fix(build): enable sourcemap resolution for compiled binaries

Fix four issues preventing sourcemaps from working in Bun-compiled binaries:

1. Events had no debug_meta because the IIFE snippet was placed before
   ESM imports (invalid ESM). Register debug IDs at module scope via
   build-time constant instead.

2. Artifact bundle ZIPs lacked the SYSB magic header required by
   the symbolic crate's SourceBundle parser. Add the 8-byte header
   in ZipWriter.

3. Bun.build reformats code (3.7k → 40k lines), breaking sourcemap
   positions. Use sourcemap: "linked" to embed a map in the binary
   that Bun's runtime uses to auto-resolve Error.stack positions
   back to esbuild output coordinates.

4. Bun's embedded map produces relative paths in Error.stack (e.g.,
   "dist-bin/bin.js"). The symbolicator's URL candidate generator
   skips relative paths silently. Normalize to absolute in beforeSend.

Author: BYK

script/build.ts

@@ -30,15 +30,15 @@
  *     bin.js.map          (sourcemap, uploaded to Sentry then deleted)
  */
 
-import { mkdirSync } from "node:fs";
+import { mkdirSync, renameSync } from "node:fs";
 import { promisify } from "node:util";
 import { gzip } from "node:zlib";
 import { processBinary } from "binpunch";
 import { $ } from "bun";
 import { build as esbuild } from "esbuild";
 import pkg from "../package.json";
 import { uploadSourcemaps } from "../src/lib/api/sourcemaps.js";
-import { injectDebugId } from "./debug-id.js";
+import { injectDebugId, PLACEHOLDER_DEBUG_ID } from "./debug-id.js";
 
 const gzipAsync = promisify(gzip);
 
@@ -104,13 +104,15 @@ async function bundleJs(): Promise<boolean> {
       target: "esnext",
       format: "esm",
       external: ["bun:*"],
-      sourcemap: "external",
+      sourcemap: "linked",
+      // Minify syntax and whitespace but NOT identifiers. Bun.build
       minify: true,
       metafile: true,
       define: {
         SENTRY_CLI_VERSION: JSON.stringify(VERSION),
         SENTRY_CLIENT_ID_BUILD: JSON.stringify(SENTRY_CLIENT_ID),
         "process.env.NODE_ENV": JSON.stringify("production"),
+        __SENTRY_DEBUG_ID__: JSON.stringify(PLACEHOLDER_DEBUG_ID),
       },
     });
 
@@ -147,20 +149,57 @@ async function bundleJs(): Promise<boolean> {
  * injection always runs (even without auth token) so local builds get
  * debug IDs for development/testing.
  */
-async function injectAndUploadSourcemap(): Promise<void> {
-  // Always inject debug IDs (even without auth token) so local builds
-  // get debug IDs for development/testing purposes.
+/** Module-level debug ID set by {@link injectDebugIds} for use in {@link uploadSourcemapToSentry}. */
+let currentDebugId: string | undefined;
+
+/**
+ * Inject debug IDs into the JS and sourcemap. Runs before compilation.
+ * The upload happens separately after compilation (see {@link uploadSourcemapToSentry}).
+ */
+async function injectDebugIds(): Promise<void> {
+  // skipSnippet: true — the IIFE snippet breaks ESM (placed before import
+  // declarations). The debug ID is instead registered in constants.ts via
+  // a build-time __SENTRY_DEBUG_ID__ constant.
   console.log("  Injecting debug IDs...");
-  let debugId: string;
   try {
-    ({ debugId } = await injectDebugId(BUNDLE_JS, SOURCEMAP_FILE));
+    const { debugId } = await injectDebugId(BUNDLE_JS, SOURCEMAP_FILE, {
+      skipSnippet: true,
+    });
+    currentDebugId = debugId;
     console.log(`    -> Debug ID: ${debugId}`);
   } catch (error) {
     const msg = error instanceof Error ? error.message : String(error);
     console.warn(`    Warning: Debug ID injection failed: ${msg}`);
     return;
   }
 
