One Diff View

Nibtree shows a file's diff in many places: the Changes diff and the Changes tab, a commit in the History panel or its own tab, a branch compare, Compare with Revision, the diff of a revision against the working tree, a shelf, Compare Files and local history. They all go through one component, GitDiffView, so they share the same toolbar, layouts, three-pane option and buttons.

Why we need it

Each place used to pick between the two-pane DiffView and the three-pane ThreePaneDiff on its own. So they drifted apart: the Changes tab had a Revert button the History panel did not, only merge commits could show three columns, and every fix had to be made several times. A user saw "the same view" behave differently depending on where it opened.

How it works

A place loads its two-pane diff as before and hands GitDiffView a DiffSource: what the diff compares.

Source	Used by	Three panes	Change buttons
changes	Changes diff	HEAD, index, work tree	Stage, Unstage, Discard (the place's own)
head	Changes tab	HEAD, index, work tree	Revert to HEAD
commit	History panel, commit tab	parent, commit, work tree (or both parents of a merge)	Revert, Apply
revisions	Branch compare, Compare with Revision, revision against work tree	older, newer, work tree (only when the newer side is not the work tree)	Revert, plus Apply when the newer side is a revision
plain	Shelf, Compare Files, local history	none	none

flowchart LR
  Place["a place loads its diff"] --> View["GitDiffView(source, diff)"]
  View --> Kind["threePaneKind(source, diff)"]
  Kind -->|"three columns on and fits"| Three["ThreePaneDiff"]
  Kind -->|"otherwise"| Two["DiffView"]
  View --> Revs["changeRevisions(source)"]
  Revs --> Actions["changeWorkTree: apply_revision_lines"]

Loading

diffSource.ts holds the pure decisions: threePaneKind (which three panes fit), panesKey (the Settings > Git choice that picks two or three columns: one for uncommitted changes, one for commits) and changeRevisions (the two revisions a change's Revert and Apply work between).

When three columns are on, GitDiffView loads the third pane itself: StagingDiffs for the index and the work tree, or WorkTreePane for the work tree against the newer side. Both reload when the repository's status or a file version changes, and panes still loaded for another file are never shown.

Revert and Apply

changeWorkTree (diffActions.ts) calls the apply_revision_lines command with the change's lines. The backend (commands/revision_lines.rs) reads both sides at their revisions (or the work tree file), builds a patch of only those lines with git::partial, and runs git apply (Apply) or git apply --reverse (Revert) on the work tree file after a --check. The index is never touched. A local history snapshot is taken first, and the patch comes back so the toast's Undo can run it the other way through restore_discarded_lines.

In three panes, the commit's bands sit between the parent and the middle, so ThreePaneDiff takes lineActions for that side: ThreeWayEditors.change(side, index) turns a band into the same line selection (side pane old, middle new).

Where the code lives

File	What it does
src/lib/diff/GitDiffView.svelte	The one view: picks the panes, loads the third one, wires the buttons
src/lib/diff/diffSource.ts	DiffSource, threePaneKind, panesKey, changeRevisions
src/lib/diff/diffActions.ts	writeIndex (staging view) and changeWorkTree (Revert, Apply, Undo)
src/lib/diff/workTreePane.svelte.ts	The work tree pane next to a commit or a compare
src-tauri/src/commands/revision_lines.rs	apply_revision_lines

Design decisions

• Places keep loading their own two-pane diff. Each one already loads, refreshes and lists files its own way; the view only needs the result and what it compares.
• Apply needs a revision on the newer side. When the newer side is the work tree, the change is already there, so only Revert is offered.
• The patch, not the texts. Applying a patch with context fails cleanly when the file moved on, instead of overwriting lines the user changed.
• Shelf, Compare Files and local history stay read-only. They are not git revisions of the same file, so a change has no clear place to go.

Tests

• src/lib/diff/diffSource.test.ts: which panes fit each source, the settings, the revisions, a band's lines and the work tree pane against the middle.
• commands/revision_lines.rs: revert and apply one change with Undo, a change that no longer fits, a root commit's new file, the index left alone, and bad input.

Keeping this page in sync

Update the table when a place starts showing diffs, when a source kind changes, or when a button is added. See also How diffs work and How reverting a change works.