swift-format causes a infinite loop on Linux if `.swift-format` is missing

[kkebo]

Description

On Linux, when all ancestor directories do not have .swift-format, swift-format causes a infinite loop. swift-format lint and swift-format format do not work.

Steps to reproduce

Please make sure that /, /home, and /home/<user name> do not contain .swift-format.

$ cd
$ echo 'let foo:Int=0' > test.swift
$ swift format lint test.swift

Expected behavior

test.swift:1:9: warning: [Spacing] add 1 space
test.swift:1:12: warning: [Spacing] add 1 space
test.swift:1:13: warning: [Spacing] add 1 space

Actual behavior

swift-format never finishes because of a infinite loop.

Environment

I use swift-format bundled in the Swift 6.0.1 toolchain.

$ uname -a
Linux Raspberry-beetle 6.6.51+rpt-rpi-2712 #1 SMP PREEMPT Debian 1:6.6.51-1+rpt2 (2024-10-01) aarch64 GNU/Linux
$ swift --version
Swift version 6.0.1 (swift-6.0.1-RELEASE)
Target: aarch64-unknown-linux-gnu
$ swift format --version
main
$ which swift-format
/home/kebo/.local/bin/swift-format
$ swiftly list
Installed release toolchains
----------------------------
Swift 6.0.1 (in use)

Installed snapshot toolchains
-----------------------------
6.0-snapshot-2024-09-17

Supplement

I think that the root cause is a combination of swift-foundation's URL and swift-format's this line.

swift-foundation's URL is different from macOS's URL.

• On Linux (Swift 6.0.1)
  • URL(filePath: "/foo", directoryHint: .notDirectory).deletingLastPathComponent().path()
    • returns "/"
  • URL(filePath: "/foo", directoryHint: .isDirectory).deletingLastPathComponent().path()
    • returns "" (empty string)
• On macOS 15.0.1 (Xcode 16.0)
  • Both return "/"

On Linux, when I added print(self.path) to the line, self.path changed as follows.

• "/foo/bar/baz"
• "/foo/bar"
• "/foo"
• "" (empty string)
• "" (empty string)
• "" (empty string)
• ... (infinite loop)

So self.path == "/" couldn't return true forever.

[kkebo]

swiftlang/swift-foundation#969 may fix this issue.

[kkebo]

#802 fixed this problem once, but it happened again with #845.

[ahoppen]

Synced to Apple’s issue tracker as rdar://137738047

[ahoppen]

Neither #802 nor #845 apply if you’re using swift-format from a Swift 6.0 toolchain because those PRs only got merged into main, not into release/6.0.

I’m cherry-picking the fixes to 6.0 in #849

[kkebo]

@ahoppen

My comment below is the result of building and testing from source code of the main branch with a Swift 6.0 toolchain.

#802 fixed this problem once, but it happened again with #845.

And thank you for fixing the issue in #848 and #849.

[ahoppen]

Oh, I see. I wasn’t sure if you built from source. Thanks for your detailed analysis.