penpot/docs/technical-guide/developer/branching.md

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3.12. Branching	Learn how Penpot file branching works — isolated file copies, a three-way entity-level merge engine, conflict resolution, the RPC API and the workspace UI. View Penpot's technical guide for self-hosting, configuration and developer insights.

File branching

Branching lets a user take an isolated, editable copy of a file (a branch), work on it without touching the original (main), and later bring the changes back through a merge. It is conceptually the same idea Git offers for source code, applied to design files: the workspace even reuses a small set of git-* icons (git-branch, git-branch-plus, git-commit, git-merge) to make the mental model obvious.

The whole feature is gated behind the :branching product flag and was added in the 2.16 API generation (all the RPC methods carry ::doc/added "2.16").

Conceptual model

Branching always reasons about three versions of the same file:

• main — the source file, the one everybody else keeps editing.
• branch — the isolated copy the user works on.
• merge base — a frozen snapshot of main taken at the exact moment the branch was created.

Comparing two versions is not enough to decide who is right when a value differs. With the third (the base) the engine can tell who changed what:

• if main still equals the base, then the branch is the one that changed it;
• if the branch still equals the base, then main is the one that changed it;
• if both changed it, to different values, that is a conflict and a human must pick a side.

This is the classic three-way merge algorithm, applied at the granularity of individual entities (a color, a shape, a typography, a token, …) rather than to the file blob as a whole.

A second, subtler property makes the whole thing possible: a branch is a copy that preserves the internal :data ids of every entity. Because "color X" in the branch and "color X" in main share the same id, the engine can pair them up and diff them. Without stable ids an id-based merge would be impossible.

Where the code lives

The feature spans the three subsystems. The core, shared logic lives in common so it can run identically in the JVM and in JavaScript test runners.

common/src/app/common/files/branch_merge.cljc          ; three-way diff + merge->changes engine
backend/src/app/rpc/commands/files_branch.clj          ; RPC commands (create/list/diff/merge/update)
backend/src/app/migrations/sql/0155-add-file-branch-table.sql  ; schema (file_branch table + is_branch)
frontend/src/app/main/data/workspace/branches.cljs     ; frontend state + RPC calls (ptk events)
frontend/src/app/main/ui/workspace/sidebar/branches.cljs       ; panels & dialogs
frontend/src/app/main/ui/dashboard/branches_popover.cljs       ; dashboard file-card popover

Tests:

common/test/common_tests/files_branch_merge_test.cljc  ; unit tests for the diff/merge engine
backend/test/backend_tests/rpc_file_branch_test.clj    ; integration tests for the RPC commands

The branching commands closely mirror the patterns in app.rpc.commands.files-snapshot, and reuse the production change pipeline (app.common.files.changes/process-changes), the file snapshot machinery (app.features.file-snapshots) and the file-duplication pipeline (app.rpc.commands.management/duplicate-file).

Data model

The migration adds one column to file and one new table.

ALTER TABLE file
  ADD COLUMN is_branch boolean NOT NULL DEFAULT false;

CREATE TABLE file_branch (
  id               uuid PRIMARY KEY,
  created_at       timestamptz NOT NULL DEFAULT clock_timestamp(),
  updated_at       timestamptz NOT NULL DEFAULT clock_timestamp(),

  branch_file_id   uuid NOT NULL REFERENCES file(id) ON DELETE CASCADE DEFERRABLE,
  source_file_id   uuid NOT NULL REFERENCES file(id) ON DELETE CASCADE DEFERRABLE,

  base_snapshot_id uuid NULL,

  -- main's revn when the base was (re)positioned
  base_revn        bigint NOT NULL,
  -- the BRANCH file's revn at the same moment (independent counter)
  base_branch_revn bigint NOT NULL DEFAULT 0,

  created_by       uuid NULL REFERENCES profile(id) ON DELETE SET NULL,

  name             text NOT NULL,
  description      text NULL,

  status           text NOT NULL DEFAULT 'open'
                      CHECK (status IN ('open', 'merged', 'archived')),

  merged_at        timestamptz NULL,
  merged_by        uuid NULL REFERENCES profile(id) ON DELETE SET NULL,
  deleted_at       timestamptz NULL
);

Key points:

