Swift / C build error related to missing definition of fds_bits.

[fibrechannelscsi]

Description
A build error occurs with a missing definition of fds_bits in certain cases. The error message generted is:

/usr/include/aarch64-linux-gnu/sys/select.h:64:15: error: '(anonymous struct)::fds_bits' from module 'Clibgraphviz' is not present in definition of 'fd_set' in module 'CDispatch'
    __fd_mask fds_bits[__FD_SETSIZE / __NFDBITS];
              ^
/usr/include/aarch64-linux-gnu/sys/select.h:59:9: note: definition has no member 'fds_bits'
typedef struct
        ^
error: fatalError

Steps to reproduce
This reproducer is a minimized version of GraphViz, available here:
https://github.com/SwiftDocOrg/GraphViz
This is not to say that there is an issue with GraphViz itself, but rather, the process to build it.

This reproducer requires five files. The directory tree looks like this:

./Sources/Clibgraphviz/gvc.h
./Sources/Clibgraphviz/arith.h
./Sources/Clibgraphviz/module.modulemap
./Sources/GraphViz/Renderer.swift
./Package.swift

Listing for Sources/Clibgraphviz/gvc.h:

#include "types.h"
#include <signal.h>

Listing for Sources/Clibgraphviz/arith.h:

#define _GNU_SOURCE 1

Listing for Sources/Clibgraphviz/module.modulemap:

module Clibgraphviz [system] {
header "arith.h"
header "gvc.h"
}

Listing for Sources/GraphViz/Renderer.swift:

import Dispatch; import Clibgraphviz

Listing for Package.swift:

// swift-tools-version:5.8
import PackageDescription
let package = Package(name: "GraphViz",
    products: [.library(name: "GraphViz", targets: ["GraphViz"])],
    targets: [.systemLibrary(name: "Clibgraphviz", pkgConfig: "libcgraph")] + [.target(name: "GraphViz", dependencies: ["Clibgraphviz"])]
)

The error only occurs when performing a clean build, namely:
swift package clean; swift build

Performing two or more builds after a clean, like so:
swift build; swift build
causes the build to succed after the second invocation.

Expected behavior
The compilation via swift build should succeed on the first invocation.

Environment

• Swift compiler version info: 2023-07-10a, 2023-10-15a
• Xcode version info: N/A
• Deployment target: Ubuntu 20, ARM64, inside a Docker container.

[YOCKOW]

I've run into the same issue with ImageMagick.
Sorry, but it occurred in my private repository, so I can only paste some build logs...

/usr/include/x86_64-linux-gnu/sys/select.h:67:15: error: '(anonymous struct)::__fds_bits' from module 'CDispatch' is not present in definition of 'fd_set' in module 'CImageMagick'
    __fd_mask __fds_bits[__FD_SETSIZE / __NFDBITS];
              ^
/usr/include/x86_64-linux-gnu/sys/select.h:59:9: note: definition has no member '__fds_bits'
typedef struct

In my experiences (Ubuntu 22.04):

• Swift 5.9 + ImageMagick 6.9.11 👉 ✅ OK
• Swift 5.9.1 + ImageMagick 6.9.11 👉 ❌ Ugh
• Swift 5.9 + ImageMagick 7.1.1 👉 ✅ OK
• Swift 5.9.1 + ImageMagick 7.1.1 👉 ✅ OK

I'm not sure why these differences happen.

[YOCKOW]

I created a reproducer repository named SwiftFdsBitsIssue69311.
I found only #define _GNU_SOURCE 1 and #include <sys/types.h> are necessary to reproduce this issue: https://github.com/YOCKOW/SwiftFdsBitsIssue69311/blob/main/Sources/CModule/header.h

There are just 25 commits from 5.9 to 5.9.1. There must be some hints...🧐
Edit: Confirmed this happens even in Swift 5.9...
May be related to #64251