resolver: bust the real-path alias of a symlinked directory with the dir cache

src/resolver/resolver.rs

@@ -2445,16 +2445,33 @@ impl<'a> Resolver<'a> {
     /// See `assertValidCacheKey` for requirements on the input
     pub fn bust_dir_cache(&mut self, path: &[u8]) -> bool {
         Self::assert_valid_cache_key(path);
+        // A symlinked directory is also cached under its real path
+        // (`DirInfo.abs_real_path`), and resolve results are realpath'd, so a
+        // follow-up resolve reads the real-path key. Bust that alias too.
+        let real_path: Option<&'static [u8]> = self
+            .dir_cache_mut()
+            .get(path)
+            .map(|info| strings::without_trailing_slash_windows_path(info.abs_real_path))
+            .filter(|real| !real.is_empty() && *real != path);
         let first_bust = self.fs_mut().fs.bust_entries_cache(path);
         let second_bust = self.dir_cache_mut().remove(path);
+        let alias_bust = match real_path {
+            Some(real) => {
+                let a = self.fs_mut().fs.bust_entries_cache(real);
+                let b = self.dir_cache_mut().remove(real);
+                a || b
+            }
+            None => false,
+        };
         bun_core::scoped_log!(
             ResolverDev,
-            "Bust {} = {}, {}",
+            "Bust {} = {}, {}, alias {}",
             bstr::BStr::new(path),
             first_bust,
-            second_bust
+            second_bust,
+            alias_bust
         );
-        first_bust || second_bust
+        first_bust || second_bust || alias_bust
     }
 
     /// bust both the named file and a parent directory, because `./hello` can resolve

test/js/bun/resolve/resolve.test.ts

@@ -899,6 +899,52 @@ describe.if(isWindows)("#30839 - imports entry pointing at a scoped package", ()
   });
 });
 
+// A directory reached through a symlink is cached under two keys: the symlink
+// path and its real path. Requiring a file in it caches both listings; when a
+// sibling file is created afterwards, only the symlink-side key was busted, so
+// the follow-up resolve of the realpath'd result hit a stale listing and
+// failed with "Cannot find module ... from ''". macOS always hits this because
+// os.tmpdir() is behind the /var -> /private/var symlink.
+// https://github.com/oven-sh/bun/issues/40585
+it("requires a newly created sibling .ts file in a directory behind a symlink", async () => {
+  using dir = tempDir("resolve-symlink-alias", {
+    "main.ts": `
+      import { mkdir, writeFile } from "node:fs/promises";
+      import { createRequire } from "node:module";
+      import { join } from "node:path";
+      import { pathToFileURL } from "node:url";
+
+      const dir = join(import.meta.dir, "link", "warm");
+      await mkdir(dir, { recursive: true });
+      const a = join(dir, "a.ts");
+      await writeFile(a, "export const A = 1;\\n");
+      createRequire(pathToFileURL(a).href)(a);
+      const b = join(dir, "b.ts");
+      await writeFile(b, "export const B = 2;\\n");
+      const result = createRequire(pathToFileURL(b).href)(b);
+      console.log(JSON.stringify(result));
+    `,
+  });
+  const root = String(dir);
+  mkdirSync(join(root, "real"));
+  // The symlink must exist before the child process starts, like /var on
+  // macOS. "junction" is the Windows-appropriate symlink kind for directories.
+  symlinkSync(join(root, "real"), join(root, "link"), "junction");
+
+  await using proc = Bun.spawn({
+    cmd: [bunExe(), "main.ts"],
+    env: bunEnv,
+    cwd: root,
+    stdout: "pipe",
+    stderr: "pipe",
+  });
+  const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+
+  expect(stderr).toBe("");
+  expect(stdout).toBe('{"B":2}\n');
+  expect(exitCode).toBe(0);
+});
+
 // dirInfoCachedMaybeLog reads the rfs.entries cache without checking the union
 // tag. If readDirectory() previously failed with a non-ENOENT error (e.g.
 // EACCES), a `.err` variant is stored there; re-resolving the directory after