Borrowed parameters cannot be used in autoclosure

[glessard]

Description

A function's borrowed parameter cannot be used in a precondition's autoclosure. The error claims that the parameter "cannot be captured by an escaping closure since it is a borrowed parameter". It's not clear why an autoclosure should be considered escaping. Note that this error occurs after type checking.

Reproduction

public func test(_ i: borrowing Int) -> Bool {
    precondition(i > 0)
    return true
}

Expected behavior

This should compile.
However,

<source>:1:20: error: 'i' cannot be captured by an escaping closure since it is a borrowed parameter
1 | public func test(_ i: borrowing Int) -> Bool {
  |                    `- error: 'i' cannot be captured by an escaping closure since it is a borrowed parameter
2 |     precondition(i > 0)
  |                  `- note: closure capturing 'i' here
3 |     return true
4 | }

https://swift.godbolt.org/z/v4d3YWrPv

Environment

Apple Swift version 6.1-dev (LLVM f4b733c38006ec1, Swift f4bea5f)
Target: arm64-apple-macosx15.0
(https://github.com/swiftlang/swift/releases/tag/swift-DEVELOPMENT-SNAPSHOT-2024-10-27-a)

Additional information

rdar://138670128

[Rajveer100]

@glessard
I reproduced the snippet, looks like this is fixed since the commit you shared?

My environment:

Target: macOS (Apple Silicon)
Commit: 1af1af7

[glessard]

This also reproduces for me using swift-DEVELOPMENT-SNAPSHOT-2024-10-27-a, like this:

[/tmp]$ cat issue77235.swift 
public func test(_ i: borrowing Int) -> Bool {
    precondition(i > 0)
    return true
}
[/tmp]$ TOOLCHAINS=org.swift.61202410271a swiftc issue77235.swift 
issue77235.swift:1:20: error: 'i' cannot be captured by an escaping closure since it is a borrowed parameter
1 | public func test(_ i: borrowing Int) -> Bool {
  |                    `- error: 'i' cannot be captured by an escaping closure since it is a borrowed parameter
2 |     precondition(i > 0)
  |                  `- note: closure capturing 'i' here
3 |     return true
4 | }

[Rajveer100]

I am not sure I understand, but to reproduce I created a .swift file and as arguments passed .../Debug.swift -typecheck with swift-frontend as the executable, and the code runs fine without any errors.

[jamieQ]

I am not sure I understand, but to reproduce I created a .swift file and as arguments passed .../Debug.swift -typecheck with swift-frontend as the executable, and the code runs fine without any errors.

this error occurs after typechecking. if you invoke the compiler frontend with -emit-sil (or no specific pipeline stage arguments) you will presumably see the same error.

[atrick]

rdar://138670128 ([GH:#77235] Borrowed parameters cannot be used in autoclosure)