On darwin, os.lstatNoLog is a thin wrapper around syscall.Lstat, which itself is a thin wrapper around libc_lstat64_trampoline.

I suspect that this is a bug in the macOS libc implementation of lstat64.

darwin/arm64 uses lstat instead of lstat64 because it has a 64-bit ino_t (https://github.com/apple/darwin-xnu/blob/8f02f2a044b9bb1ad951987ef5bab20ec9486310/bsd/sys/cdefs.h#L604-L616). But it also exhibits the same bug.

Notably, POSIX requires:

A pathname that contains at least one non-<slash> character and that ends with one or more trailing <slash> characters shall not be resolved successfully unless the last pathname component before the trailing <slash> characters names an existing directory or a directory entry that is to be created for a directory immediately after the pathname is resolved.

Change https://go.dev/cl/484216 mentions this issue: cmd/go: skip TestScript/list_goroot_symlink on darwin

A C reproducer:

#define _XOPEN_SOURCE 700
#define _DARWIN_C_SOURCE 1
#include <unistd.h>
#include <sys/stat.h>
#include <stdio.h>
#include <stdlib.h>

int main() {
	char dir[] = "/tmp/issue59586-XXXXXX";
	if (mkdtemp(dir) == NULL) {
		perror("mkdtemp");
		exit(1);
	}
	if (chdir(dir) != 0) {
		perror("chdir");
		exit(1);
	}

	if (mkdir("dir", 0777) != 0) {
		perror("mkdir dir");
		exit(1);
	}

	if (symlink("dir", "link") != 0) {
		perror("symlink(dir, link)");
		exit(1);
	}

	if (symlink("link", "linklink") != 0) {
		perror("symlink(link, linklink)");
		exit(1);
	}

	struct stat st;
	if (lstat("linklink/", &st) != 0) {
		perror("lstat linklink/");
		exit(1);
	}

	if (S_ISLNK(st.st_mode)) {
		printf("symlink unresolved\n");
		exit(1);
	} else if (!S_ISDIR(st.st_mode)) {
		printf("resolved to non-directory\n");
		exit(1);
	} else {
		printf("resolved to directory\n");
	}
}

On Linux it prints resolved to directory, but on macOS 13 it prints symlink unresolved.

gopher@Gophers-iMac-Pro-2 src % clang ./issue59586.c && ./a.out
symlink unresolved
gopher@Gophers-iMac-Pro-2 src % clang --version
Apple clang version 14.0.0 (clang-1400.0.29.202)
Target: x86_64-apple-darwin22.1.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin

Change https://go.dev/cl/484395 mentions this issue: path/filepath: add test cases for walking a symlink-to-symlink-to-dir

Looks like only darwin is affected — the BSDs and SysV derivatives are all consistent with the behavior on Linux.

Since this appears to be a kernel bug and we don't have a pressing need to work around it at the moment, moving to the Unplanned milestone.

If and when Apple fixes the macOS bug, we can remove the test-skips that refer to this issue and close it.

Here's a shell reproducer:

$ mkdir dir
$ ln -s dir link
$ ln -s link linklink
$ ls -l
total 0
drwxr-xr-x  2 rsc  primarygroup  64 Apr 13 20:12 dir
lrwxr-xr-x  1 rsc  primarygroup   3 Apr 13 20:12 link -> dir
lrwxr-xr-x  1 rsc  primarygroup   4 Apr 13 20:12 linklink -> link
$ stat dir
16777220 263323688 drwxr-xr-x 2 rsc primarygroup 0 64 "Apr 13 20:12:27 2023" "Apr 13 20:12:27 2023" "Apr 13 20:12:27 2023" "Apr 13 20:12:27 2023" 4096 0 0 dir
$ stat link
16777220 263323690 lrwxr-xr-x 1 rsc primarygroup 0 3 "Apr 13 20:12:31 2023" "Apr 13 20:12:31 2023" "Apr 13 20:12:31 2023" "Apr 13 20:12:31 2023" 4096 0 0 link
$ stat link/
16777220 263323688 drwxr-xr-x 2 rsc primarygroup 0 64 "Apr 13 20:12:27 2023" "Apr 13 20:12:27 2023" "Apr 13 20:12:27 2023" "Apr 13 20:12:27 2023" 4096 0 0 link/
$ stat linklink
16777220 263323700 lrwxr-xr-x 1 rsc primarygroup 0 4 "Apr 13 20:12:36 2023" "Apr 13 20:12:36 2023" "Apr 13 20:12:36 2023" "Apr 13 20:12:36 2023" 4096 0 0 linklink
$ stat linklink/
16777220 263323690 lrwxr-xr-x 1 rsc primarygroup 0 3 "Apr 13 20:12:31 2023" "Apr 13 20:12:31 2023" "Apr 13 20:12:31 2023" "Apr 13 20:12:31 2023" 4096 0 0 linklink/
$

The stat linklink/ at the end is the bug. It should resolve to the directory due to the trailing slash, same as stat link/.

As @bcmills mentioned above, resolving the symlink is required by POSIX, and I have confirmed that the bug is not present on FreeBSD or Linux, so this is not a case of "everyone ignores this POSIX detail".

Change https://go.dev/cl/484755 mentions this issue: path/filepath,cmd/go: skip tests involving double-symlinks on ios