fix(esbuild): Avoid import-is-undefined warning for entries without a default export

packages/bundler-plugins/src/esbuild/index.ts

@@ -55,6 +55,7 @@ interface EsbuildInitialOptions {
   define?: Record<string, string>;
   write?: boolean;
   absWorkingDir?: string;
+  logOverride?: Record<string, string>;
 }
 
 interface EsbuildPluginBuild {
@@ -199,6 +200,10 @@ export function sentryEsbuildPlugin(userOptions: Options = {}): any {
         // rebuild wraps the entry points again.
         onStart(() => debugIdWrappedPaths.clear());
 
+        // The proxy module re-exports `OriginalModule.default` statically so downstream bundlers can tree-shake it,
+        // but esbuild warns about that access when the entry point has no default export.
+        initialOptions.logOverride = { 'import-is-undefined': 'silent', ...initialOptions.logOverride };
+
         if (!initialOptions.bundle) {
           logger.warn(
             'The Sentry esbuild plugin only supports esbuild with `bundle: true` being set in the esbuild build options. Esbuild will probably crash now. Sorry about that. If you need to upload sourcemaps without `bundle: true`, it is recommended to use Sentry CLI instead: https://docs.sentry.io/platforms/javascript/sourcemaps/uploading/cli/',

packages/bundler-plugins/test/esbuild/entry-without-default-export.test.ts

@@ -0,0 +1,63 @@
+import * as fs from 'fs';
+import * as os from 'os';
+import * as path from 'path';
+import * as esbuild from 'esbuild';
+import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import { sentryEsbuildPlugin } from '../../src/esbuild';
+
+describe('entry points without a default export', () => {
+  let tmpDir: string;
+  let entry: string;
+
+  beforeEach(() => {
+    tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), 'sentry-esbuild-entry-exports-'));
+    entry = path.join(tmpDir, 'entry.js');
+  });
+
+  afterEach(() => {
+    fs.rmSync(tmpDir, { recursive: true, force: true });
+  });
+
+  function build(logOverride?: Record<string, esbuild.LogLevel>): Promise<esbuild.BuildResult> {
+    return esbuild.build({
+      entryPoints: [entry],
+      bundle: true,
+      write: false,
+      format: 'esm',
+      logLevel: 'silent',
+      absWorkingDir: tmpDir,
+      logOverride,
+      plugins: [sentryEsbuildPlugin({ telemetry: false, sourcemaps: { disable: 'disable-upload' } })],
+    });
+  }
+
+  it.each([
+    ['an ES module without exports', 'export {};'],
+    ['an ES module with only named exports', 'export const answer = 42;'],
+    ['a plain script', 'console.log("hello");'],
+  ])('does not warn for %s', async (_name, source) => {
+    fs.writeFileSync(entry, source);
+
+    const result = await build();
+
+    expect(result.warnings).toEqual([]);
+    expect(result.outputFiles?.[0]?.text).toContain('_sentryDebugIds');
+  });
+
+  it('keeps named exports of the entry point', async () => {
+    fs.writeFileSync(entry, 'export const answer = 42;');
+
+    const result = await build();
+
+    expect(result.warnings).toEqual([]);
+    expect(result.outputFiles?.[0]?.text).toMatch(/export\s*{[^}]*answer[^}]*}/);
+  });
+
+  it('keeps a user-provided override for the same esbuild message', async () => {
+    fs.writeFileSync(entry, 'export {};');
+
+    await expect(build({ 'import-is-undefined': 'error' })).rejects.toThrow(
+      /import-is-undefined|will always be undefined/,
+    );
+  });
+});