From dbfd7d2997ddc659ae720a8a8f87e3c8cec5e51c Mon Sep 17 00:00:00 2001
From: Claude Bot <claude-bot@bun.sh>
Date: Sun, 5 Oct 2025 15:25:37 +0000
Subject: [PATCH] Add dev mode support for workers in js_printer

In internal_bake_dev mode, workers now use the original path instead
of unique keys. This allows the dev server to intercept and serve
worker bundles separately.

Changes:
- js_printer.zig: Check module_type before generating worker paths
- Dev mode: Use import_record.path.pretty directly
- Production: Continue using unique key system

This is Phase 2.2 of the worker dev server implementation plan.
---
 WORKER_DEV_SERVER_PLAN.md | 476 ++++++++++++++++++++++++++++++++++++++
 src/js_printer.zig        |  16 +-
 2 files changed, 487 insertions(+), 5 deletions(-)
 create mode 100644 WORKER_DEV_SERVER_PLAN.md

diff --git a/WORKER_DEV_SERVER_PLAN.md b/WORKER_DEV_SERVER_PLAN.md
new file mode 100644
index 0000000000..a1c9b10824
--- /dev/null
+++ b/WORKER_DEV_SERVER_PLAN.md
@@ -0,0 +1,476 @@
+# Worker Support in Bake DevServer - Implementation Plan
+
+## Overview
+
+This document outlines the plan to add Web Worker support to Bake's development server. Workers in production builds already work correctly, but the dev server (`internal_bake_dev` format) currently has no worker support.
+
+## Current State
+
+### Production Build (✅ Working)
+- Workers detected via `ImportKind.worker` and `E.NewWorker` AST nodes
+- Workers bundled into separate chunks (e.g., `worker-axd28k5g.js`)
+- Path resolution via `entry_point_chunk_indices` mapping
+- Output: `new Worker("./worker-axd28k5g.js")`
+
+### Dev Server (❌ Not Implemented)
+- External dynamic imports (including workers) are **skipped** in `scanImportsAndExports.zig:660`
+- No worker handling in HMR runtime (`hmr-module.ts`)
+- No worker entry point detection in `IncrementalGraph.zig`
+- Workers would fail because they can't use the HMR module system
+
+## Implementation Strategy: Separate Entry Point Bundling
+
+We'll treat workers as independent mini-bundles, similar to how routes are handled. Each worker gets:
+- Its own bundle with the HMR runtime
+- Independent HMR WebSocket connection (optional, can share with parent)
+- Proper module resolution through the dev server
+
+### Architecture
+
+```
+Main Page                    Worker
+┌─────────────────┐         ┌──────────────────┐
+│ HMR Runtime     │         │ HMR Runtime      │
+│ Module Registry │         │ Module Registry  │
+│                 │         │                  │
+│ new Worker(url) │────────>│ Load & Execute   │
+└─────────────────┘         └──────────────────┘
+        │                            │
+        │ WebSocket                  │ WebSocket (optional)
+        ├────────────────────────────┤
+        │      Dev Server            │
+        └────────────────────────────┘
+```
+
+## Implementation Steps
+
+### Phase 1: Detection and Entry Point Management
+
+#### 1.1 Modify IncrementalGraph to Detect Workers
+**File:** `src/bake/DevServer/IncrementalGraph.zig`
+
+**Goal:** Treat worker imports as separate entry points, similar to dynamic imports.
+
+**Changes needed:**
+- In `processEdgeAttachment()`, detect `ImportKind.worker`
+- Create a separate edge kind for workers (or reuse dynamic import logic)
+- Mark worker files as entry points in the graph
+- Store worker source indices for later bundling
+
+**Key consideration:** Workers should be detected during the initial graph walk, not deferred.
+
+#### 1.2 Create Worker Route Bundles
+**File:** `src/bake/DevServer.zig`
+
+**Goal:** Each worker gets its own `RouteBundle` for independent bundling.