• is_branch on file flags the branch copy so it is hidden from the normal project/team file listings, the dashboard search, the team trash (and its restore path), and project duplication/binfile export — you don't want every branch mixed in with real files, nor restorable zombies without their file_branch row. When the source file is deleted, the delete-object cascade propagates the logical deletion to its branches (they would otherwise be unreachable forever).
• branch_file_id points to the file row that is the branch copy; source_file_id points to main. A UNIQUE index on branch_file_id guarantees a file can be the branch of at most one source.
• base_snapshot_id references the merge-base snapshot. base_revn records MAIN's revision number and base_branch_revn the BRANCH file's one at the moment the base was (re)positioned — the two files carry independent revn counters, so each side's cheap "did anything change?" gate compares against its own counter (see ahead/behind below). The migration is intentionally idempotent (IF NOT EXISTS everywhere) so instances that applied it under its old development name pick up new columns on re-apply.
• status moves through open → merged (after a successful integration) or open ↔ archived (a reversible "hide it" state). Logical deletion is handled the standard Penpot way via deleted_at rather than a hard delete.

Lifecycle of a branch

Creating a branch

The ::create-file-branch command (files_branch.clj) refuses to branch a branch (:cannot-branch-a-branch) and runs everything inside a single transaction (with SET CONSTRAINTS ALL DEFERRED, because the new file and its branch row reference each other) under the file's advisory lock (db/xact-lock!, the same one update-file takes), so the base snapshot and the duplicated copy are guaranteed to capture the SAME state of main — a concurrent save between the two would otherwise make the base differ from the branch's initial content and manufacture phantom diffs later:

1. Materialize the merge base. fsnap/create! takes a system snapshot of main labelled branch-base/<name>, with a deleted-at 3650 days in the future. The far-future deletion date keeps the snapshot from being pruned by the snapshot GC while the branch is open — the diff needs it for as long as the branch lives. The pin is released (rescheduled with the team's normal deletion delay) whenever the branch is merged, deleted or its base is repositioned, so closed branches do not leak multi-year snapshots. If the snapshot can ever not be resolved, merge/update/diff refuse with :base-snapshot-missing — silently falling back to main would degrade the three-way merge into "branch overwrites main" without conflicts.
2. Duplicate main into the branch file. mgmt/duplicate-file is run with bfc/*state* bound to {:index {file-id branch-id}} and :reset-shared-flag true. The duplicate pipeline remaps the file/media/library ids but preserves the internal :data ids — the precondition for the id-based merge.
3. Mark the new file as a branch (is_branch = true) so it stays out of the listings.
4. Insert the file_branch row with status = 'open', the base snapshot id and base_revn = (:revn file).

Before any of this it enforces edition permissions on main and checks two quotas: ::quotes/branches-per-file and ::quotes/branches-per-team (configurable via PENPOT_QUOTES_BRANCHES_PER_FILE / PENPOT_QUOTES_BRANCHES_PER_TEAM, registered in app.config).

On the frontend, create-branch (in branches.cljs) first force-persists any pending local changes, then calls :create-file-branch, so the branch starts from a fully-saved state of main.

Working on a branch

Once created, main and the branch are two live, independent files. When a branch file is opened, the frontend fetches its context via :get-file-branch-info (events fetch-branches / fetch-branch-context) and shows a branch-context-banner* at the top of the workspace indicating "you are on a branch", together with its ahead / behind counts and the merge / update actions.

Ahead / behind counts

::get-file-branches lists a file's branches and annotates each with entity-level ahead / behind / conflicts counts — the same numbers the compare dialog shows.

Computing these means running the full three-way diff, which is expensive, so there is a two-level gate (branch-diff-counts):

• Each file carries a monotonically increasing revn. The command first computes cheap revn deltas: ahead-revn = branch_revn - base_branch_revn, behind-revn = source_revn - base_revn (revn-deltas) — each side against its OWN counter; mixing them breaks after an update-from-main repositions the base.
• If both deltas are zero, the branch is in sync and the diff is skipped entirely ([0 0 0]).
• Otherwise main's :data is realized once and shared across all branches of the same source. ahead is the count of clean changes in the :branch->main direction, behind the count in the reverse direction, and conflicts is only non-zero when both sides diverged. Only open branches are diffed (merged/archived ones report [0 0 0]), and a listing never fails because of one corrupted branch: count errors degrade to zeros with a warning (the merge itself still refuses loudly).

