Wrong file descriptor passed to _subprocess_fork_exec in Linux prefork path?

[jakepetroules]

Note the following code in Subprocess+Linux.swift:

// Setup input
let fileDescriptors: [CInt] = [
    inputReadFileDescriptor?.platformDescriptor() ?? -1,
    inputWriteFileDescriptor?.platformDescriptor() ?? -1,
    outputWriteFileDescriptor?.platformDescriptor() ?? -1,
    outputReadFileDescriptor?.platformDescriptor() ?? -1,

    // repeated twice
    errorWriteFileDescriptor?.platformDescriptor() ?? -1,
    errorWriteFileDescriptor?.platformDescriptor() ?? -1,
]

Here, errorWriteFileDescriptor is passed twice, but fileDescriptors[5] is never accessed anywhere in the codebase.

Additionally, file_descriptors[4] is both dup'ed and closed.

    if (file_descriptors[1] >= 0) {
      rc = close(file_descriptors[1]);
    }
    if (file_descriptors[3] >= 0) {
      rc = close(file_descriptors[3]);
    }
    if (file_descriptors[4] >= 0) {
      rc = close(file_descriptors[4]);
    }

Was the close code meant to refer to file_descriptors[5], and it just happens to work because the same value is always passed for [4] and [5]?

[iCharlesHu]

Ahh good catch thanks!