fix(wasi): resolve path_open paths against preopen directory, not cwd

src/js/node/wasi.ts

@@ -1437,7 +1437,7 @@ var require_wasi = __commonJS({
           path_open: wrap(
             (dirfd, _dirflags, pathPtr, pathLen, oflags, fsRightsBase, fsRightsInheriting, fsFlags, fdPtr) => {
               try {
-                CHECK_FD(dirfd, constants_1.WASI_RIGHT_PATH_OPEN);
+                const stats = CHECK_FD(dirfd, constants_1.WASI_RIGHT_PATH_OPEN);
                 fsRightsBase = BigInt(fsRightsBase);
                 fsRightsInheriting = BigInt(fsRightsInheriting);
                 const read =
@@ -1512,7 +1512,7 @@ var require_wasi = __commonJS({
                 if (p.startsWith("proc/")) {
                   throw new types_1.WASIError(constants_1.WASI_EBADF);
                 }
-                const fullUnresolved = path.resolve(p);
+                const fullUnresolved = path.resolve(stats.path, p);
                 let full;
                 try {
                   full = fs.realpathSync(fullUnresolved);

test/js/bun/wasm/wasi.test.js

@@ -1,6 +1,9 @@
 import { spawnSync } from "bun";
 import { expect, it } from "bun:test";
 import { bunEnv, bunExe } from "harness";
+import { mkdtempSync, writeFileSync, rmSync } from "fs";
+import { join } from "path";
+import { tmpdir } from "os";
 
 it("Should support printing 'hello world'", () => {
   const { stdout, stderr, exitCode } = spawnSync({
@@ -20,3 +23,47 @@ it("Should support printing 'hello world'", () => {
     exitCode: 0,
   });
 });
+
+it("path_open should resolve paths against preopens, not cwd", () => {
+  // Create a temp file to read via WASI
+  const tmp = mkdtempSync(join(tmpdir(), "bun-wasi-test-"));
+  const testFile = join(tmp, "input.txt");
+  writeFileSync(testFile, "hello from preopens\n");
+
+  try {
+    // read-file.wasm: minimal Rust WASI binary that reads a file path from args
+    // and prints its contents to stdout.
+    //
+    // Built from:
+    //   cargo new --name read-file-wasi read-file-wasi
+    //   # src/main.rs:
+    //   #   use std::{env, fs, process};
+    //   #   fn main() {
+    //   #       let args: Vec<String> = env::args().collect();
+    //   #       if args.len() < 2 { eprintln!("usage: read-file <path>"); process::exit(1); }
+    //   #       match fs::read_to_string(&args[1]) {
+    //   #           Ok(c) => print!("{}", c),
+    //   #           Err(e) => { eprintln!("error: {}: {}", args[1], e); process::exit(1); }
+    //   #       }
+    //   #   }
+    //   cargo build --target wasm32-wasip1 --release
+    const { stdout, stderr, exitCode } = spawnSync({
+      cmd: [bunExe(), import.meta.dir + "/read-file.wasm", testFile],
+      stdout: "pipe",
+      stderr: "pipe",
+      env: bunEnv,
+    });
+
+    expect({
+      stdout: stdout.toString(),
+      stderr: stderr.toString(),
+      exitCode: exitCode,
+    }).toEqual({
+      stdout: "hello from preopens\n",
+      stderr: "",
+      exitCode: 0,
+    });
+  } finally {
+    rmSync(tmp, { recursive: true, force: true });
+  }
+});