The three-way diff engine

app.common.files.branch-merge is the heart of the feature. It is a pure, side-effect-free engine: it reads three :data blobs and returns a serializable summary. It never mutates anything.

three-way-entities — the per-entity truth table

three-way-entities diffs one indexed collection (id -> value) across base / theirs / ours and returns {:changes [...] :conflicts [...]}. For each id it applies this decision table (theirs is main, ours is the branch, in the default :branch->main direction):

Situation	Outcome
deleted in both	nothing
deleted in branch, main intact (= base)	clean :deleted
deleted in main, branch intact (= base)	nothing (already gone in main)
deleted in branch / modified in main	conflict :delete-modify
modified in branch / deleted in main	conflict :modify-delete
new in branch only	clean :added
new in main only	nothing
added on both, same value	nothing
added on both, different value	conflict :add-add
present in all three, branch = base	nothing (main wins)
present in all three, main = base	clean :modified (branch wins)
present in all three, branch = main	nothing (converged)
present in all three, all three differ	conflict :modify-modify

So there are exactly four conflict reasons: :delete-modify, :modify-delete, :add-add and :modify-modify. Every conflict descriptor carries :base, :main and :branch values plus a :changed-attrs map (attribute → {:main v :branch v}) so the UI can render a side-by-side diff.

Shapes are diffed stripped of their derived attrs (strip-shapes: :shapes, :touched, :selrect, :points) and the page root frame (uuid/zero) is ignored. Stripping happens at CLASSIFICATION level, not just display: this is what prevents false conflicts — both sides adding children to the same frame only differ on :shapes, and a library sync on main only flips :touched; neither is a user change, so neither may turn a clean branch edit into a modify-modify/delete conflict. Containment (:parent-id/:frame-id) is deliberately kept: reparenting is a real, user-meaningful change. The same principle strips the :modified-at bookkeeping stamp from colors, typographies and components (strip-modified-at): the apply pipeline re-touches them, so after an update-from-main the copied entities would otherwise differ from main forever.

Pages and token sets get a content-valued presence pass (presence-only): presence is diffed over the normalized content instead of a bare marker, so deleting a page or token set the other side edited raises a proper :delete-modify/:modify-delete conflict instead of silently dropping those edits; content-only modifications are filtered out (the granular passes own them) and the conflict payloads are slimmed for the wire.

compute-merge — across the whole file

compute-merge runs three-way-entities over every mergeable collection in the file and concatenates the results:

• colors, typographies, components (row metadata), media — straightforward indexed collections.
• pages (diff-pages) — page add/delete, page metadata (name/background/grid), per-page guides, flows, default-grids, plugin-data, and the shapes (:objects) of every common page. Residual page attributes that no pass handles are surfaced under the :page-attrs kind so they are refused rather than silently dropped.
• tokens (diff-tokens) — token-set add/delete, set rename, set order, themes, active theme paths, active-set toggles, and per-token values.

The result is {:changes [...] :conflicts [...] :stats {...}}, where :stats counts added / modified / deleted / conflicts. The direction argument swaps which side is "theirs" and which is "ours": :branch->main (merge / compare) vs :main->branch (update from main).

remap-refs — the local-reference fix-up

A branch is a file copy with its own ids: duplicate-file re-points every local file reference (:component-file, :fill-color-ref-file, :stroke-color-ref-file, :typography-ref-file, shadow/grid :file-id) to the branch file id, and gives the branch's file_media_object rows FRESH ids (relinking shape :metadata/:fill-image/:stroke-image, the :media index and library-color :image refs to them). If diffed as-is, every affected entity would look modified, inflating the diff and conflicts; worse, after a merge the references could not be resolved in the target file — repair would silently detach components and images would break when the branch file is GC'd.

bm/remap-refs [data id-map] rewrites exactly the same reference surface the duplication pipeline remapped, through an {old-id -> new-id} map; ids not in the map (external libraries) are untouched. The backend builds that map per operation: the branch file id plus the media pairs (media-pairs, rows matched across the two files by storage object + name + dimensions + mtype). Media added on the source side of a merge/update gets fresh ids pre-allocated before the diff, and its file_media_object rows are copied into the target file when the operation applies — so merged shapes always reference rows owned by the file that outlives the branch.

