merge_requests/mergeability/ — rule-based checks.
• Approval rules: EE under ee/app/services/approval_rules/ and friends.
• Code owners: EE under ee/app/services/code_owners/.
• Auto-merge: app/services/auto_merge/.
• Conflict resolution: backed by Gitaly's ConflictsService.

Code review

• Discussion threads (Discussion, Note, DraftNote) layered on top of merge requests.
• Suggestions (Markdown ```suggestion blocks) applied via app/services/suggestions/.
• Review apps: rendered by the CI pipeline; surfaced in the MR widget.
• Approvals (EE): rules + minimum approvers per branch.

Diff browsing

app/services/git/, lib/gitlab/diff/, and the frontend at app/assets/javascripts/diffs/ cover the diff browser. Performance-critical:

• Diffs are cached per-MR-version.
• File-level pagination and lazy-loading.
• Whitespace-only diff filtering (configurable).

Branches and protected refs

• ProtectedBranch, ProtectedTag define push/merge access by user/role/regex.
• The cop Gitlab::PolicyRuleBoolean ensures correct condition combinators.

Code Owners

EE-only. ee/app/services/code_owners/ parses CODEOWNERS files in the repo, attaches owners to MRs, and feeds approval rules.

Push rules

EE feature in ee/app/services/projects/push_rules/. Validates commit messages, branch names, file sizes, and other constraints at push time via Gitaly hooks.

Squash, rebase, cherry-pick, revert

All implemented in app/services/merge_requests/{squash_service.rb, rebase_service.rb} and app/services/commits/cherry_pick_service.rb, revert_service.rb. They call Gitaly's OperationService.

API

• REST: lib/api/merge_requests.rb, lib/api/branches.rb, lib/api/commits.rb, lib/api/repositories.rb.
• GraphQL: app/graphql/types/merge_request_type.rb, app/graphql/mutations/merge_requests/, app/graphql/resolvers/merge_requests/.

Related

• Gitaly client — every Git read/write goes through this.
• Workhorse — git over HTTP and archive download acceleration.
• CI/CD — pipelines triggered on push.
• Geo — repository replication.