+
+**Changes needed:**
+- Add a new bundle type or flag for workers (e.g., `RouteBundle.Kind.worker`)
+- Register worker bundles in `route_bundles` array
+- Create URL mapping: `/worker.js` → `/_bun/worker-[hash].js`
+
+**URL scheme:**
+```
+Source: ./src/worker.js
+Dev URL: /_bun/w/src/worker.js?v=[hash]
+```
+
+### Phase 2: Bundling and Code Generation
+
+#### 2.1 Bundle Workers with HMR Runtime
+**File:** `src/bake/DevServer/RouteBundle.zig` or equivalent bundling code
+
+**Goal:** Generate standalone worker bundles with HMR support.
+
+**Changes needed:**
+- When bundling a worker entry point, include the HMR runtime
+- Set `output_format = .internal_bake_dev`
+- Mark as worker context (affects what globals are available)
+- Generate with proper module wrapping
+
+**Bundle structure:**
+```javascript
+// Worker bundle output
+(function(hmr) {
+  // HMR runtime for worker
+
+  // Worker modules
+  hmr.load("worker.js", function(module, exports, require) {
+    // Worker code here
+    self.onmessage = function(e) { ... }
+  });
+
+  // Execute entry
+  hmr.loadExports("worker.js");
+})(__createHMR());
+```
+
+#### 2.2 Update js_printer for Dev Mode Workers
+**File:** `src/js_printer.zig`
+
+**Goal:** Transform `new Worker()` calls in dev mode to use dev server URLs.
+
+**Changes needed:**
+- Detect when `module_type == .internal_bake_dev` in `e_new_worker` handler
+- Instead of using unique keys, emit a call to an HMR helper
+- Include the original worker path for dev server resolution
+
+**Current (production):**
+```javascript
+new Worker("./worker-axd28k5g.js")
+```
+
+**Proposed (dev mode):**
+```javascript
+new Worker(__hmr__.resolveWorker("./worker.js"))
+```
+
+Or simpler (direct URL):
+```javascript
+new Worker("/_bun/w/worker.js?v=abc123")
+```
+
+### Phase 3: HMR Runtime Support
+
+#### 3.1 Add Worker Helper to HMR Runtime
+**File:** `src/bake/hmr-module.ts`
+
+**Goal:** Provide helper method for creating workers in dev mode.
+
+**Implementation:**
+```typescript
+export class HMRModule {
+  // ... existing code ...
+
+  /**
+   * Creates a worker with dev server URL resolution
+   * In dev mode, workers are bundled separately and served via dev server
+   */
+  static createWorker(specifier: Id, options?: WorkerOptions): Worker {
+    // Resolve the specifier to a dev server URL
+    // For now, just pass through - URL rewriting happens in js_printer
+    return new Worker(specifier, options);
+  }
+
+  /**
+   * Resolves a worker specifier to its dev server URL
+   * Called from generated code if needed
+   */
+  static resolveWorker(specifier: string): string {
+    // In development, workers are served from /_bun/w/[path]
+    // The bundler will have already rewritten this
+    return specifier;
+  }
+}
+```
+
+**Alternative simpler approach:** Don't add HMR methods, just rewrite URLs in js_printer directly.
+
+### Phase 4: Dev Server Request Handling
+
+#### 4.1 Serve Worker Bundles
+**File:** `src/bake/DevServer.zig`
+
+**Goal:** Handle HTTP requests for worker bundles.
+
+**Changes needed:**
+- Add route handler for `/_bun/w/*` pattern
+- Map URL back to worker RouteBundle
+- Serve bundled worker code
+- Set proper CORS headers if needed
+- Set `Content-Type: application/javascript`
+
+**Request flow:**
+```
+1. Browser: GET /_bun/w/src/worker.js?v=abc123
+2. DevServer: Lookup worker bundle for "src/worker.js"
+3. DevServer: If not bundled, trigger bundle
+4. DevServer: Return bundled worker code
+```
+
+#### 4.2 Handle Worker HMR Updates
+**File:** `src/bake/DevServer/HmrSocket.zig` or HMR event handling
+
+**Goal:** Hot-reload workers when their code changes.
