Import reordering can break programs (using @preconcurrency)

[weissi]

Description

Consider this program

@preconcurrency import Glibc
import Foundation

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

compiles and runs just fine:

$ swiftc -swift-version 6 test.swift && echo OK
OK

But running swift-format (default config) on it, breaks it:

$ 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

This is because it changed the order of the imports.

This is probably a Swift bug but you could argue it's a formatter bug too.

Related issues:

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

Reproduction

import Foundation
@preconcurrency import Glibc

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

swiftc -swift-version 6 test.swift && echo OK

Expected behavior

compiles fine in language mode 6.

Environment

Swift version 6.0.2 (swift-6.0.2-RELEASE)
Target: aarch64-unknown-linux-gnu

Additional information

No response

[allevato]

This is a duplicate of #76842.

[hborla]

Duplicate of #76842