+  // Replace the placeholder UUID with the real debug ID in the JS bundle.
+  // Both are 36-char UUIDs so sourcemap character positions stay valid.
+  try {
+    const jsContent = await Bun.file(BUNDLE_JS).text();
+    await Bun.write(
+      BUNDLE_JS,
+      jsContent.split(PLACEHOLDER_DEBUG_ID).join(currentDebugId)
+    );
+  } catch (error) {
+    const msg = error instanceof Error ? error.message : String(error);
+    console.warn(
+      `    Warning: Debug ID placeholder replacement failed: ${msg}`
+    );
+  }
+}
+
+/**
+ * Upload the (composed) sourcemap to Sentry. Runs after compilation
+ * because {@link compileTarget} composes the Bun sourcemap with the
+ * esbuild sourcemap first.
+ */
+async function uploadSourcemapToSentry(): Promise<void> {
+  const debugId = currentDebugId;
+  if (!debugId) {
+    return;
+  }
+
   if (!process.env.SENTRY_AUTH_TOKEN) {
     console.log("  No SENTRY_AUTH_TOKEN, skipping sourcemap upload");
     return;
@@ -169,7 +208,13 @@ async function injectAndUploadSourcemap(): Promise<void> {
   console.log(`  Uploading sourcemap to Sentry (release: ${VERSION})...`);
 
   try {
-    const urlPrefix = "~/$bunfs/root/";
+    // With sourcemap: "linked", Bun's runtime auto-resolves Error.stack
+    // paths via the embedded map, producing relative paths like
+    // "dist-bin/bin.js". The beforeSend hook normalizes these to absolute
+    // ("/dist-bin/bin.js") so the symbolicator's candidate URL generator
+    // produces "~/dist-bin/bin.js" — matching our upload URL.
+    const dir = BUNDLE_JS.slice(0, BUNDLE_JS.lastIndexOf("/") + 1);
+    const urlPrefix = `~/${dir}`;
     const jsBasename = BUNDLE_JS.split("/").pop() ?? "bin.js";
     const mapBasename = SOURCEMAP_FILE.split("/").pop() ?? "bin.js.map";
 
@@ -204,8 +249,11 @@ async function injectAndUploadSourcemap(): Promise<void> {
 /**
  * Step 2: Compile the pre-bundled JS into a native binary for a target.
  *
- * Uses the JS file produced by {@link bundleJs} — no sourcemap is embedded
- * in the binary (it's uploaded to Sentry separately).
+ * Uses the JS file produced by {@link bundleJs}. The esbuild sourcemap
+ * (JS → original TS) is uploaded to Sentry as-is — no composition needed
+ * because `sourcemap: "linked"` causes Bun to embed a sourcemap in the
+ * binary that its runtime uses to auto-resolve `Error.stack` positions
+ * back to the esbuild output's coordinate space.
  */
 async function compileTarget(target: BuildTarget): Promise<boolean> {
   const packageName = getPackageName(target);
@@ -215,31 +263,48 @@ async function compileTarget(target: BuildTarget): Promise<boolean> {
 
   console.log(`  Step 2: Compiling ${packageName}...`);
 