Merging a branch into main

::merge-file-branch integrates the branch back into main. Only an editor of main may do it (same rule as Figma). The whole operation runs in a transaction guarded by db/xact-lock! on both file ids (in stable order, to avoid deadlocks) — without the branch lock, edits saved to the branch while the merge runs would be silently lost when the branch is marked merged and deleted.

The flow:

1. Load main, the branch (normalized), and the base (from the snapshot).
2. Optimistic concurrency check. If the caller passed expected-main-revn and it no longer matches main's revn, it raises :file-modified ("recompute the diff and retry"). The frontend always sends it (taken from the diff's :meta :main-revn), so resolutions computed against a stale diff can never apply; on :file-modified it re-fetches the diff and asks the user to review again.
3. Conflict gate. compute-merge is run; any conflict not resolved in the resolutions map aborts with {:status :conflicts :conflicts [...]}.
4. Unsupported gate. compute-changes is run; if it reports any :unsupported kinds it aborts with {:status :unsupported :kinds [...]} — nothing is applied, so no change is ever silently lost.
5. No-op shortcut. If there are no changes to apply (the branch already matches main), the branch is closed without touching main.
6. Apply. Otherwise it:
   • takes a safety snapshot of pre-merge main (pre-merge/<name>, with the team's normal deletion delay) so the merge can be rolled back via the version history;
   • applies the change vector through cpc/process-changes, bumping revn;
   • validates the merged file (cfv/validate-file) and, if it finds problems, runs cfr/repair-file and applies the repair changes;
   • copies the file_media_object rows of media added on the branch into main, under the pre-allocated ids the changes reference;
   • writes a file_change (xlog) row, persists the file (fupd/persist-file!), marks the branch merged;
   • publishes a :file-merged message on the msgbus topic of main so every open client reloads the file in real time.

Closing the branch (finish-branch!) always releases the pinned base snapshot and, unless the caller passes :keep-branch true, logically deletes the branch and its file in the SAME transaction (delete-branch!) — merged copies do not pile up, and there is no client-driven second call that could be lost mid-way. The :file-deleted msgbus message carries the session-id, so the merging client (which is navigating to main on its own) is not raced into the dashboard by its own deletion.

Resolutions

Conflict resolutions are a simple map of entity id → :main | :branch. The id is usually a uuid, but structural conflicts use keyword ids (:active-themes, :active-sets, :page-order, :token-set-order — each distinct, so resolving one can never accidentally satisfy another). :branch takes the branch side, :main (or absent) leaves main untouched. Resolving a delete conflict to :branch really restores: a shape comes back with its whole surviving subtree, a page with its full contents, a token set with its tokens. The frontend builds this map through set-conflict-resolution (one entity) and set-all-resolutions (bulk), then passes it to the merge command.

From merge to change ops: compute-changes

A diff summary is not directly applicable; it has to become the same kind of raw change maps the editor produces. compute-changes does that translation and returns {:changes [...] :unsupported #{...}}. The RPCs pass it the compute-merge summary they already computed for the conflict gate, so the full three-way diff is not run a second time just to derive :unsupported.

Mergeable vs. unsupported kinds

mergeable-kinds is the source of truth for what can be translated:

#{:color :typography :media :shape :token :token-set :token-set-rename :token-set-order
  :token-theme :token-active-themes :token-active-sets
  :page :page-order :page-guide :page-flow :page-grid :page-plugin :component}

unsupported-kinds returns any kind present in the diff that is not in this set (notably :page-attrs, the residual page attributes). When that set is non-empty the merge is refused — the engine prefers to refuse rather than drop a change it cannot faithfully reproduce.

