QuickJS Plugin Backend

Overview

Fresh uses QuickJS for its JavaScript plugin runtime, replacing the previous deno_core (V8) backend.

Benefits:

• Reduced dependencies (~315 → ~183 crates)
• Faster compilation (no V8 snapshot generation)
• Lighter runtime (~700KB vs multi-MB V8)
• Simple single backend (QuickJS + oxc)

Status: In Progress

Component	Status
QuickJS runtime (rquickjs 0.11)	✅ Complete
TypeScript transpilation (oxc 0.108)	✅ Complete
ES module bundling	✅ Complete
Proc macro TypeScript generation	✅ Complete
ts-rs type export integration	✅ Complete
Plugin API methods	⚠️ 75/122 methods (61%)
Async operations (tokio)	✅ Complete

Test coverage: 52 unit tests + 23 e2e tests passing

Architecture

Class-Based API

The plugin API is exposed via JsEditorApi using rquickjs class bindings with automatic camelCase conversion.

Key patterns:

• #[rquickjs::class] - Expose struct to JS
• #[rquickjs::methods(rename_all = "camelCase")] - Auto-convert method names
• rquickjs::function::Opt<T> - Optional parameters
• rquickjs::function::Rest<T> - Variadic arguments
• rquickjs_serde::to_value() - Rust → JS conversion

Async Pattern

Async methods use a callback-based pattern:

1. JS calls _xxxStart() → returns callbackId
2. Rust sends PluginCommand to app
3. App executes operation, calls resolve_callback(id, result)
4. JS Promise resolves

File Structure

src/services/plugins/
├── backend/quickjs_backend.rs  # JsEditorApi implementation
├── api.rs                      # PluginCommand, EditorStateSnapshot
├── transpile.rs                # TypeScript → JS
└── thread.rs                   # Plugin thread runner

crates/fresh-plugin-api-macros/ # TypeScript definition generation
plugins/lib/fresh.d.ts          # Generated TypeScript definitions

Dependencies

• rquickjs 0.11 - QuickJS bindings
• rquickjs-serde 0.4 - Serde integration
• oxc_* 0.108 - TypeScript transpilation
• fresh-plugin-api-macros - Proc macros

Next Steps: API Completion

Missing Methods (47 methods)

The following methods need to be added to JsEditorApi in quickjs_backend.rs:

Priority 1 - Core Functionality:

• getBufferInfo(buffer_id) → BufferInfo | null
• getPrimaryCursor() → CursorInfo | null
• getAllCursors() → CursorInfo[]
• getViewport() → ViewportInfo | null
• getCursorLine() → number
• getAllCursorPositions() → number[]
• findBufferByPath(path) → number
• getBufferSavedDiff(buffer_id) → TsBufferSavedDiff | null

Priority 2 - Virtual Text/Overlays:

• addVirtualLine(buffer_id, position, text, fg_rgb, bg_rgb, above, namespace, priority)
• addVirtualText(buffer_id, id, position, text, rgb, before, use_bg)
• removeVirtualText(buffer_id, id)
• removeVirtualTextsByPrefix(buffer_id, prefix)
• clearVirtualTexts(buffer_id)
• clearVirtualTextNamespace(buffer_id, namespace)
• removeOverlay(buffer_id, handle)
• clearOverlaysInRange(buffer_id, start, end)

Priority 3 - View Transforms:

• submitViewTransform(buffer_id, split_id, start, end, tokens, layout_hints)
• clearViewTransform(buffer_id, split_id)

Priority 4 - Composite Buffers:

• createCompositeBuffer(options) → Promise<number>
• updateCompositeAlignment(buffer_id, hunks)
• closeCompositeBuffer(buffer_id)

Priority 5 - Scroll Sync:

• createScrollSyncGroup(group_id, left_split, right_split)
• setScrollSyncAnchors(group_id, anchors)
• removeScrollSyncGroup(group_id)

Priority 6 - Split Operations:

• createVirtualBufferInExistingSplit(options) → Promise<number>
• setSplitScroll(split_id, top_byte)
• setSplitRatio(split_id, ratio)
• distributeSplitsEvenly()
• setLineNumbers(buffer_id, enabled)

Priority 7 - File Explorer:

• setFileExplorerDecorations(namespace, decorations)
• clearFileExplorerDecorations(namespace)

Priority 8 - Diagnostics/LSP:

• getAllDiagnostics() → TsDiagnostic[]
• getHighlights(buffer_id, start, end) → Promise<TsHighlightSpan[]>
• disableLspForLanguage(language)

Priority 9 - Process Management:

• isProcessRunning(process_id) → boolean
• spawnProcessWait(process_id) → Promise<SpawnResult>
• killProcess(process_id) → Promise<boolean>

Priority 10 - UI:

• showActionPopup(options) → Promise<ActionPopupResult>
• deleteTheme(name) → Promise<void>

Priority 11 - Misc:

• executeActions(actions) → boolean (batch execution)
• getHandlers(event_name) → string[]
• pluginTranslate(plugin_name, key, args) → string
• fileStat(path) → FileStat

Missing Types (27 types)

Add to api.rs with #[derive(TS)] and register in ts_export.rs:

Core: BufferInfo, CursorInfo, ViewportInfo, SelectionRange, LayoutHints Virtual Buffers: CreateVirtualBufferOptions, CreateVirtualBufferInCurrentSplitOptions, CreateVirtualBufferInExistingSplitOptions, CreateVirtualBufferResult, TextPropertyEntry Composite: TsCompositeLayoutConfig, TsCompositeSourceConfig, TsCompositePaneStyle, TsCompositeHunk, CreateCompositeBufferOptions View Transform: ViewTokenWire, ViewTokenWireKind Diagnostics: TsDiagnostic, TsDiagnosticPosition, TsDiagnosticRange, TsBufferSavedDiff UI: TsActionPopupAction, TsActionPopupOptions, PromptSuggestion, ActionSpecJs File System: DirEntry, FileStat, FileExplorerDecoration

Signature Fixes

These methods exist but have incompatible signatures:

1. addOverlay - Fix parameter order (underline should come after bg colors)
2. defineMode - Add read_only parameter
3. openFile - Make line/column non-nullable (use 0 for default)
4. t() - Change from variadic to args?: Record<string, string>
5. registerCommand - Match origin/master signature
6. setPromptSuggestions - Use typed PromptSuggestion[]
7. setVirtualBufferContent - Use typed TextPropertyEntry[]
8. createVirtualBuffer/InSplit - Use typed options objects
9. spawnProcess/spawnBackgroundProcess - Make args optional
10. sendLspRequest - Make params optional with unknown | null

Future: Native Async

rquickjs supports native async via AsyncRuntime/AsyncContext and the Promised wrapper. This could replace the _xxxStart + JS wrapper pattern but would require architectural changes. The current callback-based pattern works well.

References

• rquickjs docs
• QuickJS engine
• oxc project