-  const result = await Bun.build({
-    entrypoints: [BUNDLE_JS],
-    compile: {
-      target: getBunTarget(target) as
-        | "bun-darwin-arm64"
-        | "bun-darwin-x64"
-        | "bun-linux-x64"
-        | "bun-linux-arm64"
-        | "bun-windows-x64",
-      outfile,
-    },
-    // Already minified in Step 1 — skip re-minification to avoid
-    // double-minifying identifiers and producing different output.
-    minify: false,
-  });
-
-  if (!result.success) {
-    console.error(`  Failed to compile ${packageName}:`);
-    for (const log of result.logs) {
-      console.error(`    ${log}`);
+  // Rename the esbuild map out of the way before Bun.build overwrites it
+  // (sourcemap: "linked" writes Bun's own map to bin.js.map).
+  // Restored in the finally block so subsequent targets and the upload
+  // always find the esbuild map, even if compilation fails.
+  const esbuildMapBackup = `${SOURCEMAP_FILE}.esbuild`;
+  renameSync(SOURCEMAP_FILE, esbuildMapBackup);
+
+  try {
+    const result = await Bun.build({
+      entrypoints: [BUNDLE_JS],
+      compile: {
+        target: getBunTarget(target) as
+          | "bun-darwin-arm64"
+          | "bun-darwin-x64"
+          | "bun-linux-x64"
+          | "bun-linux-arm64"
+          | "bun-windows-x64",
+        outfile,
+      },
+      // "linked" embeds a sourcemap in the binary. At runtime, Bun's engine
+      // auto-resolves Error.stack positions through this embedded map back to
+      // the esbuild output positions. The esbuild sourcemap (uploaded to
+      // Sentry) then maps those to original TypeScript sources.
+      sourcemap: "linked",
+      // Minify whitespace and syntax but NOT identifiers to avoid Bun's
+      // identifier renaming collision bug (oven-sh/bun#14585).
+      minify: { whitespace: true, syntax: true, identifiers: false },
+    });
+
+    if (!result.success) {
+      console.error(`  Failed to compile ${packageName}:`);
+      for (const log of result.logs) {
+        console.error(`    ${log}`);
+      }
+      return false;
     }
-    return false;
-  }
 
-  console.log(`    -> ${outfile}`);
+    console.log(`    -> ${outfile}`);
+  } finally {
+    // Restore the esbuild sourcemap (Bun.build wrote its own map).
+    renameSync(esbuildMapBackup, SOURCEMAP_FILE);
+  }
 
   // Hole-punch: zero unused ICU data entries so they compress to nearly nothing.
   // Always runs so the smoke test exercises the same binary as the release.
@@ -344,8 +409,10 @@ async function build(): Promise<void> {
     process.exit(1);
   }
 
-  // Inject debug IDs and upload sourcemap to Sentry before compiling (non-fatal on failure)
-  await injectAndUploadSourcemap();
+  // Inject debug IDs into the JS and sourcemap (non-fatal on failure).
+  // Upload happens AFTER compilation because Bun.build (with sourcemap: "linked")
+  // overwrites bin.js.map. We restore it from the saved copy before uploading.
+  await injectDebugIds();
 
   console.log("");
 
@@ -362,6 +429,9 @@ async function build(): Promise<void> {
     }
   }
 
+  // Step 3: Upload the composed sourcemap to Sentry (after compilation)
+  await uploadSourcemapToSentry();
+
   // Clean up intermediate bundle (only the binaries are artifacts)
   await $`rm -f ${BUNDLE_JS} ${SOURCEMAP_FILE}`;
 

script/bundle.ts

@@ -3,7 +3,7 @@ import { unlink } from "node:fs/promises";
 import { build, type Plugin } from "esbuild";
 import pkg from "../package.json";
 import { uploadSourcemaps } from "../src/lib/api/sourcemaps.js";
-import { injectDebugId } from "./debug-id.js";
+import { injectDebugId, PLACEHOLDER_DEBUG_ID } from "./debug-id.js";
 
 const VERSION = pkg.version;
 const SENTRY_CLIENT_ID = process.env.SENTRY_CLIENT_ID ?? "";
@@ -67,7 +67,9 @@ async function injectDebugIdsForOutputs(
   for (const jsPath of jsFiles) {
     const mapPath = `${jsPath}.map`;
     try {
-      const { debugId } = await injectDebugId(jsPath, mapPath);
+      const { debugId } = await injectDebugId(jsPath, mapPath, {
+        skipSnippet: true,
+      });
       injected.push({ jsPath, mapPath, debugId });
       console.log(`  Debug ID injected: ${debugId}`);
     } catch (err) {
@@ -151,6 +153,16 @@ const sentrySourcemapPlugin: Plugin = {
         return;
       }
 