Per-kind translation

flat-changes is the shared helper that walks a flat id -> value collection and emits add / modify / delete ops, honouring resolutions (a conflicting entity is emitted only when its resolution is :branch). The concrete op types it produces:

• colors / typographies / media — :add-color / :mod-color / :del-color, and the analogous :*-typography / :*-media ops.
• shapes (page-shape-changes) — the most involved pass:
  • modifications become :mod-obj with :set operations for the attrs that differ (structural attrs :shapes / :parent-id / :frame-id are excluded — they are applied via moves, not plain sets); per-attr resolutions that take a geometry attr also carry the branch's :selrect/:points so position and caches stay consistent;
  • deletions become :del-obj;
  • additions become :add-obj, emitted in topological order so a newly added parent is created before its newly added children; a modify-delete conflict resolved to :branch re-adds the shape's whole surviving subtree the same way;
  • reparenting of existing shapes becomes :mov-objects, emitted last (after new containers exist) and ordered by depth so a container moves before the shapes moved into it. Reparenting cannot be a :set :parent-id op — that would leave the shape loose in its old parent and let file repair duplicate it.
• pages — :add-page (full page incl. objects) / :del-page, :mod-page (name/background/grid), :mov-page (reorder), plus per-page :set-guide, :set-flow, :set-default-grid and :set-plugin-data.
• components — :add-component / :mod-component / :del-component (a branch soft-delete, :deleted true, is surfaced as a real :del-component). Components are emitted before shapes so :del-component can capture the main-instance objects before :del-obj removes them.
• tokens — :set-token (per-token values), :set-token-set (create/delete and rename), :move-token-set (reorder), :set-token-theme, :set-active-token-themes.

Updating a branch from main

::update-branch-from-main is the reverse direction: it brings into the branch the changes main received since the merge base. It needs edition permissions on the branch file, locks the branch file id, and applies main's changes (plus any conflicts resolved to :main) into the branch.

It works like a merge with compute-merge/compute-changes run with the sides swapped, the same :conflicts / :unsupported gates, and the same safety snapshot. The one extra step at the end is that it repositions the merge base: the base snapshot is moved forward to the current state of main (releasing the previous one), and both base_revn/base_branch_revn are refreshed. When the branch carried its own changes, base_branch_revn is stored one revn short on purpose: the new base equals MAIN, so the branch still differs from it even if its revn never moves again — the trick keeps the cheap gate open and the diff reports the real counts. UI resolutions arrive in main/branch terms and are inverted server-side (per-attr maps included) before translation.

RPC API summary

All commands live in app.rpc.commands.files-branch, are gated by check-branching-enabled!, and were added in 2.16.

Command	Kind	Purpose
::create-file-branch	mutation	Snapshot main + duplicate it into a branch
::get-file-branches	query	List branches with ahead/behind/conflicts counts
::get-branch-diff	query	Read-only three-way diff (either direction)
::merge-file-branch	mutation	Integrate a branch into main (resolutions, expected-main-revn, keep-branch)
::update-branch-from-main	mutation	Pull main's changes into the branch
::get-file-branch-info	query	Branch metadata when opening a branch file
::update-file-branch	mutation	Rename / edit description
::archive-file-branch	mutation	Archive / restore a branch
::delete-file-branch	mutation	Logically delete a branch

Frontend integration

State and events

app.main.data.workspace.branches holds the state and wraps the RPC calls as ptk events. The relevant pieces:

• State keys: workspace-branches (the list + status), workspace-branch-diff (the diff result + selected change + resolutions) and workspace-branch-context (metadata when editing a branch).
• Events: fetch-branches, create-branch, open-branch, fetch-branch-diff, set-conflict-resolution, set-all-resolutions, merge-branch, update-branch-from-main, fetch-branch-context, plus rename-branch, archive-branch, delete-branch. Each maps to the matching rp/cmd! call (:create-file-branch, :get-file-branches, :get-branch-diff, :merge-file-branch, :update-branch-from-main, …).
• reload-file-window / show-merge-result handle the post-merge UX (reacting to the :file-merged msgbus notification and showing the result).

UI components

app.main.ui.workspace.sidebar.branches provides the workspace UI:

• branches-toolbox* — the sidebar panel listing the current, open and archived branches; branch-entry* is a single branch card with rename / archive / delete actions.
• create-branch-dialog* — the create modal (name + description).
• branch-compare-dialog* — a read-only diff viewer, filterable by category (pages / components / colors / tokens) and status (added / modified / deleted).
• branch-conflicts-dialog* — the conflict-resolution UI, showing base / main / branch side by side and letting the user pick a side per conflict.
• branch-context-banner* — the top-of-workspace banner shown while editing a branch, with the ahead/behind counts and the merge / update actions.
• confirm-merge! / confirm-update! guard the irreversible operations with a confirmation modal.

app.main.ui.dashboard.branches_popover adds a popover to the dashboard file card so branches can be opened or created without entering the file.

