Bug in `fs.cpSync` handling of the `dereference` option

[jasnell]

Setup:

$ cd ~/tmp
$ touch a
$ mkdir b
$ ln -s b c

Then in Node.js:

> fs.cpSync('a', 'c', { dereference: false })
Uncaught Error: Cannot overwrite directory c with non-directory a
    at cpSyncFn (node:internal/fs/cp/cp-sync:56:13)
    at Object.cpSync (node:fs:3128:3) {
  code: 'ERR_FS_CP_NON_DIR_TO_DIR'
}
> fs.cp('a', 'c', { dereference: false }, console.log)
undefined
> null undefined

The fs.cpSync call should not be throwing in this case and does not do so in Node.js v20.x. It throws in v22.x, v24.x, and main.

/cc @anonrig @nodejs/fs

[juanarbol]

Maybe introduced by 88027e8?

[jasnell]

Almost certainly is that commit.

[jasnell]

@anonrig ... another inconsistency I spotted here:

> fs.cpSync('b', 'd', { dereference: false  })
Uncaught Error: Cannot overwrite non-directory b with directory d
    at cpSyncFn (node:internal/fs/cp/cp-sync:56:13)
    at Object.cpSync (node:fs:3111:3) {
  code: 'ERR_FS_CP_DIR_TO_NON_DIR'
}
> fs.cp('b', 'd', { dereference: false  }, console.log)
undefined
> SystemError [ERR_FS_CP_DIR_TO_NON_DIR]: Cannot overwrite non-directory with directory: cp returned EISDIR (cannot overwrite non-directory d with directory b) d
    at checkPaths (node:internal/fs/cp/cp:89:13)
    at async cpFn (node:internal/fs/cp/cp:66:17) {
  code: 'ERR_FS_CP_DIR_TO_NON_DIR',
  info: {
    message: 'cannot overwrite non-directory d with directory b',
    path: 'd',
    syscall: 'cp',
    errno: 21,
    code: 'EISDIR'
  },
  errno: [Getter/Setter: 21],
  syscall: [Getter/Setter: 'cp'],
  path: [Getter/Setter: 'd']
}

In this example, 'b' is a directory, and 'd' is a symlink to a file. Note the differences in the error messages. The cpSync error message has the ordering of the src and dest reversed

[jasnell]

And another...

-rw-rw-r--  1 jsnell jsnell    0 Jul  3 08:57 a
lrwxrwxrwx  1 jsnell jsnell    1 Jul  3 09:27 b -> a
lrwxrwxrwx  1 jsnell jsnell   18 Jul  3 09:25 c -> /home/jsnell/tmp/a
lrwxrwxrwx  1 jsnell jsnell   18 Jul  3 09:26 d -> /home/jsnell/tmp/a
jsnell@james-cloudflare-build:~/tmp$ node
Welcome to Node.js v24.3.0.
Type ".help" for more information.
> fs.cpSync('b', 'e', { dereference: true })
Uncaught Error: Recursive option not enabled, cannot copy a directory: b/
    at cpSyncFn (node:internal/fs/cp/cp-sync:56:13)
    at Object.cpSync (node:fs:3111:3) {
  code: 'ERR_FS_EISDIR'
}

'b' is being misinterpreted as a directory when it is a symlink to a file.