wasi:filesystem@0.3.0-rc-2025-09-16: Add tests for unlink errors

See WebAssembly/WASI#852.

Author: wingo

tests/rust/wasm32-wasip3/src/bin/filesystem-unlink-errors.json

@@ -0,0 +1,3 @@
+{
+    "dirs": ["fs-tests.dir"]
+}

tests/rust/wasm32-wasip3/src/bin/filesystem-unlink-errors.rs

@@ -0,0 +1,61 @@
+use std::process;
+extern crate wit_bindgen;
+
+wit_bindgen::generate!({
+    inline: r"
+  package test:test;
+
+  world test {
+      include wasi:filesystem/imports@0.3.0-rc-2026-02-09;
+      include wasi:cli/command@0.3.0-rc-2026-02-09;
+  }
+",
+    additional_derives: [PartialEq, Eq, Hash, Clone],
+    // Work around https://github.com/bytecodealliance/wasm-tools/issues/2285.
+    features:["clocks-timezone"],
+    generate_all
+});
+
+use wasi::filesystem::types::Descriptor;
+use wasi::filesystem::types::ErrorCode;
+
+fn is_acceptable_unlink_dir_result(res: Result<(), ErrorCode>) -> bool {
+    match res {
+        Err(ErrorCode::NotPermitted | ErrorCode::IsDirectory | ErrorCode::Access) => true,
+        _ => false,
+    }
+}
+
+async fn test_unlink_errors(dir: &Descriptor) {
+    let rm = |path: &str| dir.unlink_file_at(path.to_string());
+    assert_eq!(rm("").await, Err(ErrorCode::NoEntry));
+    assert!(is_acceptable_unlink_dir_result(rm(".").await));
+    assert!(is_acceptable_unlink_dir_result(rm("..").await));
+    assert!(is_acceptable_unlink_dir_result(rm("../fs-tests.dir").await));
+    assert!(is_acceptable_unlink_dir_result(rm("/").await));
+    assert_eq!(rm("/etc/passwd").await, Err(ErrorCode::NotPermitted));
+    assert_eq!(rm("/etc/passwd").await, Err(ErrorCode::NotPermitted));
+    assert_eq!(rm("z.txt").await, Err(ErrorCode::NoEntry));
+    assert_eq!(rm("parent/z.txt").await, Err(ErrorCode::NotPermitted));
+}
+
+struct Component;
+export!(Component);
+impl exports::wasi::cli::run::Guest for Component {
+    async fn run() -> Result<(), ()> {
+        match &wasi::filesystem::preopens::get_directories()[..] {
+            [(dir, dirname)] if dirname == "fs-tests.dir" => {
+                test_unlink_errors(dir).await;
+            }
+            [..] => {
+                eprintln!("usage: run with one open dir named 'fs-tests.dir'");
+                process::exit(1)
+            }
+        };
+        Ok(())
+    }
+}
+
+fn main() {
+    unreachable!("main is a stub");
+}