Testing

The pure engine is covered by common-tests.files-branch-merge-test, which exercises three-way-entities and compute-merge across the add / modify / delete / conflict scenarios and can be run in both the JVM and JavaScript runners. The RPC layer is covered end-to-end by backend-tests.rpc-file-branch-test (create / list / diff / merge). See the Unit tests section for how to run them.

Pull requests

On top of branching, pull requests add a review step before the merge: the author of a branch asks one or more team members (reviewers) to evaluate their changes. The feature is part of branching and is gated behind the same :branching product flag; it lives in:

backend/src/app/migrations/sql/0156-add-file-pull-request-tables.sql
backend/src/app/rpc/commands/files_pull_request.clj
frontend/src/app/main/data/workspace/pull_requests.cljs
frontend/src/app/main/ui/workspace/sidebar/pull_requests.cljs
backend/test/backend_tests/rpc_file_pull_request_test.clj

Model

A pull request is not a file copy. The file_pull_request row points to its file_branch and to a pinned review snapshot of the branch file (label pr-review/<title>, the same ~10-year pin/release mechanics as the merge-base snapshot). There is at most one open pull request per branch (partial unique index).

Opening a review (?pr-id= on the workspace url) opens the live branch file as a completely normal workspace file — navigable and editable, so reviewers can try and validate anything (edits go to the branch, as always) — decorated with the review banner and actions. The pinned snapshot backs two things instead of the canvas: the cheap "outdated" gate (branch_revn > review_revn) and the prototype viewer: ::get-view-only-bundle accepts an optional pr-id and serves the snapshot overlay read-only (permissions taken from the target file, edition stripped; share-links do not apply), reachable from the review banner's "Try interactions" action. ::get-pull-request-bundle serves the same snapshot overlay as a workspace-shaped file bundle for API consumers; it refuses once the pull request is closed, so the pinned state stops resolving when the review ends (closing, merging or deleting the branch releases the pin).

Because the sandbox is pinned, the author can keep editing the branch; publishing the new state to reviewers is an explicit action (::update-pull-request-snapshot) that repositions the snapshot. branch_revn > review_revn is the cheap "outdated" gate, mirroring the ahead/behind revn gates.

Reviews

Reviewers are stored in file_pull_request_review (one row per profile, pending / approved / changes-requested). A verdict records the review_revn it was issued over, so it goes stale (not deleted) when the author publishes newer changes. The aggregate review-state is derived, never stored: current changes-requested beats current approved; stale verdicts only count as "in review". Approval is informative: merging keeps requiring edition permissions on main and goes through the exact same ::merge-file-branch gates.

Stored status is only open → merged/closed (with reopen). All the UI states (approved, changes requested, outdated, conflicts) are derived per request from the reviews and the existing diff-count helpers.

Accepting a pull request is offered from the sandbox banner (and the sidebar entries) to any user with edition permissions on main, but it is just an entry point into the exact same branch merge dialog and ::merge-file-branch flow — including conflict resolution and the safety snapshot. Note that merging always integrates the LIVE branch state: an outdated pull request merges the newest changes, not the pinned review snapshot.

Lifecycle hooks

The branch lifecycle closes its pull request: merge marks it merged, branch delete/archive marks it closed (see close-branch-pull-requests! in files_branch.clj), and the delete-object cascade closes it when the branch file dies through other paths (the row itself survives as history; it is only logically deleted when MAIN dies). Reviewers are notified by email (review-request template) and through the dashboard notifications dropdown (::get-profile-pending-reviews: open pull requests where the profile has no current verdict); :pull-request-* msgbus messages on main's topic keep open clients fresh.

Current scope and limitations

The feature was built in phases, and the engine refuses anything it cannot yet reproduce faithfully rather than risk losing work:

• The merge is id-based and assumes base, main and branch share the same file data version; explicit data-version normalization before diffing is a later refinement.
• Residual page attributes (:page-attrs) are surfaced but refused, so a merge that touches them returns {:status :unsupported}.
• Comments / comment-thread positions are deliberately not migrated across a merge (the same choice Figma makes).
• The merge base snapshot is kept alive for the whole life of the branch; the far-future deleted-at is what protects it from the snapshot GC.