always @preconcurrency import Glibc/Musl/Android/Bionic/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/Bionic/Android/WASILibc swift-corelibs-foundation#5170

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.

---

This has been used to rewrite the sources:

find Sources/ -name '*.swift' | while read -r line; do sed -r -i '' 's/^( *)(@_exported )?import (Musl|Android|Bionic|Glibc|WASILibc)/\1\2@preconcurrency import \3/g' "$line"; done

[parkera]

@swift-ci test

[al45tair]

Interesting. I wonder whether this is really the right fix, or whether we should be using API notes to annotate stderr et al properly.

[weissi]

Interesting. I wonder whether this is really the right fix, or whether we should be using API notes to annotate stderr et al properly.

That seems like a pretty big project and will always miss something, no? But of course, I'd be fine with that too.

But crucially until that's done, I think this is what we should do. We can remove the @preconcurrency import once that has been completed.

[weissi]

@swift-ci test macos

[weissi]

friendly ping @parkera

[parkera]

@weissi if this one is also for 6.1, please cherry pick

[weissi]

@weissi if this one is also for 6.1, please cherry pick

That one's already done and merged: #1194