Fix module resolution: '.' in subdirectory resolves to index.ts

Previously, importing '.' or './' from within a subdirectory would
incorrectly resolve to a file with the same name in the parent
directory, rather than the index file in the current directory.

For example, importing from 'lib/run.ts':
```ts
import { foo } from ".";
```

Would incorrectly resolve to the root 'lib.ts' instead of 'lib/index.ts'.

This fix adds a check in loadAsFile() to detect when the path being
resolved is actually a directory. If the basename has no extension
(indicating it's likely a directory reference), we check if it exists
as a directory before attempting file resolution. This ensures directory
imports correctly fall through to index file resolution.

Fixes #24449

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/resolver/resolver.zig

@@ -3779,6 +3779,18 @@ pub const Resolver = struct {
             }
         }
 
+        // If the path itself is an existing directory, don't try to load it as a file.
+        // This prevents "import '.' from 'lib/foo.ts'" incorrectly resolving to a file
+        // named "lib.ts" in the parent directory instead of "lib/index.ts".
+        if (r.dirInfoCached(path) catch null) |_| {
+            if (r.debug_logs) |*debug| {
+                debug.addNoteFmt("\"{s}\" is a directory, not a file", .{path});
+            }
+            return null;
+        }
+
+        const base = std.fs.path.basename(path);
+
         const dir_path = bun.strings.withoutTrailingSlashWindowsPath(Dirname.dirname(path));
 
         const dir_entry: *Fs.FileSystem.RealFS.EntriesOption = rfs.readDirectory(
@@ -3811,8 +3823,6 @@ pub const Resolver = struct {
 
         const entries = dir_entry.entries;
 
-        const base = std.fs.path.basename(path);
-
         // Try the plain path without any extensions
         if (r.debug_logs) |*debug| {
             debug.addNoteFmt("Checking for file \"{s}\" ", .{base});

test/regression/issue/24449.test.ts

@@ -0,0 +1,54 @@
+import { expect, test } from "bun:test";
+import { bunEnv, bunExe, normalizeBunSnapshot, tempDir } from "harness";
+
+test("issue #24449 - '.' in subdirectory should resolve to index.ts, not root file with same name", async () => {
+  // Create temp directory with test files
+  using dir = tempDir("test-issue-24449", {
+    "lib.ts": `export const eulerNumber = 2.71828;`,
+    "lib/index.ts": `export const piNumber = 3.14159;`,
+    "lib/run.ts": `
+import { piNumber } from ".";
+console.log("piNumber:", piNumber);
+`,
+  });
+
+  // Spawn Bun process
+  await using proc = Bun.spawn({
+    cmd: [bunExe(), "lib/run.ts"],
+    env: bunEnv,
+    cwd: String(dir),
+    stderr: "pipe",
+  });
+
+  const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+
+  // Should import from lib/index.ts, not lib.ts
+  expect(normalizeBunSnapshot(stdout, dir)).toMatchInlineSnapshot(`"piNumber: 3.14159"`);
+  expect(exitCode).toBe(0);
+});
+
+test("issue #24449 - './' in subdirectory should resolve to index.ts, not root file with same name", async () => {
+  // Create temp directory with test files
+  using dir = tempDir("test-issue-24449-slash", {
+    "lib.ts": `export const eulerNumber = 2.71828;`,
+    "lib/index.ts": `export const piNumber = 3.14159;`,
+    "lib/run.ts": `
+import { piNumber } from "./";
+console.log("piNumber:", piNumber);
+`,
+  });
+
+  // Spawn Bun process
+  await using proc = Bun.spawn({
+    cmd: [bunExe(), "lib/run.ts"],
+    env: bunEnv,
+    cwd: String(dir),
+    stderr: "pipe",
+  });
+
+  const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+
+  // Should import from lib/index.ts, not lib.ts
+  expect(normalizeBunSnapshot(stdout, dir)).toMatchInlineSnapshot(`"piNumber: 3.14159"`);
+  expect(exitCode).toBe(0);
+});