always @preconcurrency import Glibc/Musl/Bionic/Android/WASILibc

[weissi]

Related issues:

• Default swift-format breaks my program (stops compiling) because it reorders imports that are order sensitive swift-format#933
• Import reordering can break programs (using @preconcurrency) swift#79414
• always @preconcurrency import Glibc/Musl/Android/Bionic/WASILibc swift-foundation#1175

I've got a working program

@preconcurrency import Glibc
import Foundation

await Task {
  _ = fputs("hello\n", stderr)
}.value

but alas, if swift-format reformats it, it makes it (note that the two imports are reordered)

import Foundation
@preconcurrency import Glibc

await Task {
  _ = fputs("hello\n", stderr)
}.value

which unfortunately doesn't compile

$ swift format --in-place test.swift && swiftc -swift-version 6 test.swift && echo OK
test.swift:5:24: error: reference to var 'stderr' is not concurrency-safe because it involves shared mutable state
3 | 
4 | await Task {
5 |   _ = fputs("hello\n", stderr)
  |                        `- error: reference to var 'stderr' is not concurrency-safe because it involves shared mutable state
6 | }.value
7 | 

SwiftGlibc.stderr:1:12: note: var declared here
1 | public var stderr: UnsafeMutablePointer<FILE>!
  |            `- note: var declared here

the problem is that Foundation imports Glibc/Musl but doesn't mark them @preconcurrency.

[weissi]

/ci test

[parkera]

@swift-ci test

[weissi]

@parkera this passed, can I merge it?

[parkera]

@weissi do you want to cherry pick for 6.1?

[weissi]

@weissi do you want to cherry pick for 6.1?

Great idea: #5177