+
+**Options:**
+1. **Simple:** Force page reload when worker code changes (like CSS currently does)
+2. **Advanced:** Send HMR update to worker via `postMessage` bridge
+
+**For initial implementation, use option 1 (page reload).**
+
+### Phase 5: Don't Skip Workers in Scan Phase
+
+#### 5.1 Update scanImportsAndExports
+**File:** `src/bundler/linker_context/scanImportsAndExports.zig`
+
+**Current code (line 659-660):**
+```zig
+if (!record.source_index.isValid() or this.isExternalDynamicImport(record, source_index)) {
+    if (output_format == .internal_bake_dev) continue;  // <-- This skips workers!
+```
+
+**Goal:** Don't skip workers in dev mode, but handle them specially.
+
+**Proposed change:**
+```zig
+if (!record.source_index.isValid() or this.isExternalDynamicImport(record, source_index)) {
+    if (output_format == .internal_bake_dev) {
+        // In dev mode, workers are handled as separate entry points
+        // Don't skip them - they need to be registered
+        if (record.kind == .worker) {
+            // Mark as worker entry point for dev server
+            // The dev server will bundle this separately
+            // TODO: Add to worker entry points list
+        }
+        continue;
+    }
+```
+
+## Detailed File Changes
+
+### 1. `src/js_printer.zig` (lines ~2200-2242)
+
+**Current:**
+```zig
+.e_new_worker => |e| {
+    // ... wrapper code ...
+    p.print("new Worker(");
+
+    if (p.options.unique_key_prefix.len > 0) {
+        // Production mode: use unique keys
+        const import_record = p.importRecord(e.import_record_index);
+        const source_index = import_record.source_index.get();
+        const unique_key = std.fmt.allocPrint(p.options.allocator, "{s}W{d:0>8}", .{ p.options.unique_key_prefix, source_index }) catch unreachable;
+        defer p.options.allocator.free(unique_key);
+        p.printStringLiteralUTF8(unique_key, true);
+    } else {
+        // Fallback: direct path
+        p.printStringLiteralUTF8(p.importRecord(e.import_record_index).path.text, true);
+    }
+    // ... rest
+}
+```
+
+**Proposed:**
+```zig
+.e_new_worker => |e| {
+    // ... wrapper code ...
+    p.print("new Worker(");
+
+    if (p.options.module_type == .internal_bake_dev) {
+        // Dev mode: use dev server URL
+        const import_record = p.importRecord(e.import_record_index);
+        const worker_path = import_record.path.text;
+
+        // Format: /_bun/w/[path]?v=[hash]
+        // For now, just use the pretty path - dev server will resolve it
+        p.printStringLiteralUTF8(worker_path, true);
+    } else if (p.options.unique_key_prefix.len > 0) {
+        // Production mode: use unique keys
+        const import_record = p.importRecord(e.import_record_index);
+        const source_index = import_record.source_index.get();
+        const unique_key = std.fmt.allocPrint(p.options.allocator, "{s}W{d:0>8}", .{ p.options.unique_key_prefix, source_index }) catch unreachable;
+        defer p.options.allocator.free(unique_key);
+        p.printStringLiteralUTF8(unique_key, true);
+    } else {
+        // Fallback: direct path
+        p.printStringLiteralUTF8(p.importRecord(e.import_record_index).path.text, true);
+    }
+    // ... rest
+}
+```
+
+### 2. `src/bake/DevServer/IncrementalGraph.zig`
+
+**Location:** In `processEdgeAttachment()` function
+
+**Add after existing import kind handling:**
+```zig
+// Handle worker imports as separate entry points
+if (import_record.kind == .worker) {
+    // Workers need to be bundled as separate entry points
+    // Mark this file as a worker entry point
+    // The dev server will create a separate bundle for it
+
+    // For now, treat similar to dynamic imports
+    // but mark as worker kind for special handling
