ln: add WASI support via symlink_path by DePasqualeOrg · Pull Request #11713 · uutils/coreutils

DePasqualeOrg · 2026-04-08T11:15:39Z

This PR replaces the error-returning WASI stub with a real symlink implementation using std::os::wasi::fs::symlink_path.

Changes

Import std::os::wasi::fs::symlink_path as symlink alongside the existing unix and windows symlink imports
Remove the WASI fn symlink stub that returned io::ErrorKind::Unsupported
Add #![cfg_attr(target_os = "wasi", feature(wasi_ext))] for access to std::os::wasi::fs

Limitations

Relative symlink targets work. Absolute symlink targets (e.g., ln -s /tmp/foo link) are rejected by WASI runtimes due to capability-based sandboxing — this is a platform constraint, not a code limitation.

Build requirements

Rust nightly (for std::os::wasi::fs, gated with feature(wasi_ext)).

Testing

Verified working on Wasmer and Wasmtime with relative symlink targets.

github-actions · 2026-04-08T11:40:00Z

GNU testsuite comparison:

Skip an intermittent issue tests/cut/bounded-memory (fails in this run but passes in the 'main' branch)
Note: The gnu test tests/pr/bounded-memory is now being skipped but was previously passing.
Congrats! The gnu test tests/expand/bounded-memory is now passing!
Congrats! The gnu test tests/printf/printf-surprise is now passing!

oech3 · 2026-04-08T11:47:22Z

error[E0554]: `#![feature]` may not be used on the stable release channel
 --> src/uu/ln/src/ln.rs:6:33
  |
6 | #![cfg_attr(target_os = "wasi", feature(wasi_ext))]
  |                                 ^^^^^^^^^^^^^^^^^

DePasqualeOrg · 2026-04-08T12:45:26Z

I added a new commit to address the CI failures.

The WASI CI uses stable Rust, but std::os::wasi::fs::symlink_path requires the unstable feature(wasi_ext) gate. This commit replaces it with libc::symlink (available via wasi-libc), removes the feature(wasi_ext) gate, and adds libc as a dependency. Same functionality, compiles on stable.

github-actions · 2026-04-08T13:01:10Z

GNU testsuite comparison:

Skip an intermittent issue tests/cut/bounded-memory (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/rm/isatty (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/date/date-locale-hour (passes in this run but fails in the 'main' branch)
Note: The gnu test tests/pr/bounded-memory is now being skipped but was previously passing.
Note: The gnu test tests/tail/pipe-f is now being skipped but was previously passing.
Congrats! The gnu test tests/expand/bounded-memory is now passing!
Congrats! The gnu test tests/printf/printf-surprise is now passing!

github-actions · 2026-04-08T13:12:04Z

GNU testsuite comparison:

Skip an intermittent issue tests/pr/bounded-memory (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/tty/tty-eof (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/expand/bounded-memory is now passing!
Congrats! The gnu test tests/printf/printf-surprise is now passing!

sylvestre · 2026-04-08T14:18:20Z

src/uu/ln/src/ln.rs

+pub fn symlink<P1: AsRef<Path>, P2: AsRef<Path>>(src: P1, dst: P2) -> io::Result<()> {
+    use std::os::wasi::ffi::OsStrExt;
+
+    let src_c = CString::new(src.as_ref().as_os_str().as_bytes())


can we use libc or rustix instead?
i really would like to avoid CString

sylvestre · 2026-04-08T14:18:43Z

could you please add a test?
(or enable one for wasi)
thanks

sylvestre · 2026-04-08T14:42:15Z

still need a test :)

DePasqualeOrg · 2026-04-08T14:44:00Z

It's now using rustix instead.

It looks like the existing integration tests cover symlink creation, but CI has skip-tests: true for wasm32-wasip1, since there's no WASI runtime.

sylvestre · 2026-04-08T14:52:44Z

we do run it here :
https://github.com/uutils/coreutils/blob/main/.github/workflows/wasi.yml

sylvestre · 2026-04-08T14:59:39Z

@oech3 please don't use this PR for this discussion

github-actions · 2026-04-08T15:26:09Z

GNU testsuite comparison:

Skip an intermittent issue tests/cut/bounded-memory (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/pr/bounded-memory (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/date/date-locale-hour (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/expand/bounded-memory is now passing!
Congrats! The gnu test tests/printf/printf-surprise is now passing!

DePasqualeOrg · 2026-04-08T19:13:27Z

I have enabled integration tests for WASI in #11717. I suggest that that PR be reviewed first, and after it's merged I can enable symlink tests in this PR.