+      // Replace the placeholder UUID with the real debug ID in each JS output.
+      // Both are 36-char UUIDs so sourcemap character positions stay valid.
+      for (const { jsPath, debugId } of injected) {
+        const content = await Bun.file(jsPath).text();
+        await Bun.write(
+          jsPath,
+          content.split(PLACEHOLDER_DEBUG_ID).join(debugId)
+        );
+      }
+
       if (!process.env.SENTRY_AUTH_TOKEN) {
         return;
       }
@@ -194,6 +206,7 @@ const result = await build({
     SENTRY_CLI_VERSION: JSON.stringify(VERSION),
     SENTRY_CLIENT_ID_BUILD: JSON.stringify(SENTRY_CLIENT_ID),
     "process.env.NODE_ENV": JSON.stringify("production"),
+    __SENTRY_DEBUG_ID__: JSON.stringify(PLACEHOLDER_DEBUG_ID),
     // Replace import.meta.url with the injected shim variable for CJS
     "import.meta.url": "import_meta_url",
   },

script/debug-id.ts

@@ -10,3 +10,13 @@ export {
   getDebugIdSnippet,
   injectDebugId,
 } from "../src/lib/sourcemap/debug-id.js";
+
+/**
+ * Placeholder UUID used by esbuild's `define` for `__SENTRY_DEBUG_ID__`.
+ *
+ * After esbuild finishes and the real debug ID is computed from the
+ * sourcemap content hash, this placeholder is replaced in the JS output
+ * via `String.replaceAll`. The placeholder is exactly 36 characters
+ * (standard UUID length) so character positions in the sourcemap stay valid.
+ */
+export const PLACEHOLDER_DEBUG_ID = "deb00000-de60-4d00-a000-000000000000";

src/lib/constants.ts

@@ -7,6 +7,17 @@ import { getEnv } from "./env.js";
 /** Build-time constant injected by esbuild/bun */
 declare const SENTRY_CLI_VERSION: string | undefined;
 
+/**
+ * Build-time debug ID for sourcemap resolution, injected by esbuild.
+ *
+ * During the build, esbuild's `define` replaces this identifier with a
+ * placeholder UUID string literal. After esbuild finishes, the build
+ * script replaces the placeholder with the real debug ID (derived from
+ * the sourcemap content hash). The same-length swap keeps sourcemap
+ * character positions valid.
+ */
+declare const __SENTRY_DEBUG_ID__: string | undefined;
+
 /** Default Sentry SaaS hostname */
 export const DEFAULT_SENTRY_HOST = "sentry.io";
 
@@ -106,3 +117,31 @@ export function getUserAgent(): string {
  */
 export const SENTRY_CLI_DSN =
   "https://1188a86f3f8168f089450587b00bca66@o1.ingest.us.sentry.io/4510776311808000";
+
+/**
+ * Register the build-time debug ID with the Sentry SDK's native discovery.
+ *
+ * The SDK reads `globalThis._sentryDebugIds` (a map of Error.stack → debugId)
+ * during event processing to populate `debug_meta.images`, which the server
+ * uses to match uploaded sourcemaps.
+ *
+ * Previously this was done by a runtime IIFE snippet prepended to the bundle
+ * output by `injectDebugId()`. That broke ESM because the snippet appeared
+ * before `import` declarations. Placing the same logic here — inside the
+ * module, after all imports — is valid ESM and feeds the SDK's existing
+ * mechanism directly.
+ */
+if (typeof __SENTRY_DEBUG_ID__ !== "undefined") {
+  try {
+    // biome-ignore lint/suspicious/useErrorMessage: stack trace capture only
+    const stack = new Error().stack;
+    if (stack) {
+      // biome-ignore lint/suspicious/noExplicitAny: SDK reads this untyped global
+      const g = globalThis as any;
+      g._sentryDebugIds = g._sentryDebugIds || {};
+      g._sentryDebugIds[stack] = __SENTRY_DEBUG_ID__;
+    }
+  } catch (_) {
+    // Non-critical — sourcemap resolution degrades gracefully
+  }
+}