path/filepath: EvalSymlinks ignores link type on Windows

[neild]

Windows makes a distinction between symlinks to a file and to a directory. A file link pointing to a directory cannot be traversed, nor can a directory link pointing to a file.

filepath.EvalSymlinks doesn't pay any attention to the type of links, however, and will resolve links that Windows will not. It probably should behave consistently with the rest of the OS.

Possible testcases (currently failing):

func TestWindowsEvalSymlinksDirectoryLinkToFile(t *testing.T) {
        dir := tempDirCanonical(t)
        if err := os.WriteFile(dir+"/target", nil, 0666); err != nil {
                t.Fatal(err)
        }
        mustExec(t, "cmd", "/c", "mklink", "/D", dir+`\symlink`, dir+`\target`)
        if _, err := filepath.EvalSymlinks(dir + `\symlink`); err == nil {
                t.Errorf("EvalSymlinks(symlink) succeeded; want error (directory link to file target)")
        }
        if _, err := os.ReadFile(dir + `\symlink`); err == nil {
                t.Errorf("ReadFile(symlink) succeeded; want error (directory link to file target)")
        }
}

func TestWindowsEvalSymlinksFileLinkToDirectory(t *testing.T) {
        dir := tempDirCanonical(t)
        if err := os.Mkdir(dir+"/target", 0777); err != nil {
                t.Fatal(err)
        }
        mustExec(t, "cmd", "/c", "mklink", dir+`\symlink`, dir+`\target`)
        if _, err := filepath.EvalSymlinks(dir + `\symlink`); err == nil {
                t.Errorf("EvalSymlinks(filelink) succeeded; want error (file link to directory target)")
        }
        if _, err := os.ReadDir(dir + `\symlink`); err == nil {
                t.Errorf("ReadDir(symlink) succeeded; want error (file link to directory target)")
        }
}

func mustExec(t *testing.T, cmd string, args ...string) {
        output, err := exec.Command(cmd, args...).CombinedOutput()
        if err != nil {
                t.Fatalf("command failed: %q\n%v", cmd, string(output))
        }
}

[neild]

/cc @qmuntal

[gabyhelp]

Related Issues

• path/filepath: windows: EvalSymlinks produces incorrect results when called with "." inside a symlink #12451 (closed)
• path/filepath: EvalSymlinks is broken for relative paths on Windows #16793 (closed)
• path/filepath: filepath.EvalSymlinks returns without error for non-symlink, valid paths #23503 (closed)
• path/filepath: EvalSymlinks(".") and EvalSymlinks("C:.") return different output on Windows #16886 (closed)
• path/filepath: EvalSymlinks failure #21511 (closed)
• path/filepath: EvalSymlinks fails when target is file #29449 (closed)
• path/filepath: Walk recurses on directory symlinks on Windows #17540 (closed)
• path/filepath: EvalSymlinks of container mapped directory returns an error #23512

Related Code Changes

• path/filepath: fix EvalSymlinks fails when target is file on Windows
• path/filepath: test EvalSymlinks returns canonical path on windows

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[prattmic]

cc @robpike @rsc for path/filepath