`FileIterator` returns broken URLs when the working directory is `/`

[kkebo]

Description

When you use the -r option and workingDirectory.path is "/", String(path.dropFirst(workingDirectory.path.count + 1)) will remove the first character of the file path, so FileIterator returns broken URLs and swift-format can't read any file.

swift-format/Sources/SwiftFormat/Utilities/FileIterator.swift

Line 149 in 3ca1a18

? String(path.dropFirst(workingDirectory.path.count + 1))

How to reproduce the issue

For instance, on wasm32-unknown-wasi, URL(fileURLWithPath: ".") will be /, so this is the problem.

And also, the issue can be reproducible on normal platforms like this:

$ pwd
/
$ ls -l | grep *.swift
.rw-r--r--. root root  12 B  Thu Oct 24 02:39:39 2024 test.swift                                                                                                     
$ swift format lint -rs .
<unknown>: error: Unable to open est.swift: file is not readable or does not exist

My environment:

• Linux aarch64
• Swift 6.0 development snapshot toolchain (6.0-snapshot-2024-10-08)

  Swift version 6.0.3-dev (LLVM 81a2745a5c40b5f, Swift 8f95e04bb5d9d9a)
  Target: aarch64-unknown-linux-gnu
  

• swift-format bundled with the Swift toolchain

[ahoppen]

Synced to Apple’s issue tracker as rdar://138492445

[macshome]

I've got a simple fix for this, just trying to find a way to add test coverage for it. As it stands this particular code path wasn't covered to begin with and it would be nice to do it now.

I also don't know what I should do about Windows support...

[kkebo]

Resolved by #865