Add an opt-in Ignore whitespace control to local Review diffs #333

User problem and benefit

Reindentation or spacing changes can bury a small substantive edit in a large local patch. Threadlane's Review panel currently offers no way to suppress that noise without leaving the application.

Add an opt-in Ignore whitespace control to the local Review diff document, for both a selected file and All changes. It changes only the displayed patch, never repository content, commit selection, or agent context. Keep it off by default: whitespace can be meaningful in indentation-sensitive languages and string literals.

Source inspiration and evidence

Source-code/documentation research only; neither source application nor Threadlane was launched or visually inspected.

• Synara, revision ff9e89dc16365181c7d112a5764f68989ed6f32e: its diff options menu has a checked Ignore whitespace-only changes option. Its checkpoint diff implementation conditionally passes --ignore-all-space to Git. Borrow the explicit, reversible presentation option—not its checkpoint infrastructure.
• T3 Code, revision c2fa9fc911daeac97df4760f95fc57dca42b84c8: its diff toolbar exposes a pressed toggle with accessible Show/Hide whitespace changes labels. The query inputs carry that option to the backend; the Git argument builder adds --ignore-all-space. Borrow real Git filtering and explicit state, not DOM-side removal of patch lines.

This is a smaller, more immediately reusable improvement than adopting rich pasted-text attachments or a new diff renderer. Conversation/terminal search, attachment previews, file completion, review progress, and terminal-to-chat handoff were excluded because existing issues already cover them.

Threadlane baseline and reuse

Checked current main at bca44c42a6072612fde47f472bdd6f8469dadaee; these relevant files are identical to the available worktree:

• RightPanelView::open_file_diff / open_combined_diff already load patches off-thread and reject stale results using project, title, and review_diff_revision.
• sync_pending_document renders local patches through the existing TextViewState; render_files owns the document header. No renderer replacement is needed.
• threadlane-git::diff_file / worktree_diff use unfiltered Git output and staged/unstaged/untracked fallbacks. Other callers include commit-message generation; their behavior must stay unfiltered.

Proposed UX and interaction states

1. Scope and entry: in the local diff document header, add a standard kit Checkbox labeled Ignore whitespace, unchecked initially. It applies only to this Review panel's local patch view, remains selected across files/All changes in the same checkout, and resets on checkout/project change and app restart. Do not show it for editable files, GitHub PR diffs, history/stash previews, or editor-tab diff exports in this first increment. Keep existing Back/Close commands reachable. At narrow widths allow a compact second header row rather than clipping controls.
2. Visible semantics: while enabled, retain the checked label and show Whitespace ignored · Display only near the patch. Help/accessibility description: Ignores whitespace when comparing lines. Whitespace can affect program behavior. File counts and commit selection are unchanged. Do not call this a semantic diff or claim the remaining patch is safe to commit. File lists, additions/deletions totals, and selected files continue to describe the unfiltered working tree.
3. Loading/error: toggling reloads the same target in the background. Show Updating diff…; do not present the previous patch under the new filter label as if current. Allow a later toggle to supersede an earlier request. A failure shows Could not load diff with Retry and the option to turn filtering off; it must not masquerade as an empty patch. Local reads require no GitHub credentials/network and retain existing permission errors.
4. Empty and non-text changes: a successful empty filtered patch says No text changes to show with whitespace ignored, with a Show whitespace changes button. Never substitute Working tree clean. Keep binary, rename, mode-change, and other metadata that Git returns; do not remove entire files based on a zero-text count. Untracked/new files remain visible as additions. Ordinary unfiltered empty/error behavior remains distinct.
5. Keyboard and lifecycle: Tab reaches the checkbox; Space toggles with a visible focus ring and announced checked state. Activation must not move focus into the patch or trigger commit/discard. Reject late results after file/project changes, Back/Close, or a newer toggle. Use existing themed component sizing, semantic colors and roles; no hover-only control or color-only indication.

