Stream: git-wasmtime

Topic: wasmtime / issue #12172 Windows symlink oddness

Wasmtime GitHub notifications bot (Dec 16 2025 at 14:11):

wingo opened issue #12172:

This simple test fails on Windows:

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-2025-09-16;
      include wasi:cli/command@0.3.0-rc-2025-09-16;
  }
",
    additional_derives: [PartialEq, Eq, Hash, Clone],
    // Work around https://github.com/bytecodealliance/wasm-tools/issues/2285.
    features:["clocks-timezone"],
    generate_all
});

async fn test_symlink() {
    match &wasi::filesystem::preopens::get_directories()[..] {
        [(dir, _)] => {
            dir.symlink_at("..".to_string(), "t".to_string())
                .await
                .unwrap();
            dir.unlink_file_at("t".to_string()).await.unwrap();
        }
        [..] => {
            eprintln!("usage: run with one open dir");
            process::exit(1)
        }
    }
}

struct Component;
export!(Component);
impl exports::wasi::cli::run::Guest for Component {
    async fn run() -> Result<(), ()> {
        test_symlink().await;
        Ok(())
    }
}

fn main() {
    unreachable!("main is a stub");
}

The issue is that creating a symlink to .. doesn't work and fails with EPERM, whereas on POSIX platforms any permission check is only made when dereferencing the symlink.

Similarly, ln_s("does-not-exist".to_string(), "whatever".to_string).await.unwrap() fails on Windows with ENOENT. I can make a symlink to a file that does exist, however. I only tested via CI, on https://github.com/WebAssembly/wasi-testsuite/pull/195.

What's going on? Is this another area of WASI in which we have to relax the requirements?

Wasmtime GitHub notifications bot (Dec 16 2025 at 14:11):

wingo added the bug label to Issue #12172.

Wasmtime GitHub notifications bot (Dec 17 2025 at 14:17):

wingo commented on issue #12172:

More oddness:

            dir.create_directory_at("child.cleanup".to_string())
                .await
                .unwrap();
            dir.symlink_at("../a.txt".to_string(), "child.cleanup/b".to_string())
                .await
                .unwrap();

I.e. I can't symlink to a file from a parent directory? Works on POSIX, whether making the symlink from the parent (as above) or from the child.

Wasmtime GitHub notifications bot (Dec 18 2025 at 17:07):

fitzgen added the wasi:impl label to Issue #12172.

Wasmtime GitHub notifications bot (Dec 18 2025 at 17:07):

fitzgen added the wasi:tests label to Issue #12172.

Wasmtime GitHub notifications bot (Dec 18 2025 at 17:07):

fitzgen added the wasi label to Issue #12172.

Wasmtime GitHub notifications bot (Dec 18 2025 at 18:42):

alexcrichton commented on issue #12172:

I know very little about Windows symlinks myself but I wouldn't be surprised if they're different from unix-style symlinks in subtle and surprising ways. Similar to this I don't think we have much recourse other than acknolwedging the reality that symlinks are the same at 10k feet but implemented entirely differently under the hood.

Last updated: Jan 09 2026 at 13:15 UTC