+    log("Worker import detected: {s} -> {s}", .{
+        key,
+        ctx.parse_graph.input_files.items(.source)[import_record.source_index.get()].path.pretty
+    });
+
+    // TODO: Register worker entry point
+    // This will be picked up by the bundler to create a separate worker bundle
+}
+```
+
+### 3. `src/bake/DevServer.zig`
+
+**Add worker bundle management:**
+```zig
+// Add to DevServer struct
+/// Map from worker source index to bundle index
+worker_bundles: std.AutoHashMapUnmanaged(IncrementalGraph(.server).FileIndex, usize) = .{},
+
+// Add helper method
+pub fn getOrCreateWorkerBundle(
+    this: *DevServer,
+    worker_source_index: IncrementalGraph(.server).FileIndex,
+) !*RouteBundle {
+    // Check if worker bundle already exists
+    if (this.worker_bundles.get(worker_source_index)) |bundle_index| {
+        return &this.route_bundles.items[bundle_index];
+    }
+
+    // Create new worker bundle
+    const bundle_index = this.route_bundles.items.len;
+    try this.route_bundles.append(this.allocator(), RouteBundle{
+        // TODO: Initialize worker bundle
+        .kind = .worker,
+        .entry_point = worker_source_index,
+        // ... other fields
+    });
+
+    try this.worker_bundles.put(this.allocator(), worker_source_index, bundle_index);
+    return &this.route_bundles.items[bundle_index];
+}
+```
+
+## Testing Plan
+
+### Test 1: Basic Worker in Dev Mode
+```javascript
+// main.js
+const worker = new Worker('./worker.js');
+worker.postMessage('hello');
+
+// worker.js
+self.onmessage = (e) => {
+  console.log('Worker received:', e.data);
+  self.postMessage('world');
+};
+```
+
+**Expected:**
+- Dev server bundles worker.js separately
+- Worker loads and executes
+- Messages work bidirectionally
+- No console errors
+
+### Test 2: Worker with Dependencies
+```javascript
+// worker.js
+import { helper } from './helper.js';
+self.onmessage = (e) => {
+  self.postMessage(helper(e.data));
+};
+
+// helper.js
+export function helper(x) { return x * 2; }
+```
+
+**Expected:**
+- Worker bundle includes helper.js
+- Module resolution works in worker context
+- Helper function executes correctly
+
+### Test 3: Worker HMR (Simple)
+```javascript
+// worker.js
+self.onmessage = (e) => {
+  self.postMessage('v1');
+};
+
+// Edit to:
+self.onmessage = (e) => {
+  self.postMessage('v2');
+};
+```
+
+**Expected (initial implementation):**
+- Page reloads when worker code changes
+- Worker uses new code after reload
+
+**Expected (future):**
+- Worker hot-reloads without page reload
+- New worker code executes
+- Existing worker terminates gracefully
+
+## Future Enhancements
+
+### 1. True Worker HMR
+- Workers can hot-reload without terminating
+- Use `postMessage` bridge to notify worker of updates
+- Worker can accept/reject updates like modules
+
+### 2. Shared Workers
+- Support `new SharedWorker()`
+- Multiple pages can share worker instances
+- Coordinate HMR across all connected pages
+
+### 3. Service Workers
+- Support `navigator.serviceWorker.register()`
+- Special handling for service worker lifecycle
+- Mock service worker APIs in dev mode
+
+### 4. Worker Module Type
+- Support `new Worker(url, { type: 'module' })`
+- Native ES module workers
+- Different bundling strategy for module workers
+
+## Success Criteria
+
+Phase 1 complete when:
+- [x] Production worker bundling works (DONE)
+- [ ] Workers detected as entry points in dev server
+- [ ] Worker bundles created and served
+- [ ] Basic test case works in dev mode
+- [ ] No regressions in production builds
+
+Full implementation complete when:
+- [ ] All test cases pass
+- [ ] HMR triggers page reload on worker changes
+- [ ] Documentation updated
+- [ ] Edge cases handled (worker errors, missing files, etc.)