Scoped implementation plan

1. Git leaf: extend crates/threadlane-git/src/git.rs with the smallest option-aware variants needed by the two review loaders; retain current public wrappers as unfiltered defaults for all existing callers. Reuse path validation, --no-ext-diff, and Git error handling. Pass --ignore-all-space through the appropriate tracked HEAD/staged/unstaged paths; do not strip whitespace or patch lines in Rust. Represent a successful empty result separately from an error and UI prose.
   • Important correctness boundary: an empty successful HEAD diff is a valid comparison result, not evidence of an unborn HEAD. Only use the staged/unstaged fallback when that comparison is unavailable. A temporary-repository experiment confirmed that git diff -w HEAD can be empty while git diff -w --cached is nonempty when staged and unstaged edits cancel. Blindly keeping the current empty-output fallback would display the wrong comparison.
   • Collect untracked additions independently of whether tracked output is nonempty; ensure both filter modes cover the same file universe. Keep this limited to correct composition of the touched helper, not a general Git refactor.
2. State and reload: in crates/threadlane-ui-right-panel/src/view.rs, keep the option and active diff target in RightPanelView. Use a small explicit target (File(path) versus AllChanges) instead of inferring identity from the rendered title. Route toggles and PanelEvent::ReviewLoaded refresh through that target; the current refresh path parses the title as a file path, which cannot safely reload All changes. Include mode/target in request identity and guard pending results when applying them, not just when receiving them. Clear stale pending content when invalidating a request.
3. UI composition: extend the existing document header and status/empty/error rendering in render_files/sync_pending_document; retain TextViewState and the background executor. Reuse the already-imported kit Checkbox/Button. Follow AGENTS.md and the project GPUI Kit design guide: visible state, region-scoped controls, theme/rem tokens, named keyboard controls, restrained hierarchy. No changes to the binary shell, daemon, protocol, persistent settings, or dependencies.
4. Tests: extend crates/threadlane-git/src/tests.rs, crates/threadlane-ui-right-panel/src/tests.rs, and the existing in-module GPUI tests in src/view.rs. Preserve retain_review_selection and its tests. Mount interaction tests under initialized gpui_component::Root as required by project instructions.

Acceptance criteria and validation

• File and All changes diffs can toggle whitespace filtering; mixed edits retain non-whitespace differences, and disabling it restores the full patch.
• Filtered-empty, clean, loading, error and non-text/metadata outcomes remain distinguishable. Staged/unstaged cancellation, unborn HEAD, detached HEAD, and tracked-plus-untracked changes have regression fixtures.
• Filtering never changes files, index, selected commit files, raw status counts, generated commit prompts, editor exports, or GitHub PR review state. Validate working-tree bytes and index before/after the read-only operations.
• Rapid toggles, refresh, navigation and project/worktree changes cannot publish a stale mode/target. All changes refresh stays an aggregate diff. Closing during a request cannot reopen the document.
• Keyboard-only use, accessible name/checked state, narrow panels, larger fonts, and light/dark themes remain usable; errors permit recovery without losing commit selection.

Implementation validation: cargo nextest run -p threadlane-git, cargo nextest run -p threadlane-ui-right-panel, cargo check -p threadlane-gpui, and git diff --check. Manually exercise a real window with whitespace-only and mixed patches, new/deleted/binary files, Unicode/spaced paths, rapid toggles and checkout switches; check VoiceOver and focus behavior. These implementation tests have not been run as part of this research-only proposal.

Nonduplication and tradeoffs

Reviewed all 87 existing open/closed issues, searching titles, bodies and comments by whitespace/spacing/indentation/formatting, diff/patch/review, filtering/hiding/noise, and related workflow concepts. Nearby scopes:

• #271 / PR #274 add Environment Git status and navigation; #291 / PR #294 add commit/pull/push/branch actions. Their closing PR descriptions and relevant discussion do not cover patch whitespace filtering. The image-only issue references could not be visually inspected because the embedded browser was unavailable; the scope assessment uses those linked implementation records and current source instead.
• #311 concerns GitHub-backed Viewed markers and Next unviewed, not local patch presentation.
• #156 concerns GitHub authentication, PR lifecycle, checks, review feedback and transport. This proposal makes no GitHub mutation or PR-review change.

Git --ignore-all-space can hide meaningful indentation and whitespace inside strings: default-off, explicit scope and a persistent indicator are essential. Raw file totals will intentionally differ from the filtered display. Changing filter mode can alter hunk structure and scroll position; retaining the same target matters more than pretending old line offsets are stable. Large-patch rendering limits are unchanged; this is not a virtualization or AST-diff project.