test(nextjs): Add regression tests for node export condition split

Assert that the `node` condition of the root export has an
`import`/`require` split whose entries point at files that actually exist
in the ESM and CJS build output, and that the ESM server module graph
contains no extensionless `next/*` deep imports (which are unresolvable by
Node's ESM resolver because `next` ships no `exports` map).

Ref #22791

Author: Mohith26

packages/nextjs/test/exportsMap.test.ts

@@ -0,0 +1,79 @@
+import { existsSync, readFileSync } from 'node:fs';
+import { dirname, resolve } from 'node:path';
+import { describe, expect, it } from 'vitest';
+
+/**
+ * The `node` export condition must offer an `import`/`require` split like its sibling conditions. When it was a bare
+ * string pointing at the CJS server build, every ESM consumer under a plain Node.js loader received the CJS build
+ * (`node` matches before the top-level `import` condition), so `cjs-module-lexer` could not see the bindings
+ * re-exported from `@sentry/core` / `@sentry/node`: named imports failed to link and namespace imports contained
+ * silently-undefined members.
+ *
+ * Regression test for https://github.com/getsentry/sentry-javascript/issues/22791
+ */
+describe('package.json exports map', () => {
+  const packageRoot = resolve(__dirname, '..');
+  const packageJson = JSON.parse(readFileSync(resolve(packageRoot, 'package.json'), 'utf8')) as {
+    exports: Record<string, Record<string, unknown>>;
+  };
+
+  const nodeCondition = packageJson.exports['.']?.['node'] as Record<string, string> | undefined;
+
+  it('has an `import`/`require` split under the `node` condition of the root export', () => {
+    expect(nodeCondition).toBeInstanceOf(Object);
+    expect(typeof nodeCondition?.import).toBe('string');
+    expect(typeof nodeCondition?.require).toBe('string');
+  });
+
+  it('points the `node.import` condition at an existing file in the ESM build output', () => {
+    expect(nodeCondition?.import).toMatch(/\/esm\//);
+    expect(existsSync(resolve(packageRoot, nodeCondition?.import as string))).toBe(true);
+  });
+
+  it('points the `node.require` condition at an existing file in the CJS build output', () => {
+    expect(nodeCondition?.require).toMatch(/\/cjs\//);
+    expect(existsSync(resolve(packageRoot, nodeCondition?.require as string))).toBe(true);
+  });
+});
+
+/**
+ * `next` does not declare an `exports` map, so Node's ESM resolver requires explicit file extensions for deep imports
+ * like `next/constants.js`. Extensionless specifiers work in webpack/turbopack but throw `ERR_MODULE_NOT_FOUND` under
+ * a plain Node.js loader, which would make the ESM server build (reachable via `node.import`) unloadable.
+ *
+ * Regression test for https://github.com/getsentry/sentry-javascript/issues/22791
+ */
+describe('ESM server build is loadable by plain Node.js', () => {
+  it('uses explicit file extensions for all `next/*` deep imports in the ESM server module graph', () => {
+    const packageRoot = resolve(__dirname, '..');
+    const entry = resolve(packageRoot, 'build/esm/index.server.js');
+    expect(existsSync(entry)).toBe(true);
+
+    const importSpecifierRegex = /(?:from|import)\s*['"]([^'"]+)['"]/g;
+    const visited = new Set<string>();
+    const queue = [entry];
+    const extensionlessNextImports: string[] = [];
+
+    while (queue.length > 0) {
+      const file = queue.pop() as string;
+      if (visited.has(file) || !existsSync(file)) {
+        continue;
+      }
+      visited.add(file);
+
+      const source = readFileSync(file, 'utf8');
+      for (const match of source.matchAll(importSpecifierRegex)) {
+        const specifier = match[1] as string;
+        if (specifier.startsWith('.')) {
+          const resolved = resolve(dirname(file), specifier);
+          queue.push(resolved.endsWith('.js') ? resolved : `${resolved}.js`);
+        } else if (/^next\/.+/.test(specifier) && !/\.[cm]?js$/.test(specifier)) {
+          extensionlessNextImports.push(`${specifier} (in ${file.replace(packageRoot, '')})`);
+        }
+      }
+    }
+
+    expect(visited.size).toBeGreaterThan(1);
+    expect(extensionlessNextImports).toEqual([]);
+  });
+});