On wasm32-wasip1, std::os::unix::fs::symlink is not available, but WASI preview 1 provides path_symlink which Rust exposes as std::os::wasi::fs::symlink_path. Import it under the symlink alias so the existing call site works without changes. Follows the same pattern as cp.rs for enabling wasi_ext.

Avoids Path::exists() returning false for a live symlink whose target stat fails (observed under wasmtime), and also keeps a dangling .~N~ symlink from being overwritten by a --backup=numbered rename.

- test_symlink_to_dir_2args uses an absolute host tmpdir path that isn't visible inside the WASI sandbox. - test_ln_non_utf8_paths requires non-UTF-8 filenames, which WASI forbids. - test_relative_src_already_symlink hits a read_link-on-absolute-path failure specific to wasmtime launched through cargo test's spawn.

Adds test_ln:: to the wasmtime integration test list and drops ln from the pending-tools TODO. Documents the read_link-on-absolute-paths gap in wasi-test-gaps.md.

DePasqualeOrg · 2026-04-12T16:18:12Z

Now that #11717 is merged, I've added ln to the list of tools covered by the WASI integration tests. Most of the test_ln cases pass as is; three of them are skipped via #[cfg_attr(wasi_runner, ignore)]:

test_symlink_to_dir_2args: passes an absolute host tmpdir path, which the sandbox doesn't map.
test_ln_non_utf8_paths: WASI requires UTF-8 argv/filenames.
test_relative_src_already_symlink: fs::read_link on an absolute path (/file2) returns EPERM under wasmtime, but only when the binary is launched through std::process::Command from the cargo-test harness. Direct wasmtime invocation and a minimal external spawner both work. fs::symlink_metadata on the same path always works. This reproduces on macOS and Linux. A likely fix is to keep uucore::fs::canonicalize in relative-path form instead of joining onto the absolute current_dir.

One previously failing test (test_symlink_existing_backup) is fixed rather than skipped: uucore::backup_control now uses fs::symlink_metadata(...).is_ok() instead of Path::exists() to probe for .~N~ backups. exists() follows symlinks, so it was returning false for a live .~1~ symlink whose target stat fails under wasmtime, causing ln's --backup=nil path to fall through to the simple-backup form instead of bumping to .~2~. Using symlink_metadata also correctly treats dangling .~N~ symlinks as existing, which matters under --backup=numbered where the old check would otherwise overwrite the dangling slot. (For reference, GNU's backupfile.c avoids the question entirely by scanning the directory with readdir rather than stat-ing each candidate.)

Testing

Ran on macOS locally with RUSTFLAGS=--cfg wasi_runner: 47 passed, 2 ignored (the third skipped test is Linux-only and doesn't compile on macOS). Also verified on Ubuntu 24.04 via Docker by running a test binary compiled without the cfg, so the annotations weren't applied; every test_ln case passed except the three we're skipping, confirming those are the only incompatibilities.

github-actions · 2026-04-12T16:23:59Z

GNU testsuite comparison:

Skip an intermittent issue tests/cut/bounded-memory (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/tty/tty-eof (fails in this run but passes in the 'main' branch)
Congrats! The gnu test tests/dd/no-allocate is now passing!
Congrats! The gnu test tests/printf/printf-surprise is now passing!

DePasqualeOrg mentioned this pull request Apr 8, 2026

wasi: add cat/sort/tail/touch integration coverage and related fixes #11712

Open

DePasqualeOrg force-pushed the wasi-ln-symlink branch from fdc57ce to ea6e1d0 Compare April 8, 2026 13:03

sylvestre reviewed Apr 8, 2026

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DePasqualeOrg added 6 commits April 12, 2026 15:24

ln: use wasi-libc symlink instead of unstable symlink_path

cd91996

ln: use rustix::fs::symlink instead of libc + CString on WASI

49bff40

uucore: use symlink_metadata for backup lookup

ab44c39

Avoids Path::exists() returning false for a live symlink whose target stat fails (observed under wasmtime), and also keeps a dangling .~N~ symlink from being overwritten by a --backup=numbered rename.

ci(wasi): run ln integration tests

0bdca75

Adds test_ln:: to the wasmtime integration test list and drops ln from the pending-tools TODO. Documents the read_link-on-absolute-paths gap in wasi-test-gaps.md.

DePasqualeOrg force-pushed the wasi-ln-symlink branch from 8b311dd to 0bdca75 Compare April 12, 2026 16:17

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