+
+## Open Questions
+
+1. **Worker HMR WebSocket**: Should workers have their own WebSocket connection, or communicate via `postMessage` with the parent page?
+   - **Answer:** Start simple - parent page relays HMR events via postMessage if needed. For initial version, just reload page.
+
+2. **Worker URL scheme**: What URL pattern should we use for workers in dev mode?
+   - **Proposal:** `/_bun/w/[relative-path]?v=[hash]`
+   - Alternative: `/__worker/[hash].js`
+
+3. **Worker-specific globals**: How do we handle worker-only globals (`self`, `importScripts`)?
+   - **Answer:** Workers bundle with appropriate target context. The HMR runtime should detect worker context.
+
+4. **Module vs Classic workers**: Should we support both?
+   - **Answer:** Start with classic workers (default). Module workers can be added later.
+
+## Dependencies
+
+This implementation depends on:
+- Existing production worker bundling (DONE)
+- Existing HMR infrastructure
+- Existing IncrementalGraph system
+- No external dependencies needed
+
+## Timeline Estimate
+
+- **Phase 1 (Detection & Entry Points):** 2-4 hours
+- **Phase 2 (Bundling & Code Gen):** 3-5 hours
+- **Phase 3 (HMR Runtime):** 1-2 hours
+- **Phase 4 (Request Handling):** 2-3 hours
+- **Phase 5 (Scan Phase Fix):** 1 hour
+- **Testing & Debug:** 3-4 hours
+
+**Total:** ~12-19 hours of focused development
+
+## Notes
+
+- Start with the simplest possible implementation (page reload on worker change)
+- Ensure production builds continue to work perfectly
+- Test frequently with real examples
+- Document as we go
diff --git a/src/js_printer.zig b/src/js_printer.zig
index 2f8f452eaf..397e483b1d 100644
--- a/src/js_printer.zig
+++ b/src/js_printer.zig
@@ -2208,10 +2208,16 @@ fn NewPrinter(
                     p.addSourceMapping(expr.loc);
                     p.print("new Worker(");
 
-                    // Generate a unique key for the worker instead of the direct path
-                    // This will be resolved to the actual worker chunk path later
-                    if (p.options.unique_key_prefix.len > 0) {
-                        const import_record = p.importRecord(e.import_record_index);
+                    const import_record = p.importRecord(e.import_record_index);
+
+                    // In dev mode, use the direct path - the dev server will resolve it
+                    // In production mode, use unique keys for chunk path resolution
+                    if (p.options.module_type == .internal_bake_dev) {
+                        // Dev mode: use the original path
+                        // The dev server will serve this worker as a separate bundle
+                        p.printStringLiteralUTF8(import_record.path.pretty, true);
+                    } else if (p.options.unique_key_prefix.len > 0) {
+                        // Production mode: use unique keys for chunk resolution
                         // Use the source_index from the import record, not the import_record_index
                         // This allows the linker to map from source_index to chunk_index using entry_point_chunk_indices
                         const source_index = import_record.source_index.get();
@@ -2220,7 +2226,7 @@ fn NewPrinter(
                         p.printStringLiteralUTF8(unique_key, true);
                     } else {
                         // Fallback to direct path if unique_key_prefix is not available
-                        p.printStringLiteralUTF8(p.importRecord(e.import_record_index).path.text, true);
+                        p.printStringLiteralUTF8(import_record.path.text, true);
                     }
 
                     // Print options if present and not missing